Next-to-Leading-Order QCD corrections to J/\psi(\Upsilon)+\gamma production at the LHC

TL;DR

This paper calculates NLO QCD corrections to J/psi+gamma and Upsilon+gamma production at the LHC, showing significant cross section enhancements and polarization changes, providing insights into heavy quarkonium production mechanisms.

Contribution

It presents the first NLO QCD correction calculations for J/psi+gamma and Upsilon+gamma production, highlighting the comparable contributions of color-singlet and color-octet mechanisms.

Findings

Cross section for J/psi+gamma is doubled at NLO.

Differential cross section increases by two orders of magnitude at high p_t.

J/psi polarization shifts from transverse to longitudinal at NLO.

Abstract

In this work, we calculate the next-to-leading-order (NLO) QCD corrections to the process $p+p \to J/\psi + \gamma$ via the color-singlet mechanism at the LHC. The results show that the partial cross section ($p_t^{J/\psi}>$3GeV and $|y^{J/\psi,\gamma}|<$3) is enhanced by a factor of about 2.0, and the differential cross section can be enhanced by two orders of magnitude in the large transverse momentum region of $J/\psi$. Furthermore, the polarization of $J/\psi$ changes from transverse polarization at leading-order to longitudinal polarization at NLO. For the inclusive $J/\psi$ hadroproduction, it is known that the color-octet contributions are one order of magnitude larger than the color-singlet contribution, and the polarization distribution is dominated by the color-octet behavior at NLO. In contrast, for $J/\psi+\gamma$ production the color-singlet contribution is of the same order as the color-octet contribution, and the polarization distribution arises from both the color-singlet and color-octet. Therefore, measurements of $J/\psi$ production associated with a direct photon at the hadron collider could be an important supplement to testify the theoretical framework treating with the heavy quarkonium. In addition, an NLO QCD correction to $\Upsilon+\gamma$ production at the LHC is also presented in this paper.