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

TL;DR

This study investigates how the polarization states of Y(nS) mesons vary with particle multiplicity in proton-proton collisions at 7 TeV, using CMS data, and finds no significant polarization change across multiplicities within uncertainties.

Contribution

It provides the first measurement of Y(nS) polarization dependence on multiplicity in pp collisions at 7 TeV, expanding understanding of quarkonium production.

Findings

No significant polarization change observed with multiplicity.

Large uncertainties limit definitive conclusions for Y(2S) and Y(3S).

Results are consistent across different transverse momentum ranges.

Abstract

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.