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

Abstract

We analyze the measured spectra of π ± , K ± , p(p) in pp collisions at √ 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 0 s , Λ(Λ) and Ξ − 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:hep-ph/1301.4470] that addresses the conditions for applicability of hydrodynamics in pp and pA collisions.

Indication of change of phase in high-multiplicity proton-proton events at LHC in string percolation model

“…In this scenario of the QGP study, an unexpected feature, namely the "ridge" in the long range near side angular correlation, in distinct class of "high multiplicity" events of proton-proton collisions [10] at √ s = 7 TeV at LHC has triggered revival of an old school of thought [11][12][13][14] of the possibility of formation of a collective medium in pp collisions also. Several of subsequent theoretical and phenomenological studies [15][16][17][18][19][20][21][22][23], in different approaches, endorse the possibility, indicating the need for further investigations in understanding the high-multiplicity pp events vis-a-vis the QGP.In this article, we address the issue of collectivity in high multiplicity pp events in the framework of the String Percolation Model, that has successfully explained the collectivity and the change of phase in nucleus-nucleus collisions [24][25][26]. Also SPM describes the centre-of-mass energy dependence of mid-rapidity multiplicity [25] and the pseudorapidity distributions [26] of produced charged particles in pp collisions, for the entire range of energy, available so far.…”

“…In this scenario of the QGP study, an unexpected feature, namely the "ridge" in the long range near side angular correlation, in distinct class of "high multiplicity" events of proton-proton collisions [10] at √ s = 7 TeV at LHC has triggered revival of an old school of thought [11][12][13][14] of the possibility of formation of a collective medium in pp collisions also. Several of subsequent theoretical and phenomenological studies [15][16][17][18][19][20][21][22][23], in different approaches, endorse the possibility, indicating the need for further investigations in understanding the high-multiplicity pp events vis-a-vis the QGP.…”

Study of collectivity in $pp$ collisions at LHC energies.

“…The same data are explained by using blast wave (BGBW) models in [1], where the authors extract a common flow velocity β and common kinetic temperature T kin using simultaneous fit. The authors also hint for the presence of collectivity from the BGBW analysis.…”

Indication of Collective flow and Transparency in p-p Collisions at LHC.

“…The occurrence of the high energy density events in high multiplicity p -p collisions [22,23] at CERN-SPS motivated searches for hadronic deconfinement in these collisions at √s NN = 0.54 TeV at SPS [18] and at √s NN = 1.8 TeV [19,20] at the Tevatron, Fermilab. A common radial flow velocity for meson and anti-baryon found from the analysis of the transverse momentum data of the Tevatron [19] had been attributed to as an evidence for collectivity due to the formation of QGP [24].…”