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The dependence of the strangeness saturation factor on the system size, centrality and energy is studied in relativistic heavy-ion collisions. 相似文献
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J. Cleymans J. Stålnacke E. Suhonen G. M. Weber 《Zeitschrift fur Physik C Particles and Fields》1992,55(2):317-323
An equation of state is presented which takes the finite size of baryons and of mesons consistently into account and incorporates the contributions of both nonstrange and strange hadrons. All extensive quantities (energy, particle number, entropy) are modified by a factor taking into account the excluded volume due to baryon repulsion. Intensive quantities (pressure) are not modified. This is achieved by introducing a baryon chemical potential, B, which is shifted from its point-like value,
B
0
, by a term proportional to the finite volume of a hadron,V
0, as follows: B=
B
0
+ V0[P0(T,
B
0
)–P0(T, 0)], whereP
0 is the pressure for pointlike particles. The last term is necessary to conserve baryon number at the phase transition point. The differences between the new equation of state and those considered previously in the literature are discussed. It is shown that kaon condensation sets in only in the mixed phase of the transition, where hadrons, quarks and gluons are present simultaneously in thermodynamical equilibrium. 相似文献
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The inelastic leptoproduction of heavy resonances J (J = J/ψ, Ψ,…) is investigated in a model where γvg → Jg is assumed to be the dominant mechanism. Analytic expressions for the differential cross section as well as for the helicity amplitudes are presented. A detailed numerical analysis of the angular distribution of the muon pair arising from the decay of the heavy resonance in its rest frame is presented. 相似文献
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J. Cleymans K. Redlich H. Satz E. Suhonen 《Zeitschrift fur Physik C Particles and Fields》1993,58(2):347-355
We consider two scenarios for the expansion of a quark-gluon plasma. If the evolution is slow enough, the system can remain in equilibrium throughout its entire history up to the freeze-out of a hadron gas; for a very rapid expansion, it may break up into hadrons before or at the confinement transition, without ever going through an equilibrium hadron phase. We compare hadron production rates in the two approaches and show that for a hadronisation temperatureT?200 MeV and baryonic chemical potential μ B ?500 MeV, their predictions essentially coincide. Present data on strange particle production lead to values in this range and hence cannot provide a distinction between the two scenarios. Pion, nucleon and non-strange meson production seem to require a considerably lower freeze-out temperature and baryonic chemical potential. In the hadron gas picture, this is in accord with the difference in mean free path of the different hadrons in the medium; it suggests a sequential freeze-out, in which strange hadrons stop interacting earlier than non-strange hadrons. In the quark-gluon plasma break-up, the hadronic final state fails to provide the high entropy per baryon observed in non-strange hadron production. The break-up moreover leads to a decrease of the entropy per baryon; hence it must be conceptually modified before it can be considered as a viable hadronisation mechanism. 相似文献
7.
Numerical values for axion decay channel branching ratio in positronium decays are presented. From the 3S1 state the maximum is of the order of 10?6. If the axion mass were to be in the vicinity of the positronium mass, the best way of observing the signal would be the decay from the 21P1 state. The feasibility of attaining this by optical pumping is indicated. 相似文献
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Recent measurements of angular distributions in π?N→μ+μ? + … are compared with theoretical expectations based on the naive Drell-Yan model including transverse momentum for the constituents and lowest order QCD corrections. 相似文献
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The average multiplicity in deep inelastic electro- and neutrinoproduction at large ω(ω~s/Q2 + 1) is related in Feynman's version of the parton model to the average multiplicities in high-energy electron-positron annihilation and hadron-hadron scattering. The relation is: , where Ce+e? and Ch are, respectively, the coefficients of ln(s/M1⊥2) in the multiplicities from e+-e? and P-P in to hadrons, and M1⊥ is an average transverse mass. 相似文献
10.
The recently measured angular distribution of one of the leptons produced in π−N → μ+μ-+… is compared with theoretical calculations done in the framework of QCD. 相似文献