Measurement of the ratio of prompt $\chi_{c}$ to $J/\psi$ production in $pp$ collisions at $\sqrt{s}=7$ TeV

TL;DR

This study measures the ratio of prompt $\chi_c$ to $J/\psi$ production in proton-proton collisions at 7 TeV, providing insights into charmonium production mechanisms and testing theoretical models against experimental data.

Contribution

It presents the first measurement of the $\chi_c$ to $J/\psi$ production ratio at 7 TeV, comparing results with theoretical predictions and highlighting discrepancies with certain models.

Findings

Results agree with next-to-leading order non-relativistic QCD predictions.

Significant discrepancy observed with leading-order colour singlet model, especially at low $p_T$.

Provides valuable data for understanding charmonium production mechanisms.

Abstract

The prompt production of charmonium $\chi_{c}$ and $J/\psi$ states is studied in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}=7$ TeV at the Large Hadron Collider. The $\chi_{c}$ and $J/\psi$ mesons are identified through their decays $\chi_{c}\rightarrow J/\psi \gamma$ and $J/\psi\rightarrow \mu^+\mu^-$ using 36 pb$^{-1}$ of data collected by the LHCb detector in 2010. The ratio of the prompt production cross-sections for $\chi_{c}$ and $J/\psi$, $\sigma (\chi_{c}\rightarrow J/\psi \gamma)/ \sigma (J/\psi)$, is determined as a function of the $J/\psi$ transverse momentum in the range $2 < p_{\mathrm T}^{J/\psi} < 15$ GeV/$c$. The results are in excellent agreement with next-to-leading order non-relativistic expectations and show a significant discrepancy compared with the colour singlet model prediction at leading order, especially in the low $p_{\mathrm T}^{J/\psi}$ region.