Speaker
Description
A purely data-driven fit of J/psi, psi(2S) and chi_c1,2 measurements reported by ATLAS and CMS, including the recently measured chi_c decay distributions, constrains the polarization of the directly produced J/psi mesons to a remarkably small and pT-independent value: lambda_theta = 0.04 +- 0.06. If this observation of seemingly unpolarized quarkonium production is confirmed by more precise polarization measurements, we may be be seeing a significant violation of the non-relativistic QCD (NRQCD) velocity scaling rules, which determine the magnitudes of the colour octet contributions. Can the NRQCD factorization expansion be made compatible with such an observation? Whatever the answer, high-precision polarization measurements will improve our fundamental understanding of quarkonium production.
