Event activity dependence of ϒ(nS) production in √sNN = 5.02 TeV pPb and √s = 2.76 TeV pp collisions

The production of ϒ(1S), ϒ(2S), and ϒ(3S) is investigated in pFb and pp collisions at centre-of-mass energies per nucleon pair of 5.02TeV and 2.76TeV, 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 |yCM| \u3c 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 | ƞ | \u3c 2.4, and the sum of transverse energy deposited at forward pseudorapidity, 4.0 \u3c |ƞ| \u3c 5.2. The ϒ cross sections normalized by their event activity integrated values, ϒ (nS)/h ϒ (nS)i, 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