$η_c$ production at the LHC challenges nonrelativistic-QCD factorization

Mathias Butenschoen; Zhi-Guo He; Bernd A. Kniehl

Paper

$η_c$ production at the LHC challenges nonrelativistic-QCD factorization

Abstract

We analyze the first measurement of

production, performed by the LHCb Collaboration, in the nonrelativistic-QCD (NRQCD) factorization framework at next-to-leading order (NLO) in the strong-coupling constant

and the relative velocity

of the bound quarks including the feeddown from

mesons. Converting the long-distance matrix elements (LDMEs) extracted by various groups from

yield and polarization data to the

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.