Multiplicity dependence of non-extensive parameters for strange and multi-strange particles in proton-proton collisions at $\sqrt{s} = 7$ TeV at the LHC

Abstract.

The transverse momentum ($p_{T}$) spectra in proton-proton collisions at $\sqrt{s} = 7$ TeV, measured by the ALICE experiment at the LHC are analyzed with a thermodynamically consistent Tsallis distribution. The information about the freeze-out surface in terms of freeze-out volume, temperature and the non-extensivity parameter, q, for $K^{0}_{S}$, $\Lambda +\bar{\Lambda}$, $\Xi^{-} + \bar{\Xi}^{+}$ and $\Omega^{-} + \bar{\Omega}^{+}$ are extracted by fitting the $p_{T}$ spectra with the Tsallis distribution function. The freeze-out parameters of these particles are studied as a function of the charged particle multiplicity density (d$N_{ch}$/d$\eta$. In addition, we also study these parameters as a function of the particle mass to see any possible mass ordering. The strange and multi-strange particles show mass ordering in volume, temperature, non-extensive parameter and also a strong dependence on multiplicity classes. It is observed that with increase in particle multiplicity, the non-extensivity parameter, q decreases, which indicates the tendency of the produced system towards thermodynamic equilibration. The increase in strange particle multiplicity is observed to be due to the increase of temperature and may not be due to the size of the freeze-out volume.