η_c Hadroproduction at Large Hadron Collider Challenges NRQCD Factorization

II. Institut für Theoretische Physik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany

Published online: 22 March 2017

Abstract

We report on our analysis [1] of prompt η_c meson production, measured by the LHCb Collaboration at the Large Hadron Collider, within the framework of non-relativistic QCD (NRQCD) factorization up to the sub-leading order in both the QCD coupling constant α_s and the relative velocity v of the bound heavy quarks. We thereby convert various sets of J/ψ and χ_c,J long-distance matrix elements (LDMEs), determined by different groups in J/ψ and χ_c,J yield and polarization fits, to η_c and h_c production LDMEs making use of the NRQCD heavy quark spin symmetry. The resulting predictions for η_c hadroproduction in all cases greatly overshoot the LHCb data, while the color-singlet model contributions alone would indeed be sufficient. We investigate the consequences for the universality of the LDMEs, and show how the observed tensions remain in follow-up works by other groups.