Rapidity dependence of soft mesons as a signature of resonance matter production in nucleus-nucleus collisions

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Abstract
Enhanced production of soft—i.e., low transverse momentum—pions has been experimentally observed in nucleus-nucleus collisions at beam energies of 14.5A GeV [the Brookhaven National Laboratory Alternating Gradient Synchrotron (AGS)] and 200A GeV (CERN Super Proton Synchrotron). Here the rapidity dependence of soft pion and kaon production for the reaction Si(14.5A GeV)+Au is studied in the framework of the relativistic quantum molecular dynamics (RQMD) approach. The softest mesons from decaying resonance matter, which turns out to be the main production mechanism in RQMD, show a peculiar rapidity dependence, a weakening of the signal in the central rapidity region of the participant nucleons. This is in striking contrast to expectations from all other suggested mechanisms like mean fields, collective flow, and quantum statistical effects. The prediction can be tested by forthcoming experiments at the AGS in the near future. It is also predicted that a similar, though quantitatively much weaker, signal can be observed in the kaon spectra.