Transverse momentum spectra of hadrons in pp, pA and AA collisions

The transverse momentum spectra of the produced hadrons have been compared to a model which is based on the assumption that a nucleus-nucleus collision is a superposition of isotropically decaying thermal sources at a given freeze out temperature. The freeze-out temperature in nucleus-nucleus collisions is fixed from the inverse slope of the transverse momentum spectra of hadrons in nucleon-nucleon collision. The successive collisions in the nuclear reaction leads to gain in transverse momentum, as the nucleons propagate in the nucleus following a random walk pattern. The average transverse rapidity shift per collision is determined from the nucleon-nucleus collision data. Using these information we obtain parameter free result for the transverse momentum distribution of produced hadrons in nucleus-nucleus collisions. It is observed that such a model is able to explain the transverse mass spectra of produced pions at SPS energies. However it fails to satisfactorily explain the transverse mass spectra of kaons and protons. This indicates the presence of collective effect which cannot be accounted for by the initial state collision broadening of transverse momentum of produced hadrons, the basis of random walk model.