Y(nS) polarizations versus particle multiplicity in pp collisions at sqrt(s) = 7 TeV

The polarizations of the Υ(1S)Υ(1S), Υ(2S)Υ(2S), and Υ(3S)Υ(3S) mesons are measured as a function of the charged particle multiplicity in proton–proton collisions at View the MathML sources=7 TeV. The measurements are performed with a dimuon data sample collected in 2011 by the CMS experiment, corresponding to an integrated luminosity of 4.9 fb−1. The results are extracted from the dimuon decay angular distributions, in two ranges of Υ(nS)Υ(nS) transverse momentum (10–15 and 15–35 GeV), and in the rapidity interval |y|<1.2|y|<1.2. The results do not show significant changes from low- to high-multiplicity pp collisions, although large uncertainties preclude definite statements in the Υ(2S)Υ(2S) and Υ(3S)Υ(3S) cases.