Event activity dependence of $ Y $ (nS) production in $ \sqrt{{{s_{NN }}}} $ = 5.02 TeV pPb and $ \sqrt{s} $ = 2.76 TeV pp collisions

Abstract

The production of Υ(1S), Υ(2S), and Υ(3S) is investigated in pPb and pp collisions at centre-of-mass energies per nucleon pair of 5.02 TeV and 2.76 TeV, respectively. The datasets correspond to integrated luminosities of about 31 nb −1 (pPb) and 5.4 pb −1 (pp), collected in 2013 by the CMS experiment at the LHC. Upsilons that decay into muons are reconstructed within the rapidity interval |y CM | < 1.93 in the nucleonnucleon centre-of-mass frame. Their production is studied as a function of two measures of event activity, namely the charged-particle multiplicity measured in the pseudorapidity interval |η| < 2.4, and the sum of transverse energy deposited at forward pseudorapidity, 4.0 < |η| < 5.2. The Υ cross sections normalized by their event activity integrated values, Υ(nS)/ Υ(nS) , are found to rise with both measures of the event activity in pp and pPb. In both collision systems, the ratios of the excited to the ground state cross sections, Υ(nS)/Υ(1S), are found to decrease with the charged-particle multiplicity, while as a function of the transverse energy the variation is less pronounced. The event activity integrated double ratios, [Υ(nS)/Υ(1S)] pPb /[Υ(nS)/Υ(1S)] pp , are also measured and found to be 0.83 ± 0.05 (stat.) ± 0.05 (syst.) and 0.71 ± 0.08 (stat.) ± 0.09 (syst.) for Υ(2S) and Υ(3S), respectively.

Shadowing effects onJ/ψandΥproduction at energies available at the CERN Large Hadron Collider

“…Finally, note that the intriguing CMS Υ(nS)/Υ(1S) ratios measured as a function of both the number of tracks at midrapidity and the transverse energy at forward rapidity [18] are not addressed. This effect, also seen in p + p collisions, is not attributable to initial-state modifications of the parton densities and, as such, is outside the scope of this work.…”

Study of ϒ $$ \varUpsilon $$ production and cold nuclear matter effects in pPb collisions at s NN $$ \sqrt{s_{NN}} $$ = 5 TeV

“…The production ratios R nS/1S have been measured in pPb [32] and PbPb [33] collisions for central rapidities by the CMS experiment and the ratios of these quantities to R nS/1S measured in pp collisions show clear sequential suppression of Υ production, which indicates stronger (cold or hot) nuclear matter effects on the excited Υ states. LHCb can extend those studies to the forward and backward rapidity regions.…”

Prospects for Quarkonium Measurements in p–A and A–A Collisions at the LHC

“…This interpretation will need to be reassessed with the Run 2 data, which starts to become available [25]. In addition, a decrease of the yield ratio between the excited ϒ states normalised to the ground state as a function of midrapidity multiplicity has been observed in p-A and in pp [47] data. This observation might be related to the same physics as the ψ(2S) suppression.…”

“…This observation might be related to the same physics as the ψ(2S) suppression. In addition to measurements as a function of multiplicity in pp [48,47] as well as in p-Pb [47,49], centrality-differential measurements in p-A collisions aiming at the distillation of the purely geometrically induced effects have been put forward in two publications by the ALICE Collaboration [50,51] and in preliminary results by ATLAS [52] using different approaches. The ALICE measurement shows a centrality dependence of the stronger suppression of ψ(2S).…”