Measurement of the Y(1S), Y(2S), and Y(3S) polarizations in pp collisions at sqrt(s) = 7 TeV

TL;DR

This study measures the polarization states of Y(1S), Y(2S), and Y(3S) mesons in proton-proton collisions at 7 TeV, finding no significant polarization effects within the analyzed kinematic range.

Contribution

It provides the first detailed polarization measurements of Y(nS) mesons at 7 TeV in specific kinematic regions using CMS data.

Findings

No large transverse or longitudinal polarization observed.

Polarization parameters are consistent with zero within uncertainties.

Results constrain theoretical models of quarkonium production.

Abstract

The polarizations of the Y(1S), Y(2S), and Y(3S) mesons are measured in proton-proton collisions at sqrt(s) = 7 TeV, using a data sample of Y(nS) to oppositely charged muon pair decays collected by the CMS experiment, corresponding to an integrated luminosity of 4.9 inverse femtobarns. The dimuon decay angular distributions are analyzed in three different polarization frames. The polarization parameters lambda[theta], lambda[phi], and lambda[theta,phi], as well as the frame-invariant quantity lambda-tilde, are presented as a function of the Y(nS) transverse momentum between 10 and 50 GeV, in the rapidity ranges abs(y) < 0.6 and 0.6 < abs(y) < 1.2. No evidence of large transverse or longitudinal polarizations has been seen in the explored kinematic region.