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Register a new userExcitation function of entropy and pion production from AGS to SPS energies
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Entropy production in the initial compression stage of relativistic heavy-ion collisions from AGS to SPS energies is calculated within a three-fluid hydrodynamical model. The entropy per participating net baryon is found to increase smoothly and does not exhibit a jump or a plateau as in the 1-dimensional one-fluid shock model. Therefore, the excess of pions per participating net baryon in nucleus-nucleus collisions as compared to proton-proton reactions also increases smoothly with beam energy.
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A relativistic transport model is used to study Xi- production in 2-11A GeV Au+Au collisions. Introducing the strangeness-exchange reactions between antikaons and hyperons as the sources for Xi-, we find that the cascade yield in these collisions is in reasonable agreement with the data. Although the Xi- abundance does not reach chemical equilibrium unless the cross section for strangeness-exchange reactions is enhanced by six times, it exhibits the strongest enhancement with increasing centrality of collision and with increasing beam energy.
Global strangeness production in relativistic heavy ion collisions at SPS and RHIC is reviewed. Special emphasis is put on the comparison with the statistical model and the canonical suppression mechanism. It is shown that recent RHIC data on strange particle production as a function of centrality can be explained by a superposition of a fully equilibrated hadron gas and particle emission from single independent nucleon-nucleon collisions in the outer corona.
We present a fully relativistic formalism for describing neutrino-induced $Delta$-mediated single-pion production from nuclei. We assess the ambiguities stemming from the $Delta$ interactions. Variations in the cross sections of over 10% are observed, depending on whether or not magnetic-dipole dominance is assumed to extract the vector form factors. These uncertainties have a direct impact on the accuracy with which the axial-vector form factors can be extracted. Different predictions for $C_5^A(Q^2)$ induce up to 40-50% effects on the $Delta$-production cross sections. To describe the nucleus, we turn to a relativistic plane-wave impulse approximation (RPWIA) using realistic bound-state wave functions derived in the Hartree approximation to the $sigma$-$omega$ Walecka model. For neutrino energies larger than 1 GeV, we show that a relativistic Fermi-gas model with appropriate binding-energy correction produces comparable results as the RPWIA which naturally includes Fermi motion, nuclear-binding effects and the Pauli exclusion principle. Including $Delta$ medium modifications yields a 20 to 25% reduction of the RPWIA cross section. The model presented in this work can be naturally extended to include the effect of final-state interactions in a relativistic and quantum-mechanical way. Guided by recent neutrino-oscillation experiments, such as MiniBooNE and K2K, and future efforts like MINER$ u$A, we present $Q^2$, $W$, and various semi-inclusive distributions, both for a free nucleon and carbon, oxygen and iron targets.
We investigate charged and neutral current neutrino-induced incoherent pion production off nuclei within the GiBUU model at energies relevant for the MiniBooNE and K2K experiments. Special attention is paid to the entanglement between measured CCQE and CC1pi+ cross sections. We further give predictions and compare to recent data measured at MiniBooNE.
Inclusive and semi-inclusive measurements are presented for antiproton ($bar{p}$) production in proton-nucleus collisions at the AGS. The inclusive yields per event increase strongly with increasing beam energy and decrease slightly with increasing target mass. The $bar{p}$ yield in 17.5 GeV/c p+Au collisions decreases with grey track multiplicity, $N_g$, for $N_g>0$, consistent with annihilation within the target nucleus. The relationship between $N_g$ and the number of scatterings of the proton in the nucleus is used to estimate the $bar{p}$ annihilation cross section in the nuclear medium. The resulting cross section is at least a factor of five smaller than the free $bar{p}-p$ annihilation cross section when assuming a small or negligible formation time. Only with a long formation time can the data be described with the free $bar{p}-p$ annihilation cross section.
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