Studies of Baryon Resonances with the HADES Spectrometer and Pion Beams @ GSI
(H. Niewodniczanski Institute of Nuclear Physics PAN)
Aula Leale (LNF INFN)
The HADES (High Acceptance DiElectron Spectrometer) detector, installed at GSI in Darmstadt, was designed to measure e+epairs (dielectrons) in the 13.5 AGeV energy range. The experimental program of HADES focuses on two main goals. The first one is to measure dielectron emission from a compressed baryonic matter formed in heavy ion collisions and investigate inmedium hadron properties. The second goal is to study dielectron production in elementary proton–proton (pp) and pion–proton (mp) collisions and learn about hadron electromagnetic structure. Both objectives are complementary in a sense that the understanding of the in-medium effects involves also investigations of the dielectron invariant mass spectra in elementary mp,pp reactions. The elementary collisions, especially those with pion beams, also offer a great opportunity to unambiguously fix the description of baryonic resonances and their coupling to the light vector mesons (rho/omega) which plays essential role for the inmedium modifications. Therefore, to understand resonances production mechanisms a systematic energy scan and high precision data are needed. In 2014 a large dataset of m-p scattering have been obtained at four pion beam momenta (0.656, 0.69, 0.748 and 0.8 GeV/c). The data have been included into the multichannel Partial Wave Analysis (PWA) developed by the BonnGatchina group. A combined PWA analysis of all available data provides better understanding of the vector mesonresonance couplings and their impact on the transition formfactors. Recently, a new model of dielectrons productions in the exclusive reaction m N->Ne+e- within an effective field theory approach was proposed. Experimental and theoretical investigations of the reaction is in a great importance in determining the electromagnetic properties of baryon resonances. Therefore, the available calculations needs to be verified. In this seminar the analysis method and the recent results of m-p scattering for various channels will be presented. Also comparison to the current PWA calculations will be discussed. In an outlook, plans for utilizing the pion beams with the upgraded HADES detector and FAIR Phase0 experiments will be outlined.