Measurement of the prompt J/psi and psi(2S) polarizations in pp collisions at sqrt(s) = 7 TeV

TL;DR

This paper reports measurements of prompt J/psi and psi(2S) meson polarizations in proton-proton collisions at 7 TeV, using CMS data, finding no significant polarization effects across various kinematic regions.

Contribution

First comprehensive polarization measurements of prompt J/psi and psi(2S) mesons at 7 TeV in multiple kinematic regions with no observed large polarization.

Findings

No evidence of large transverse or longitudinal polarization.

Measurements extend beyond previously explored kinematic regions.

Results provide constraints for quarkonium production models.

Abstract

The polarizations of prompt J/psi and psi(2S) mesons are measured in proton-proton collisions at sqrt(s) = 7 TeV, using a dimuon data sample collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.9 inverse femtobarns. The prompt J/psi and psi(2S) polarization parameters lambda[theta], lambda[phi], and lambda[theta,phi], as well as the frame-invariant quantity lambda(tilde), are measured from the dimuon decay angular distributions in three different polarization frames. The J/psi results are obtained in the transverse momentum range 14 < pt < 70 GeV, in the rapidity intervals abs(y) < 0.6 and 0.6 < abs(y) < 1.2. The corresponding psi(2S) results cover 14 < pt < 50 GeV and include a third rapidity bin, 1.2 < abs(y) < 1.5. No evidence of large transverse or longitudinal polarizations is seen in these kinematic regions, which extend much beyond those previously explored.