J/ψ polarization in pp collisions at √s=7 TeV

Phys Rev Lett. 2012 Feb 24;108(8):082001. doi: 10.1103/PhysRevLett.108.082001. Epub 2012 Feb 23.

Abstract

The ALICE Collaboration has studied J/ψ production in pp collisions at √s=7 TeV at the LHC through its muon pair decay. The polar and azimuthal angle distributions of the decay muons were measured, and results on the J/ψ polarization parameters λ(θ) and λ(φ) were obtained. The study was performed in the kinematic region 2.5<y<4, 2<p(t)<8 GeV/c, in the helicity and Collins-Soper reference frames. In both frames, the polarization parameters are compatible with zero, within uncertainties.