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The Future Nuclear and Hadronic Physics at the CERN-AD workshop (FuPhy2024) aims to start a discussion on possible interesting measurements to be performed at the Antiproton Decelerator (AD)/Extra Low ENergy Antiproton (ELENA) facility at CERN.
The goal is to involve experimental, theoretical, and accelerator communities to develop and generate new ideas and proposals for the future of low-energy antimatter physics using antiprotons. The topics of interest include:
The workshop will take place at the Stefan Meyer Institute, located at Georg Coch Platz 2 in Vienna, from April 8th to April 10th, 2024.
In case it is not possible to attend in person, remote participation is also available. Presentations can be conducted both in person and remotely.
The workshop fee, fixed at 100 €, must be paid in cash during the workshop.
Social Dinner
The social dinner will take place on Tuesday at 6:30 p.m. at MELKER STIFTSKELLER, located at Schottengasse 3, A-1010 Wien
https://www.melkerstiftskeller.at/
Low energy antiproton and antineutron annihilation at rest was studied at the CERN/LEAR facility between 1983 and 1996. However, the annihilation mechanism is still not fully understood and measurements at very low energies have not been performed. This talk will briefly review the current knowledge and provide guidelines for future possible experiments at the CERN AD/ELENA.
Antiproton-nucleus annihilation at rest is a process that is not well understood, despite previous experimental and theoretical work on its different aspects. One of the main reasons for its complexity are final-state interactions (FSIs), i.e. the interactions between the primary mesons and the residual nucleus. No existing model is able to describe all observables of the annihilation process, and measurements at ultra-low energies are scarce. The antiproton-nucleus reactions at rest have a notable application in experiments at the Antiproton Decelerator (AD) at CERN, the purpose of which are atomic-physics and high-precision tests of fundamental symmetries. They rely on Monte Carlo simulations that were developed for high energy physics, but these simulations perform unsatisfactorily when applied to energies relevant for these experiments.
In this talk, we will present recent experimental work on antiproton-nucleus annihilation at the ASACUSA experiment at CERN using slow extracted antiprotons and thin targets, showing results from measurements with carbon, molybdenum and gold. Additionally, we will introduce a new project aimed at measuring the multiplicity of the annihilation prongs, along with their angular and energy distribution, covering almost 4π solid angle. The results of this study, which involves approximately 15 different nuclei, will provide a necessary benchmark for current and future models, serving as a foundation for more accurate Monte Carlo simulations. At the same time, the obtained data will offer quantitative and qualitative insights into the final state interactions and their evolution with atomic number, potentially identifying novel nuclear physics processes not yet included in existing models.
INCL is a nuclear reaction code that simulates reactions between a light particle and a nucleus with energies ranging from a few MeV to a few GeV. It has been evolving for several decades and can use several types of projectile: nucleon, pion, Kaon, Lambda, Sigma, but also light nuclei (A < 19).
The characteristics of all the particles (nucleon, pion, eta and omega meson, Kaon, Lambda, Sigma) and residual nuclei (including hypernuclei) produced are stored.
To obtain the final result, INCL is combined with a de-excitation code, usually the ABLA code.
Both codes are implemented in the Geant4 particle transport code.
We have recently added a new type of projectile: the antiproton.
Antiprotons can interact with a nucleus in two different ways: at rest (they are captured in an electron orbit) and in flight (they penetrate the nucleus and initiate collisions with nucleons).
Both scenarios are available in INCL.
After a brief introduction to INCL, I will present how it handles interactions with antiprotons (hypotheses and ingredients) and show some comparisons with experimental data.
The Pontecorvo reactions are rare antiproton annihilation processes forbidden on a free nucleon but allowed on nucleons bound in nuclei. Some measurements were performed in the past at CERN’s LEAR by using deuterium target.
The measurement of branching ratios of reactions is of interest as it can contribute to clarifying the annihilation mechanism, discriminating among different existing theoretical models.
Feasibility study of a measurement of Pontecorvo reactions in $^{3}\textrm{He}$ ($\overline{p} ^{3}\textrm{He}\rightarrow pn$) at the AD facility using a simple experimental setup as an alternative to the conventional employment of a magnetic spectrometer is presented and discussed.
Despite a century since E. Rutherford's discovery of neutrons, many aspects of this particle remain uncertain. Notably, neutron halos, exemplifying the quantum realm, were revealed through indirect measurements a few decades ago. In a pioneering effort, the PUMA experiment at CERN [1] exploits the unique property of antiprotons – the sensitivity of the annihilation process to the nuclear density's tail – to investigate the asymmetry in neutron/proton distribution at the nuclei's surface. Our focus is on providing theoretical guidance to support this ambitious experiment. To that end, we study the scattering of antinucleons from various targets by introducing an $N\bar{N}$ optical potential into the No-Core Shell Model combined with the Resonating Group Method (NCSM/RGM) [2]. I will present our preliminary findings on the scattering of antinucleon from ${}^2$H, ${}^3$H, and ${}^3$He targets, including our results for low-energy observables (phaseshift, scattering length) as well as scattering cross-section.
References
[1] T. Aumann, W. Bartmann, O. Boine-Frankenheim, A. Bouvard, A. Broche, F. Butin, D. Calvet, J. Carbonell, P. Chiggiato, H. De Gersem, R. De Oliveira, T. Dobers, F. Ehm, J. F. Somoza, J. Fischer, M. Fraser, E. Friedrich, A. Frotscher, M. Gomez-Ramos, J.-L. Grenard, A. Hobl, G. Hupin, A. Husson, P. Indelicato, K. Johnston, C. Klink, Y. Kubota, R. Lazauskas, S. Malbrunot-Ettenauer, N. Marsic, W. F. O Müller, S. Naimi, N. Nakatsuka, R. Necca, D. Neidherr, G. Neyens, A. Obertelli, Y. Ono, S. Pasinelli, N. Paul, E. C. Pollacco, D. Rossi, H. Scheit, M. Schlaich, A. Schmidt, L. Schweikhard, R. Seki, S. Sels, E. Siesling, T. Uesaka, M. Vilén, M. Wada, F. Wienholtz, S. Wycech, and S. Zacarias, European Physical Journal A 58, 88 (2022).
[2] P. Navrátil, S. Quaglioni, G. Hupin, C. Romero-Redondo, and A. Calci, Physica Scripta 91,053002 (2016).
Low-energy antiprotons are known to be promising tools to probe the nuclear structure [1]. In particular, the measurement of antiprotonic atom decays and nucleon-antinucleon annihilation products is expected to provide reliable data to study the tail of nuclear densities, which has motivated the antiProton Unstable Matter Annihilation (PUMA) project [2] at CERN. Although a qualitative picture of what will happen in the PUMA experiments is known, a fully microscopic treatment of the antiproton-nucleus systems remains to be developed. Our main aim is to solve the few-body Schrodinger equation for the cases accessible by ab initio methods. It is also of paramount importance to test the model-dependence of physical observables relative to the nucleon-nucleon and nucleon-antinucleon interactions input.
Optical potentials are traditionally used to account for the complex annihilation dynamics [3]. In the present work [4], we consider an alternative approach based on a coupled-channel potential, where the annihilation is modelled by the addition of effective meson channels [5]. The model-dependence is investigated by considering the microscopic calculation of the antiproton-deuteron annihilation: the scattering lengths and the resonance energies of the antiprotonic states are computed by solving the Faddeev equations in configuration space [6], and then compared to those obtained with optical models [7].
References
[1] J. Eades and F. J. Hartmann, Rev. Mod. Phys. 71 (1999) 373.
[2] T. Aumann et al., Eur. Phys. J. A 58 (2022) 88.
[3] C. B. Dover, T. Gutsche, M. Maruyama, and A. Faessler, Prog. Part. Nucl. Phys. 29 (1992) 87.
[4] P.-Y. Duerinck, R. Lazauskas, and J. Dohet-Eraly, Phys. Rev. C 108 (2023) 054003.
[5] E. Ydrefors and J. Carbonell, Eur. Phys. J. A 57 (2021) 303.
[6] L. D. Faddeev, Zh. Eksp. Teor. Fiz. 39 (1960) 1459 ; Sov. Phys. JETP 12 (1961) 1014.
[7] R. Lazauskas and J. Carbonell, Phys. Lett. B 820 (2021) 136573 ; P.-Y. Duerinck, R. Lazauskas, and J. Carbonell, ibid. 841 (2023) 137936.
We propose a new method to measure the evolution of the neutron skin thickness between different isotopes. We consider antiproton--nucleus interactions close to the production threshold of $\Lambda \overline{\Lambda }$ and $\Sigma^-\overline{\Lambda }$ pairs. At low energies, $\Lambda \overline{\Lambda }$ pairs are produced in $\overline{\text{p}} +\text{p}$ collisions, while $\Sigma^-\overline{\Lambda }$ pairs can only be produced in $\overline{\text{p}} +\text{n}$ interactions.
Within a simple geometrical picture we show that the production ratios for $\Sigma^-\overline{\Lambda }$ and $\Lambda \overline{\Lambda }$ pairs for two different isotopes are directly related to the variation of the neutron skin thickness for the two nuclei. Performing high statistics calculations with the Gie\ss en Boltzmann--Uehling--Uhlenbeck (GiBUU) transport model for several isotope pairs we verify a strong connection between double ratio of the
$\Lambda \overline{\Lambda }$ and $\Sigma^-\overline{\Lambda }$ production probabilities and the difference of the neutron skin.
PUMA (antiProton Unstable Matter Annihilation) is a new experiment at CERN since 2021. It aims to utilise antiprotons to probe the nucleonic composition of the tail of the nuclear density distribution of both stable and exotic nuclei. Antiprotons are trapped with the ions of interest: after formation of antiprotonic atoms, the antiprotons will annihilate on the nucleus’s surface with a proton or a neutron. This process yields annihilation products whose total electric charge allows to reconstruct the isospin distribution and thus grants access to a new observable: the neutron-to-proton ratio. These insights can provide a new perspective for investigating quantum phenomena such as nuclear halos and neutron skins. In order to apply this technique on exotic nuclei which exhibit these phenomena, PUMA aims to transport up to one billion antiprotons from the AD (Antiproton Decelerator) to the ISOLDE (Isotope Separator On-Line Device) facility in a transportable trap. In this talk, the motivations of PUMA at AD and the objectives before and after LS3 will be presented. Furthermore, an overview of the current progress of the installation and commissioning of PUMA at AD will be given.
Using low-energy antiprotons, the antiProton Unstable Matter Annihilation (PUMA) experiment [1] aims to probe the isospin composition in the density tail of radioactive nuclei. For this purpose, the isotopes of interest are trapped with antiprotons in a dedicated Penning trap. By measuring the charge of the reaction products of the antiproton-nucleon annihilation, the experiment will provide the neutron-to-proton annihilation ratio as a new observable for nuclear structure theory. The experiment allows to investigate neutron skin formation of neutron-rich nuclei as well as halo nuclei. In a first measurement campaign before CERN’s long shutdown 3 (LS3), the PUMA collaboration plans to demonstrate this technique using hydrogen and helium isotopes. Furthermore, e.g. $^{16}$O, $^{40}$Ar and the Xe isotopic chain will serve as candidates to test the analysis with medium-mass nuclei.
This talk focuses on the future prospects of PUMA beyond LS3 and further. A currently planned future update is the implementation of a laser-ablation ion source, which enables the investigation of a broader range of stable nuclei. This modification will allow to study for example the proton-closed shell isotopic chains of $^{40-48}$Ca and $^{112-124}$Sn, as well as the closed shell nucleus $^{208}$Pb. These nuclei are of particular interest because they are ideal candidates to study neutron skins which have a strong link to the slope parameter (L) of the nuclear equation of state. Thus, a systematic characterization of neutron skins, e.g., contributes to our understanding of neutron stars.
A possible future path of PUMA includes the study of hypernuclei. The extent to which the formation of antiproton atoms leads to the production of hypernuclei has been investigated in simulations [2]. Only using $^{16}$O, $^{40}$Ar, $^{84}$Kr and $^{132}$Xe as target nuclei, it was shown that the formation of antiprotonic atoms provides access to over 100 currently undiscovered hyperisotopes with production rates in the order of 10$^{-5}$ to 10$^{-4}$ per annihilation. Initial ideas have therefore been sketched out as to how the PUMA infrastructure can continue to be used for the investigation of hypernuclei after the measurement campaigns have been completed.
[1] PUMA Collaboration, PUMA, antiProton unstable matter annihilation. Eur. Phys. J. A 58, 88 (2022)
[2] Schmidt, A., Gaitanos, T., Obertelli, A. et al. Production of hypernuclei from antiproton capture within a relativistic transport model. Eur. Phys. J. A 60, 55 (2024)
The neutron-antineutron oscillation violates the baryon number conservation and is of great importance in the context of testing the Grand Unified Theories and understanding the origin of the baryon asymmetry of the universe [1]. Currently, the oscillation time is constrained to be $> 0.86 \times 10^8$ s for free neutrons and $> 2.7 \times 10^8$ s for bound neutrons [2,3]. In view of future experiments to improve the limit with free neutrons, there have been recent proposals that require the knowledge of the nuclear potentials experienced by low-energy antineutrons [4,5].
In this context, there is a renewed interest in the antinucleon-nucleus interaction. The data currently available are mainly from antiprotonic atom spectroscopy and antinucleon-nucleus scattering/annihilation cross-section measurements at the time of LEAR. Although optical potential models have been developed which well describe the s-wave scattering lengths of antiprotons with nuclei, it has been pointed out that there is a serious discrepancy between the theoretical model and the experimental data [6].
In this presentation, the above topics are reviewed, and experiments that can potentially be conducted in this context will be discussed.
[1] D.G. Phillips II et al., Phys. Rep. 612, 1 (2016).
[2] M. Baldo-Ceolin et al., Z. Phys. C 63, 409 (1994).
[3] K. Abe et al. (Super-Kamiokande), Phys. Rev. D 91, 072006 (2015).
[4] K. V. Protasovet al. Phys. Rev. D 102, 075025 (2020).
[5] V. Gudkov et al., Phys. Lett. B 808, 135636 (2020).
[6] E. Friedman, Hyperfine Interact. 234, 77 (2015).
I will discuss the feasibility of an Antiproton Interferometry experiment in the slow extraction beamline of the ASACUSA experiment at the AD. A possible application to the study of Aharonov-Bohm effect with the antiproton will be discussed.
A deeply bound di-baryon composed of uuddss quarks, could be stable or sufficiently long-lived to comprise all or part of the Dark Matter. State-of-the-art lattice QCD calculations have been focussed on the existence (or not) of a weakly bound di-Lambda molecule (H-dibaryon), easily missing a deeply bound state Theoretical mass predictions using QCD sum rules range from 1200 MeV (excluded by the stability of nuclei) to unbound, while other approaches show similarly wide range of predictions. Clearly, experiment is needed to settle the question of the existence of this state, yet discovering it experimentally is surprisingly challenging. This talk will provide an overview of the properties of a deeply bound sexaquark and experimental searches undertaken to date.
Using antineutrons as probes has proved to be a smart way to achieve precise and high-quality results in nuclear and particles physics experiments, thanks to their unique features, complementary to those of antiprotons. In fact, being neutral particles, antineutrons are not subject to Coulomb scattering in a target; moreover, in the interaction with protons at rest pure I=1 eigenstates can be formed. The same situation can only be achieved with antiprotons if they interact on deuterons, but in this case the target nucleon is characterized by the Fermi motion so its momentum is hard to be precisely assessed.
From the technical point of view, producing antineutron beams with enough intensity and momentum resolution to perform dedicated experiments is not easy. Antineutron beams have been designed and put into operations since the early Eighties, as secondary beams produced following the annihilation of antiprotons, or the Charge-exchange (CEX) pbar p -> nbar n reaction. Only in the early Nineties a second-generation experiment at LEAR, OBELIX (PS201), was equipped with a section expressely conceived for the production of an antineutron beam through CEX. The produced beam could reach an intensity on the order of 100 nbars/s and a momentum, measured via Time-of-Flight, ranging continuously from ~40 to about 400 MeV/c. A total of about 35 millions of antineutron annihilations on hydrogen and/or nuclear targets were collected, which allowed to perform unprecedented studies of the dynamics of the annihilation processes and to obtain the first meson spectroscopy results ever in reactions induced by antineutrons.
However, not all of the performed observations reached a thorough comprehension and a few issues were left open: from the role of different isospin sources in the annihilation process, to the possible existence of a long-searched below-threshold baryonium bound state, to spectroscopic studies of reactions with mesons featuring open and hidden strangeness. For this reason, a fresh set of precise measurements would be desireable.
In this talk a survey on the still existing open riddles in low-energy antiproton (and antinucleon at large) physics will be presented, with some ideas for possible measurements of interest at a new antiproton facility.
The Antimatter Factory at CERN focuses on producing low-energy antiprotons for high-precision antimatter experiments. It comprises the Antiproton Decelerator (AD), which is an adaptation of the '80s Antiproton Collector (AC), and the recently commissioned Extra Low ENergy Antiproton ring (ELENA), which was commissioned in 2018. Initially, the AD could support only a single experiment at a time, typically in eight-hour shifts, delivering approximately 3e7 antiprotons at 5.3 MeV with a two-minute repetition period. Currently, with the integration of ELENA, the facility can supply four bunches of 1e7 antiprotons each at 100 keV, maintaining the same repetition period, and is capable of serving up to four experiments simultaneously or more in a sequential round-robin arrangement. The introduction of ELENA has significantly enhanced performance, suggesting new possibilities for low-energy antimatter physics research. This progress, along with the increasing complexity of the facility, calls for a thorough review of its consolidation strategy to ensure its longevity. Moreover, it presents an opportunity to contemplate future upgrades to meet the evolving demands of the scientific community. This presentation will detail the present performance and will explore feasible upgrade options for the current facility.
MELKER STIFTSKELLER
Schottengasse 3
A-1010 Wien
https://www.melkerstiftskeller.at/
Antimatter has held a significant position in both the scientific community and popular culture for many years. It has captured attention ranging from testing CPT violation to its portrayal in Hollywood movies. Numerous investigations into antiproton and its interaction with matter have been undertaken. However, the antinuclei composed of multiple antinucleons, such as the antideuteron, remain relatively unexplored territory.
In this talk, I will present our recent plan to explore new physics chance by utilizing the antideuteron beam at the K1.8 beam line of J-PARC. Based on the GiBUU calculation, we propose to measure the optical potential between antideuteron and Carbon nucleus; further more, we will examine the annihilation mechanism between multiple antinucleons and nucleons.
The generation of low-energy anti-nuclei for experimentation is a formidable challenge, stemming from the difficulty of primarily producing anti-nuclei in more than minuscule quantities during high-energy collisions. A notable exception is the antideuteron, for which several production mechanisms are known with a variety of efficiencies (from 0.1 to 10^-5) and momentum/energy distributions. This presentation explores the perspectives offered by a low-energy antideuteron beam in advancing antimatter physics and assesses its technical feasibility, with a special focus on utilizing the capabilities of the existing AD/ELENA infrastructure.
From dark matter and dark energy, to neutrino oscillations and the lack of antimatter in the universe, there is growing evidence that the Standard Model is incomplete. Tests of Quantum Electrodynamics (QED) with few-electron systems offer a promising avenue for looking for new physics, as QED is the best understood quantum field theory and extremely precise predictions can be obtained for few-electron systems. Unfortunately, despite decades of effort, QED is poorly tested in the regime of strong coulomb fields, precisely the region where new exotic physics may be most visible. I will present a new paradigm for probing higher-order QED effects using spectroscopy of Rydberg states in exotic atoms, where orders of magnitude stronger field strengths can be achieved while nuclear uncertainties may be neglected [1]. Such tests are now possible due to the advent of quantum sensing detectors and new facilities providing low-energy intense beams of exotic particles for precision physics. First measurements have been successfully conducted at J-PARC with muonic atoms [2], but antiprotonic atoms offer the highest sensitivity to strong-field QED. I will present an overview of the PAX project, now funded by an ERC starting grant, that aims to develop a new experiment for antiprotonic atom x-ray spectroscopy with a large-area transition edge sensor (TES) x-ray detector at CERN. The PAX platform can also be used to study nuclear interactions and properties, and possible synergies with existing AD experiments will be presented.
[1] N. Paul et al, Physical Review Letters 126, 173001 (2021)
[2] T. Okumura et al, Physical Review Letters 30, 173001 (2023)
In the last decades, exotic few-body atoms, in which an electron is replaced by an exotic particle, have attracted great scientific interest. These systems are indeed very useful to determine accurately the properties of their constituting exotic particles. For instance, an antiproton can be captured by a helium atom in a high orbital momentum state (typically L = 30 to 35) to form the so-called antiprotonic helium, a three-body system made of an alpha-particle, an electron, and an antiproton. This atom is in a high-L quasibound resonant state with very narrow width, hence long Auger lifetime. The radiative transitions between these quasibound states enable one to study these systems experimentally, and the recent study of antiprotonic helium led to the up-to-now most precise value of the antiproton mass [1,2]. Similar studies have been conducted with other exotic atoms, such as the pionic helium [3,4].
In order to give a comprehensive theoretical understanding of antiprotonic helium, I will present a method for computing non-relativistic resonance energies and widths for a wide range of the total orbital momentum L. I developed an approach combining the Lagrange-mesh method in perimetric coordinates [5,6] and the complex Kohn variational principle [7,8] in order to obtain the S-matrix related to the emission of the electron from the three-body system. By extrapolating this S-matrix in the complex plane from the real axis [9], the widths of the states are determined. These widths are directly related to the Auger lifetimes of the system. I will show that this approach is suited for studying very accurately the resonances of these systems for a wide range of the orbital momentum L. In addition, I will present how to take some relativistic corrections into account, as well as how to compute the radiative lifetimes between quasibound states.
References :
[1] M. Hori, A. Sótér, D. Barna et al. Nature 475, 484–488 (2011).
[2] V. I. Korobov, Physical Review A 77, 042506 (2008).
[3] M. Hori, H. Aghai-Khozani, A. Sótér et al. Nature 581, 37–41 (2020).
[4] Z. D. Bai, V. I. Korobov, Z. C. Yan, et al. Physical Review Letters, 128, 183001 (2022).
[5] D. Baye, J. Dohet-Eraly, and P. Schoofs, Physical Review A 99, 22508 (2019).
[6] D. Baye and J. Dohet-Eraly, Physical Review A 103, 022823 (2021).
[7] V. I. Korobov and I. Shimamura, Physical Review A 56, 4587 (1997).
[8] A. Kievsky, Nuclear Physics A, 624, 125-139 (1997).
[9] S. A. Rakityansky, S. A. Sofianos, and N. Elander, Journal of Physics A, 40, 14857 (2007).
The abundant production of hyperons in antiproton-proton annihilations open new avenues in the investigations of strong interactions and fundamental symmetries. In recent years, the BESIII experiment has demonstrated the merits of studying spin polarised and correlated hyperon-antihyperon pairs with several pioneering measurements of hyperon structure and precise tests of CP conservation.
With a beam of stored antiprotons, the PANDA experiment can take hyperon physics to a new level, benefitting from the expected huge samples of hyperon-antihyperon pairs. In this talk, I will discuss the potential of hyperon physics with PANDA in particular but also with antiproton beams in general.