Relativistic corrections to exclusive $\chi_{cJ} + \gamma$ production from $e^+ e^-$ annihilation

TL;DR

This paper calculates relativistic corrections to the exclusive production of chi_cJ plus gamma in electron-positron annihilation using NRQCD, including new contributions from octet operators, and provides cross section estimates with uncertainties.

Contribution

First calculation of relativistic corrections including octet contributions for chi_cJ + gamma production in e+e- annihilation within NRQCD framework.

Findings

Cross section for chi_c0 + gamma: (1.3 ± 0.4) fb

Cross section for chi_c1 + gamma: (15.4 ± 6.7) fb

Cross section for chi_c2 + gamma: (4.7 ± 2.6) fb

Abstract

We calculate in the non-relativistic QCD (NRQCD) factorization framework all leading relativistic corrections to the exclusive production of $\chi_{cJ}+\gamma$ in $e^+ e^-$ annihilation. In particular, we compute for the first time contributions induced by octet operators with a chromoelectric field. The matching coefficients multiplying production long distance matrix elements (LDMEs) are determined through perturbative matching between QCD and NRQCD at the amplitude level. Technical challenges encountered in the non-relativistic expansion of the QCD amplitudes are discussed in detail. The main source of uncertainty comes from the not so well known LDMEs. Accounting for it, we provide the following estimates for the production cross sections at $\sqrt{s} = 10.6\textrm{ GeV}$: $\sigma (e^+ e^- \to \chi_{ c0} + \gamma) = (1.3 \pm 0.4) \textrm{ fb}$, $\sigma (e^+ e^- \to \chi_{ c1} + \gamma) = (15.4 \pm 6.7) \textrm{ fb}$, and $\sigma (e^+ e^- \to \chi_{ c2} + \gamma) = (4.7 \pm 2.6) \textrm{ fb}$.