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

TL;DR

This paper examines $ ext{η}_c$ production at the LHC within the NRQCD framework, revealing significant discrepancies between NLO predictions and experimental data, and highlighting the success of the color-singlet model.

Contribution

It provides the first NLO NRQCD analysis of $ ext{η}_c$ production and compares it with experimental data, emphasizing the limitations of NRQCD in this context.

Findings

NLO NRQCD predictions overshoot LHCb data

Color-singlet model accurately describes $ ext{η}_c$ production

Heavy-quark spin symmetry used to relate LDMEs

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.