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

Understand

The polarizations of the Y(1S), Y(2S), and Y(3S) mesons are measured as a function of the charged particle multiplicity in proton-proton collisions at sqrt(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 inverse femtobarns.
• The results are extracted from the dimuon decay angular distributions, in two ranges of Y(nS) transverse momentum (10-15 and 15-35 GeV), and in the rapidity interval abs(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 Y(2S) and Y(3S) cases.