The 14th International Conference on Hypernuclear and Strange Particle Physics, HYP2022, will take place in Prague, Czech Republic, from June 27 through July 1, 2022. It is the next conference in a series that started in Heidelberg (1982), followed then by conferences at Brookhaven (1985), Padova (1988), Shimoda (1991), Vancouver (1994), Brookhaven (1997), Torino (2000), JLab (2003), Mainz (2006), Tokai (2009), Barcelona (2012), Sendai (2015), and Norfolk/Portsmouth (2018).
Topics to be discussed at the conference include:
The HYP2022 Conference will be hosted by:
Nuclear Physics Institute, Czech Academy of Sciences, Rez
Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague
The Conference will be preceded by the Indian-Summer School of Physics.
We cordially invite you to participate and contribute to the scientific program of the Conference.
The International Conference on Hypernuclear and Strange Particle Physics (HYP) takes place every two years, bringing together physicists that do research on hadron processes and nuclear systems containing strangeness, from single to multi-strangeness systems, and from few-body systems to neutron stars. The last HYP edition was held in Portsmouth VA (U.S.A.) already four years ago due the pandemic crisis. This talk presents an overview of the progress made in strangeness nuclear physics and related fields over this period. It will be seen that, despite the difficult times and challenging circumstances, the creativity and hard work of this community has kept the field alive, providing many interesting results and achievements, which pave the way to face the new challenges ahead.
Heavy-ion collisions at collision energies of a few GeV, explored by e.g. HADES or the STAR fixed-target program, study the properties of matter under extreme conditions like expected in merging neutron stars. At these energies, the lightest hadrons containing strangeness are produced close to their free nucleon nucleon threshold energy. Furthermore, due to the substantial stopping of the colliding nucleons in the collision zone, the fireball is dominated by (net-)baryons.
In this contribution we present preliminary results on the production and emission of light nuclei ($d$, $t$, ${}^{3}He$), $\Lambda$ hyperons as well as ${}^{3}_{\Lambda}H$ and ${}^{4}_{\Lambda}H$ hypernuclei. The weakly decaying particles are reconstructed via their two-body decay channels, $\Lambda\,\rightarrow\,p\,+\,\pi^{-}$, ${}^{3}_{\Lambda}H\,\rightarrow\,{}^{3}He\,+\,\pi^{-}$ and ${}^{4}_{\Lambda}H\,\rightarrow\,{}^{4}He\,+\,\pi^{-}$, which are identified based on their weak decay topologies with the help of an artificial neural network (ANN). All particles are analyzed multi-differentially as a function of transverse momentum, rapidity and centrality. This constitutes the first successful measurement of hypernuclei at mid-rapidity in heavy-ion collisions at $\sqrt{s_{NN}} = 2.55$ GeV and we contribute to the word data of hypernuclei lifetimes by performing a lifetime measurement of the ${}^{3}_{\Lambda}H$ and ${}^{4}_{\Lambda}H$. Finally, we discuss our results with respect to hypernuclei measurements by other heavy-ion experiments e.g. STAR, HypHI and ALICE as well as prospects for upcoming measurements with e.g. CBM.
The STAR experiment provides a perfect machinery for studying strange matter for more than two decades. Recently, we applied the express analysis, which allows online monitoring of the collected physics results. High quality of express calibration and reconstruction provide a unique possibility to run the express production and observe almost in real time strange particles including mesons, hyperons, resonances and even hypernuclei.
The STAR BES II program including fixed target Au+Au collisions taken in 2018--2021 is particularly suited to study hypernuclei. Light hypernuclei are expected to be abundantly produced at low energy heavy-ion collisions. The production mechanism of hypernuclei together with measurement of their properties will provide information on the hyperon-nucleon interactions, which are essential ingredients for understanding of nuclear matter equation-of-state at high net baryon densities, and, hence, the structure of neutron stars.
With the heavy fragment trigger introduced for the 2021 data taking, we were able to run the express stream production at the STAR HLT farm. The collected data were sufficient to observe the $^5_{\Lambda}\mbox{He}\rightarrow$$^{4}\mbox{Hep}\pi^-$ with more than $11\sigma$ significance, measure binding energy as a function of hypernuclei mass, and study hypernuclei decay properties with the Dalitz plot technique.
As the lightest hypernucleus, hypertriton serves as an important benchmark for hypernuclear physics: its ground state spin, iso-spin and uniquely small binding energy (~130 keV) has been used to derive the fundamental property of YN interaction since its discovery. For a long time, it has been generally accepted that the hypertriton has a similar lifetime as free Lambda hyperon
because of the large separation between Lambda and deuteron inside the hypertriton as a consequence of its small binding energy. However, since 10 years ago, several heavy-ion based experiments (HypHI in 2013, ALICE in 2016 and STAR in 2018) reported a surprisingly short lifetime. Though some of the listed experiments updated them results latterly, it is clear that an independent experimental approach is needed to improve the situation.
Our J-PARC E73 experiment is dedicated to perform the hypertriton lifetime measurement with an independent approach. We employ the so called strangeness exchange reaction $^3$He($K^-, \pi^0$)$^3_\Lambda$H at J-PARC K1.8BR beam line in Japan. A distinguished advantage of our method is to selectively populate the spin non-flip hypertriton ground state, which is not guaranteed for the heavy-ion based experiments. In order to measure out-going $\pi^0$ meson, we invented a new photon-tagging method, which enables us to effectively select the strangeness exchange reaction even without the missing mass information. The populated hypertriton can be identified with the $\pi^-$ meson decayed from $^3_\Lambda$H hypernucleus. The hypertriton lifetime can then be obtained by measuring the $\pi^-$ meson decay time directly, which is different from the decay length method used by the heavy-ion based experiments. In this presentation, we will describe the E73 experimental setup and the current status.
The hyperon-nucleon (Y-N) interaction is an essential ingredient in the description of the equation-of-state of high-baryon-density matter. Light hypernuclei (A = 3, 4), being simple Y-N bound states, serve as cornerstones of our understanding of the Y-N interaction. Precise measurements of the lifetimes of light hypernuclei can help provide input to our understanding in the Y-N interaction.
Light hypernuclei are expected to be abundantly produced in intermediate to low energy heavy-ion collisions due to the high baryon density. As a result, the STAR Beam Energy Scan Phase II program, spanning an energy range $\sqrt{s_{\rm{NN}}}=3$-$27$ GeV, is particularly suited for hypernuclei studies. In this talk, recent results on the lifetimes of light hypernuclei $({}^{3}_{\Lambda}$H, ${}^{4}_{\Lambda}$H, ${}^{4}_{\Lambda}$He$)$ measured in $\sqrt{s_{\rm{NN}}}=3$ and $7.2$ GeV Au+Au collisions will be presented. The results will be compared to previous measurements and theoretical calculations, and the physics implications will be discussed.
In the last decade, ALICE has been one of the main experiments for the study of the (anti)(hyper) nucleosynthesis at collider.
From the study of the production of antinuclei in all collision systems to the measurement of the antinuclei interaction cross section with matter, ALICE is exploring the full spectrum of measurements involving (anti)(hyper)nuclei thanks to the copious amount of data collected.
In this talk I will give an overview of the physics programme of ALICE in the sector of antinuclei and hypernuclei and the possibilities of the next experiments.
Recent relativistic heavy ion (RHI) collision experiments have extracted conflicting values of the hypertriton (${}_\Lambda^3\mathrm{H}$) lifetime ($\tau({}_\Lambda^3\mathrm{H})$). While the ALICE Collaboration's reported $\tau({}_\Lambda^3\mathrm{H})$ is comparable to the free $\Lambda$ lifetime, the STAR Collaboration's reported value is considerably shorter. A similarly large spread of values has been obtained also in earlier measurements.
Recently, we revisited theoretically this ${}_\Lambda^3\mathrm{H}$ lifetime puzzle [1], using ${}_\Lambda^3\mathrm{H}$ and ${}^3\mathrm{He}$ wave functions computed within the ab initio no-core shell model employing interactions derived from chiral effective field theory to calculate the two-body decay rate $\Gamma({}_\Lambda^3\mathrm{H}\to{}^3\mathrm{He}+\pi^-)$. We found significant but opposing contributions arising from $\Sigma NN$ admixtures in ${}_\Lambda^3\mathrm{H}$ and from $\pi^- -{}^3\mathrm{He}$ final-state interaction, as well as substantial theoretical uncertainties attributed to (hyper)nuclear structure uncertainties. To derive $\tau({}_\Lambda^3\mathrm{H})$, we evaluated the inclusive $\pi^-$ decay rate $\Gamma_{\pi^-}({}_\Lambda^3\mathrm{H})$ by using the measured branching ratio $\Gamma({}_\Lambda^3\mathrm{H}\to{}^3\mathrm{He}+\pi^-)/\Gamma_{\pi^-}({}_\Lambda^3\mathrm{H})$ and added the $\pi^0$ contributions through the $\Delta I = \frac{1}{2}$ rule. The resulting $\tau({}_\Lambda^3\mathrm{H})$ varies strongly with the rather poorly known $\Lambda$ separation energy $E_{\mathrm{sep}}({}_\Lambda^3\mathrm{H})$ and it is possible to associate each one of the distinct RHI $\tau({}_\Lambda^3\mathrm{H})$ measurements with its own underlying value of $E_{\mathrm{sep}}({}_\Lambda^3\mathrm{H})$.
[1] A. Pérez-Obiol, D. Gazda, E. Friedman, A. Gal, Revisiting the hypertriton lifetime puzzle, Phys. Lett. B 811, 135916 (2020).
Direct $\Lambda n$ scattering data is extremely important and needed based on the newly confirmed Charge-Symmetry-Breaking (CSB) at a level of ~270 keV from the binding energy difference observed between ground states of $^4_{\Lambda}$He and $^4_{\Lambda}$H. Especially, the $\Lambda n$ data does not exist at all, thus the properties of $\Lambda n$ interaction has been assumed to be identical to that of $\Lambda p$ interaction. The resonance of $\Lambda nn$ system, if it does exist, may provide a unique and the only experimental data that can be used to determine the unknown properties of $\Lambda n$ interaction [1].
Because the $^3{\rm H}(e, e’K^+)(\Lambda nn)$ reaction is unique for studying the possible neutral $Ynn$ systems, a mass spectroscopy experiment (E12-17-003) with a pair of nearly identical high resolution spectrometers and a tritium target was performed in Hall A at Jefferson Lab. Although the experimental condition with the existing apparatus was not optimized for production of hypernuclei, enhancements, which may correspond to a possible $\Lambda nn$ resonance and a pair of $\Sigma NN$ states, were observed with an energy resolution of about 1.21~MeV $(\sigma)$. Since the statistics is low, definitive identifications cannot be made. However, the result is definitely interesting and an optimized experiment for further investigation with much improved statistics is needed.
In addition, although bound A = 3 [2, 3] and 4 $\Sigma$-hypernuclei have been predicted, only an A = 4 $\Sigma$-hypernucleus ($^4_{\Sigma}He$) was found [4], utilizing the $(K^-, \pi^-)$ reaction on a $^4$He target. The possible bound $\Sigma NN$ state is likely a $\Sigma^0 nn$ state, although this has to be confirmed by future experiments.
Reference
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[4] T. Nagae, T. Miyachi, T. Fukuda, H. Outa, T. Tamagawa, J. Nakano, et al., Phys. Rev. Lett. 80, (1998) 1605-1609.
The detection of double hypernucleus having two units of Strangeness has now reached 46 sample events. The only experiment that has continued to detect double-hypernuclei for the last 35 years is experiments using nuclear emulsion as a detector in Japan. During that period, significant progress has been made in experimental and analytical techniques. Under such technological developments, it has been found that in double lambda hypernuclei, the binding energy of the two lambda hyperons to the nucleus varies linearly with the atomic mass number. Some systems formed by $\Xi^-$ and 14-nitrogen show very deep bound states, and s- and p-orbits appear as nuclear level structure in $^{15} {\rm C}_{\Xi}$, which confirms the existence of the $\Xi$ hypernucleus. In the near future, it is expected that a machine-learning model can be implemented to scan the entire region of the emulsion to detect double hypernuclei in about a thousand samples and obtain more detailed information.
One of the important research goal is to understand $\Xi N$ interaction. For this purpose, at J-PARC, they are planning to produce several bound $\Xi$ hypernuclei. In addition, it is requested to guide what kind of $\Xi$ hypernuclei would be produce as bound state. Considering this situation, I report $\Xi$ hypernuclei with $A=4$ to 10 , that is, $NNN\Xi$, $\alpha \Xi N$, $\alpha\Xi NN$, and $\alpha \alpha \Xi N$, and what terms of $\Xi N$ interaction we will obtain information on. Also, I discuss how we produce these $\Xi$ hypernuclei at J-PARC.
Recent experimental results for the cascade hypernucleus $^{15}_{\hskip0.27em\Xi}$C ($^{14}$N$+\Xi^-$) are analyzed together with data for $^{12}_{\hskip0.27em\Xi}$Be and $^{13}_{\hskip0.27em\Xi}$B within a Skyrme-Hartree-Fock theoretical approach. Optimal Skyrme parameters are determined for a consistent description of the KISO, IBUKI, KINKA, BNL-E885, BNL-E906, KEK-E224, and KEK-E176 data regarding these nuclei. The important role of deformation for $^{13}_{\hskip0.27em\Xi}$B is pointed out. The shape of the $\Xi^-$ mean field in $^{12}_{\hskip0.27em\Xi}$Be is analyzed in some detail.
Five $\Xi^- p\to \Lambda\Lambda$ two-body capture events in $^{12}$C and $^{14}$N emulsion nuclei, in which a pair of single-$\Lambda$ hypernuclei is formed and identified by their weak decay, have been observed in $(K^-,K^+)$ emulsion exposures at KEK and J-PARC. Applying a $\Xi^-$-nucleus optical potential methodology to study atomic and nuclear transitions, we confirm that these capture events occur from Coulomb assisted $1p_{\Xi^-}$ nuclear states. Long-range $\Xi N$ shell-model correlations are found essential to achieve consistency between the $^{12}$C and $^{14}$N events. The resulting $\Xi$-nuclear interaction is strongly attractive, with $\Xi$ potential depth in nuclear matter $V_{\Xi}\geq 20$ MeV. Implications to multi-strangeness features of dense matter are outlined.
X-ray spectroscopy of hadronic atoms give us various information on the strong interaction between hadrons and nuclei. At J-PARC, we are aiming for the world-first detection of the X rays from atoms with a doubly strange hyperon, $\Xi^-$. Recently, two experiments, J-PARC E07 and J-PARC E03, have been performed for the detection of X rays from $\Xi$ atoms. Overview and status of these measurements will be presented. We will also discuss future plan of X-ray spectroscopy on $\Xi$-atoms, which can be performed together with high resolution $\Xi$ hypernuclear spectroscopy
using newly constructed S-2S spectrometer. Preparation status will be shown in this contribution.
We study the energy spectra of $\Xi$ hypernuclei $^{15}_\Xi$C and $^{12}_{\Xi}$Be with a relativistic mean field (RMF) model. The RMF parameters are optimized to reproduce the average energy of KINKA and IRRAWADDY events for the ground state and also the average energy of KISO and IBUKI events for the excited state in $^{15}_\Xi$C. The depth of the $\Xi-N$ mean field potential is found to be about $-14$ -- $-12$ MeV in the nuclear matter limit. We further introduce two-body residual $s$- and $p$-wave interactions between the valence nucleon(s) and $\Xi$ particle. We found that the $s$-wave interaction alone deduced from the HAL Lattice-QCD results is too weak to reproduce the energy difference between IRRAWADDY and KINKA events. The $p$-wave interaction is added and fitted to reproduce the energy difference. The resulting $p$-wave interaction together with the $s$-wave one gives a reasonable agreement with the observed events. The model is further applied to predict the energy spectrum of $^{12}_\Xi$Be.
The inclusion of new ingredients that are expected to be specially relevant at higher energies could reveal more information about the physics behind the NLO terms of the chiral Lagrangian. In the present work, we explore the relevance of including partial waves higher than the $L=0$, which is usually the only component considered in the literature to study the ${\bar K}N$ scattering phenomenology. In particular, we focus on the p-wave contribution, the effect of which is expected to be non-negligible, as we aim at obtaining the ${\bar K}N$ scattering amplitudes at higher energies, necessary to describe the $\eta\Lambda$, $\eta\Sigma^0$, $K^0\Xi^0$ and $K^+\Xi^-$ production reactions. Extending the ${\bar K}N$ interaction to p-wave components is also relevant for studies of bound ${\bar K}$ mesons in nuclei since their local momentum can acquire sizable values.
We study for the first time the $p\Sigma^-\to K^-d$ and $K^-d\to p\Sigma^-$ reactions close to threshold and show that they are driven by a triangle mechanism, with the $\Lambda(1405)$, a proton and a neutron as intermediate states, which develops a triangle singularity close to the $\bar{K}d$ threshold. We find that a mechanism involving virtual pion exchange and the $K^-p\to\pi^+\Sigma^-$ amplitude dominates over another one involving kaon exchange and the $K^-p\to K^-p$ amplitude. Moreover, of the two $\Lambda(1405)$ states, the one with higher mass around $1420$ MeV, gives the largest contribution to the process. We show that the cross section, well within measurable range, is very sensitive to different models that, while reproducing $\bar{K}N$ observables above threshold, provide different extrapolations of the $\bar{K}N$ amplitudes below threshold. The observables of this reaction will provide new constraints on the theoretical models, leading to more reliable extrapolations of the $\bar{K}N$ amplitudes below threshold and to more accurate predictions of the $\Lambda(1405)$ state of lower mass.
The measurements of $\pi\Sigma$ mass distributions in the $\gamma p \longrightarrow K^{+} \pi\Sigma$ photoproduction reaction [1, 2] probe the energy region of the $\Lambda(1405)$ resonance, just below the $\bar{K}N$ threshold, and present new challenges for the theoretical models of $\bar{K}N-\pi\Sigma$ coupled channels interactions. Adopting the model presented in [3] we describe the photoproduction reaction in terms of tree level amplitudes followed by the meson-baryon rescattering in the final state. For the latter we employ the $MB \longrightarrow \pi\Sigma$ amplitudes generated by our recent $\bar{K}N$ model [4]. Although our approach is similar to the one used earlier in [5], we use a different way to unitarize the photoproduction amplitude and avoid some non-relativistic approximations adopted in [5].
Our preliminary results show that the tree level photoproduction graphs (Weinberg-Tomozawa, Born and anomalous ones) provide relatively small and flat $\pi\Sigma$ mass distributions. It is the final state $MB$ rescattering (with the $K^{+}$ treated as a spectator) that is responsible for the peak structure and larger magnitude of the computed cross sections. A direct comparison of the generated $\pi\Sigma$ mass spectra with those reported by the CLAS collaboration [1] is currently finalized and will be presented at the meeting.
[1] K. Moriya et al. (CLAS Collaboration), Phys. Rev. C 88 (2013) 045201.
[2] N. Wickramaarachchi et al. (GlueX Collaboration), a talk at the HYP22 conference.
[3] P.C. Bruns, arXiv:2012.11298 [nucl-th].
[4] P.C. Bruns, A. Cieplý, Nucl. Phys. A 1019 (2022) 122378.
[5] S.X. Nakamura and D. Jido, PTEP 2014 (2014), 023D01; arXiv:1310.5768 [nucl-th].
The attractive nature of $\bar{K}N$ interaction has stimulated theoretical and experimental searches for $K^-$ bound states in different systems. In particular, many theoretical calculations devoted to the lightest possible system $\bar{K}NN$ have been performed using different methods: Faddeev equations with coupled channels, variational methods, and some others, see a review \cite{review} and references therein. All of them agree that a quasi-bound state in the $K^- pp$ system exists but they yield quite diverse binding energies and widths. The experimental situation is unsettled as well: several candidates for the $K^- pp$ state were reported by different experiments, but the measured binding energies
and decay widths of such state differ from each other and are far from all theoretical predictions.
Detection of the heavier four-body $\bar{K}NNN$ system could be easier than in the case of $\bar{K}NN$ since direct scattering of $K^-$ on three-body nuclei can be performed. Some theoretical works were devoted to the question of the quasi-bound state in the $\bar{K}NNN$ system with different quantum numbers, but more accurate calculations within Faddeev-type equations are needed. The reason is that only these dynamically exact equations written in momentum representation can treat energy dependent $\bar{K}N$ potentials, necessary for the this system, exactly.
We solved four-body Faddeev equations in GS form [1] in order to search for the quasi-bound state in the $\bar{K}NNN$ system. We used our experience with the three-body AGS calculations and our two-body potentials, constructed for them. Namely, three models of the $\bar{K}N$ interaction were used: two phenomenological potentials and a chirally motivated one. All three potentials describe low-energy $K^- p$ scattering and $1s$ level shift of kaonic hydrogen with equally high accuracy. This will allow us to study the dependence of the four-body results on the two-body input. Dependence of the results on the nucleon-nucleon interaction model was studied as well.
[1] P. Grassberger, W. Sandhas, Nucl. Phys. B 2, 181 (1967).
In recent years, the possible existence of deeply-bound $\bar K$ nuclear bound states has been widely discussed as a consequence of the strongly attractive $\bar KN$ interaction in I = 0 channels. Very recently, J-PARC E15 experiment reported an observation of the simplest kaonic nuclei, $\bar KNN$, in the $\Lambda p$ invariant-spectrum of the in-flight $K^-$ reaction on helium-3 [PLB789(2019)620, PRC102(2020)044002]. If the observed structure is truly the kaonic nuclear state, we can expect other kaonic nuclei can be produced in the same $K^-$ induced reaction. Observation of other kaonic nuclei would provide a further support for the existence of such exotic states. Furthermore, mass-number dependence of kaonic nuclear systems would be of great importance to study interplay between the $\bar KN$ attraction and the $NN$ repulsion at short distances.
Here, we focus on the second simplest system, $\bar KNNN$ with I = 0. This state could be populated by simply replacing the helium-3 target in J-PARC E15 with helium-4. Although the branching ratio is not known, one of the expected decay modes is $\Lambda d$, whose final particles are charged ones only. By detecting the $\Lambda d$ pair and by identifying neutron via the missing-mass method, we can exclusively study the $\Lambda dn$ final states in the same manner of $\Lambda pn$ in E15.
We already had a chance to collect $K^-$-induced data on helium-4 as a feasibility test of a lifetime measurement of light hypernuclei (J-PARC T77). Approximately 6$\times 10^9$ $K^-$ particles at 1 GeV/$c$ are delivered to the helium-4 target in $\sim$3-day beam time in June 2020. This number corresponds to $\sim$1/7 of that in E15. The decay particles are detected with the same cylindrical detector system as E15. In a preliminary analysis, we successfully reconstructed several hundreds of $\Lambda dn$ events.
In this contribution, we would like to present the latest results of the $\Lambda dn$ analysis described above, and discuss future prospects towards more comprehensive investigation of the $\bar KNNN$ system.
We investigated the meson-baryon scattering using time-order perturbation theory (TOPT) based on a manifestly Lorentz-invariant formulation of baryon chiral perturbation theory. Effective potentials are defined as sums of two-particle irreducible contributions of time-ordered diagrams and the renormalized scattering amplitudes are obtained by solving the integral equation, which is derived self-consistently in TOPT.
Our developed formalism has been successfully applied to the pion-nucleon scattering at leading order, and it has been also extended to the meson-baryon scattering in S=-1 sector. By solving the coupled-channel integral equations with the full off-shell dependence of the effective potential and applying subtractive renormalization, we analyzed the renormalized scattering amplitudes and obtain the two-pole structure of the $\Lambda(1405)$ resonance.
[1] X.-L. Ren, E. Epelbaum, J. Gegelia and U.-G. Meißner, Meson-baryon scattering in resummed baryon chiral perturbation theory using time-ordered perturbation theory, Eur. Phys. J. C80 (2020) 406, [arXiv:2003.06272 [hep-ph]].
[2] X.-L. Ren, E. Epelbaum, J. Gegelia and U.-G. Meißner, The $\Lambda(1405)$ in resummed chiral effective field theory, [arXiv:2102.00914 [hep-ph]].
The last two decades witnessed the discovery of a large number of hadron resonances beyond expectation. They are candidates of exotic hadrons. This talk will review the theoretical understanding of exotic hadrons with strangeness and charm, focusing on hadronic molecules.
Belle and Belle II are B-factory experiments using electron-positron collisions. Not only particle physics, but also hadron spectroscopy is actively pursued in the experiments. In this talk, we will present recent results on exotic (and conventional) hadrons from the Belle experiment and on the status and prospects of the Belle II experiment.
In this talk we will review the present status of the role played by hyperons in determining the properties of neutron and proto-neutron stars. In particular, we review the so-called “hyperon puzzle”, i.e., the problem of strong softening of the equation of state of dense matter due to the presence of hyperons which leads to maximum masses of compact stars that are not compatible with the recent observations of about 2 solar mass millisecond pulsars. We discuss some of the solutions that were proposed to tackle this problem. We also re-examine the influence of hyperons on the cooling of newly born neutron stars as well as on the development of the r-mode instability. We discuss also the effecy of hyperons on transport properties including the thermal condictivity, the shear viscosity and the momentum transfer rates.
Understanding the dynamics of hadrons with strangeness has received a lot attention over the past decades in connection with the study of exotic atoms, the analysis of strangeness production in particle and nuclear research facilities, and the investigation of different strange phases in the interior of neutron stars. One venue of interest in the field of strangeness is the study of strange mesons (K and Kbar), and their dynamics with nucleons and nuclear matter. In this talk I will comment on the KbarN interaction, that is governed by the presence of the Λ(1405), and discuss the formation of exotic bound states, such as KbarNN. Moreover,I will analyze the properties of K and Kbar in dense nuclear matter, strangeness production in nuclear collisions and kaon condensation in neutron stars.
The hyperon puzzle is one of the primary problems in neutron star physics. $\Lambda$ baryons are expected to appear in neutron star matter at $(2-4)\rho_0$ when two-body interactions based on hypernuclear data are used, but hyperons soften the equation of state (EOS) and make it difficult to explain the existence of $2M_\odot$ neutron stars. Thus $\Lambda$ should feel a strong repulsive potential in dense nuclear matter. Phenomenologically, it is possible to introduce repulsion at high density by introducing, for example, $\Lambda NN$ 3-body repulsion. It is also known that repulsion appears at high densities in model calculations based on the chiral effective field theory (chiral EFT) [1], but there is no experimental support of this repulsion.
Now, let us focus on the directed flow of $\Lambda$, which is considered to be sensitive to the potential at high densities. It was shown that the proton directed flow in the collision energy range $2~\mathrm{GeV} <\sqrt{s_{NN}}<20~\mathrm{GeV}$ can be explained by the hadron transport model [2]. The repulsive EOS contributes positively to the slope in the early stage (compression stage), while the tilted ellipsoid contributes negatively in the late stage (expansion stage). Sum of these contributions causes the $dv_1/dy$ sign change at $\sqrt{s_{NN}} \simeq 10~\mathrm{GeV}$ [3]. This mechanism predicts that the $\Lambda$ directed flow slope becomes negative at lower beam energies since $\Lambda$ does not exist before the collision, but the data [4] show the balance energy of $\Lambda$ is similar to that of proton. Then the positive contribution needs to be larger and the repulsion should be stronger for $\Lambda$.
In this work, we study the directed flow of $\Lambda$ by using the transport model, JAM2-RQMDv [2] and estimate the potential of $\Lambda$ at high densities. We use the Fermi momentum expansion of the potential as given in Ref. [5], and try to constrain the slope ($L_\Lambda$) and the curvature ($K_\Lambda$) parameters of the $\Lambda$ potential from the $v_1$ slope data. We demonstrate that the $\Lambda$ potential from the chiral EFT [1], which are stiffer than the naive potential, $U_\Lambda(\rho)\simeq U_N(\rho)\times 2/3$, roughly explains the data [4]. This would be the first support of the strongly repulsive $\Lambda$ potential at high densities by the terrestrial experiment.
[1] D. Gerstung, N. Kaiser, W. Weise, Eur. Phys. J. A 56 (2020), 175; M. Kohno, Phys. Rev. C 97 (2018), 035206.
[2] Y. Nara, A. Ohnishi, Phys. Rev. C 105 (2022), 014911 [arXiv:2109.07594 [nucl-th]].
[3] L. Adamczyk et al. [STAR], Phys. Rev. Lett. 112 (2014), 162301.
[4] P. Shanmuganathan et al. [STAR], Nucl. Phys. A 956 (2016), 260.
[5] I. Tews, J. M. Lattimer, A. Ohnishi, E. E. Kolomeitsev, Astrophys. J. 848 (2017), 105.
In non-central heavy-ion collisions (HIC), the large initial angular momentum can induce a non-vanishing polarization for hadrons with non-zero spin. The global spin alignment of vector mesons, quantified by the $00^{th}$ element of spin density matrix $(\rho_{00})$, can offer information on the spin-orbital interactions of the QCD medium. Surprisingly large signal of vector meson ρ00 compared to hyperon spin polarization poses challenges to the conventional theoretical understanding of polarization in HIC. Preliminary observations from Beam Energy Scan (BES) of large deviations of $\rho_{00}$ from 1/3 for $\phi(1020)$ mesons can only be explained by introducing the vector meson strong force fields.
In this talk, we will review the details on global spin alignment of $\phi(1020)$ and $K^∗(892)$ using high statistics BES data of Au+Au collisions at RHIC and discuss its physics implication.
The matter created in non-central heavy-ion collisions is expected to have an initial orbital angular momentum carried by two colliding nuclei. Such an angular momentum would be transferred to the global polarization due to the spin-orbit coupling. The STAR Collaboration observed global polarization of \Lambda hyperons in Au+Au collisions in a wide range of collision energy $\sqrt{s_{NN}}$ = 3-200 GeV, indicating a thermal vorticity of the system. Also, non-trivial collective velocity field due to anisotropic flow leads to vorticity, and therefore polarization, along the beam direction. Unlike the case of the global polarization, theoretical models based on thermal vorticity fail to describe the local polarization in its magnitude and sign, which is under intense discussion. In this talk, recent results on global and local polarization of hyperons ($\Lambda$, $\Xi$, $\Omega$) in heavy-ion collisions will be reviewed.
We’ll discuss our recent progress on studying light hypernuclei by using heavy ion beams, nuclear emulsions and machine learning techniques. In recent years, hypernuclear studies can also be performed by using energetic heavy ion beams, and some of these experiments have revealed unexpected results on three-body hypernuclear states, i.e., shorter lifetime [1-7] and larger binding energy [8] of the lightest hypernucleus, the hypertriton, than what was formerly determined and the unprecedented bound state with a Lambda hyperon with two neutrons [9]. These results have initiated several ongoing experimental programs all over the world to study these three-body hypernuclear states precisely. We are studying those light hypernuclear states by employing different approaches from the other experiments. We employ heavy ion beams on fixed nuclear targets with the WASA detector and the Fragment separator FRS at GSI (the WASA-FRS project) in Germany for measuring their lifetime precisely [10]. The experiment was already performed in the first quarter of 2022, and the data analyses are in progress. We also analyze the entire volume of the nuclear emulsion irradiated by kaon beams in the J-PARC E07 experiment [11] in order to measure their binding energies at the world best precision [10]. We have already uniquely identified events associated with the production and decays of the hypertriton, and the binding energy of the hypertriton is to be determined. We also search events of double-strangeness hypernuclei in the E07 emulsion to understand the nature of Lambda-Lambda and Xi-nucleon interactions. We are using Machine Learning techniques for all our projects with heavy ion beams and nuclear emulsions [10]. These projects will be extended [10] at FAIR in Germany, HIAF in China and J-PARC in Japan.
[1] C. Rappold, et al., Nucl. Phys. A 913, 170–184 (2013).
[2] The STAR Collaboration, Science 328, 58–62 (2010).
[3] Y. Xu for the STAR Collaboration in Proceedings of the 12th International Conference on Hypernuclearand Strange Particle Physics (HYP2015) 021005 (2017).
[4] L. Adamczyk, et al., Phys. Rev. C 97, 054909 (2018).
[5] J. Chen, et al., Phys. Rep. 760, 1–39 (2018).
[6] J. Adam, et al., Phys. Lett. B 754, 360–372 (2016).
[7] S. Acharya, et al., Phys. Lett. B 797, 134905 (2019).
[8] J. Adam, et al., Nat. Phys. 16, 409–412 (2020).
[9] C. Rappold, et al., Phys. Rev. C 88, 041001 (2013).
[10] Takehiko R. Saito et al., Nature Reviews Physics volume 3, pages 803-813 (2021).
[11] H. Ekawa, et al., Prog.Theor. Exp. Phys. 2019, 021D02 (2019).
Scattering experiments involving a hyperon and a proton are the most effective methods for investigating two-body hyperon–nucleon ($YN$) interactions, as is the case in various intensive studies on $pp$ and $np$ scattering, which are aimed at understanding nucleon–nucleon ($NN$) interactions. Scattering observables, such as differential cross sections and spin observables, are essential experimental inputs for constructing theoretical frameworks of $YN$ interactions assuming a broken flavor SU(3) symmetry. However, regarding hyperon–proton scattering experiments, no experimental progress has been made from the experiments conducted throughout the 1970s in which hydrogen bubble chambers were employed. This is owing to the experimental difficulties stemming from the low intensity of the hyperon beam and its short lifetime.
A new hyperon–proton scattering experiment, dubbed J-PARC E40, was performed to measure differential cross sections of the $\Sigma^+ p$, $\Sigma^- 𝑝$ elastic scatterings and the $\Sigma^- p \rightarrow \Lambda n$ scattering by identifying a lot of $\Sigma$ particles in the momentum region ranging from 0.4 to 0.8 GeV/𝑐 produced by $\pi^{\pm} p \rightarrow → K+ X$ reaction. We successfully measured the differential cross sections of these three channels with a drastically improved accuracy with a fine angular step. These new data will become important experimental constraints to improve the theories of the two-body baryon-baryon interactions.
Following this success, we proposed a new experiment to measure the differential cross sections and spin observables by using a highly polarized $\Lambda$ beam for providing quantitative information on the $\Lambda N$ interaction.
In this presentation, we will present the results of three $\Sigma p$ channels and future prospects of the $\Lambda p$ scattering experiment.
A large amount of data collected over the past several decades allowed a detailed understanding of the nucleon-nucleon (NN) interaction. On the other hand, experimental difficulties prevent us from obtaining a comprehensive understanding of interactions involving other members of the baryon octet -- namely the hyperons (Y). Such difficulties are associated with the short lifetime of hyperons, which prevents us from being able to produce precise elastic scattering experiments using conventional experimental approaches. Recent advancements in accelerator and detector technologies allow us, however, to isolate and study in great precision interactions between hyperons and nucleons by studying exclusive reactions in hyperon (Y) photoproduction channels. Specifically, high-statistics data collected using the CLAS detector housed in Hall-B of the Thomas Jefferson laboratory allow us to obtain a large set of observables, including cross section information [1] on the YN interaction and place stringent constraints on the underlying dynamics. This talk will present the recent results from the CLAS collaboration on the determination of the elastic Lambda-proton scattering cross section, as well an overview of ongoing efforts on the determination of both cross section measurements and polarisation observables determination for other YN and YNN reactions.
[1] J. Rowley, et. al. Phys. Rev. Lett. 127, 272303 (2021)
We review the main mechanisms leading to the production of light and intermediate mass nuclei and hypernuclei in relativistic nuclei collisions. We demonstrate that in these many-body phenomena one can separate and describe the processes characterising excited nuclear matter properties which have a primary importance for nuclear/particle physics and astrophysics. Such deep-inelastic high-energy collisions do lead to the fragmentation (multifragmentation) of nuclear matter and, in addition, the hyper-fragments can be abundantly produced [1,2]. The binding energies of hyperons can be determined from the correlated hypernuclei yields [3,4], and this gives a chance to evaluate experimentally the hyperon effects in nuclear matter. The promising process for such a research is the disintegration of large excited nuclear and hyper-nuclear residues produced in peripheral nucleus-nucleus collisions. In central collisions, we prove a novel mechanism responsible for combining nucleons and hyperons into large clusters [5]: These cluster can be formed by the residual nuclear interaction at a low sub-nuclear density when the nuclear matter expands. One can describe this process within the statistical approach as a disintegration of the excited finite clusters of low (freeze-out) density. In the same time we have obtained the limitation on the temperature of such clusters which is important for all statistical nucleation processes in the expanding matter. Our approach is able to describe the FOPI experimental data measured in central collisions, in particular, nuclei yields, nuclei kinetic energies, and the modification of the nuclear isotope yields with increasing the beam energy. Previously, it was not possible with other models. This novel mechanism leads to the correlations of the produced nuclear species and to producing unstable hypernuclei states that can be used for the nuclei/hypernuclei identification. The transport and statistical models are used to describe the whole reaction. Concerning to hypernuclei studies we demonstrate the advantages of such reactions over the traditional hypernuclear methods: A broad distribution of predicted hypernuclei in masses and isospin allows for investigating properties of exotic hypernuclei. We point at the abundant production of multi-strange nuclei that will give an access to multi-hyperon systems and strange nuclear matter. The realistic estimates of hypernuclei yields in various collisions are presented.
[1] A.S. Botvina, et al., Phys. Rev. C95, 014902 (2017).
[2] A.S. Botvina, et al., Phys. Rev. C94, 054615 (2016).
[3] N. Buyukcizmeci, et al., Phys. Rev. C98, 064603 (2018).
[4] N. Buyukcizmeci, et al., Eur. Phys. J. A56, 210 (2020).
[5] A.S. Botvina, et al., Phys. Rev. C103, 064602 (2021).
In this talk, I will present the latest status of first-principles lattice QCD calculations of hadron interactions, in particular for those with strangeness. I introduce our theoretical framework, the HAL QCD method, and discuss its advantage over the traditional method.
I will then show our numerical results obtained near the physical point, as well as the recent experimental confirmation of the lattice QCD predictions. Future prospects with the world's fastest supercomputer "Fugaku" will be also presented.
The instability of hyperons against the weak interaction hinders the experimental extraction of baryon-baryon low-energy observables in the strange sector. In this energy regime, a reliable numerical procedure to obtain information of nuclear physics quantities is lattice QCD, a high-demanding numerical approach to solve the complex dynamics of strongly-interacting systems directly from the degrees of freedom of the Standard Model, quarks and gluons. In this talk, I will present the results obtained by the NPLQCD collaboration, constraining the coefficients from the relevant effective field theories of two non-relativistic baryons, as well as the results from a variational calculation using a large interpolating operator set.
Bridging the gap between nuclear physics and its fundamental theory, quantum chromodynamics (QCD), is of great importance. Since QCD is non-perturbative at low energies, lattice simulations, dubbed LQCD, are the only viable way to obtain ab initio QCD predictions for low energy nuclear physics.
These calculations are done, however, in a finite box, and are limited only to systems composed of a few particles. Here, we use baryonic effective field theory (EFT), designed to provide a low energy description of QCD using baryonic degrees of freedom, to extrapolate the lattice results from finite to infinite volumes, and to extend QCD-based predictions to larger systems. The calculations are done in the limit of SU(3) flavor symmetry, where the mass of the up and down quarks is set to be equal to that of the strange quark.
We construct the relevant EFT at leading order and fit it to the available LQCD results. This EFT is then used to extrapolate the results to the continuum limit. Moreover, we predict the energy in a two-body irreducible representation which cannot be resolved in the current LQCD calculations, and postdict the $^4$He energy, finding it consistent with LQCD results. We show that doing a few more three baryons LQCD calculations would enable us to fix the entire EFT coefficients and thus to predict the whole spectrum of light nuclei and hypernuclei.
We present results on the anisotropic transverse flow of kaons ($K^+$, $K^0_S$ and $K^-$) in Au+Au collisions at $\sqrt{s_\mathrm{NN}} = 2.42\,\mathrm{GeV}$ measured with HADES. It was proposed already in the mid-nineties that kaon flow close to its production threshold might be a good probe for the kaon-nucleon potential and, consequently, for the nuclear equation-of-state (PRL 74 (1995) 235). The presented analysis was performed on more than 2 billion events of the 40% most central collisions which opened the possibility to analyze kaon flow differentially as a function of transverse momentum, rapidity and centrality, even in this low energy regime. The measurements are compared to microscopic transport model predictions and to other data at similar collision energies. Implications on the properties of compressed nuclear matter will be discussed.
HYDRA (HYpernuclei Decay at R3B Apparatus) is a physics program within the R3B collaboration at the decay spectroscopy of hypernuclei produced from heavy-ion collisions at GSI/FAIR. The program aims at measuring with high resolution the in-flight pionic decay of light and medium mass hypernuclei. The pion tracker is conceived as a time projection chamber(TPC) inside the GLAD magnet of the R3B setup. As a first step, a prototype TPC was built to implement all the technologies proposed for the full TPC.
The full experimental setup has been simulated within the R3BROOT framework. Simulations were used to optimise the geometry and to define conditions for a forthcoming experiment at GSI/FAIR. Results will be detailed. The first experiment to be proposed with the HYDRA prototype, aiming at the matter radius of hypernuclei such as the hypertriton, expected to be halo, from interaction cross section (ICS) measurement. Hypernuclei have a very short lifetime (~200ps) and direct measurement of their ICS is difficult. Therefore, to determine the ICS measurements of the mesonic decay vertex distribution of the hypernuclei will be performed.
This talk will provide an overview of the HYDRA physics program and a description of the experimental method to be used to determine the hypertriton matter radius.
ALICE determines the scattering parameters of D mesons with light-flavor hadrons
Daniel Battistini for the ALICE Collaboration
The strong interaction among D mesons and light-flavor hadrons was completely out of experimental reach until recently. The scattering parameters governing elastic and inelastic D-pion/kaon/proton collisions are completely unknown. This poses strong limitations not only to the search of molecular states composed of charm and non-charm hadrons, but also to the study of the rescattering of charm mesons following their formation in ultrarelativistic heavy-ion collisions. In such collisions a colour-deconfined medium, called quark–gluon plasma (QGP), is formed. The system experiences a hydrodynamic expansion cooling down until the chemical freeze-out, which is followed by a hadronic phase. The knowledge of the scattering parameters of charm hadrons with non-charm hadrons would be a crucial ingredient for models based on charm-quark transport in a hydrodynamically expanding QGP to describe the typical observables of heavy-ion collisions.
In this talk we will report on the first estimation of the scattering parameters governing the strong interaction of the D-proton channel measured by the ALICE Collaboration in high-multiplicity pp collision at $\sqrt{s}$ = 13 TeV at the LHC. The strong interaction is studied with the femtoscopy method, and the analysis is extended to D-kaon and D-pion combinations. It is demonstrated that all the relevant scattering parameters for the interaction of D mesons with light-flavor hadrons will be experimentally determined thanks to the upgrades of the ALICE experimental apparatus planned for the LHC Run 4 and 5 data taking periods.
The production of (anti)deuterons in relativistic heavy-ion collisions is still theoretically not well understood. The particle yield can be qualitatively described by two different mechanisms of particle creation. The first of the two, the coalescence model, describes the (anti)deuteron’s creation as a result of final-state interactions among (possibly off-shell) nucleons after the chemical freeze-out. The second, the thermal model, predicts the formation of the (anti)deuterons inside the fireball even before the chemical freeze-out where these particles would be in equilibrium with other hadrons. The way of particle formation influences the characteristics of particle-emitting source and therefore, the experimental study of the source size of (anti)deuterons is one of the first steps for answering this question.
The presented analysis is based on the measurement of femtoscopic correlation functions of pion-deuteron pairs in Pb--Pb collisions at $\sqrt{s_{\rm NN}}=5.02$ TeV using the ALICE detector. The study of pion-deuteron source with the femtoscopy method is used to improve the understanding of (anti)deuterons production. Therefore, the pion-deuteron particle-emitting source size evaluated as a function of the pair transverse mass $m_{\rm T}$ is compared to the results obtained for identical pairs of pions, kaons and protons. Knowledge about the source size of deuterons can be further used for constraining the details of the strong interaction of deuterons with other particles such as kaons or protons.
We present two methods, the Nucleon-Lambda Tamm Dancoff Approximation (NL TDA) and the Equation of Motion Phonon Method (EMPM) suitable for calculating hypernuclear energy spectra and structure. These methods are applicable for hypernuclei of wide range of masses with one Lambda particle replacing one nucleon in an even-even nuclear cores. Using an effective Lambda-nucleon potential both methods were applied to calculate the energy spectrum of $^{12}_{\Lambda}$B and also one body density matrix elements (OBDME). The OBDME were applied to calculate the cross section in electroproduction of $^{12}_{\Lambda}$B. We obtained reasonable agreement with the previous theoretical studies and the experimental data. This allows us to provide theoretical prediction (by applying the same methods and Lambda-nucleon potentials) of the cross section in electroproduction of $^{40}_{\Lambda}$K and $^{48}_{\Lambda}$K.
Missing-mass spectroscopy by using the $(e,e^{\prime}K^{+})$ reaction was developed at Jefferson Lab (JLab). The energy resolution of 0.5 to 1 MeV/$c^{2}$ in FWHM is achievable thanks to a high quality beam provided by JLab and high resolution spectrometers dedicated to hypernuclear measurements. In addition, one of important features is an accurate energy calibration by using $\Lambda$ and $\Sigma^{0}$ productions from a proton target, leading to the energy accuracy of $|\Delta B_{\Lambda}|<100~{\rm keV}$.
We are preparing for experiments in which light to heavy mass targets will be used [E12-19-002 (A = 3, 4), E12-15-008 (A = 40, 48), E12-20-013 (A = 208)]. I will present an experimental overview and the expected results for $^{3}_{\Lambda}$H ($1/2^{+}$ or $3/2^{+}$) and $^{4}_{\Lambda}$H ($1^{+}$) measurements which have been approved by JLab PAC last year. We aim to measure $\Lambda$ binding energies of these $\Lambda$ hypernuclei with the energy accuracy of less than 100 keV to investigate a puzzle of contradiction between the lifetime and binding energy of hypertriton, and to study the $\Lambda$N charge symmetry breaking.
The existence of the bound state of iso-triplet three-body hypernucleus $\Lambda$nn attracts attention since possible events were reported by HypHI collaboration at GSI. Missing-mass spectroscopy with the $(e,e^{\prime}K^{+})$ reaction has been performed at Jefferson Lab (JLab) to investigate the $\Lambda$nn hypernucleus (JLab E12-17-003 Experiment). A tritium gas of 0.1 g enclosed by a target cell made by Al alloy was used as an experimental target. Data analyses were divided into three as follows: (i) a peak search with a count-base spectrum, (ii) study of the $\Lambda$-n final state interaction from an energy spectrum of quasi-free Lambda production, and (iii) cross section analysis for the virtual photoproduction of $\Lambda$nn.
In the analysis (iii), event-selection criteria were optimized to derive the cross section. Therefore, the number of events was smaller by 10—15% compared to the count-base spectrum. In addition, systematic errors were imposed due to uncertainties that originated from the cross-section analysis such as an acceptance correction. As a result, no significant structures were observed at the $\Lambda$nn threshold region in the cross-section spectrum. We obtained the upper limits of the differential cross section at the 90% confidence level to be 21 and 31 nb/sr for assumptions of $(-B_{\Lambda}, \Gamma)=(0.25, 0.8)$ and $(0.55, 4.7)~{\rm MeV}$, respectively, which are theoretically predicted energies and decay widths. I will present the experimental overview and the result of the cross-section analysis (K.N. Suzuki et al., Prog. Theor. Exp. Phys. 2022, 013D01 (2022), DOI: 10.1093/ptep/ptab158).
Electroproduction of hypernuclei is an object of current interest. Precise and reliable predictions of the cross sections in hypernucleus electroproduction are important both in planning experiments and data analysis. We will discuss some uncertainties in description of the reaction mechanism based on impulse approximation, particularly, we will show effects of proton motion in the target nucleus (Fermi motion effects) and other kinematical effects usually used in current calculations. Including the Fermi motion allows us to go beyond the "frozen proton approximation" and in this way improve our previous DWIA calculations assuming an optimum value of the target-proton momentum.
To this end we have also developed a general CGNL-like formalism for the elementary amplitude which allows to evaluate the two-component form of the amplitude in a general reference frame. The effects of various approaches will be demonstrated on the angular and energy dependent cross sections in hypernucleus electroproduction.
Physicists investigate the subatomic world by bombarding their subject of study with a hail of tiny subatomic “bullets”. From the way these “bullets” bounce off their target one can infer a wealth of detailed information about the target’s structure. Different kinds of subatomic “bullets” probe different aspects of the target, certain important aspects of the force holding atomic nuclei together can only be investigated by shooting particles called antineutrons and hyperons, which are believed to be very difficult to produce and control. However these usually rare particles can be produced in copious amounts and easily launched as a spinoff of a “super J/ψ factory”. This opens fresh research opportunities in particle and nuclear physics, as well as in astrophysics and medical physics, requiring no additional infrastructure.
As a recent topic of heavy flavor systems, exotic charmonia called $X,Y,Z$ have been observed experimentally above the meson-meson threshold. Masses of $X,Y,Z$, however, are not reproduced by the Cornell potential only with the degrees of freedom of $\bar{c}c$. This indicates that the $X,Y,Z$ states have coupled channel effects of $\bar{c}c$ and meson-meson states strongly.
Because of the color confinement of quarks, the $\bar{c}c$ potentials diverge at large distance. On the other hand, the meson-meson potentials vanish at large distance, because the interaction range is limited by the inverse pion mass. What then is the effect of the coupling to the two-hadron channels in the $\bar{c}c$ potentials and vice versa? It is expected that the coupling to the meson-meson channel affect $\bar{c}c$ potentials and the coupling of mesons with $\bar{c}c$ affect meson-meson potentials.
In this talk, we consider the channel couplings between the $\bar{c}c$ and meson-meson potentials, and investigate the properties of the effective potentials which are obtained by eliminating one of the channels.[1]
We show that these effective potentials $V_{\rm eff}(E)$ at energy $E$ are written as follows
$$
\langle \boldsymbol{r'}_{\bar{D}D} | V^{\bar{D}D}_{\rm eff}(E)|\boldsymbol{r}_{\bar{D}D} \rangle =V^{\bar{D}D}(\boldsymbol{r})\delta( \boldsymbol{r'}- \boldsymbol{r}) +\sum_n \frac{\langle \boldsymbol{ r'}_{\bar{D}D} | V^{t}|\phi_n \rangle \langle \phi_n| V^{t} |\boldsymbol{r}_{\bar{D}D} \rangle}{E-E_n}, \\
\langle \boldsymbol{r'}_{\bar{c}c} | V^{\bar{c}c}_{\rm eff}(E)|\boldsymbol{r}_{\bar{c}c} \rangle = V^{\bar{c}c}(\boldsymbol{r})\delta(\boldsymbol{r'}-\boldsymbol{r})+\int d \boldsymbol{p} \frac{\langle \boldsymbol{r'}_{\bar{c}c} | V^{t}|\boldsymbol{p}_{\rm full} \rangle \langle
\boldsymbol{p}_{\rm full} |V^{t} |\boldsymbol{r}_{\bar{c}c} \rangle}{E -E_{\boldsymbol{p}}+i0^+},
$$
where $\boldsymbol{r}$ and $\boldsymbol{r'}$ are coordinates before and after interactions, $V$ is potentials of internal interactions, $V^t$ is the transition potential of channel couplings, $|\phi_n \rangle$ is the eigenstate of the $\bar{c}c$ Hamiltonian with energy $E_n$, and
$|{\boldsymbol p}^{\rm full} \rangle$ is the meson-meson eigenstate with energy $E_{\boldsymbol{p}}$.
We discuss that the coupling to the eliminated channel induces the non-local and energy dependent effective potential, irrespective of the behavior of the transition potential. In addition, when the hadron channel having continuous scattering eigenstates is eliminated, the resulting $\bar{c}c$ potential contains an imaginary part. The physical property which stems from imaginary part, however, may be lost by the finite terms of the derivative expansion.
[1] H. Feshbach, Ann. Phys. 5, 357 (1958); ibid., 19, 287 (1962).
We employ a feed-forward artificial neural network (ANN) to extrapolate, at large model spaces, the hypernuclear No-Core Shell Model results of Refs. Few-Body Syst, 55 (2014) 857 and Few-Body Syst. 62 (2021) 94 for the $\Lambda$ separation energies of the lightest hypernuclei, $^3_\Lambda$H, $^4_\Lambda$H and $^4_\Lambda$He, obtained with chiral nucleon-nucleon and hyperon-nucleon potentials.
We find that an ANN with a single hidden layer of eight neurons is sufficient to extrapolate correctly the $\Lambda$ separation energies of the three hypernuclei considered. This is in agreement with the universal approximation theorem which assures that any continuous function can be realized by a network with just one hidden layer.
We are going to perform missing mass spectroscopy of various $\Lambda$ hypernuclei using the $(e,e'K^{+})$ reaction at the Thomas Jefferson National Accelerator Facility (JLab). This experimental campaign contains the first measurement of medium-mass hyperisotopes of $^{40}_{\Lambda}\mathrm{K}$ and $^{48}_{\Lambda}\mathrm{K}$ using isotopically enriched calcium target [JLab E12-15-008]. The intense electron beam and high resolution spectrometers achieve will much better energy resolution, at a sub-MeV level, than the existing hadronic experiments. Precise and accurate measurement of the medium-mass hyperisotopes will enable us to investigate the ${\Lambda}N$ interaction in nuclei including the ${\Lambda}NN$ three-body force which plays a key role for the stiffness of neutron stars. I will talk about the experimental prospects and the expected results of these measurements based on detailed simulation and study.
At K1.8 beam line in the Hadron Hall of J-PARC, high-precision missing-mass spectroscopy for $\Xi$ hypernuclei ( J-PARC E70 experiment ) is in preparation. In the J-PARC E70 experiment, the high-intensity $1.8 ~{\rm GeV}/c$ $K^{-}$ meson beam will be used for production of $\Xi$ hypernuclei ($^{12}_{\Xi}$Be) via $(K^{-}, K^{+})$ reaction. A newly installed magnetic spectrometer "S-2S" has a high momentum resolution $\Delta p/p = 6.0 \times 10^{-4}$ (FWHM) which will enable high precision spectroscopy of $\Xi$ hypernuclei with energy resolution of less than 2 MeV (FWHM).
As well as the S-2S magnets, we install an active fiber target as $^{12}$C target, multi wire drift chambers (MWDC), particle-identification (PID) counters. The active fiber target consists of scintillation fibers and prevents energy straggling from getting resolution worse. MWDCs are installed at upstream and downstream sides of the S-2S magnets to detect $K^{+}$ track. Detected $K^{+}$ tracks give momenta of $K^{+}$. Not only $K^{+}$ but also a huge number of protons and $\pi^{+}$s as background events pass through S-2S. Thus we need to suppress these backgrounds with PID counters: aerogel Cherenkov counter for $\pi^{+}$ suppression, water Cherenkov counter for proton suppression and Time-of-Flight (ToF) counter for offline PID. Preparation of these detectors is currently in progress for beamtime which will begin from January 2023. In this talk, I will present detector specifications and a preparation status of the above detectors.
Measurement of density of emulsion layer is very important for analyzing double strangeness hypernuclei. Because the mass of double hypernucleus is reconstructed by measuring the kinetic energy which is converted from the range of decay daughter nuclei in nuclear emulsion plate using range-energy relation. Alpha tracks from thorium and uranium series, which have monochromatic energy, were used to calibrate density of emulsion layers for the last five decades. However, the relation between the number of alpha tracks and the error of mass reconstruction have not been sufficiently studied because of time-intensive method to search alpha decay events in the emulsion plate. Recently, scanning system for alpha decay events have been developed by applying the convolutional neural network. Nowadays, we are able to investigate several hundred number of alpha tracks in a reasonable time by the developed method. In this study, around 1500 alpha tracks from three emulsion plates were used to estimate between density of emulsion layer with the dependence of number of alpha tracks and the corresponding energy error. In addition, we will introduce the difference of kinetic energy error generated from the error of density of emulsion layer and range straggling.
The hypertriton ($^3_\Lambda$H) lifetime puzzle stands for the deviation between the physical picture derived from the binding energy in the old emulsion experiment and the measured lifetime in heavy-ion experiments. To pin down the hypertriton lifetime puzzle, it is clear that an independent experimental approach is needed to improve the situation. We plan to populate and measure the hypertriton lifetime using strangeness exchange reaction, $^3$He($K^-, \pi^0$) $^3_\Lambda$H, as J-PARC E73 experiment at the J-PARC K1.8BR beamline in Japan.
Besides the direct lifetime measurement, the E73 experiment can also provide important information for the hypertriton binding energy. A recent theoretical calculation suggests that the ratio ($\sigma_{{^3_\Lambda\rm{H}}}$/$\sigma_{{^4_\Lambda\rm{H}}}$) of the production cross section can be used to study the binding energy of the hypertriton [1]. From this ratio, it is possible to place a limit on the binding energy. We will show the production cross sections of $^3_\Lambda$H and $^4_\Lambda$H in the ($K^-, \pi^0$) reaction for the first time and compare these results with theoretical calculation deduced from DWIA.
[1] T. Harada, Y. Hirabayashi, Nucl. Phys. A 1015 (2021) 122301.
One of methods to study the properties of hot and dense nuclear matter created in high-energy nuclear collisions is femtoscopic measurements. This method provides information about space-time characteristics of the particle emission region, which has a size and lifetime of the order of $10^{-15}$ m and $10^{-23}$ s, respectively. From non-identical particle correlations, one can obtain information about asymmetry in the emission process between those two kinds of particles. Such an emission asymmetry gives knowledge of which type of particles, on average, are emitted earlier and from which region of the source. Using different combinations of pion, kaon, and proton pairs, one can obtain complete knowledge on geometric and dynamic (emission time) properties of the particle emitting source. Such investigation could provide information about differences among the emissions of light mesons (pions), strange mesons (kaons), and baryons (protons).
In this poster, the STAR results on femtoscopic observables of various particle combinations of pions, kaons, and protons from Au+Au collisions at Beam Energy Scan program will be presented.
The Julich-Bonn-Munich Group aims at an extensive study of the baryon-baryon (BB) interaction involving strange baryons ($\Lambda$, $\Sigma$, $\Xi$) within SU(3) chiral effective field theory. An overview of achievements and new developments over the past few years will be provided. Among the issues covered are:
$\bullet$ Derivation of the leading charge-symmetry breaking (CSB) interaction in the $\Lambda N$ system and its application in a study of CSB effects in $A$=$4$ $\Lambda$-hypernuclei.
$\bullet$ Updated results for the $\Xi N$ interaction at NLO and implication of that interaction for $\Xi$-hypernuclei.
$\bullet$ Possible extension of the $\Lambda N$-$\Sigma N$ interaction to next-to-next-to-leading order.
$\bullet$ Constraints on the BB interaction from information on two-particle momentum correlation functions as measured in heavy ion collisions or in high-energy proton-proton collisions.
We investigate $S=-1$ and $-2$ hypernuclei with $A=4-7$ employing the Jacobi-NCSM approach [1] and in combination with baryon-baryon (BB) interactions derived within the frame work of chiral effective field theory. The employed BB interactions are softened using the so-called similarity renormalization group (SRG) [2] in order to speed up the convergence. Such a SRG evolution is only approximately unitary when the SRG induced higher-body forces are omitted. Impact of the SRG evolution and of the two almost phase-equivalent YN NLO13 [3] and NLO19 [4] potentials on the $\Lambda$ separation energies of $A=4-7$ hypernuclei is thoroughly studied [5]. Finally, we report our first results for $\Lambda\Lambda (\Xi)$ hypernuclei based on chiral YY potentials at LO [6] and NLO [7]. The NLO result for $^{\text{ }\text{ }\text{ } \text{}6}_{\Lambda \Lambda}\text{He}$ is consistent with experiment. Both interactions also yield a bound state for $^{\text{ }\text{ }\text{ } \text{}5}_{\Lambda \Lambda}\text{He}$ whereas the $^{\text{ }\text{ }\text{ } \text{}4}_{\Lambda \Lambda}\text{H}$ system is predicted to be unbound [8]. Using the $\Xi$N NLO potential we found three shallow bound states for the NNN$\Xi$ system while the $^5_{\Xi}\mathrm{H}$ and $^7_{\Xi}\mathrm{H}$ are more tightly bound [9].
[1] P. Navratil, G. P. Kamuntavicius, and B.R. Barrett, Phys. Rev. C61, 044001 (2000).
[2] S. K. Bogner, R. J. Furnstahl, and R. J. Perry, Phys. Rev. C 75, 061001 (2007).
[3] J. Haidenbauer and others Nucl. Phys. A 915, 24 (2013).
[4] J. Haidenbauer, U.-G. Meißner, and A. Nogga, Eur. Phys. J. A 56, 91 (2020).
[5] H. Le, J. Haidenbauer, U.-G. Meißner, and A. Nogga, Eur. Phys. J. A 56, 301 (2020).
[6] H. Polinder, J. Haidenbauer, and U.-G. Meißner, Phys. Lett. B653, 29 (2007).
[7] J. Haidenbauer and U.-G. Meißner, Eur. Phys. J. A 55, 23 (2019).
[8] H. Le, J. Haidenbauer, U.-G. Meißner, and A. Nogga, Eur. Phys. J. A 57, 217 (2021).
[9] H. Le, J. Haidenbauer, U.-G. Meißner, and A. Nogga, Eur. Phys. J. A 57, 339 (2021).
The two-particle momentum correlation function from high-energy nuclear collisions is beginning to be used to study hadron-hadron interaction. In this talk, we discuss how the hadron-hadron interaction can be determined from the correlation function data. Based on the theoretical and experimental studies in strangeness sectors, we review the importance of the coupled-channel effect and the source size dependence. Finally, we discuss the future prospect on the femtoscopic study especially focussing on charm sector.
Light hypernuclei containing one or two $\Lambda$ baryons is the subject of an ongoing experimental campaign aiming to study the spectrum of these systems, as well as the 2 and 3-body interaction between $\Lambda$ hyperons and nucleons.
In this presentation we review the theoretical study of these systems within the framework of Baryonic Effective Field Theory (BEFT). Constrained to reproduce the available low energy data, BEFT solves the longstanding overbinding problem of the $\Lambda$-$^5$He hypernucleus, and predicts the existence of bound double-lambda Hypernuclei still under debate.
Its application to study the continuum spectrum of hypernuclear trios, reveals the existence of a virtual state in the $\Lambda n p$ $J^{\pi}=\frac{3}{2}^{+}$ channel, leading to cross-section enhancement near threshold. For the $\Lambda n n$ $J^{\pi}=\frac{1}{2}^{+}$ channel it predicts a resonance state, depending, however, on the value of the $\Lambda$-nucleon scattering length.
Recently, BEFT was also applied to study the $^4_\Lambda$H- $^4_\Lambda$He charge symmetry breaking, yielding an estimate for the $\Lambda -\Sigma^0$ admixture amplitude $A_{I=1} \approx 1.5\%$ in agreement with the value deduced by Dalitz and von-Hippel from the baryon octet mass.
A new experiment is prepared at the Mainz Microtron facility to determine the hypertriton Lambda binding energy via decay pion spectroscopy, which was successfully pioneered with hydrogen-4-$\Lambda$ in the last decade. The experiment makes use of a novel high luminosity lithium target with a length of 50$\,$mm while being only 0.75$\,$mm thick to keep momentum smearing of the decay pions low.
A proper target to beam alignment as well as the observation of the deposited heat is achieved with a newly developed thermal imaging system. Together with a precise beam energy determination via the undulator light interference method a recalibration of the magnetic spectrometers will be done to obtain a statistical and systematic error of about 20$\,$keV. The experiment will run during summer of 2022.
This project is supported by the Deutsche Forschungsgemeinschaft, Grant Number PO256/7-1 and the European Union’s Horizon 2020 research and innovation programme No. 824093.
The hyperon puzzle in neutron stars is one of the most challenging questions to be solved in nuclear and astrophysics nowadays. To approach this problem, we need to clarify possible repulsion in the $\Lambda N$ interaction in dense nuclear matter, in other words, possible repulsion in the $\Lambda NN$ three-body force. In order to extract information on the $\Lambda NN$ three-body force, precise measurement of $\Lambda$ hypernuclear binding energies is proposed at J-PARC, employing a new beam line which will be constructed in the extended Hadron Experimental Facility planned at J-PARC. The data should be combined with elaborated theoretical studies as well as other experimental information, although such theoretical exploration seems quite challenging. In this topical session, we discuss how we can investigate the $\Lambda NN$ three-body force and elucidate dense matter in neutron stars in collaboration with theorists and experimentalists.
On the endeavour to explore the strong interaction among hadrons, the ALICE Collaboration has extended the experimental measurements beyond those of two particles, studying three-body interactions. These measurements provide unique information on many aspects of strongly-coupled systems, like exotic bound states and the genuine three-body interactions. The latter constitute an important ingredient in the calculation of the equation of state of neutron stars.
The results presented in this talk are obtained using high-multiplicity pp collisions at $\sqrt{s}$ = 13 TeV recorded by ALICE at the LHC. The first measurement of the p-p-p and p-p-$\Lambda$ correlations will be discussed. The genuine three-body effects in both triplets are obtained by subtracting the independently determined two-particle correlations from the measured three-particle correlation functions, by utilising the formalism of the three-particle cumulants. In both systems, a non-zero cumulant is observed, giving a hint to the existence of genuine three-body effects.
The same approach is used to measure p-p-$\mathrm{K^+}$ and p-p-$\mathrm{K^-}$ correlations. Both measured three-particle correlation functions can be explained assuming two-body interactions only. In particular, the measured zero p-p-$\mathrm{K^-}$ cumulant indicates negligible three-body effects in such system suggesting that the formation of the exotic kaonic bound states can not be driven by three-body forces.
Remarkable progress has been achieved in recent decades towards quantitative understanding of nuclear forces and currents in the framework of chiral effective field theory. While accurate and precise two-nucleon potentials from chiral EFT are already available, the three nucleon forces are less well understood and constitute an important frontier in nuclear physics. I will review the current status and selected applications of three-nucleon forces in the framework of chiral effective field theory and discuss prospects for the near future.
Two-body hyperon-nucleon interaction models often assume additional 3-body $\Lambda NN$ terms to reproduce the empirically derived value of $D = 30$ MeV for the $\Lambda$-nucleus potential depth. There is no consensus yet on the sign and size of such 3-body terms. Applying consistently a density-dependent $\Lambda$-nucleus optical potential to binding energy calculations of observed $1s$ and $1p$ states in the mass range $A = 12-208$, we constrain the $\Lambda NN$ contribution to $D$ by $14 \pm 2$ MeV repulsion at symmetric nuclear matter density $0.17 {\rm fm}^{-3}$ [1] in rough agreement with some theoretical models.
[1] E. Friedman, A. Gal, in preparation (03/2022).
A survey is given on the issue of strangeness contributions to the composition of dense matter in the core of neutron stars. The first part of this presentation reviews empirical constraints on the neutron star equation-of-state. The second part focuses primarily on our present understanding of hyperon-nuclear three-body forces and their role in providing a possible solution to the so-called "hyperon puzzle".
The study of the strong interaction among hadrons is an essential question in nuclear physics. It has implications both for fundamental theories, such as QCD, as well as for the understanding of the structure of dense stellar objects, such as neutron stars.
Traditionally, the experimental access to the properties of the strong force is primarily realized by scattering and hypernuclei experiments. These do not provide the possibility to perform precision measurements for hadrons containing strangeness and probe primarily the two-body interaction. Consequently, the parameters of effective theoretical models, such as Chiral Effective Field Theory, cannot be constrained with the precision required to obtain solid physics conclusions on the aforementioned topics. These limitations are particularly relevant for the study of dense nuclear matter, where extensive knowledge of the genuine three-body forces is required.
In the past several years the use of correlation techniques, applied to particles created at high-energy colliders, have been proven capable of complementing and expanding our existing knowledge of the two-particle interactions, particularly in the strangeness sector. The present contribution provides an overview of the milestones reached by using correlation techniques to investigate the strong nuclear force. The main highlights are the precision studies within the nucleon-hyperon sector, alongside the extension of the analysis methods into the three-body sector.
Geometry and dynamics of the particle-emitting source in heavy-ion collisions can be inferred via the femtoscopy method. Two-particle correlations at small relative momentum exploit Quantum Statistics (QS) and the Final State Interactions (FSI), which allow one to study the space-time characteristics of the source of the order of $10^{−15}$ m and $10^{−23}$ s. Femtoscopic measurements allow one also to explore FSI, especially the Strong one, which is unknown for many two-particle systems. The RHIC program covers a significant part of the QCD Phase Diagram using collisions of Au nuclei for several beam energies from 7.7 to 200 GeV which baryon-rich region is studied via femtoscopy. These measurements complement those obtained from AGS, SPS, and SIS experiments. Strange hadron measurements together with non-strange ones provide complementary information about source characteristics. Strangeness is a significant observable for many regimes of collision energies. Two-particle correlations that include strange particles offer essential information regarding strangeness production in heavy-ion collisions at different collision energies. In addition, the results of non-identical particles enable studies of space-time asymmetries in the emission process.
This talk shows the femtoscopic measurements of various strange particle combinations at different collision energies and centralities.
HADES is a versatile spectrometer for studying various aspects of low energy QCD operating at the SIS18 synchrotron located at the GSI/FAIR in Darmstadt,
Germany. Primarily designed to study dilepton production in proton and heavy ion induced collisions with its capability to identify also hadrons become an excellent tool to explore strange hadrons production. Λ, Σ, Ξ(1321), Λ(1405), Λ(1520), Σ(1385) hyperons, kaons and φ mesons were studied in the few AGeV region providing many interesting results on strangeness production in elementary and heavy ion collisions in the few AGeV beam energy range. In this talk highlights from former studies of elementary collisions and opportunities emerging from a recent high statistics p+p run at 4.5 GeV will be presented.
In the journey to explore the strong interaction among hadrons, ALICE has for the first time flared out its femtoscopic studies to nuclei. The large data sample of high-multiplicity pp collisions at $\sqrt{s} = 13$ TeV allows the measurement of the proton-deuteron (p-d), kaon-deuteron ($\mathrm{K^{\pm}}$-d) and the Lambda-deuteron ($\Lambda$-d) momentum correlations. The femtoscopic study of these systems opens the door to investigate the formation mechanism of the light nuclei in hadron-hadron collisions.
In this contribution, the measured correlation functions for p-d, $\mathrm{K^{\pm}}$-d and $\Lambda$-d are presented and compared to theoretical predictions. In the case of p-d correlations, the data shows a shallow depletion at low relative momenta, while the full-fledged model calculations which include all relevant interactions predict a strong repulsive signal. Possible explanations include a late formation of the deuterons leading to the suppression of strong interactions between protons and deuterons. Likewise, the experimentally obtained $\mathrm{K^{\pm}}$-d correlation function shows a Coulomb-like depletion which is well reproduced by the theoretical two-body Coulomb interaction. This result presents a complementary information to the p-d on the late formation of deuterons. In addition, the measured $\Lambda$-d correlation is in agreement with hypothesis of no strong interaction due to the late formation of deuterons, supporting the findings in p-d.
Relativistic heavy-ion collisions can study properties of nuclear matter in high-energy experiments like the STAR experiment. One of the methods to learn about bulk matter is the femtoscopy technique, which relies on information carried by the particles produced during the collisions. The emission source parameters, like space-time characteristics, are provided using femtoscopic quantities. High statistics data from RHIC can make it possible to study the correlations between strange particles, like charged and neutral kaons. The pair-wise interactions between the identical kaons that form the basis for femtoscopy are quantum statistics and the Coulomb interaction for $K^\pm$$K^\pm$, and quantum statistics and the final-state interaction through the $f_0$(980)/$a_0$(980) threshold resonances for $K^0_S$$K^0_S$. The interactions between non-identical kaons pairs of $K^0_S$$K^\pm$ are essential, as the strong FSI is described only by the $a_0$(980) resonance, which could be a four-quark state.
This talk will present the femtoscopic measurements of strange particles with charged and neutral kaons correlations in Au+Au collisions at the RHIC energy. The experimental results will be compared with the theoretical predictions.
We consider the experimental data on yields of protons, strange $\Lambda$’s, and multistrange baryons ($\Xi$, $\Omega$), and antibaryons production on nuclear targets, and the experimental ratios of multistrange to strange antibaryon production, at the energy region from SPS up to LHC, and compare them to the results of the Quark-Gluon String Model calculations. In the case of heavy nucleus collisions, the experimental dependence of the $\Xi^{+}/\Lambda$ and, in particular, of the $\Omega^+/\Lambda$ ratios, on the centrality of the collision, shows a manifest violation of quark combinatorial rules.
Measurements of anisotropic flow can be used to study transport properties and the evolution of the quark-gluon plasma (QGP), the hot and dense medium produced in heavy-ion collisions that expands collectively. In recent years, several similar features have been observed in high-multiplicity collisions of small systems, such as pp or p--Pb. However, it is still under debate whether the origin of flow in small system is due to the creation of the QGP or other physics mechanisms.
In this talk, measurements of flow coefficients obtained from multiparticle correlations measured in Pb--Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV will be presented for different particle species, including strange ($\rm K^{\pm}, K^0_s, \Lambda$) and multi-strange ($\Xi^{\mp}, \Omega^{\mp}$) hadrons. However, such measurement is very challenging in small collision systems due to the significant non-flow contamination. Thanks to the unique pseudorapidity coverage of ALICE, we use the ultra-long-range di-hadron correlations together with the template fit method to obtain non-flow suppressed flow coefficients of identified particles, including strange hadrons ($\rm K^{\pm}, K^0_s, \Lambda$), in p-Pb and pp collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV and $\sqrt{s} = 13$ TeV, respectively. In the low $p_{\rm T}$ region, a mass ordering typical for Pb--Pb collisions is also observed in pp and p-Pb collisions, and in p--Pb can be described by hydrodynamic models. For the first time, with a statistical significance larger than 3$\sigma$, a baryon-meson splitting is observed at the intermediate $p_{\rm T}$ region in p-Pb collisions. These measurements can be quantitatively described by the model calculations which implement particle production mechanism from quark coalescence. It shows the evidence of partonic collectivity of strange quarks in p-Pb collisions.
NA61/SHINE is a multi-purpose fixed-target experiment located at the H2 beamline of the CERN North Area. One of the main goals of the experiment is to study the phase transition and search for the critical point of the strongly interacting matter. Strangeness production is a long-known valuable probe for understanding particle production in high-energy physics due to the absence of strange valence quarks in the initial collision state.
This talk will present the results on strangeness production in p+p, Be+Be, and Ar+Sc collisions in the SPS energy range ($\sqrt{s_{NN}}$=5.1-17.3 GeV) measured by NA61/SHINE. The talk will emphasize the importance of the results for discussion of onset of deconfinement and onset of fireball. The obtained results will be compared to available world data and selected theoretical models.
The study of the strong interaction among stable and unstable hadrons is a fundamental question in nuclear physics and it is a key ingredient for the determination of the Equation of State of dense stellar objects, such as neutron stars. Two-particle correlation measurements are a prominent tool to probe the strong interaction with high precision even in the multi-strangeness sector, where traditional measurements, including scattering and hypernuclei experiments, are insufficient to provide strong constraints to the theoretical modeling. The ALICE Collaboration has demonstrated that high-multiplicity pp collisions are particularly well suited for these correlation measurements due to the enhanced production of strangeness in such collisions. Combined with the excellent tracking and particle identification capabilities of the ALICE detector, the laboratory for precision studies of the strong interaction among strange hadrons is set up. $\Lambda$-hadron systems are of great interest because the absence of Coulomb interaction allows to focus exclusively on the strong interaction. In this contribution, the latest ALICE results on the study of the two-body interactions in four different strangeness systems, namely $p - \Lambda$ (S=-1), $\Lambda - K^-$ and $\Lambda - \Lambda$ (S=-2), and $\Lambda - \Xi^-$ (S=-3), will be presented and their interpretation in the context of the available theoretical predictions will be discussed.
The overall scanning method of the entire volume of the nuclear emulsion irradiated in the E07 experiment at J-PARC can provide to discover events that were not observed by the already-completed analyses with the emulsion-counter-hybrid method. Therefore, further analysis with the overall scanning technique can be used to observe a large number of single-$\Lambda$ hypernuclei, however, it requires large human loads in visual inspections by optical microscopes for analyzing the big data from the nuclear emulsions. We have developed analysis methods employing the machine learning in order to reduce significantly the human load, and it enables to analyze the events for $\Lambda$ hypernuclei. We are currently working for searching and analyzing events associated with the production and the stopped two-body decay of the hypertriton in order to determine its binding energy at the world-best precision. The analysis of the E07 nuclear emulsion with the overall scanning will also be extended to study a large number of single- and double-strangeness hypernuclei. Details of the on-going project and its perspective will be discussed.
Very recently, from January till March in 2022, the WASA-FRS HypHI experiment was performed at GSI for measuring the lifetime of the hypertriton and the ${}^{4}_{\Lambda}\mathrm{H}$ hypernucleus precisely as well as for confirming whether or not the $nn\Lambda$ bound state can exist. The experiment has been carried out with the WASA central detector with a complex of additional dedicated detectors mounted together at the mid-focal plane of the high-momentum-resolution forward spectrometer, so-called the fragment separator FRS. Hypernuclei of interest have been produced by induced reactions of ${}^{6}\mathrm{Li}$ projectiles at $1.96\,\mathrm{AGeV}$ on a diamond target of $9.87\,\mathrm{g/cm^{2}}$. Negative charged $\pi$ mesons from two-body decays of hypernuclei of interest are measured by the WASA and the other detectors, and residual nuclei after the $\pi^{-}$ decay are measured by the FRS with a momentum resolving power of $10^4$. Details of the experiment and preliminary results will be discussed.
The distribution of neutrons with respect to protons in heavy nuclei is strongly related to isospin dependence of the nuclear equation of state. There exist several experimental methods to determine the neutron skin thickness in these nuclei: scattering of hadronic probes like $\pi$, p, and $\alpha$ particles on nuclei, antiproton-nucleus scattering or absorption, the electromagnetic dipole strength, and coherent $\pi^0$ photoproduction. Large systematic uncertainties of these methods are mainly related to the isospin insensitivity of these reactions. This problem can be avoided by studying the parity violation in longitudinally polarized elastic electron scattering on nuclei. However, this process exhibits an extremely small cross section asymmetry and, therefore, requires very long measuring periods.
In this contribution, we propose a new method using the pair production of hyperon-antihyperon pairs in antiproton-nucleus interactions which can be explored at PANDA@FAIR. The measurement relies on the isospin selectivity of the exclusive $\overline{p}+p \rightarrow \overline{\Lambda} + \Lambda$ and $\overline{p}+n \rightarrow \overline{\Lambda} + \Sigma^-$ channels, which can be detected in parallel at beam momenta close to their production threshold. Besides the isospin selectivity, these reactions exhibit large cross sections. Using GiBUU simulations, we have studied the sensitivity of these cross sections and their ratios to variations of the neutron skin thickness along Kr and Xe isotope chains.
The production of hyperons serves as a tool to investigate the strong interaction in the non-perturbative energy regime. While there are several experimental results for $\Lambda$ hyperons in p+p reactions, measurements of the $\Sigma^{0}$ production are scarce. This talk presents a study of the $\Sigma^{0}$ production mechanism via the exclusive reaction $pp \to pK^{+}\Sigma^{0}$ at a beam energy 3.5 GeV with the HADES detector. The daughter Lambda hyperon $\Sigma^{0} \rightarrow \Lambda \gamma$ (BR $\approx$ 100%) was reconstructed via the decay mode $\Lambda \rightarrow p \pi^{-}$ (BR $\approx$ 63.9\%) partly within the main HADES acceptance and partly within the forward wall acceptance. A kinematic refit was applied by constraining the secondary proton and the pion to the nominal $\Lambda$ mass and the overall missing mass to the photon mass.
The dynamics of the reaction $pp \to pK^{+}\Sigma^{0}$ was investigated by studying the angular distributions in the CMS, Gottfried-Jackson and helicity frames. The angular distributions in the CMS frame supports the pion exchange mechanism. Furthermore, the helicity angular distributions are highly non-isotropic, which is a clear indication that there is a resonant component of the $\Sigma^{0}$ production. In order to provide a better description of the experimental angular distributions, the Bonn-Gatchina Partial Wave Analysis (Bo-Ga PWA) has been employed. However, due to the low statistics, it was not possible to obtain an unambiguous determination of the relative contribution of each intermediate nucleon resonance to the overall final state. Nevertheless, significant contributions of nucleon resonances $\mathrm{N^{*}(1710)}$ ($\mathrm{J^{P}}$=1/2$^{+}$), $\mathrm{N^{*}(1900)}$ ($\mathrm{J^{P}}$=3/2$^{+}$) and $\mathrm{\Delta^{*}(1900)}$ ($\mathrm{J^{P}}$=1/2$^{-}$) are preferred by the PWA fit.
We are aiming for measurement of X rays form $\Xi^-$ atom to obtain the information on $\Xi$A interaction.
In 2021, We performed $\Xi^-$-Fe atomic X-ray spectroscopy experiment (J-PARC E03) at J-PARC K1.8 beam line. $\Xi^-$ hyperons were produced via the (K$^-$, K$^+$) reaction. Beam K$^-$ and scatterd K$^+$ were measured by magnetic spectrometers and X rays from $\Xi^-$-Fe atom werw detected by Ge detector array.
We will show the overview of the experiment and the analysis status.
The $\Lambda$ binding energy difference, which is called the charge symmetry breaking in the ground states of a pair of A = 4 hypernuclei, \hl and \hel, was measured to be $\Delta B_{\Lambda}^4(0_{g.s.}^{+})\approx 350~$keV in nuclear emulsion experiments in 1970s. In the 2015 experiment from J-PARC, the binding energy difference in excited states $\Delta B_{\Lambda}^4(1_{exc}^{+})\approx 30~$keV was found to be much smaller than the ground states. In 2016, the A1 collaboration updated the values to $\Delta B_{\Lambda}^4(0_{g.s.}^{+})\approx 233~$keV and $\Delta B_{\Lambda}^4(1_{exc}^{+})\approx -83~$keV. These values are difficult to be reproduced in existing theoretical models. The full understanding of the charge symmetry breaking in A = 4 hypernuclei still remains an open question.
As a part of the STAR fixed target program, the STAR detector took the data in Au+Au collisions at $\sqrt{s_{NN}}=3~$GeV in 2018. The high production yield of hypernuclei provides an opportunity to measure the binding energies of both A = 4 hypernuclei in ground states in the same experiment to address this charge symmetry breaking puzzle. In this talk, we will present the measurement of the charge symmetry breaking in A = 4 hypernuclei in Au+Au collisions at $\sqrt{s_{NN}}=3~$GeV. The signal reconstruction and binding energy measurement of \hl and \hel, including corrections and systematic uncertainty evaluation, will be discussed. Combined with the energy levels of excited states, our preliminary result for the $\Lambda$ binding energy difference in excited states shows a negative value and its magnitude is comparable to the value of ground states. These results will be compared to previous measurements and theoretical models. Future study with a factor of 7 more events from STAR taken in 2021 will also be discussed.
The field of strangeness physics is still post seven decades from its birth holds the exclusive characteristic of having more conjectures than answers in both theoretical and experimental dimensions. One of the major among the open question is the knowledge about background effect on various hyperon-baryon channels playing crucial role from heavy-ion collisions to celestial objects to name a few. To bridge the gap between observed phenomenon and theoretical understanding, the present study focuses on exploring the changes in the hyperon-baryon interaction at various nuclear densities that can eventually act crucial role in predicting unknown possibilities of the field. This approach starts by building a vacuum hyperon-nucleon interaction model based on Boson -Exchange specifically maintaining SU(3) flavor symmetry and taking special care of the channel mixing. Bethe-Goldstone equation is then explored to investigate the medium properties over the bare interaction. A detailed investigation of the density dependence revealed clear changes in the low energy parameters with the variation of the medium shown for higher Strangeness channels. As an interesting input to hyper-matter studies, induced effective three- and many-body interaction effects are explored from density variation of K-matrix terms and low energy parameters.
The E12-17-003 Experiment was carried out successfully at Jefferson lab in 2018 using a pressurized tritium target. By utilizing the Hall A high-resolution spectrometers and the $^{3}H(e,e’K^{+})Λnn$ reaction, enhancements which may correspond to the possible $Λnn$ resonance and a pair of $ΣNN$ sate were observed with an energy resolution of 1.21 MeV (σ), although the greater statistics are required to make the definite identifications. The experimentally measured $Λnn$ state can provide unique constraints in determining the $Λn$ interaction for which no scattering data exist. In addition, although bound A = 3 and 4 $Σ$ hypernuclei have been predicted, only an A = 4 $Σ$ hypernucleus ($^{4}_{\Sigma}He$) was experimentally observed using the $(K^{−} ,π^{−} )$ reaction on a $^{4}$He target. The bound $ΣNN$ state is possibly a $Σ^{0}nn$ state, although this has to be confirmed by future experiments. This presentation will give a description of this experiment, its analysis, and its results.
Bishnu Pandey on behalf of Jefferson Lab hypernuclear collaboration.
A recent JLab experiment exploiting the $^3$H(e,e'K$^+$)$^3_\Lambda$n reaction to investigate the existence of a threshold $^3_\Lambda$n resonance that would place constraints on the $\Lambda$n scattering length, observed a structure in the spectrum that was interpreted to be a $\Sigma$NN resonance [1,2]. Such a $\Sigma$NN resonance could have isospin T=0 or T=1. Garcilazo argued in 1987 on the basis of rank-one separable potentials that no T=2 $\Sigma$NN bound state or resonance should exist [3]. Stadler et al. later demonstrated that there was little possibility of a T=2 bound state or narrow resonance based on the Juelich one-boson exchange potential [4]. However, continuum Faddeev calculations were needed to address the existence of T=0 and T=1 $\Sigma$NN resonance states.
In 1993 Afnan et al. found that a near threshold T=0 resonance should exist while exploring $\Lambda$d elastic scattering on the basis of a separable potential model of the $\Lambda$N-$\Sigma$N coupled channel interaction [5]. Later, Garcilazo et al. utilizing a separable potential approximation to a chiral constituent quark model of the hyperon-nucleon interaction, concluded that the T=0 and T=1 spin-1/2 channels of the $\Sigma$NN system were the only attractive channels which might support near threshold resonances, the T=1 channel being the more attractive [6]. In 1992 Barakat et al. had attempted to observe a $\Sigma$NN resonance in an experiment at BNL in which a $^3$He(K$^-$,$\pi^+$) in flight K$^-$ beam was used [7]. No quasibound structure appeared in the spectrum. However, Harada et al. [8] performed a distorted wave impulse calculation in 2014 which reproduced the Barakat $^3$He(K$^-$,$\pi^+$) spectrum with no evidence of a resonance, but their model results did indicate that a T=1 resonance should be seen in a $^3$He(K$^-$,$\pi^-$) in flight experiment.
Because the $^3$H(e,e'K$^+$)$\Sigma$NN electro-disintegration reaction should produce both T=0 and T=1 resonances, if they exist, we have revisited our $\Lambda$d elastic scattering calculation and confirmed our results for the T=0 $\Sigma$NN resonance in our s-wave separable potential calculation. In addition we have located the T=1 $\Sigma$NN resonance pole in our model. In our calculation the two poles are quite close to one another in terms of the real part of the energy. In contrast to the calculation by Garcilazo et al., our T=0 channel is the more attractive. Thus the details of the theoretical hyperon-nucleon interactions matter. However, based upon the two Faddeev-type calculations, it seems fair to say that the T=0 and T=1 resonances are likely to lie close to one another, and it will be difficult to say explicitly from the existing data[1,2] what is the resonance content of the observed structure in the spectrum. We should note that when we expanded our separable potential model to include a tensor force in the NN spin-triplet interaction, the pole position
of the T=0 resonance was little changed, as one would anticipate, whereas the T=1 resonance showed less attraction. Unfortunately, we do not have a tensor force to include in the $\Sigma$N interaction.
References:
[1] B. Pandey et al., Phys. Rev. C Lett. (to appear).
[2] K. N. Suzuki et al., Prog. Theor. Exp. Phys. 2022, 013D01 (2022).
[3] H. Garcilazo, J. Phys. G 13, L65 (1987).
[4] A. Stadler and B. F. Gibson, Phys. Rev. C 50, 512 (1994).
[5] I. R. Afnan and B. F. Gibson, Phys. Rev. C 47, 1000 (1993).
[6] H. Garcilazo, T. Fernandez-Carames, and A. Valcarce, Phys. Rev. C 75, 034002 (2007).
[7] M. Barakat and E. V. Hungerford, Nucl. Phys. A 547, 157c (1992).
[8] T. Harada and Y. Hirabayashi, Phys. Rev. C 89, 054603 (2014).
We report on our recent result [1] concerning in-medium $\Lambda$ isospin impurity derived from charge symmetry breking (CSB) in the mirror hypernuclei ${\rm ^4_\Lambda H}-{\rm ^4_\Lambda He}$. Using pionless effective field theory and partially conserved baryon-baryon SU(3) flavor symmetry we find that the in-medium admixture amplitude ${\cal A}_{I=1}$ in the dominantly isospin $I=0$ $\Lambda$ hyperon retains its free-space value $\approx 1.5\%$ inferred by Dalitz and von Hippel [2] and recent QCD+QED lattice calculations [3]. In agreement with recent work [4] we observe that CSB affects spin-singlet and spin-triplet $\Lambda N$ channels differently - in opposite directions, with the former dominating by an order of magnitude. This difference might be explained as a consequence of SU(3) flavor symmetry.
[1] M. Schafer, N. Barnea, A. Gal, arXiv:2202.07460v2 [nucl-th] (2022).
[2] R. H. Dalitz and F. von Hippel, Phys. Lett 10, 153 (1964).
[3] Z. R. Kordov, R. Horsley, Y. Nakamura et al. Phys. Rev. D 101, 034517 (2020).
[4] J. Haidenbauer, U.-G. Meissner, and A. Nogga, Few-Body Syst. 62, 105 (2021).
The measurement of the production and the lifetime of the hypertriton with the ALICE detector at the LHC is presented to address some of the key open questions of hypernuclear and particle physics.
The hypertriton is a bound state of a proton (p), a neutron (n) and a Λ and it is characterized by a very low binding energy and a large wave function. It is still unclear how such a fragile object can survive the extreme environment created in ultrarelativistic heavy-ion collisions and the measurement of the production yields in Pb-Pb collisions can shed light on the production mechanism of such a system.
The study of the hypertriton characteristics also provides insights into the strong interaction between the lambda and ordinary nucleons and when studied in small colliding systems, like pp and p-Pb collisions, the hypertriton can give useful constraints for the nucleosynthesis models.
Thanks to the very large dataset collected so far in pp, p–Pb and Pb–Pb collisions, the ALICE collaboration has performed systematic and precise measurements of the hypertriton production, lifetime and binding energy, thus also contributing to solving the longstanding hypertriton lifetime puzzle.
In this contribution, an overview of those results will be presented and compared with the existing theoretical predictions.
To understand the mechanism of the sizable charge symmetry breaking between $^4_\Lambda$H and $^4_\Lambda$He, we plan to measure the gamma-transition energy of $^4_\Lambda$H ($1^+→0^+$) with a high-resolution Germanium detector array (Hyperball-J) at J-PARC (E63 experiment). The $^4_\Lambda$H is efficiently produced as hyperfragments from the in-flight $^7$Li $(K^-,\pi^-)$ reaction. However, the $^4_\Lambda$H hypernucleus cannot be identified well by the $(K^-,\pi^-)$ reaction because various hypernuclei are produced as hyperfragments in the reaction. Therefore, for identification of the hypernucleus, we will perform a triple coincidence measurement with the in-flight $(K^-,\pi^-)$ reaction, gamma-ray, and weak decay for the first time. We measure the monochromatic pion from their two-body weak decay ($^4_\Lambda$H $→ ^4$He $+ \pi^-$) with a range counter composed of the multi-layered plastic scintillator (RC) and two layers of hodoscopes measuring pion tracks (TD).
The RC should meet two requirements. First, it is installed inside of the Hyperball-J, where the space is limited and the magnetic field from spectrometers exists. Therefore, it is necessary to optimize the detector geometry and the readout method. The area and the thickness of the counter are designed to be 275 mm × 110 mm and 6 mm × 24 layers, respectively. The readout method using wavelength shifting fibers embedded in the plastic scintillator and connected with MPPCs (multi-pixel photon counter) is adopted. Second, the RC must have a resolution of range measurement enough to distinguish between the pions from the two-body decays of $^4 _\Lambda$H and $^3 _\Lambda$H with a confidence level of more than 3 sigma. The momentum of pion from $^4 _\Lambda$H is 133 MeV/$c$ and that from $^3 _\Lambda$H is 114 MeV/$c$, and the required-energy resolution is 2 MeV for the range difference of 35 mm. The tracking device (TD) has two layers (TD-Y, TD-Z) of strip-shaped plastic scintillators with a 15 mm width, and it is installed in front of the RC.
We fabricated a prototype range counter with a thickness of one-third of the full of detector for E63 and conducted a test experiment at the K1.8 beamline at J-PARC using $\pi^-$ and proton beams. As a result, we found that the prototype had the ability to measure the pion energy accurately enough in the energy region required for E63. Based on the results, we are currently fabricating a whole set of the RC and the TD for the beamtime coming near future. This method will enable gamma-ray spectroscopy of various hyperfragments which cannot be produced by $(K^-,\pi^-)$ or $(\pi^+, K^+)$ reactions.
The strong interaction between an antikaon and a nucleon is at the origin of various interesting phenomena in kaon-nuclear systems. In particular, the interaction in the isospin $I=0$ channel is sufficiently attractive to generate a quasi-bound state, the $\Lambda(1405)$ resonance, below the $\bar{K}N$ threshold. Based on this picture, it may be expected that the $\bar{K}N$ interaction also generates quasi-bound states in kaon-nuclear systems, sometimes called kaonic nuclei. At the same time, the $\bar{K}N$ quasi-bound picture of the $\Lambda(1405)$ is also related to the discussion of hadronic molecules in hadron spectroscopy. In this talk, an overview is presented of the theoretical studies developed for kaon-nucleon and kaon-nuclear systems [1]. We start from the modern understanding of the $\Lambda(1405)$ resonance [2]. We then discuss the $\bar{K}N$ interaction [3] and various aspects of few-body kaonic nuclei [4]. Related topics, such as the $K^−p$ momentum correlation functions in high-energy collisions and the studies of kaonic atoms, are also discussed.
[1] T. Hyodo and W. Weise, arXiv:2202.06181 [nucl-th].
[2] Y. Ikeda, T. Hyodo and W. Weise, Phys. Lett. B 706, 63 (2011); Nucl. Phys. A 881, 98 (2012)
[3] K. Miyahara and T. Hyodo, Phys. Rev. C 93, 015201 (2016); K. Miyahara, T. Hyodo and W. Weise, Phys. Rev. C 98, 025201 (2018)
[4] S. Ohnishi, W. Horiuchi, T. Hoshino, K. Miyahara and T. Hyodo, Phys. Rev. C 95, 065202 (2017)
The existence of a quasi-bound state of antikaon and nucleus, kaonic nucleus, has been discussed ever since the $\bar{K}N$ interaction in $I=0$ channel was confirmed to be strong attractive.
The $\bar{K}NN$ quasi-bound state is the lightest kaonic nucleus which is considered to be $I=1/2$ and $J^\pi = 0^-$.
To search for the $I_{z}=+1/2~\bar{K}NN$ state we conducted the J-PARC E15 experiment using the in-flight $K^-$-beam at J-PARC. Because the $K^-$-beam momentum of $1~{\rm GeV}/c$ used in the experiment maximizes the elementary cross section of nucleon knocked-out reactions, $(K^-,~N)$, the $I_z=+1/2~\bar{K}NN$ state is expected to be produced by sequential reaction of the primary $(K^-,~n)$ reaction followed by an absorption process of intermediate $\bar{K}$ to residual nucleons. Production of the $I_z=+1/2~\bar{K}NN$ state was examined by an exclusive analysis for the simplest non-mesonic reaction, $K^- \, ^{3}{\rm He} \to \Lambda pn$, in which $\Lambda p$ pair is expected to be decay products of the $\bar{K}NN$.In the $\Lambda p$ invariant-mass spectrum, we observed a distinct peak at the energy region below the $\bar{K}NN$ mass threshold. Because its peak position does not depend on the momentum transfer to the $\Lambda p$ system, the peak is produced by a resonance. Although the spectral decomposition was performed using the simple Breite-Wigner formula, whole distribution is reproduced well. The evaluated mass position and decay width are consistent with theoretical predictions, thus we concluded that the observed peak is a signal of the $I_z=+1/2~\bar{K}NN$ state.
As future prospects, there are two approaches to establish the kaonic nuclei more robustly. One is to search for heavier kaonic nuclei, and another is to study the observed $\bar{K}NN$ state more precisely. Thus, we have planed to perform series of experiments to study of kaonic nuclei using in-fight $K^-$ reactions at J-PARC.
As an analogy to $\bar{K}NN$ production with the $(K^-,~n)$ reaction, heavier kaonic nuclei could be produced similarly by replacing $^{3}{\rm He}$-target with heavier targets. As the first step to search for heavier kaonic nuclei, $\bar{K}NNN$ state will be searched for with the $^{4}{\rm He}(K^-,~n)$ reaction. For the $\bar{K}NN$ state, determination of spin-parity is the most important to confirm the observed state is a quantum state as well as to clarify its internal structure. $J^\pi$ of the $\bar{K}NN$ can be determine from the spin-spin correlation of the $\Lambda p$-pair from the $\bar{K}NN$ decay with a model independent manner.
As another measurement for the $\bar{K}NN$, we will measure the $^{3}{\rm He}(K^-,~p)\Lambda n$ reaction to search for the $I_z=-1/2~\bar{K}NN$ state.
To perform these measurements, we will construct a new solenoid spectrometer system to have neutron detection capability and a proton polarimeter system.
I would like to present the summary of J-PARC~E15 experiment and an overview of our future plan.
The $\overline{\rm K}$p system is characterised by the presence of several coupled channels, systems like $\rm \overline{K}^0$n and $\rm \pi\Sigma$ with a similar mass and the same quantum numbers as the $\rm{K}^{-}$p state. The strengths of these couplings to the $\rm{K}^{-}$p system are of crucial importance for the understanding of the nature of the $\Lambda(1405)$ and of the attractive $\rm{K}^{-}$p strong interaction.
In this talk, we will present the measurements of the $\rm{K}^{-}$p and $\rm{K}_{s}^{0}$p correlation function in relative momentum space obtained in pp collisions at $\sqrt{s}~=~13$ TeV, in p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeV, and Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeV.
The emitting source size varies between 1 and 2 fm for pp, p-Pb and peripheral Pb-Pb, whereas for central Pb--Pb collisions it is between 5 and 9 fm. As the source size increases the effect of the inelastic contributions is suppressed and the shape of the correlation function is mostly driven by the elastic interaction.
The strength and the effects of the $\rm \overline{K}^0$n and $\rm \pi\Sigma$ inelastic channels on the measured $\rm{K}^{-}$p correlation function are investigated in the different colliding systems by comparing the data with state-of-the-art models of chiral potentials. Finally, a novel data-driven approach to determine the coupling weights, necessary to quantify the amount of produced inelastic channels in the correlation function, is presented. The comparison of chiral potentials to the measured $\rm{K}^{-}$p interaction indicates that, while the $\rm \pi\Sigma$-$\rm{K}^{-}$p dynamics is well reproduced within the model, the coupling to the $\rm \overline{K}^0$n channel in the model is currently underestimated.
So far, the $(e,e' K^+)$ reaction spectroscopy is the only way to achieve sub-MeV energy resolution in Lambda hypernuclear reaction spectroscopy. As a part of the J-PARC hadron hall extension project, a new momentum dispersion matching beamline HIHR will be constructed. It will open the door to other reaction spectroscopy for precise measurement of Lambda hypernuclei with pion beams.
I will give future prospects on a campaign of JLab hypernuclear experiments, and the SpiK project, supra-precision $(\pi,K^+)$ spectroscopy of Lambda hypernuclei at J-PARC HIHR.
$s$-shell to $sd$-shell hypernuclear gamma-ray spectroscopies were carried out at KEK-PS, BNL-AGS and J-PARC using germanium detector arrays as the series of Hyperball project. These precise measurements of hypernuclear level structures gave various information on the $\Lambda$N interaction. In particular, the result from the gamma-ray spectroscopy of $^4_\Lambda$He ($1^+ \to 0^+$) M1 transition (J-PARC E13) confirmed the existence of the charge symmetry breaking in $\Lambda$N interaction and its spin dependence. In this talk, a recent summary of the hypernuclear gamma-ray spectroscopy will be presented.In addition, prospects at future J-PARC Experimental Facility will be introduced.
Although not perfectly conserved, SU(3) group structures are useful guidelines for interactions of octet baryons by the exchange of scalar, pseudo-scalar, and vector nonet mesons by providing constraints on meson-baryon vertices in terms of a few fundamental SU(3) coupling constants - as incorporated in baryon interaction models. As discussed in [1,2], the SU(3) relations are especially useful for the derivation of a density functional theory for nucleons and hyperons, highly demanded for hypernuclear investigations over the full range of the nuclear mass table and for explorations of the still unsolved question on hyperons in neutrons stars. Various attempts have been made to extend energy density functionals, originally derived for nucleonic matter only, into the hypernuclear sector by adding hyperon interactions with empirically derived parameters. That approach, however, is hampered by the fact that data are only available for light S=-1 single-$\Lambda$ hypernuclei. Since by construction the relevant SU(3) aspects are implicit to the nucleon sector, it is tempting to explore to what extent SU(3) relations can be used to extract from the nucleonic functionals the fundamental coupling constants $g_D$, $g_F$, and $g_S$ as functionals of the density. If successful, the results provide a simple and transparent approach to investigate the meson-hyperon vertices of the mean--field producing condensed meson fields. As an example, the scheme is discussed for the covariant Giessen EDF derived from Dirac-Brueckner G-matrix interactions. In-medium meson-baryon vertices are extracted for scalar and vector mesons. Their density dependence is discussed and results for hypernuclear binding energies and spectral distributions for hyperon bound and continuum states are presented. Single- separation energies are compared to results obtained with EDF and mean-field approaches explicitly incorporating the SU(3) aspects. Implications for neutron star matter will be addressed.
[1] H. Lenske, M. Dhar, Th. Gaitanos, and Xu Cao, Prog.Part.Nucl.Phys. 98 (2018) 119-206.
[2] H. Lenske, M. Dhar, Lect.Notes.Phys. 948 (2018) 161-253.
The microscopic composition and properties of matter at super-saturation densities have been a subject of intense investigation for decades. The scarcity of experimental and observational data has led to the necessary reliance on theoretical models. However, there remains great uncertainty in these models, which, of necessity, have to go beyond the over-simplified assumptions that high-density matter consists only of nucleons and leptons. Heavy strange baryons, mesons and quark matter in different forms and phases have to be included to fulfill basic requirements of fundamental laws of physics.
In my contribution, I will concentrate on the role of hyperons which, according to fundamental physical laws, inevitably appear at densities above a threshold in cold dense matter and at all densities in hot matter in astrophysical compact objects. The Quark-Meson-Coupling-Model (QMC) [1] is ideally suited for such research. The model is based on interaction between quarks in individual baryons instead between the baryons as entities without internal structure. This feature significantly simplifies matters as the same parameter set is used for both, nucleon-only matter and matter with the full baryon octet. I will report the latest results of application of the QMC model to hyperonic matter and neutron stars, highlighting the vital role of experimental data on hypernuclei in constraining the model parameters. The (lack of) the so-called `hyperon puzzle’ in the QMC model will be discussed. Finally, suggestions and full support for future experiments at JPARC will be given.
(1) P.A.M. Guichon, J.R. Stone and A.W. Thomas, Progress in Nuclear and Particle Physics, 100, 262 (2018).
We review the composition and the properties of neutron stars and proto-neutron stars with a nucleonic and hypernucleonic core within a relativistic mean-field approach. We make use of the FSU2H model, which has been updated according to the recent analysis on the Xi baryon potential, and extend it to include finite temperature corrections. The calculations are done at both constant temperature and constant entropy per baryon, thus exploring the different conditions that can be found in proto-neutron stars, binary mergers remnants and supernova explosions. The inclusion of the hyperons dramatically changes the composition of the star. In particular, at large temperatures, the hyperon abundances are significant even at low densities. This can have a strong impact on several astrophysical observables, such as the mass, radius and tidal deformability of the star.
We propose an experiment for measuring the beta decay of $\Lambda$ hypernuclei to study possible modification of baryon structure in nuclear matter due to the interaction between the quarks in the baryon and the meson field in nuclear matter. The QMC (Quark Meson Coupling) model predicts that the axial charge $g_A$ of a $\Lambda$ decreases by 10% at maximum in nuclear matter, and the beta decay rate of a $\Lambda$ decreases by 20% at maximum. We plan to use the $_\Lambda^5He$ hypernucleus, which will be produced via the$^6Li(\pi^+,K^+)_\Lambda^6Li$, $_\Lambda^6Li→_\Lambda^5He+p$ reaction at J-PARC K1.1 beamline. To clearly measure the effect of the baryon modification, we will determine the beta decay rate within a 4.5% accuracy by measuring the branching ratio and the lifetime with accuracies of 4% and 2%, respectively. Measuring the branching ratio, a huge background of $\pi^0$ and $\pi^-$ from the $Λ’s$ main decay modes should be reduced down to the order of 1% of the beta decay electron signal. For this purpose, we designed apparatus around the$^6Li$ target made of plastic and lucite Cerenkov counters together with a BGO 4$\pi$ calorimeter and studied how to remove the background by simulation using the GEANT4 code. Via elaborated analysis methods for background suppression, the background rate from the $\Lambda$’s main decay modes is found to be reduced down to 4% of the beta decay electron signal. Furthermore, nonmesonic weak decay ($\Lambda p→np$ and $\Lambda n→nn$) and quasi-free $\Lambda$ production may also make background. We simulated these background processes, and these background rates are found to be reduced to ~15.5% of the beta decay electron signal. In a rough estimate, the systematic error in the beta decay branching ratio can be ~ 6% by subtracting the background events within 30% accuracy. Thus we found that this beta decay experiment is feasible.
There is presently no consensus on how the $\phi$ meson mass and width will change once it is put in a dense environment such as nuclear matter. While many theoretical works exist, connecting them with experimental measurements remains non-trivial task, as the $\phi$ meson in nuclear matter is usually produced in high-energy pA reactions, which are generally non-equilibrium processes.
In this presentation I will report on an ongoing project [1], attempting to simulate pA reactions in which the $\phi$ meson is produced in nuclei, making use of a transport approach [2]. Results of simulations of 12 GeV/30 GeV p+C and p+Cu reactions will be presented and comparisons between obtained dilepton spectra and experimental data of the E325 experiment at KEK [3] will be made.
Furthermore, predictions for the ongoing J-PARC E16 experiment [4] for both
dilepton and $K^+K^-$ spectra will be given and discussed.
[1] P. Gubler and E. Bratkovskaya, in progress.
[2] W. Cassing and E.L. Bratkovskaya, Nucl. Phys. A 831, 215 (2009).
[3] R. Muto et al., Phys. Rev. Lett. 98, 042501 (2007).
[4] S. Ashikaga et al., (J-PARC E16 Collaboration), JPS Conf. Proc. 26, 024005 (2019).
$\Xi^-$ atomic X-ray spectroscopy is a useful method for understanding the strong interaction in the S=-2 sector. One of the experimental difficulties is that the in-flight decay of $\Xi^-$ hyperon makes a huge background. We introduced a selection of $\Xi^-$-stop events using a nuclear emulsion, expecting a clean X-ray spectrum with a good significance. We performed the first Ξ- atomic measurement with a counter-emulsion hybrid method at the J-PARC K1.8 beam line (J-PARC E07). $\Xi^-$ hyperons were produced via the ($K^-, K^+$) reaction. The magnetic spectrometers and silicon strip detectors analyzed the production of $\Xi^-$ hyperon and $\Xi^-$ tracks. The prediction of the position where $\Xi^-$ hyperon hit at the emulsion surface by counters shortened the time for the emulsion image analysis. The $\Xi^-$ atomic X rays were measured by the germanium detectors array, called Hyperball-X.
We show the $\Xi^-$ Ag and $\Xi^-$ Br atomic X-ray measurement results at J-PARC E07 experiment.
The $(e, e'K^+)$ reaction experiments with several nuclear targets performed recently at the Jefferson Lab have provided high-resolution spectroscopic data. They are very fruitful in disclosing hypernuclear structure details and also in understanding hyperon-nucleon fundamental interaction properties.
Among others, the $^{10}$B $(e, e'K^+)$ $_{\,\Lambda}^{10}$Be reaction data are quite interesting, because they have shown extra subpeaks which seem difficult to be explained within the conventional model with the $p$-shell nuclear natural-parity configurations. In order to describe this novel hypernuclear structure, we have extended the model space by introducing the new configurations which include unnatural-parity nuclear core-excited states. In the extended model for each hypernuclear state of $J^{\pm}$, we take four types of configurations, $[J_{\mathrm{c}(i)}^+ \otimes s^{\Lambda}]_{J^+}$, $[J_{\mathrm{c}(i)}^+ \otimes p^{\Lambda}]_{J^-}$, $[J_{\mathrm{c}(i)}^- \otimes s^{\Lambda}]_{J^-}$, and $[J_{\mathrm{c}(i)}^- \otimes p^{\Lambda}]_{J^+}$, where $J_{\mathrm{c}(i)}^{\pm}$ denotes all the possible spin-parity states of core-nucleus, and $s^{\Lambda}$ and $p^{\Lambda}$ denote the single-particle states of $\Lambda$ hyperon. We take into account all the states of core-nuclei in the $0\hbar\omega$ and $1\hbar\omega$ space, which are labeled with $i$. It is interesting to point out that the nuclear core eigenstates with different parities are mixed by the $\Lambda$ participation. For the $_{\,\Lambda}^{10}$Be hypernucleus, natural- and unnatural-parity nuclear-core configurations, $[ J_{\mathrm{c}(i)}^+ \otimes p^{\Lambda} ]_{J^-}$ and $[ J_{\mathrm{c}(i)}^- \otimes s^{\Lambda} ]_{J^-}$, can be mixed easily by the $\Lambda N$ interaction at appropriate excitation energy. We emphasize that, for the first time, this configuration mixing successfully explains the extra subpeaks in the $^{10}$B $(e, e'K^+)$ reaction experiments.
For adjacent hypernuclei with $A=9$-$12$, we will show the energy levels and the DWIA cross-sections of $(K^-, \pi^-)$, $(\pi^+, K^+)$, and $(\gamma, K^+)$ reactions that are calculated within the extended model space. We focus on the interesting behavior of $\Lambda$ $p$-state. In $_{\Lambda}^{9}$Be, it is well known that the $\Lambda$ $p$-state splits into two orbital states, $p$-perpendicular and $p$-parallel states, which is due to the strong coupling with nuclear core deformation having the $\alpha$-$\alpha$ structure. We will discuss the theoretical spectrum of $^{10}$B $(K^-, \pi^-)$ $_{\,\Lambda}^{10}$B and $^{11}$B $(K^-, \pi^-)$ $_{\,\Lambda}^{11}$B reactions, and will show the two peaks corresponding to the $p$-perpendicular and $p$-parallel states. The extended model study will be useful for new projects of $(K^-, \pi^-\gamma)$ and $(\pi^+, K^+\gamma)$ reaction experiments with high-intensity and high-resolusion that are being planned at J-PARC.
Intense $K^-$ beam at J-PARC will enable us to investigate strangeness $-2$ systems, namely $\Xi$-hypernuclei and double-$\Lambda$ hypernuclei. In particular, the high-resolution S-2S spectromter will be a key ingredient for a systematic study of these systems by means of $(K^-,K^+)$ reactions.
The J-PARC E75 experiment plans to produce $^5_{\Lambda\Lambda}{\mathrm{H}}$ as a decay product of $^{7}_{\Xi}{\mathrm{H}}$. In the first phase, we will investigate the formation of $^{7}_{\Xi}{\mathrm{H}}$ by the $^7\mathrm{Li}(K^-,K^+)$ reaction.
We will report the outline of the E75 experiment.
Hyperon-proton scattering experiment is one of the most direct methods to study the $YN$ interaction, as in the case of the $NN$ interaction. Although it was experimentally difficult due to short lifetime of hyperons for a long time, we successfully performed novel high-statistics $\Sigma p$ scattering experiment at J-PARC (J-PARC E40 experiment). One of the physics motivations was verification of a strong repulsive force due to Pauli effect in the quark level (quark Pauli effect) in $\Sigma N (I=3/2)$ system by measuring the differential cross sections of the $\Sigma^+ p$ elastic scattering.
The experiment was performed at the K1.8 beam line in the J-PARC Hadron Experimental Facility by June 2020 for the data collection of the $\Sigma^+ p$ scattering.
Both of production of $\Sigma^+$ beam via the $\pi^+p \to K^+ \Sigma^+$ reaction and the $\Sigma^+ p$ scattering occurred in a liquid hydrogen ($\text{LH}_2$) target. The $\Sigma^+$ production reaction was analyzed using the two spectrometers and the momentum of the $\Sigma^+$ beam was tagged event by event. The recoil proton from the $\Sigma^+ p$ scattering was measured using CATCH, detector system surrounding the $\text{LH}_2$ target.
The $\Sigma^+ p$ scattering was identified by checking the consistency for the recoil proton between the measured energy and the calculated energy from kinematics. In total, approximately 2400 $\Sigma^+ p$ elastic scattering events were identified in the $\Sigma^+$ momentum range of 0.44 to 0.80 GeV/$c$.
The differential cross sections of the $\Sigma^+ p$ scattering were derived for the three separated-momentum regions. Their uncertainties were typically less than 20% with an angular step of $\Delta\cos\theta_{\text{CM}}=0.1$, and the data quality was drastically improved in comparison with past experiments. The obtained values of differential cross sections are around 2 mb/sr, which are not so large as most theoretical predictions.
Moreover, owing to precise data points and the simple representation of the $\Sigma^+ p$ system with respect to the multiplets of the $BB$ interaction, we could experimentally derive the phase shifts of the $^3S_1$ and $^1 P_1$ channels for the first time by performing the phase-shift analysis for the obtained differential cross sections. Especially, the phase shift of the $^3S_1$ channel, wherein a large repulsive core due to the quark Pauli effect was predicted, was evaluated to be $20^\circ<|\delta_{^3S_1}|<35^\circ$ for the present momentum range. This result suggests that the strength of repulsive force in $\Sigma N (I=3/2)$ system is moderate.
In this presentation, I will introduce J-PARC E40 experiment and analysis procedures to derive the differential cross sections and phase shifts of the $^3S_1$ and $^1P_1$ states for the $\Sigma^+ p$ elastic scattering.
By comparing our results to theoretical calculations, the nature of the $\Sigma^+ p$ interaction will also be discussed.
Recently, we have proposed a new experiment (J-PARC P90 experiment) to measure the missing-mass spectrum around the $\Sigma N$ threshold in the $d(K^-, \pi^-)$ reaction at 1.4 GeV/$c$. A clear enhancement was observed near the $\Sigma N$ threshold, so called "$\Sigma N$ cusp", for a long time ago. However, the dynamical origin of this enhancement remains unclear as yet. Especially, whether "$\Sigma N$ cusp" is cusp or unstable bound state has not been determined yet. One of the key to make it clear is to improve the missing-mass resolution and statistics. In this experiment, we can achieve the missing-mass resolution of 0.4 MeV in $\sigma$ by using K1.8 beam line and S-2S spectrometers at J-PARC. Moreover, we will additionally install the time projection chamber (HypTPC), which was developed for the other J-PARC experiment (E42: H-dibaryon search), to suppress quasi-free backgrounds by detecting the charged tracks of the decay products. We can deduce the scattering length of $\Sigma N$ system with isospin T = 1/2 and spin triplet channel in this experiment. In this presentation, we will show the detailed information of this new experiment.
The $\Xi$particle-nucleon interaction is the last piece of the nuclear force study that has been extended to the strange quark, and the $\Xi$ hypernuclear spectroscopy experiment will provide us the rich information. We are planning a series of $\Xi$ hypernuclear spectroscopy experiments using $(K^-, K^+)$ reactions at the Japan Proton Accelerator Re-search Complex (J-PARC), K1.8 beamline.
The $K^-$ beam with a momentum of 1.8 GeV/c is transported to the target by the K1.8 beamline spectrometer. The scattered $K^+$ associated with the $\Xi$ hypernuclei production is detected with the newly constructed magnetic spectrometer S-2S at the forward scattering angle. S-2S consists of two quadrupole magnets and one dipole magnet with the acceptance of 60 msr, and measure the momentum of the scattered $K^+$, which momentum is around 1.3 GeV/c, with a resolution of $\Delta$p/p~$5.0\times10^{-4}$. The $\Xi$ hypernuclei are identified in the missing mass spectrum, and their binding energies are determined with an accuracy of a few MeV (FWHM).
As the first experiment, a $^{12}_{\Xi}\rm{Be}$ hypernucleus spectroscopy experiment using a CH$_2$ active target is planned. The usage of an active target enables us to compensate for the event-by-event energy loss of the $K^-$ beam and scattered $K^+$ inside the target.
In order to further investigate the $\Xi$-nucleon interaction precisely, it is necessary to systematically measure the binding energies of various $\Xi$ hypernuclei using different targets. We are particularly interested in spectroscopic experiments on $^{10}_{\Xi}\rm{Li} $ hypernucleus. $^{10}_{\Xi}\rm{Li} $ hypernucleus consists of two $\alpha$ particles, one neutron, and one $\Xi$ particle, and are very unique because the interaction between $\alpha$ and $\Xi$ can be obtained. To produce the $^{10}_{\Xi}\rm{Li} $ hypernucleus, it is necessary to use the $^{10}\rm{B}(K^-, K^+)X$ reaction with a $^{10}\rm{B}$ target. It is not possible to fabricate an active target to compensate for the energy loss in case of the boron target. Therefore, the parameters of the experiment, such as target thickness, must be carefully set to achieve high statistics and high resolution at the same time.
In this presentation, we will discuss the physical motivation for the study of the $^{10}_{\Xi}\rm{Li} $ hypernucleus, and the validity of the experiment based on simulations.
We have used an isobar model to study the $K^+\Sigma^-$ photoproduction reaction on a neutron target with focus on the resonance region. In order to achieve a reasonable agreement with the data, we included spin-3/2 and spin-5/2 nucleon resonances in the consistent formalism [1,2], where spurious lower-spin modes vanish in the amplitude, together with a $\Delta$ resonance and two kaon resonances on top of the Born terms.
The free parameters of the model were adjusted to the experimental data from the CLAS [3] and LEPS [4] Collaborations on differential cross sections and photon beam asymmetry. The cornerstone of this analysis was an upgrade of the fitting method. Previously, we used only the plain $\chi^2$ minimization, which cannot prevent us from overfitting the data. We, therefore, introduced a regularization method, the least absolute selection shrinkage operator (LASSO), which, together with information criteria, restricts the number of nonzero parameters and prevent us from overfitting the data.
In our analysis [5], we arrived at two models: Fit M, whose parameters were fitted with the Minuit code only, and fit L, where we used the more advanced LASSO. Both models describe the data in a similar way and we observe only slight differences in the $\text{d}\sigma/\text{d}\Omega$ data description at very forward angles where the fit M is flat whereas fit L produces two broad peaks, and in the photon beam asymmetries above 2 GeV at backward kaon angles where the fit M produces a bump. Surprisingly, no hyperon resonances are needed for the correct data description in either model. On the other hand, the $N(1720)3/2^+$ nucleon resonance was found to be very important in both models.
[1] V. Pascalutsa, Phys. Rev. D 58, 096002 (1998).
[2] T. Vrancx, L. De Cruz, J. Ryckebusch, and P. Vancraeyveld, Phys. Rev. C 84, 045201 (2011).
[3] N. Zachariou et al., arXiv:2106.13957.
[4] H. Kohri et al. (LEPS Collaboration), Phys. Rev. Lett. 97, 082003 (2006).
[5] P. Bydžovský, A. Cieplý, D. Petrellis, D. Skoupil, and N. Zachariou, Phys. Rev. C 104, 065202 (2021).
The recent observation of two-solar-mass neutron stars rules out most of the current models of hyperonic matter equation of state, which favour the appearance of hyperons in the neutron star interior but predict maximum masses (Mmax) incompatible with data. This issue, referred to as “hyperon puzzle”, strongly suggests that the present understanding of nuclear interactions involving hyperons is far from complete. Owing to the severe difficulties involved in the extraction of the potential describing $YN$ interactions from $YN$ scattering data, the study of hypernuclear spectroscopy is the most effective approach to obtain new information, much needed to unravel the hyperon puzzle. For this reason the JLab hypernuclear collaboration has proposed to Jlab PAC a coherent series of studies of the $(e,e’K^+)$ reaction, to be performed using targets spanning a wide range of mass. The purpose of this analysis was investigation of the $\Lambda N$ interactions in a variety of nuclear media. We submitted to the PAC a proposal on $^{40}_{\Lambda}$Κ and $^{48}_{\Lambda}$Κ targets, mainly focused on the isospin dependence of hyperon dynamics, which was approved. The hypernuclei $^{40}_{\Lambda}$Κ and $^{48}_{\Lambda}$Κ, show very different isospin asymmetry ($\delta = 0.05$ and 0.188, respectively) that allows us to extract isospin dependence of the 3-body $\Lambda NN$ force. Note that in the non-strange sector the contribution of three-nucleon forces, which is known to be large and repulsive in nuclear matter at equilibrium density, is believed to be much smaller and attractive in $^{40}$Ca. For this reason valuable additional information can be obtained by expanding the kaon electroproduction program to include a study of the $^{208}{\rm Pb}(e,e' K^+ ) ^{208}_{\Lambda}{\rm Tl}$ reaction. Thanks to the extended region of constant density and the large neutron excess, $^{208}$Pb provides the best available proxy of neutron star matter. Therefore, the use of a $^{208}$Pb target will allow investigating hypernuclear dynamics in a new environment, in which three-body interactions are expected to play an important role. In addition, the availability of accurate $^{208}{\rm Pb}(e, e’p)^{207}{\rm Tl}$ data will allow extracting the Λ binding energies from the measured $(e,e’K^+)$ cross section using a largely model independent procedure. The results of this analysis will provide essential information, needed to constrain and improve the available models of $YN$ and $YNN$ potentials and confirm wether hyperonic three body forces could be the solution of the hyperon puzzle.
The $K^+ \; \Sigma^-$ photoproduction off the neutron is investigated with an Isobar model. Measurements of differential cross sections and photon beam asymmetries from the LEPS and CLAS collaborations were used to fit the parameters of the model, which are mainly the coupling constants of numerous resonances. However, fitting a model with a large number of free parameters can be problematic and often leads to overfitting the data. In such cases, the inclusion of a penalty term in the error function helps improve the quality of the fit and, if combined with certain information theoretic criteria, the fitting process effectively selects an optimal subset of the resonances involved.
We have been performed a high resolution hypernuclear mass spectroscopy measurement by the $(e,e’K^{+})$ reaction at the Thomas Jefferson National Accelerator Facility (JLab). The differential cross section for the $\Lambda/\Sigma^0$ electroproduction is fundamental information to estimate yields of hypernuclei in experiments. Although $\Lambda/\Sigma^0$ photoproduction has been studied well by CLAS, SAPHIR, LEPS and so on, $\Lambda/\Sigma^0$ electroproduction data is very limited quantitatively and qualitatively.
We performed the E12-17-003 experiment in JLab Hall-A in 2018. In this experiment, we have taken data on a gas hydrogen target, which is important not only for an absolute mass scale calibration, but for the study of $\Lambda/\Sigma^0$ electroproduction. In this talk, I will report the results of the differential cross section for the $p(e,e'K^{+})\Lambda/\Sigma^0$ reaction at $Q^2\sim0.5$ $(\mathrm{GeV}/c)^2$.
In the nucleon-nucleon ($NN$) interaction, realistic nuclear force models have been established with $NN$ scattering data. On the other hand, there are relatively large uncertainties due to limited $\Lambda N$ scattering data in case of the $\Lambda N$ interaction. The spectroscopic studies of $\Lambda$ hypernuclei have played an important role in knowledge of the effective $\Lambda n$ interaction.
An $nn\Lambda$ is a neutral baryon system which consists of two neutrons and a $\Lambda$. The study of the pure $\Lambda$-neutron system such as $nn\Lambda$ is expected to give us information on the $\Lambda n$ interaction. Although HypHI group at GSI reported measuring events which were a possibility of the bound $nn\Lambda$ [1], existence of the $nn\Lambda$ was not confirmed due to the limited significance. Since search for the $nn\Lambda$ with independent experiment is important, we measured the ${\rm ^3 H}(e,e'K^+)nn\Lambda$ reaction spectroscopy (E12-17-003) at Jefferson Lab (JLab) Hall A in 2018.
In this experiment, the $nn\Lambda$ and $\Lambda$ quasi-free ($\Lambda$-QF) production would be produced by a cryogenic tritium gas target with the thickness of 84.8 mg/cm$^2$ and a high intensity and high energy primary electron beam (${\rm I_{e}}=$22.5 $\mu$A, ${\rm E_{e}=}$4.32 GeV). The missing mass was obtained by measuring momenta of $K^+$ ($p_K=$1.8 GeV/c) and scattered electrons ($p_{e'}=$2.2 GeV/c) with two High Resolution Spectrometers (HRSs) which are the standard equipment at JLab Hall A. Validity of the missing mass was studied with the $\Lambda$ and $\Sigma^0$ mass in the ${\rm H}(e,e'K^+)\Lambda/\Sigma^0$ reaction. However, we could not find any clear peaks on the missing mass spectrum [2].
$\Lambda$-QF events in the ${\rm ^3 H}(e,e'K^+)X$ reaction were observed in this experiment. The $\Lambda$-QF distribution has an event excess around the $nn\Lambda$ threshold region. A similar excess was already found by the previous experiment that measured $\Lambda$-QF productions with the ${\rm ^3 He}(e,e'K^+)X$ reaction and it gave important information about $\Lambda n$ final state interaction (FSI) [3]. Ref. [3] successfully reproduced the excess on the missing mass by using an effective range ($r$) and a scattering length ($a$) of several effective $\Lambda N$ potential models. Since the measured system in this experiment is the pure neutral system, the $\Lambda$-QF distribution has important information about the $\Lambda n$ FSI. We fitted the $\Lambda$-QF distribution by changing the effective range and scattering length so that fitting chi-square becomes minimum.
I will present this experimental overview and the analysis result of the $\Lambda n$ FSI from the $\Lambda$-QF distribution.
[1] C. Rappold et al., Physical Review C 88, 041001 (2013).
[2] K.N. Suzuki et al., Prog. Theor. Exp. Phys. 2022, 013D01 (2022).
[3] F. Dohrmann et al., Phys. Rev. C 76, 054004 (2007).
A large-acceptance superconducting spectrometer for a series of hadron experiments, Hyperon Spectrometer, has been developed at J-PARC. The first experiment, E42, was performed using the Hyperon Spectrometer in 2021 to search for an exotic 6-quark state, the H-dibaryon. The E42 detector is sensitive to search for the H-dibaryon over a broad mass range, measuring ${\Lambda}p\pi^−, \Lambda\Lambda$, and $\Xi^-p$ systems in the $^{12}\mathrm{C}(K^−, K^+)$ reaction at $p_{K^−} = 1.8~\mathrm{GeV}/c$. In addition, we are preparing the following experiment to search for a new resonance, $\Lambda(1665)$, suggested by earlier experiments. The $\Lambda(1665)$ could be a completely new exotic state that the quark model can not explain. We will determine the spin-parity of this new resonance with the Hyperon Spectrometer. This presentation will report an overview of these exotic hadron search experiments and the current performance and future upgrades of the Hyperon Spectrometer.
We performed the J-PARC E40 experiment to measure the $\Sigma p$ scattering from 2018 to 2020. Together with the $\pi^{-}p\to K^{+}\Sigma^{-}$ data, the $\pi^-p\to K^0\Lambda$ events were accumulated as by-product data. The analysis confirmed that $\Lambda$ could be identified with reasonable accuracy of S/N ratio $\sim2.67$. Plus, we found the polarization of $\Lambda$ ($P_{\Lambda}$) was preliminarily derived as 1.009 $\pm$ 0.049 for the $K^{0}$ angular range of $0.7 < cos\theta_{CM,K^{0}} < 0.8$, using the following equation:
\begin{equation}
\frac{1}{N_0}\frac{dN}{d\cos\theta_p} = \frac{1}{2}(1+\alpha P_{\Lambda}\cos\theta_p),
\end{equation}
where $N_0$ is the yield of the decay proton, $\alpha$ is the asymmetry parameter (= $0.750\pm0.009\pm0.004$). This result has higher accuracy than the past measurement [1].
The result above indicates that we can measure not only the $\Lambda p$ differential cross-section ($(d\sigma / d\Omega)_{\Lambda p}$) but also spin observables such as analyzing power ($A_{y}$) and depolarization ($D_{yy}$) with $\sim100\%$ polarized $\Lambda$ beam. These quantities are essential inputs for establishing the realistic $\Lambda N$ interaction.
Therefore, we plan a new $\Lambda p$ scattering experiment at J-PARC K1.1, Ibaraki, Japan [2] to measure $(d\sigma / d\Omega)_{\Lambda p}$, $A_{y}$ and $D_{yy}$ with better than 10$\%$ accuracy. I will mainly talk about the $P_{\Lambda}$ analysis in J-PARC E40 data and briefly introduce the next $\Lambda p$ scattering experiment.
[1] R. D. Baker et al., Nucl. Phys. B 141, 29 (1978).
[2] K. Miwa et al., J-PARC proposal P86., 2021.
Recently, a few $\Xi$-hypernuclear events have been reported from emulsion experiments. The $\Xi$-nucleus interaction was found to be attractive. However, the binding energies and their widths of $\Xi$ hypernuclei are still uncertain based on the emulsion events, so energy spectra measured with higher statistics by spectroscopic experiments are needed.
We are going to perform a high-resolution spectroscopy of $\Xi$ hypernuclei in a missing-mass method via the $(K^{−}, K^{+})$ reaction (J-PARC E70 experiment). The experiment will be carried out at the J-PARC K1.8 beamline, which provides a high-intensity $K^{−}$ beam, with a newly constructed high resolution magnetic spectrometer S-2S. An active fiber target (AFT) will be used as an experimental target. The expected statistics and missing-mass resolutions are about 100 counts and 2 $~\textrm{MeV}/c^{2}$ (FWHM), respectively, which enable us to investigate the structure of a $\Xi$ hypernucleus with a higher signal sensitivity than previous experiments.
The AFT is composed of about 900 scintillation fibers, and the carbon nuclei contained in the scintillation fibers will be used as the target nuclei to produce $^{12} _{\Xi}$Be hypernuclei. 100 fibers per set are arranged orthogonally to the incident $K^{−}$ beam (xx'yy'), for a total of 9 sets. Scintillation light is read out from both ends of a fiber by SiPM (MPPC), and thus the total number of channels is up to 1800. The AFT enables us to directly measure the energy loss of $K^{\pm}$ particles in the target event by event because the yield of output scintillation light is proportional to the energy loss. As a result, the target missing-mass resolution of 2 $~\textrm{MeV}/c^{2}$ (FWHM) are expected to be achieved.
In this talk, I will report the status of the AFT and discuss the prospects of the J-PARC E70 experiment.
The ΛΛ pairing effects in spherical and deformed multi-L hyperisotopes are investigated in the framework of the Skyrme-Hartree-Fock approach employing a d pairing force with the pairing strength of L hyperons being 4/9 of that for nucleons. For spherical hyperisotopes, the occurrences of magic numbers -S = 2, 8, 18, 20, 34, 58, 68, and 70, which are attributed to a Woods-Saxon-like Λ hyperon potential, are evidenced by the sudden drop of 2Λ separation energies and the vanishing pairing gaps and pairing energies. The results are compared with equivalent ones in recent Hartree-Fock-Bogoliubov and relativistic-Hartree-Bogoliubov calulations. For the deformed hyperisotopes, more possible Λ hyperon magic numbers -S = 4, 6, 10, 14, 26, 30, and 32 are found based on the analysis of the single-particle energy levels, and are all sensitive to the quadrupole deformation β2. The steps of the 2Λ separation energies are accordingly smaller than in spherical hyperisotopes, and the possibilities for pairing are consistently reduced.
Light quarks form diquark clusters in hadrons and hadronic matter. We construct a chiral effective theory of spin 0 (scalar-pseudo-scalar) and 1 (axial-vector and vector) diquarks. The masses of the diquarks contain chiral invariant and non-invariant terms. The latter is given in terms of chiral condensate and thus variant in finite temperature and/or density. The parameters of the effective theory can be determined by the lattice data for diquarks as well as the masses of the single-heavy baryons (such as $\Lambda_Q$, $\Sigma_Q$ and so on with $Q= c$ or $b$). We find the mass terms of the scalar-pseudo-scalar diquarks contain a special $U_A(1)$ anomaly term, which induces an inverse mass hierarchy for the pseudo-scalar diquarks. The heavy baryon is modeled by a bound state of a heavy quark $Q$ and a diquark. We find that the inverse mass hierarchy results in qualitative difference of the mass spectra of $\Lambda_Q$ and $\Xi_Q$. The dependences of the scalar and axial-vector diquarks on the chiral order parameter are largely different. As a result, reduced chiral condensate may result in the inversion of the scalar and axial-vector diquarks, which may be observed as a change of the heavy baryon spectrum in dense matter. We apply the same model to the heavy tetraquark $T_{QQ}$ and obtain its spectrum.
Reference
M. Harada, Y.R. liu, M. Oka and K. Suzuki, Phys. Rev. D $\bf 101$, 054038 (2020),
Y. Kim, Y.R. Liu, M. Oka, and K. Suzuki, Phys. Rev. D ${\bf 104}$, 054012 (2021),
Y. Kim, M. Oka, and K. Suzuki, arXiv: 2202.06520 (2022).
Because the $\Lambda(1405)$ cannot be explained by the $qqq$ picture in the constituent quark model, it is expected to have an internal structure of, for instance, the $\bar{K}N$ molecular state. In recent experiments, many candidates for exotic hadrons have been discovered in the heavy quark sector such as $XYZ$ mesons, for which hadronic molecular states and tetraquark states are proposed. While intensive studies are performed to clarify the nature of those candidates, here we aim at discussing them from the viewpoint of the hadronic molecules.
To analyze the internal structure of the candidates for exotic hadrons, the weak-binding relation was developed as a model-independent approach [1,2]. It is the relation between observables and the compositeness which is the fraction of the hadronic molecular component of hadrons. In Ref. [2], the internal structure of $\Lambda(1405)$ is found to be dominated by the $\bar{K}N$ molecular state by using the weak-binding relation. However, the previous works did not take into account the effect of the effective range. To apply the weak-binding relation to systems with a large effective range, we need to consider a range correction to the weak-binding relation.
In this talk, we show that the weak-binding relation cannot be applied to the system with a large effective range [3]. As the range correction to the weak-binding relation, we modify the correction terms which arise from the higher order terms of the expansion. We perform the numerical calculations to check whether the modification of the weak-binding relation works or not [4]. For the calculation, we consider the effective field theory where the exact value of the compositeness is known by definition, the scattering length and effective range are independently controllable by varying the model parameters. By comparing with the compositeness from the weak-binding relation, we search for the applicable parameter regions. We find the parameter region where only the improved weak-binding relation can be applied, so the modification of correction terms of the relation works well. We apply the improved weak-binding relation to the actual hadrons, hypernuclei, and atomic systems (deuteron, $X(3872)$, $N\Omega,\Omega\Omega$ dibaryon, ${}^{3}_{\Lambda}{\rm H}$, ${}^{4}{\rm He}$ dimer), and estimate the compositeness to discuss their internal structures [5]. We show that all states are dominated by the composite components. From the results of the $X(3872)$ and the $N\Omega$ dibaryon, we find that the range correction is need to estimate the compositeness of physical states.
[1] S. Weinberg, Phys. Rev. 137, B672 (1965).
[2] Y. Kamiya and T. Hyodo, PTEP 2017, 023D02 (2017).
[3] T. Kinugawa and T. Hyodo, arXiv:2112.00249.
[4] T. Kinugawa and T. Hyodo, arXiv:2111.06619.
[5] T. Kinugawa and T. Hyodo, arXiv:2201.04283.
The SU(3) flavor symmetry in the quark model for baryons allows as many $\Xi$ resonances as $N^{*}$ and $\Delta^{*}$ combined. Only a handful of these states have been identified experimentally and among these states, only six states have three and four-star status according to PDG. The GlueX experiment, in Jefferson Lab's Hall D using a photon beam of energies up to 12 GeV allows us to study the Cascade baryon spectrum. In this presentation, we present the preliminary cross section results for the photoproduction of $\Xi(1820)^{*-}$ baryon in the reaction $\gamma p \rightarrow K^{+}Y^{0*}\rightarrow K^{+}K^{+}\Xi^{*-}$ with $\Xi^{*-}\rightarrow K^{-} \Lambda$. We are presenting the results for the Phase -I GlueX data for the incident photon beam energy range 6.0 to 11.4 GeV. These are the first total cross section results for $\Xi(1820)^{*-}$ in photoproduction.
While various theoretical studies have been performed for the excited $\Xi(1620)$ and $\Xi(1690)$ states, their nature was not well understood due to the lack of experimental data. Recently, the invariant mass distribution of the $\Xi_c\rightarrow\pi\pi\Xi$ decay was observed by the Belle collaboration [1].
By fitting the invariant mass distribution with the Breit-Wigner distribution, the mass and decay width of the $\Xi(1620)$ were obtained as $M_R=1610$ MeV and $\Gamma_R=30$ MeV, respectively. This result provides precise spectra of the $\Xi(1620)$ and $\Xi(1690)$ resonances, and therefore it is desired to perform detailed theoretical analysis.
In this work, we study the excited $\Xi$ states as dynamically generated resonances in the meson-baryon scattering amplitude using the the chiral unitary approach. In the previous study [2], the mass and width of the $\Xi(1620)$ were predicted to be $M_R=1607 $ MeV and $\Gamma_R=280$ MeV, with the natural values of the subtraction constants. Further, we find that the peak of the imaginary part does not appear by calculating this scattering amplitude of Ref. [2] on the real axis. Because of the difference between the results of Ref. [2] and those by Belle, it is required to improve the model of $\Xi(1620)$. By adjusting the subtraction constants of $\pi\Xi$ and $\bar{K}\Lambda$ channels, we successfully reproduce the mass and width of $\Xi(1620)$ by Belle. We, however, find that the threshold effect shifts the resonance peak near the threshold, by comparing the coupled channels meson-baryon scattering amplitude with the Breit-Wigner distribution. We conclude that the cation must be paid to determine the resonance pole near the threshold.
In future, studying the invariant mass distribution of the $\Xi_c\rightarrow\pi\pi\Xi$ decay in comparison with the Belle data, we aim at the determination of the spin and parity of the $\Xi$ resonances.
References
[1] Belle collaboration, M. Sumihama et al., Phys. Rev. Lett. 122, 072501 (2019).
[2] A. Ramos, E. Oset and C. Bennhold, Phys. Rev. Lett. 89. 252001 (2002).
We have studied the exotic doubly charmed $D^{*} D$ system providing a natural explanation for the peak recently observed by LHCb, in terms of $D^{*+} D^0$ and $D^{*0} D^+$ with isospin I=0. The width has been evaluated accurately based on the decay widths of the $D^{*}$ states. The $D^0 D^0 \pi^+$ decay mode of the bound state formed is studied in detail, showing a narrow peak below the $D^{*+} D^0$ threshold and some strength above it, as observed in the experiment. The remarkable agreement of this approach and the latter experimental analysis supports strongly the molecular nature of this state, the first example of a meson with two open charmed quarks. This study can be naturally extended to the bottom sector giving interesting features for the $B^{*}B\,(I=0)$ counterpart found there.
The recent discoveries of the pentaquark, $P_C$, states and $XYZ$ mesons in the charmed quark sector has initiated a new epoch in hadron physics. The existence of exotic multi-quark states beyond the conventional three and two quark systems has obviously been realised. Such states could manifest as single colour bound objects, or evolve from meson-baryon and meson-meson interactions, creating molecular like systems and re-scattering effects near production thresholds. Intriguingly, similar effects may be evidenced in the light, $uds$ sector in meson photoproduction. Access to a low momentum exchange and forward meson production region is crucial. The BGOOD photoproduction experiment is uniquely designed to explore this kinematic region; it is comprised of a central calorimeter complemented by a magnetic spectrometer in forward directions.
Our results indicate a peak-like structure in the $\gamma n \rightarrow K^0\Sigma^0$ cross section at $W\sim2$ GeV consistent with a meson-baryon interaction model which predicted the charmed $P_C$ states. The same $K^*\Sigma$ molecular nature of this proposed N*(2030) is also supported in our measurement of $\gamma p \rightarrow K^+\Lambda(1405) (\rightarrow \pi^0\Sigma^0)$, where it is predicted to drive a triangle mechanism. Additionally, a sharp drop in the $\gamma p \rightarrow K^+\Sigma^0$ cross section at very forward angles at $W \sim1.9$ GeV is observed.
Supported by DFG projects 388979758/405882627 and the European Union’s Horizon 2020 programme, grant 824093.
The hadron physics sector with strangeness content faces a promising era with the arrival of new experimental data on the strong interaction between antikaons and nucleons (nucleii). The most recent and the upcoming measurements performed with traditional and new experimental approaches will be reviewed.
Measurements of correlations between particle pairs with low relative momentum via femtoscopy have been recently demonstrated to be very sensitive to the effects of the final state strong interaction. Its application to (anti)kaon--proton pairs produced in different collision systems by the ALICE Collaboration delivers unique information on the interaction and channel couplings. Such measurements are now extended for the first time to three-body correlations providing information on the genuine three-particle interaction.
Among more traditional approaches, the first measurement of the kaonic deuterium X-rays by SIDDHARTA2 will enable access to the full isospin dependence of the scattering lengths. Studies of antikaon reactions in light nuclei at DA$\Phi$NE and J-PARC provide new measurements of cross sections at very low momentum in different inelastic channels, non resonant amplitudes below threshold and the identification and measurement of the properties of nuclear kaonic bound states, such as the very debated ppK$^{-}$.
The new data place stringent constraints and provide an updated scenario towards the description of the low-energy antikaon--nucleon interactions and the understanding of the nature and structure of the $\Lambda$(1405).
Kaonic atoms are atomic systems where an electron is replaced by a negatively charged kaon, containing a strange quark, which interacts with the nucleus also by the strong interaction. As a result, the study of kaonic atoms offers the unique opportunity to perform experiments equivalent to scattering experiments, but at vanishing relative energy. These experiments will allow to study the strong interaction between the antikaon and the nucleon or the nucleus “at threshold”, providing crucial information on the interplay between spontaneous and explicit chiral symmetry breaking in low-energy QCD.
An overview of the progress achieved in performing precision light kaonic atom experiments at DAFNE (LNF-INFN, Italy) and at J-PARC (Japan) in the last twenty years, which also solved long-pending inconsistencies with theoretical calculations generated by old measurements, will be presented. Specifically, kaonic hydrogen and kaonic helium results will be discussed. Finally, an outlook of the kaonic deuterium measurement started at DAFNE and the plans for the kaonic deuterium measurement at J-PARC will be given.
The strong interaction theory in the low energy regime, is still missing fundamental experimental results in order to achieve a breakthrough in its understanding. Among these, the investigation of the low-energy kaon-nucleon/nuclei processes plays a key-role. The talk will give an outline of the results obtained by the AMADEUS experiment performed at the DAFNE Collider of LNF-INFN.
The studies on the non-resonant hyperon pion formation amplitude below the K-N threshold and implications on the nature of the Λ(1405) will be reviewed. An updated report of the branching ratios and of the low-energy cross sections measurements (for kaon momenta up to 130 MeV/c) of the K- single and multi-nucleon absorptions on various light nuclear targets will be given.
I shall conclude with future plans on kaonic-nuclei interaction studies at DAFNE.
The low-energy $K^-N$ interaction is currently described by chiral coupled-channel meson baryon interaction models. Above threshold, all the models agree between each other since their parameters are fitted to available low-energy $K^-N$ observables. However, in the subthreshold region, relevant for $K^-$ bound states, various models have different energy-dependence, which leads to a large variety in predictions [1]. The confrontation of the chiral $K^-N$ potentials with kaonic atom data revealed the necessity to consider the absorption of $K^-$ on two and more nucleons, which is not included in the chiral models. The $K^-$ multinucleon absorption was first described by a phenomenological optical potential [2]. It was shown that only the Prague, Kyoto-Munich and Barcelona models are consistent with experimental data on $K^-$ atoms [3] and from AMADEUS collaboration [5]. A considerable imaginary part coming from the multinucleon absorption ruled out existence of narrow $K^-$-nuclear quasibound states in nuclei with $A>6$ [4].
The first connection of the $K^-NN$ absorption to chiral models was done by Sekihara et al. [5]. We have developed a microscopic model for the $K^-NN$ absorption in nuclear matter [6]. The absorption was described as a meson-exchange process and the primary $K^-N$ interaction strength was derived from the state-of-the-art chiral models. The medium modifications of the $K^-N$ scattering amplitudes due to the Pauli principle were taken into account. The model was applied in calculations of kaonic atoms for the first time. The description of the data significantly improved when the two nucleon absorption was considered. The branching ratios for various $K^-$ absorption channels in $^{12}$C$ + K^-$ atom were calculated and compared with old bubble chamber data, as well as with the latest data from the AMADEUS collaboration [7].
References:
[1] J. Hrtánková and J. Mareš, Phys. Rev. C 96 (2017) 015205.
[2] E. Friedman, A.Gal, Nucl. Phys. A 959 (2017) 66.
[3] K. Piscicchia et al., Phys. Lett. B 782 (2018) 339.
[4] J. Hrtánková and J. Mareš, Phys. Lett. B 770 (2017) 342.
[5] T. Sekihara, J. Yamagata-Sekihara, D. Jido, Y. Kanada-En’yo, Phys. Rev. C 86 (2012) 065205.
[6] J. Hrtánkova, À. Ramos, Phys. Rev. C 101 (2020) 035204.
[7] R. Del. Grande et al., Eur. Phys. J. C 79 (2019) 190.
Among the light baryons, the $J^\pi = \frac{1}{2}^-$ $\Lambda(1405)$ baryon is an important special case by sitting just below the $\bar{K}N$ threshold and decaying almost exclusively to $\Sigma\pi$. It has long been hypothesized to be either a molecular bound state or a continuum resonance, or that it is a simple quark-model resonance, the $P$-wave companion of the $\Lambda(1520)$. In recent years chiral unitary models have suggested$^a$ that there are two isospin zero poles present in this mass region, and that the ``line shape" of the $\Lambda(1405)$ depends to what extent each of the two poles are stimulated in a given reaction. Evidence for this interpretation was reported by the CLAS collaboration$^b$ in elementary photoproduction, albeit with limited statistics. Below the $N\bar{K}$ threshold, the $\Lambda(1405)$ decays to the three $\Sigma\pi$ charge combinations, but the $\Sigma^{0}\pi^{0}$ mode is purely $I=0$, uncontaminated by complications arising from $I=1$ scattering processes contributing to the reaction mechanism in the $\Sigma^{+}\pi^{-}$ and $\Sigma^{-}\pi^{+}$ decays, nor from production and decay of the nearby $\Sigma^{0}(1385)$ hyperon.
The GlueX experiment at Jefferson Lab has been used to study the $\Lambda(1405) \to \Sigma^{0}\pi^{0}$ decay mode with a photon beam in the energy range 6.5 - 11.6 GeV incident on a liquid hydrogen target and using a large acceptance charged particle tracking and electromagnetic calorimeter system. We focus on the preliminary results of $d\sigma/dM_{\Sigma^{0}\pi^{0}}$ in the $-(t-t_{min})$ range 0 - 1.5 GeV$^2$ from analyzing the reaction $\gamma p \to K^{+}\Lambda^*$ using the data collected during the first phase of the GlueX experiment.
Simultaneous fits were done to the hyperon line shapes for $\gamma p \to K^+\Sigma^0\pi^0 $ and $\gamma p \to K^+K^-p$, where the latter reaction is used as a source of events above $N\bar{K}$ threshold. The $\Lambda(1405)$ appears with a highly distorted line shape that can be decomposed into a set of coherent Breit-Wigner amplitudes interfering with each other and with the nearby $\Lambda(1520)$. We include the effect of the Flatte-type distortions evident at the $\bar{K}N$ threshold, where unitarity and analyticity affect the line shapes, including data from the above-threshold decay $\Lambda(1405) \to K^- p$.
$^a$cf. recent review: M. Mai, U-G, Meissner, Eur. Phys. J. A 51, 30 (2015)
$^b$K. Moriya et al.(CLAS Collaboration), Phys. Rev. C 87, 035206 (2013)
The GlueX experiment located at Jefferson Lab studies the spectrum of hadrons using photoproduction on a $LH_2$ target in a wide variety of final states. With its detector system capable of measuring neutral and charged final state particles over almost the full solid angle, and very good particle identification capabilities, GlueX can measure many different hadrons containing strangeness. A linearly polarized photon beam allows the measurement of polarization observables, which contain information about the production mechanisms involved in generating strange particles in photoproduction. In addition, GlueX can perform precise cross-section measurements, which help to study the spectrum of strange hadrons. In this presentation, the GlueX experiment is introduced, and recent progress of its strangeness program will be discussed. We will present recent results on $\Lambda$(1520) spin-density matrix elements and ongoing studies of the $\Lambda$(1405) lineshape. We will also present our recent progress on measurements of $\Lambda\bar\Lambda$ photoproduction and cross-section measurements of $\Xi^{(*)}$ photoproduction. Also, future prospects for strangeness measurements at GlueX will be discussed.
A new magnetic spectrometer S-2S is being installed at the K1.8 beam line of J-PARC, Japan. The installation is planned to be completed this year. The first experimental attempt is to measure the binding energy of a $\Xi$ hypernucleus $^{12}_{\Xi}$Be by a missing-mass method through the $(K^{-},K^{+})$ reaction. An expected binding-energy resolution is about $2~$MeV (FWHM) which is the best among existing data. In addition, we are planning a systematic investigation of double-strangeness nuclei following the $^{12}_{\Xi}$Be measurement. In the talk, experimental programs for the strangeness nuclear physics by using the new spectrometer S-2S at J-PARC will be introduced.
Study of nuclear matter attracts wide interests in the field of hadron physics research. A project to study high-density nuclear matter using heavy ion collisions in a beam energy range of few GeV is being prepared at J-PARC. According to past experiments and model calculations, such heavy ion collisions can produce a high-baryon density matter, which has few times larger density than a normal nuclear matter. We can study properties of hadrons in a high-density matter and properties of matter itself directly.
We have designed a heavy-ion acceleration scheme and spectrometer for the experiment. We can achieve beam energies of 1-12 AGeV/c and the collision rates of $10^{11}$ Hz. One the main purpose of the experiment is to explore the phase structures of the QCD phase diagram in a high-baryon density regime such as the first-order phase boundary and the QCD critical point, and search for color-superconducting phase. We will also measure various strange particles/nuclei and study their correlations to unveil the EOS of the matter. In addition, we also measure hadron properties, such as interactions, mass, width and decay rates, in a dese medium. Such measurements will give a bright experimental information on hadron physics in a high-density region.
In this presentation, we will show details of the project. The project is planned using a staging approach to realize the experiment as soon as possible, As the first phase of the project, we will perform the experiment with upgrades of the existing J-PARC E16 spectrometer with $10^{8}$ Hz beams. The E16 experiment is an on-going experiment at J-PARC and aims to measure properties of vector mesons in a nucleus. We will introduce details of measurements at the first phase.
Also, relations with the current activities on hadron physics studies at J-PARC will be shown.
The J-PARC Hadron Experimental Facility was constructed with an aim to explore the origin and evolution of matter in the universe through the experiments with intense particle beams. In the past decade, many results on particle and nuclear physics have been obtained at the present facility. To expand the physics programs to unexplored regions never achieved, the extension project of the Hadron Experimental Facility has been extensively discussed. We will discuss the physics of the extension of the Hadron Experimental Facility for resolving the issues in the fields of the strangeness nuclear physics, hadron physics, and flavor physics.
The present status and perspectives of hypernuclear physics (strangeness nuclear physics) are summarized based on the presentations reported in the HYP2022 conference. The talk will cover experimental activities at J-PARC, JLab, LHC, DA$\Phi$NE, GSI/FAIR, MAMI etc., and highlights of recent results and near future plans are reviewed. By combining with theoretical progress, a personal view of the future prospect in this field will be also presented.