$\eta_c$ production at the LHC challenges nonrelativistic-QCD factorization

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 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