This talk will discuss recent results from the CLAS Collaboration of interest to the Hadron Physics community. This will include a number of recent publications on the topic of hadron spectroscopy and also some information about upcoming hadron physics experiments planned at CLAS12. In particular, new results from two-pion electroproduction will be compared with calculations, in a search for...
The constituent quark model (CQM) describes the nucleon as a system of three constituent, or valence, quarks. Despite the successes of the CQM (e.g. masses, electromagnetic couplings, and magnetic moments), there is compelling evidence for the presence of sea quarks from other observables such as the observed flavor asymmetry of the proton, the proton spin crisis, and the systematics of strong...
The BGO-OD experiment at the ELSA accelerator facility uses an
energy tagged bremstrahlung photon beam to investigate the internal
structure of the nucleon. The setup consists of a highly segmented BGO
calorimeter surrounding the target, with a particle tracking magnetic spectrometer at forward angles.
BGO-OD is ideal for investigating the photoproduction of hadrons of
non-zero strangeness....
We use Regge phenomenology and the structure of the hyperon ($\Lambda$ and $\Sigma$) spectrum to gain insight on the nature of the two $\Lambda$(1405) resonances. We find that only of these resonances is compatible with a three-quark state.
We have recently studied the interaction of meson-baryon systems with strangeness -2 and our results explain why some Xi-baryons are narrower than expected. For instance, the latest BABAR and BELLE data show that the width of ฮ(1690) is of the order of 10 MeV. With our coupled channel calculation of the pseudoscalar meson-baryon and vector meson-baryon systems with chiral and hidden local...
A comparison of experimentally observed excited nucleon states to phenomenological quark model predictions or lattice QCD calculations reveal large differences, especially concerning the number of excited states. An important tool to probe the nucleon excitation spectrum is the study of meson photoproduction reactions. In order to extract the contributing resonances from the experimental data...
Photoproduction of $\eta$ and $\eta'$ on the nucleons was analyzed
within a new version of the $\eta$MAID model.
The model includes 23 nucleon resonances in the $s$ channel and $t$-channel
exchange of vector and axial-vector mesons with Regge cuts.
Parameters of the resonances were obtained from a fit to the new experimental data
of the A2 Collaboration and available data from CBELSA/TAPS,...
A powerful tool to investigate the properties of nucleon resonances is the detailed study of the excitation spectrum of the nucleons. It consists of many resonances which contribute with different strength to distinct decay channels. To obtain information about the contributing resonances,
the experimental measurement of several well chosen single
and double polarization observables is needed...
Photoproduction of meson pairs (in particular $\pi\pi$ and $\pi\eta$ pairs) has gained a lot of interest because it gives access to nucleon resonances that decay not directly to the nucleon ground state but in a cascade decay involving an excited intermediate state. Much emphasize has been put on neutral final states ($\pi^0\pi^0$ and $\pi^0\eta$ pairs) which are not much effected by...
While QCD is regarded as a mature theory of interacting quarks, due to the complexity of the nucleon, a successful description of its spectrum of excited states remains a huge challenge. The photo-couplings to excited $N$* states provide benchmark tests for models. These require a determination of photo-production amplitudes and are extracted through detailed partial-wave analyses (PWA), which...
The A2 Collaboration at the Mainz Microtron MAMI measures photon absorption cross sections using circularly and linearly polarized 'Bremsstrahlung' photons up to an energy of ~1.5GeV and a polarized Frozen Spin Target. We use a 4 $\pi$ detection system with the 'Crystal Ball' as central part.
One important experimental topic is the investigation of the nucleons excitation spectrum. ...
New measurements of the helicity dependence of the total inclusive photo-absorption cross section and of the partial cross sections for several reaction channels on the proton and on the neutron were carried out at the tagged photon beam facility of the MAMI accelerator (Mainz) by the A2 experiment in the energy region 200 < E$_\gamma$ < 1500 MeV.
These new, high-quality doubly-polarized...
The search for undiscovered excited states of the nucleon continues to be a focus of experiments at the Thomas Jefferson National Accelerator Facility (JLab). A large effort was done using the CEBAF Large Acceptance Spectrometer (CLAS) detector to provide the database, which will allow nearly model-independent partial wave analyses (PWA) to be carried out in the search for such states....
The search for non-strange dibaryon bound/resonance states has a long history.
A dibaryon state is of interest, which can be a molecule consisting of
two baryons or a spatially compact hexaquark object. The d*(2380) resonance
observed in the $pn$-collision reactions by the CELESIUS/WASA and WASA-at-COSY [1,2]
collaborations may be attributed to an isoscalar $\Delta\Delta$ quasi-bound...
We carry out hadron photoproduction experiments at E$\gamma$=1.5-3.0 GeV at SPring-8/LEPS. We took charged pion data on the proton at forward angles for the first time and the data were analyzed recently. The differential cross sections for the $\pi^{-}\Delta^{++}$ and $\pi^{+}\Delta^{0}$ reactions are compared. In the $\pi^{-}\Delta^{++}$ reaction $\bar{u}u$ is produced, while in the...
We report on the first observation of excited hadronic states in the beauty sector, with emphasis on beauty baryons.
Similar techniques are used to search the LHCb data for states observed in other datasets, such as the tetraquark state X(5568) whose evidence was reported by D0.
Furthermore, we discuss the searches for doubly heavy baryons, such as the doubly charmed Xicc and charmed-beauty...
$\Omega_{bbb}$ is triply heavy beauty quark baryon which makes the system very interesting. We do not have any experimental observed states for $\Omega_{bbb}$ \cite{olive}; but many lattice calculations \cite{brown, PAD2014} as well as theoretical predictions \cite{vijande2015, kwei2} have been performed for ground and excited states of this baryons. We use Hypercentral Constituent Quark model...
In the framework of the Bonn-Gatchina approach we performed a combined analysis of the Kp collision reactions. All available data from the reactions with one and two pseudo-scalar mesons in the final states are included in the analysis as well as the data with production of one vector meson. The analysis shows clearly the existence of new hyperons in the mass region above 1900 MeV and a...
We discuss the method to investigate the hadron compositeness from the analytic structure of the scattering amplitude.
Recently, there have been the discussions on the relation between the hadron structure and the position of the CDD (Castillejo-Dalitz-Dyson) zero, which is defined as the zero of an amplitude [1].
We consider a resonance in a coupled channel amplitude, in which a CDD zero...
Using the Regge-like formula $(M-m_Q)^2=\pi\sigma L$ between hadron mass $M$ and angular momentum $L$ with a heavy quark mass $m_Q$ and a string tension $\sigma$, we analyze heavy-light systems like $D/D_s/B/B_s$ mesons and charmed and bottomed baryons.
Numerical plots are obtained for $D/B$ mesons of experimental data whose slope coefficient becomes nearly equal to 1/2 of that for light...
We investigate the decays of the charmed baryons aiming at the systematic understanding of hadron internal structures based on the quark model by paying attention to heavy quark symmetry. We evaluate the decay widths and branching ratio for the pion emission for the known excited Lambca_c baryons. We find an interesting selection rule for the decays depending on their internal structure.
We...
Using more than 900 fb-1 data collected with the Belle detector at
the KEKB asymmetric-energy e+e- collider, we report observation of
excited charmed baryon states. We also provide their mass and width
measurements (with an order of magnitude of improvement). In addition,
direct production cross-section of charmed baryons is also presented.
LHCb continues to expand its world-leading sample of charmed hadrons collected during LHCโs Run 1 (2010-2012) and Run 2 (2015- present). With this data set, LHCb is discovering many previously unobserved charmed states and making the most precise determinations of the properties of known states. LHCbโs latest work on the spectroscopy of charmed hadrons is presented.
The search for resonances, both exotic and otherwise, as intermediate states in beauty and charm hadron decays at LHCb has been extremely productive in recent times. We present recent results in the amplitude analysis of these decays. Among others, this includes studies of Lb -> D p pi decays, which allow to constrain the spin/parity of the Lc(2940)+ state for the first time, and evidence for...
We examine the interaction of $D N$ and $D^* N$ states, together with their coupled channels, by using an extension of the local hidden gauge formalism from the light meson sector, which is based on heavy quark spin symmetry. The scheme is based on the use of the impulse approximation at the quark level, with the heavy quarks acting as spectators, which occurs for the dominant terms where...
