Identification of baryon resonances in central heavy-ion collisions at energies between 1 and 2 AGeV

Abstract

The mass distributions of baryon resonances populated in near-central collisions of Au on Au and Ni on Ni are deduced by defolding the $p_t$ spectra of charged pions by a method which does not depend on a specific resonance shape. In addition the mass distributions of resonances are obtained from the invariant masses of $(p, \pi^{\pm})$ pairs. With both methods the deduced mass distributions are shifted by an average value of -60 MeV/c$^2$ relative to the mass distribution of the free $\Delta(1232)$ resonance, the distributions descent almost exponentially towards mass values of 2000 MeV/c^2. The observed differences between $(p, \pi^-)$ and $(p, \pi^+)$ pairs indicate a contribution of isospin $I = 1/2$ resonances. The attempt to consistently describe the deduced mass distributions and the reconstructed kinetic energy spectra of the resonances leads to new insights about the freeze out conditions, i.e. to rather low temperatures and large expansion velocities

Analysis of rapidity spectra of negative pions ind + 12C,12C + Olimov1, Iqbal2, Glagolev3 et al. 2013Phys. Rev. C13000View full textAdd to dashboardCite

“…[1][2][3][4][5][6][7][8][9] that a significant fraction of the pions produced in relativistic hadronnucleus and nucleus-nucleus collisions in bubble chamber experiments of the Joint Institute for Nuclear Research (JINR, Dubna, Russia) originated from decay of resonances. The dominant role of resonances in pion production at the energies of the order of a few GeV/nucleon or less was also revealed in earlier papers [10][11][12][13][14]. The decay kinematics of resonances was shown to be responsible for low transverse momentum enhancement of pion spectra in hadron-nucleus and nucleus-nucleus collisions at incident beam energies from 1 to 15 GeV per nucleon [9,13,14].…”

“…The major contribution (R 1 ∼ 90%) to the total multiplicity of the π − mesons came from spectral temperature T 1 ∼ 78-84 MeV, whereas, the relative yield of the high-temperature T 2 ∼ 146-155-MeV component was much lower (R 2 ∼ 10%) [18]. The spectral temperatures T 1 and T 2 and their relative contributions did not depend, within fitting errors, on the degree of collision centrality in 12 C + 12 C collisions at 4.2A GeV/c. The spectral temperatures of the π − mesons extracted in Ref.…”

“…The deuterons and 12 C nuclei were made to interact with the carbon nuclei and protons of the propane molecules and the tantalum 181 Ta foils placed in the propane bubble chamber [22,[34][35][36]. Methods of selection of inelastic d + 12 C, 12 C + 12 C, and 12 C + 181 Ta collision events in this experiment were explained in detail in Refs. [22,[34][35][36].…”

“…We aim to study the dependences of experimental rapidity distributions of negative pions, produced in d + 12 C, 12 C + 12 C, and 12 C + 181 Ta collisions at a momentum of 4.2 GeV/c per nucleon, as well as the dependences of the average transverse momenta of negative pions on their rapidity, the mass numbers of projectile and target nuclei, and degree of collision centrality. All the experimental results will systematically be compared with the corresponding results extracted by using the QGSM [26][27][28][29].…”

“…This analysis will enable the extraction of interesting information on the extent of change in the shape of the rapidity spectra of the produced negative pions and its dependences on the masses of projectile and target nuclei as well as the collision centrality. To see the influence of nuclear effects, if any, on rapidity as well as the transverse momentum versus rapidity spectra of the negative pions, the spectra of π − mesons in d + 12 C, 12 C + 12 C, and 12 C + 181 Ta collisions at 4.2A GeV/c will be compared with the corresponding spectra of π − in proton-proton collisions at the same incident momentum per nucleon. The results that come from the present analysis may be useful to help interpret the relevant experimental data obtained from high-energy heavy-ion collisions.…”