149 research outputs found
Open charm and charmonium production at RHIC
We calculate open charm and charmonium production in Au + Au reac- tions at ps = 200 GeV within the hadron-string dynamics (HSD) transport approach employing open charm cross sections from pN and N reactions that are fitted to results from PYTHIA and scaled in magnitude to the available experimental data. Charmonium dissociation with nucleons and formed mesons to open charm (D + ¯D pairs) is included dynamically. The comover dissociation cross sections are described by a simple phase-space model including a single free parameter, i.e. an interaction strength M2 0 , that is fitted to the J/ suppression data for Pb + Pb collisions at SPS energies. As a novel feature we implement the backward channels for char- monium reproduction by D ¯D channels employing detailed balance. From our dynamical calculations we find that the charmonium recreation is com- parable to the dissociation by comoving mesons. This leads to the final result that the total J/ suppression at ps = 200 GeV as a function of centrality is slightly less than the suppression seen at SPS energies by the NA50 Collaboration, where the comover dissociation is substantial and the backward channels play no role. Furthermore, even in case that all di- rectly produced J/ mesons dissociate immediately (or are not formed as a mesonic state), a sizeable amount of charmonia is found asymptotically due to the D + ! J/ + meson channels in central collisions of Au + Au at ps = 200 GeV which, however, is lower than the J/ yield expected from f pp collis ns
Baryon stopping and strange baryon and anti-baryon production at ultrarelativistic energies
The amount of proton stopping in central Pb+Pb collisions from 20–160 A GeV as well as hyperon and antihyperon rapidity distributions are calculated within the UrQMD model in comparison to experimental data at 40, 80, and 160 A GeV taken recently from the NA49 collaboration. Furthermore, the amount of baryon stopping at 160A GeV for Pb+Pb collisions is studied as a function of centrality in comparison to the NA49 data. We find that the strange baryon yield is reasonably described for central collisions, however, the rapidity distributions are somewhat more narrow than the data. Moreover, the experimental antihyperon rapidity distributions at 40, 80, and 160 A GeV are underestimated by up to factors of 3—depending on the annihilation cross section employed—which might be addressed to missing multimeson fusion channels in the UrQMD model. Pacs-Nr.: 25.75.2q, 24.10.Jv, 24.10.L
Baryon stopping and strange baryon/antibaryon production at SPS energies
The amount of proton stopping in central Pb+Pb collisions from 20 160 A·GeV as well as hyperon and antihyperon rapidity distributions are calcu- lated within the UrQMD model in comparison to experimental data at 40, 80 and 160 A·GeV taken recently from the NA49 collaboration. Further- more, the amount of baryon stopping at 160 A·GeV for Pb + Pb collisions is studied as a function of centrality in comparison to the NA49 data. We find that the strange baryon yield is reasonably described for central colli- sions, however, the rapidity distributions are somewhat more narrow than the data. Moreover, the experimental antihyperon rapidity distributions at 40, 80 and 160 A·GeV are underestimated by up to factors of 3 - depending on the annihilation cross section employed - which might be addressed to missing multi-meson fusion channels in the UrQMD model. PACS 25.75.+
Nucleus-nucleus collisions at high baryon densities
We study central collision of Pb + Pb at 20, 40, 80 and 160 A·GeV within the UrQMD transport approach and compare rapidity distributions of ,K+,K and with the recent measurements from the NA49 Collaboration at 40, 80 and 160 A·GeV. It is found that the UrQMD model reasonably describes the data, however, systematically overpredicts the yield by < 20%, whereas the K+ yield is underestimated by < 15%. The K yields are in a good agreement with the experimental data, the yields are also in a reasonable correspondence with the data for all energies. We find that hadronic flavour exchange reactions largely distort the information about the initial strangeness production mechanism at all energies considered. PACS: 25.75.+
Anti-strange meson-baryon interaction in hot and dense nuclear matter
We present a study of in-medium cross sections and (off-shell) transition
rates for the most relevant binary reactions for strange pseudoscalar meson
production close to threshold in heavy-ion collisions at FAIR energies. Our
results rely on a chiral unitary approach in coupled channels which
incorporates the - and -waves of the kaon-nucleon interaction. The
formalism, which is modified in the hot and dense medium to account for Pauli
blocking effects, mean-field binding on baryons, and pion and kaon
self-energies, has been improved to implement full unitarization and
self-consistency for both the - and -wave interactions at finite
temperature and density. This gives access to in-medium amplitudes in several
elastic and inelastic coupled channels with strangeness content . The
obtained total cross sections mostly reflect the fate of the
resonance, which melts in the nuclear environment, whereas the off-shell
transition probabilities are also sensitive to the in-medium properties of the
hyperons excited in the -wave amplitudes [, and
]. The single-particle potentials of these hyperons at finite
momentum, density and temperature are also discussed in connection with the
pertinent scattering amplitudes. Our results are the basis for future
implementations in microscopic transport approaches accounting for off-shell
dynamics of strangeness production in nucleus-nucleus collisions.Comment: 33 pages, 7 figures; enhanced discussion in Sec. 3; order of
presentation of results modified in Sec. 4; updated reference list; corrected
typos and wording; version to match publication in Phys. Rev.
Strange meson-baryon interaction in hot and dense medium: recent progress for a road to GSI/FAIR
We report recent results on the dynamics of strange hadrons in two-body
reactions relevant for near-threshold production in heavy-ion collisions at
GSI/FAIR and NICA-Dubna. In particular, scattering in hot and dense
nuclear matter is studied within a chiral unitary framework in coupled
channels, setting up the starting point for implementations in microscopic
off-shell transport approaches. We focus on the calculation of transition rates
with special attention to the excitation of hyperon resonances and isospin
effects. Additionally, we explore "unconventional" strangeness generation by
meson-meson and meson-baryon interactions in connection with recent HADES
observations of deep sub-threshold and production.Comment: 4 pages, 2 figures. To be published in the Proceedings of the 15th
International Conference on Strangeness in Quark Matter (SQM2015), 6-11 July
2015, JINR, Dubna, Russi
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