${\eta }_c$ production at the LHC challenges nonrelativistic-QCD factorization

Abstract

We analyze the first measurement of ${\eta }_c$ production, performed by the LHCb Collaboration, in the nonrelativistic-QCD (NRQCD) factorization framework at next-to-leading order (NLO) in the strong-coupling constant ${\alpha }_s$ and the relative velocity $v$ of the bound quarks including the feeddown from $h_c$ mesons. Converting the long-distance matrix elements (LDMEs) extracted by various groups from $J/\psi$ yield and polarization data to the ${\eta }_c$ case using heavy-quark spin symmetry, we find that the resulting NLO NRQCD predictions greatly overshoot the LHCb data, while the color-singlet model provides an excellent description.

Comments: 5 pages, 2 figures, minor changes, note regarding arXiv:1411.7350 [hep-ph] added, accepted for publication in Physical Review Letters