Experimental results in pion induced reaction with carbon and polyethylene targets obtained by HADES-GSI

0557368 - ÚJF 2023 CZ eng D - Thesis
Rodriguez Ramos, Pablo
Experimental results in pion induced reaction with carbon and polyethylene targets obtained by HADES-GSI.
Ústav jaderné fyziky AV ČR. Defended: Fakulta jaderná a fyzikálně inženýrská, Katedra fyziky, ČVUT. 14. 6. 2021. - Praha, 2021. 188 s.
Institutional support: RVO:61389005
Keywords : HADES * FAIR * dileptons * baryonic resonance * pion beam * VDM * vector meson
OECD category: Nuclear related engineering
https://www.fjfi.cvut.cz/cz/studium/doktorske-studium/archiv-doktorskych-praci/997-ramos-pablo-rodriguez

In the summer of 2014, HADES collaboration was conducting measurements with secondary pion beam at GSI using carbon and polyethylene targets. The program was devoted to study the electromagnetic baryonic transitions in the time-like region. In particular, the experiment has been carried out in the second resonance region, (N(1520), N(1535)), at √ s = 1.49 GeV, in that kinematical region the off-shell (ρ, ω) vector meson are expected to play a crucial role. The decay of the baryonic resonance into ρN is of special interest because it is connected with the in-medium modifications of the ρ meson spectral function at finite baryon densities. Using the polyethylene and carbon target allow us to study the inclusive e +e − production and the exclusive π −p → ne+e − reaction, in addition to hadronic channels. The normalization of spectra has been done using elastic scattering of pion on polyethylene and carbon. Predictions of the Dalitz decay of the baryonic esonances N(1520) and N(1535) treated as point-like, underestimate the invariant mass yield larger than Me+e− > 300 MeV/c 2. The description of the excess in the yield is achieved taking into account the time-like electromagnetic form factors using a Vector Dominance Model (VDM) formalism, which generates the off-shell ρ production using the results from the Bonn-Gatchina Partial Waves Analysis (PWA) of two pion production measured during the same experiment. HADES data is the only sample with charged double pion channels and therefore it is sensitive to the ρ production. The add in of the off-shell ρ contribution either in the inclusive or exclusive invariant mass distribution improved significantly the description of
the spectra, and therefore, the validity of the VDM formalism for baryon electromagnetic transitions. Current results stimulate further experiments using pion beam to study electromagnetic transitions in the third resonance region, also hyperon Dalitz decay in proton induced reactions are expected.
The second part of the thesis report about a commissioning experiment carried out at MAMI facility in the Johannes Gutenberg Universität, Mainz (Germany), connected with the Electromagnetic CALorimeter (ECAL) which is being developed to complement the dilepton spectrometer HADES. The HADES spectrometer is currently operating on the beam of SIS18 accelerator in GSI, in future, it will be moved to a new location in the CBM cave of the future FAIR complex. Electromagnetic calorimeter (ECAL) enables the HADES experiment to measure data on neutral meson production in heavy ion collisions at the energy range of 2-10 A GeV on the beam of the future accelerator SIS100, but also with the lower energy beam of the current accelerator SIS18. The calorimeter will be based on 978 massive lead glass modules read out by photomultipliers and a novel front-end electronics, it will cover forward angles 12◦ < θ < 45◦ and almost full azimuthal angle. Secondary gamma beam with energies ranging from 81 MeV up to 1399 MeV from MAMI-C Mainz facility was used to verify selected technical solutions.
The photon beam hit the setup at three different positions (−4 cm, −2 cm, center of the module = 0 cm, +2 cm) and under three inclinations (angles 0◦ , 6 ◦ and 12◦ with respect to the module’s longitudinal axis), in order to study the energy leakage between neighboring modules. Two prototypes of front-end electronics (“Cracow” and PaDiWa AMPS) were tested as well. Relative energy resolution was measured using modules with three different types of photomultipliers.
Permanent Link: http://hdl.handle.net/11104/0331410