Eur. Phys. J. A (2020) 56: 252
https://doi.org/10.1140/epja/s10050-020-00258-x

Regular Article - Theoretical Physics

Deciphering QCD dynamics in small collision systems using event shape and final state multiplicity at the Large Hadron Collider

¹ Discipline of Physics, Indian Institute of Technology Indore, Simrol, Indore, 453552, India
² Present address: Instituto de Ciencias Nucleares, UNAM, Deleg. Coyoacán, Ciudad de México, 04510, Mexico
³ Variable Energy Cyclotron Centre, 1/AF, Bidhan Nagar, Kolkata, 700064, India

^* e-mail: Raghunath.Sahoo@cern.ch

Received: 13 July 2020
Accepted: 21 September 2020
Published online: 6 October 2020

Abstract

The high-multiplicity pp collisions at the Large Hadron Collider energies with various heavy-ion-like signatures have warranted a deeper understanding of the underlying physics and particle production mechanisms. It is a common practice to use experimental data on the hadronic transverse momentum ($$p_T$$) spectra to extract thermodynamical properties of the system formed in heavy-ion and high multiplicity pp collisions. The non-availability of event topology dependent experimental data for pp collisions at $$\sqrt{s}$$ = 13 TeV on the spectra of non-strange and strange hadrons constrains us to use the PYTHIA8 simulated numbers to extract temperature-like parameters to study the event shape and multiplicity dependence of specific heat capacity, conformal symmetry breaking measure (CSBM) and speed of sound. The observables show a clear dependence on event multiplicity and event topology. Thermodynamics of the system is largely governed by the light particles because of their relatively larger abundances. In this regards, a threshold in the particle production, $$\mathrm{N}_{ch} \simeq $$ (10–20) in the final state multiplicity emerges out from the present study, confirming some of the earlier findings in this direction. As for heavier hadrons with relatively small abundances, a similar threshold is observed for $$\langle \mathrm{N}_{ch} \rangle \simeq $$ 40 hinting towards formation of a thermal bath where all the heavier hadrons are in equilibrium.