Measuring space-time properties of baryon resonances around 1 GeV using intensity correlations

We measured the Δ(1232) radius using Bose-Einstein correlations (BEC) between two neutral pions from photo-production off a hydrogen/deuterium target at the incident photon energies around 1 GeV. The experiment was carried out at Research Center for Electron Photon Science (ELPH) in Tohoku University with a 4π electromagnetic calorimeter complex, named FOREST. For low-multiplicity BEC measurements, we developed an event mixing technique by introducing additional mixing constraints to delicately reduce the effect of other non-BEC correlations arising from global conservation law and resonance decays. In addition, a new BEC observing model was established to extract radius information from BEC effects in the presence of resonance decays.

Photoproduction of mesons and Compton scattering on the proton: Selected results from the A2 Collaboration at MAMI

The A2 Collaboration performs a manifold research program using real photons in the Crystal Ball/TAPS experiment at the MAMI accelerator facility in Mainz. The experiments take advantage of high- intensity unpolarized, linearly or circularly polarized photon beams, and unpolarized or polarized targets. The detector setup provides almost complete coverage in solid angle and is well suited for the detection of multi particle final states. In order to probe the internal structure of the nucleon, the spectrum of baryon resonances is studied via measurements of unpolarized cross sections and various polarization observables in single and double meson photoproduction. The program aiming to determine the scalar and spin polarizabilities of the nucleons with high precision is performed with the Compton scattering experiments. In 2017, the focal plane detector used in the tagging system of the Crystal Ball/TAPS experiment was completely renewed, allowing new measurements with unprecedentedly high precision. This paper presents recent selected results from the A2 Collaboration at MAMI.

Towards a theory of baryon resonances

In this talk, I discuss methods that allow for a systematic and model-independent calculation of the hadron spectrum. These are lattice QCD and/or its corresponding Effective Field Theories. Assorted results are shown and I take the opportunity to discuss some misconceptions often found in the literature.

Resonance behaviour of the reactions pp → {pp}sπ0 and pd → pdππ in the 1-2 GeV region

Resonance peaks observed in the cross sections of the reaction pp → {pp}sπ0, where {pp}s is the 1S0 state of the proton pair, and pd → pdππ in the GeV region are considered in the framework of mechanisms involving known baryon and two-baryon resonances.

Measurement of helicity dependence of single π0 photoproduction on deuteron

The study of the properties of the baryon resonances gives essential constraints on models for nucleon structure. Pion-photoproduction is a powerful tool to excite the nucleon to an intermediate resonant state and, in combination with polarised beams/targets, plays an important role in the investigation of the nucleon resonances. Data for polarisation observables accessible using a polarised photon beam and/or polarised nucleon targets are scarce in many channels, especially in those involving a neutron target. A systematic measurement is performed at the Mainz facility by the A2@MAMI collaboration. This talk will focus on the experiment performed at the Mainz Microtron, using a circularly polarised photon beam and a longitudinally polarised deuteron target, in conjunction with the large acceptance Crystal Ball/TAPS detection setup. An overview of the status of the experiment will be given, together with the preliminary results of polarised cross section from deuteron and of the double polarization observable E for the single π0 photoproduction reaction from the quasi-free proton and quasi-free neutron.

The production of π±, K±, p and p̄ in p–Pb collisions at sNN = 5.02 TeV

In this study, we are reporting comprehensive results on [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] production in the transverse momentum range of [Formula: see text] 4 GeV/c at midrapidity of [Formula: see text] 0.5 GeV/c, in p–Pb collisions at [Formula: see text] = 5.02 TeV. HIJING 1.0 and UrQMD 3.4 event generators are used to perform simulations and the results are compared with the ALICE and RHIC data. It is observed from the comparison that the yields for the baryons are more complex compared to the mesons and the complexity in baryons is due to the striping dynamics (spectators, leading particles of projectiles) of inner nucleus protons and neutrons. Though all the mesons could be produced during the interaction, they have maximum longitudinal momentum [Formula: see text]; baryons and mesons could be produced as a result of decay of massive baryon-resonances. Yields for the [Formula: see text] mesons are greater than the yield for the [Formula: see text] mesons. These are the well-known results from the RHIC data, which stated that the Cronin Effect is mainly due to [Formula: see text] mesons that can be produced as a result of multi-particle inner nucleus cascade. There exists the regions where yields for the [Formula: see text] mesons and baryons are same that may be due to the appearance of parton nature. The code used in simulation includes the parton dynamics earlier than it is included in the experiment.