Measurement of the cross-section ratio $\sigma(\chi_{c2})/\sigma(\chi_{c1})$ for prompt $\chi_c$ production at $\sqrt{s}=7$ TeV

TL;DR

This study measures the ratio of prompt production cross-sections of $ ext{chi}_{c2}$ to $ ext{chi}_{c1}$ mesons in proton-proton collisions at 7 TeV, providing insights into charmonium production mechanisms.

Contribution

First measurement of the $ ext{chi}_c$ cross-section ratio as a function of $J/ extpsi$ transverse momentum at 7 TeV, testing QCD models against experimental data.

Findings

Results agree with NLO non-relativistic QCD at high $p_T$

Data lie above leading-order colour singlet predictions

Provides constraints for charmonium production models

Abstract

The prompt production of the charmonium $\chi_{c1}$ and $\chi_{c2}$ mesons has been studied in proton-proton collisions at the Large Hadron Collider at a centre-of-mass energy of $\sqrt{s}=7$ TeV. The $\chi_c$ mesons are identified through their decays $\chi_c\to J/\psi\,\gamma$ with $J/\psi \to \mu^+ \mu^-$ using 36 $\mathrm{pb^{-1}}$ of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for the two $\chi_c$ spin states, $\sigma(\chi_{c2})/\sigma(\chi_{c1})$, has been determined as a function of the $J/\psi$ transverse momentum, $p_{\mathrm{T}}^{J/\psi}$, in the range from 2 to 15 GeV/$c$. The results are in agreement with the next-to-leading order non-relativistic QCD model at high $p_{\mathrm{T}}^{J/\psi}$ and lie consistently above the pure leading-order colour singlet prediction.