No abstract

No abstract

No abstract

We calculate the total and the differential cross section for np scattering at low energies in the isospin I = 1 channel within the so-called extended Linear Sigma Model. This model contains conventional (pseudo)scalar and (axial-)vector mesons, as well as the nucleon and its chiral partner within the mirror assignment. In order to obtain good agreement with experimental data analysis results we need to consider two additional resonances: the lightest scalar state f0(500) and a dibaryon state with quantum numbers I = 1, J P = 0 + (a.k.a. 1 S0 resonance). The resonance f0(500) is coupled to nucleons in a chirally invariant way through the mirror assignment and is crucial for a qualitatively correct description of the shape of the differential cross section. On the other hand, the dibaryon is exchanged in the s-channel and is responsible of the large cross section close to threshold. We compare our results to data analysis results performed by the SAID program of the CNS Data Analysis Center (in the following "SAID results").

We consider a phase-space model for particle production in nuclear collisions. Once the multiplicities of the individual particle species are known, single-inclusive momentum spectra can be computed after making simplifying assumptions for the matrix element for multiparticle production.Comparison of the calculated spectra with data for pions and kaons from central Pb+Pb collisions at E Lab = 158 AGeV reveals a residual longitudinal phase-space dominance in the final state of the reaction. We account for this by modifying the isotropic, relativistic invariant phase space in a way which retains boost invariance in beam direction but suppresses large transverse momenta. Adjusting a single parameter, we obtain a reasonably good description of transverse momentum and rapidity spectra for both pions and kaons.