Identified particle production in Pb-Pb and pp collisions at LHC energies

SYNOPSIS The main goal of ultra relativistic heavy-ion collisons is to investigate the strongly interacting matter, called the Quark Gluon Plasma (QGP), expected to produce in such collisions. The Large Hadron Collider (LHC) at CERN provides an unique opportunity to study such strongly interacting matter at extreme energy densities. The short lived resonances are very useful tool in high energy collisions to study the dynamics and properties of a strongly interacting medium. In particular, the K ⇤ 0 (892) meson is important because its lifetime (4 fm/c) is comparable to the time scale of the hot and dense matter produced. Owing to short lifetime, the characteris- tic properties such as mass, width, yield and transverse momentum spectra of K ⇤ 0 is very sensitive to the dynamics and in-medium e ↵ ects. Basically the decay products of K ⇤ 0 , the pions and kaons, may undergo in-medium e ↵ ects. The decay products of high momentum resonances have a larger probability to escape the system and thereby de- tected, while that of low momentum resonances can be re-scattered by other hadrons present in the medium. Thus, we can not reconstruct back the resonance and the signal is lost. On the other hand, the pions and kaons in the medium can re-generate K ⇤ 0 via pseudo-elastic interactions ( K ⇡ ! K ⇤ 0 ! K ⇡ )duringthephasebetween the chemical freeze-out (when inelastic collision ceases) and the kinetic freeze out (when elastic collision ceases). This re-generation process could compensate for the K ⇤ 0 yield, lost in re-scattering, if the system formed has a long expansion time. It was observed that the pion-pion interaction cross section is five times larger than the kaon-pion interaction cross section. The pion-pion interaction cross-section is responsible for the re-scattering, while the kaon-pion cross-section for the re-generation processes. Thus, the interplay of the two processes, re-scattering and re-generation, will decide the final resonance yield and a resonance to non-resonance particle ratio can be used to understand these processes.