Event activity dependence of Upsilon (nS) production in sqrt(s)_NN= 5.02 TeV pPb and sqrt(s) = 2.76 TeV pp collisions

The production of Y(1S), Y(2S), and Y(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 inverse nanobarns (pPb) and 5.4 inverse picobarns (pp), collected in 2013 by
the CMS experiment at the LHC. Upsilons that decay into muons are reconstructed
within the rapidity interval abs(y[CM]) < 1.93 in the nucleon-nucleon
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 abs(eta) < 2.4, and the sum of transverse energy
deposited at forward pseudorapidity, 4.0 < abs(eta) < 5.2. The Y cross sections
normalized by their event activity integrated values, Y(nS)/<Y((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, Y(nS)/Y(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,
[Y(nS)/Y(1S)][pPb] / [Y(nS)/Y(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 Y(2S) and Y(3S), respectively.