Measurement of $\sigma_{\chi_{c2}} {\cal B}(\chi_{c2} \to J/\psi \gamma)/ \sigma_{\chi_{c1}} {\cal B}(\chi_{c1} \to J/\psi \gamma)$ in $p\bar{p}$ Collisions at $\sqrt{s} =$ 1.96 TeV

TL;DR

This paper reports a precise measurement of the ratio of production cross sections times branching fractions for $ ext{chi}_c2$ and $ ext{chi}_c1$ particles decaying into $J/\psi$ and a photon in proton-antiproton collisions at 1.96 TeV, improving previous results.

Contribution

The study provides the most precise measurement to date of the ratio of prompt $ ext{chi}_c2$ to $ ext{chi}_c1$ production in hadron collisions, covering specific kinematic ranges.

Findings

Measured ratio $R_p = 0.395 \\pm 0.016(stat.) \\pm 0.015(sys.)$.

Improved the precision of prompt $ ext{chi}_c$ production measurements.

Covered kinematic range $p_T(J/\psi)>4.0$ GeV/$c$, $|\\eta(J/\\psi)|<1.0$, $p_T(\\gamma)>1.0$ GeV/$c$.

Abstract

We measure the ratio of cross section times branching fraction, $R_p \equiv \sigma_{\chi_{c2}} {\cal B}(\chi_{c2} \to J/\psi \gamma)/ \sigma_{\chi_{c1}} {\cal B}(\chi_{c1} \to J/\psi \gamma)$, in 1.1 fb$^{-1}$ of $p\bar{p}$ collisions at $\sqrt{s} =$ 1.96 TeV. This measurement covers the kinematic range $p_T(J/\psi)>4.0$ GeV/$c$, $|\eta(J/\psi)| < 1.0$, and $p_T(\gamma)>1.0$ GeV/$c$. For events due to prompt processes, we find $R_p = 0.395\pm0.016(stat.)\pm0.015(sys.)$. This result represents a significant improvement in precision over previous measurements of prompt $\chi_{c1,2}$ hadroproduction.