$\eta_c$ production at LHC and indications on the understanding of $J/\psi$ production

TL;DR

This paper evaluates prompt $ta_c$ production at the LHC using next-to-leading order nonrelativistic QCD, constraining the $J/$ color-octet matrix element and informing the understanding of quarkonium production mechanisms.

Contribution

It provides a complete NLO evaluation of $ta_c$ production and constrains the $J/$ color-octet matrix element using recent experimental data.

Findings

The upper bound on the $J/$ color-octet matrix element is consistent with previous $J/$ yield and polarization studies.

The results describe measurements well but conflict with some theoretical estimates.

Provides insights into nonrelativistic QCD factorization for quarkonium production.

Abstract

We present a complete evaluation for the prompt $\eta_c$ production at the LHC at next-to-leading order in $\alpha_s$ in nonrelativistic QCD. By assuming heavy quark spin symmetry, the recently observed $\eta_c$ production data by LHCb results in a very strong constraint on the upper bound of the color-octet long distance matrix element $1S0$ of $J/\psi$. We find this upper bound is consistent with our previous study of the $J/\psi$ yield and polarization and can give good descriptions for the measurements, but inconsistent with some other theoretical estimates. This may provide important information for understanding the nonrelativistic QCD factorization formulism.