Speaker
Description
The transverse momentum ($p_{\rm T}$) 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 $p_{\rm T}$
spectra with Tsallis distribution function. The freeze-out parameters of these
particles are studied as a function of charged particle multiplicity
density ($dN_{ch}/d\eta$). In addition, we also study these parameters
as a function of 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 has been observed that the Tsallis distribution
provides a very good description of the transverse momentum
distributions of strange and multi-strange particles produced in
$p+p$ collisions at $\sqrt{s}$ = 7 TeV without incorporating the
radial flow. The parameters obtained show variations with the
multiplicity in the collision. Notably is the variation of the
non-extensive parameter, $q$ which decreases towards the value one
as the multiplicity increases, except for the $K_s^0$, which shows no
clear dependence. This shows the tendency of the produced system to
equilibrate with higher multiplicities. This goes inline with the
expected
multi-partonic interactions, which increase for higher multiplicities
in $p+p$ collisions and is thus responsible for
bringing the system towards thermodynamic equilibrium. The variable
$T$ shows a systematic increase with multiplicity, the heaviest
baryons showing the steepest increase. This is an indication of a mass
hierarchy in particle freeze-out. The radius has a tendency to remain
constant at high multiplicities. These changes have implications for the
kinetic freeze-out conditions where the heavy multi-strange hadrons
are seen to have an earlier kinetic freeze-out, meaning they come from
a smaller volume at a higher temperature. These results show that the
Tsallis distribution is an excellent tool to analyze high-energy $p+p$ collisions.
| List of tracks | Fluctuation in initial conditions, collective flow and correlations |
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