Jun 12 – 16, 2017
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Europe/Zurich timezone

Multiplicity Dependence of Thermodynamic Parameters for Strange and Multi-Strange Hadrons in Proton-Proton Collisions at $\sqrt {s}$ = 7 TeV at the LHC

Jun 13, 2017, 5:05 PM
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Nikhef Science Park 105 1098XG Amsterdam The Netherlands


Arvind Khuntia (Indian Institute of Technology Indore (IN))


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
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

Primary authors

Arvind Khuntia (Indian Institute of Technology Indore (IN)) Sushanta Tripathy (Indian Institute of Technology Indore (IN)) Raghunath Sahoo (Indian Institute of Technology Indore (IN)) Jean Cleymans (University of Cape Town)

Presentation materials