Indication of transverse radial flow in high-multiplicity proton-proton collisions at the Large Hadron Collider

Abstract

We analyze the measured spectra of $\pi^\pm$, $K^\pm$, $p$($\bar p$) in $pp$ collisions at $\sqrt {s}$ = 0.9, 2.76 and 7 TeV, in the light of blast-wave model to extract the transverse radial flow velocity and kinetic temperature at freeze-out for the system formed in $pp$ collisions. The dependency of the blast-wave parameters on average charged particle multiplicity of event sample or the `centrality' of collisions has been studied and compared with results of similar analysis in nucleus-nucleus ($AA$) and proton-nucleus ($pA$) collisions. We analyze the spectra of $K_{s}^0$, $\Lambda$($\bar \Lambda$) and $\Xi^-$ also to see the dependence of blast-wave description on the species of produced particles. Within the framework of the blast-wave model, the study reveals indication of collective behavior for high-multiplicity events in $pp$ collisions at LHC. Strong transverse radial flow in high multiplicity $pp$ collisions and its comparison with that in $pA$ and $AA$ collisions match with predictions from a very recent theoretical work [Shuryak and Zahed 2013 arXiv:1301.4470] that addresses the conditions for applicability of hydrodynamics in $pp$ and $pA$ collisions.