Physics Letters B
The polarizations of the ϒ(1S), ϒ(2S), and ϒ(3S) mesons are measured as a function of the charged particle multiplicity in proton–proton collisions at s=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) transverse momentum (10–15 and 15–35 GeV), and in the rapidity interval |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) and ϒ(3S) cases.
Baarmand, M M.; Bhopatkar, Vallary; Colafranceschi, Stefano; Hohlmann, Marcus; Kalakhety, H; Noonan, D; Roy, Tuhin S.; Yumiceva, Francisco X.; and CMS Collaboration, "ϒ(nS) Polarizations Versus Particle Multiplicity In pp Collisions At s=7 TeV" (2016). Aerospace, Physics, and Space Science Faculty Publications. 114.