System size dependence of hadron p_T spectra in p+p and Au+Au collisions at sqrt{s_{NN}} = 200 GeV

We make a systematic study of transverse momentum ($p_T$) spectra of hadrons produced in $p+p$ and in different centralities of Au+Au collisions at $\sqrt{s}=200$\,GeV using phenomenological fit functions. The Tsallis distribution gives a very good description of hadron spectra in $p+p$ collisions with just two parameters but does not produce the same in Au+Au collisions at intermediate $p_{T}$. To explain the hadron spectra in heavy ion collisions in a wider $p_{T}$ range we propose a modified Tsallis function by introducing an additional parameter which accounts for collective flow. The new analytical function gives a very good description of both mesons and baryons spectra at all centralities of Au+Au collisions in terms of parameters having a potential physics interpretation. With this modified Tsallis function we study the spectra of pions, kaons, protons, $\Lambda(1115)$ and $\Xi^{-}$ as a function of system size at $\sqrt{s_{NN}}$ = 200 GeV. The parameter representing transverse flow increases with system size and is found to be more far baryons than that for mesons in central Au+Au collisions. The freeze-out temperature for baryons increases with centrality in Au+Au collisions more rapidly than for mesons.