Measurement of ${\sigma }_{{\chi }_{c2}}\mathcal{B}({\chi }_{c2}\to J/\psi \gamma )/{\sigma }_{{\chi }_{c1}}\mathcal{B}({\chi }_{c1}\to J/\psi \gamma )$ in $p\overline{p}$ Collisions at $\sqrt{s}=1.96\mathrm{TeV}$

We measure the ratio of cross section times branching fraction, $R_p={\sigma }_{{\chi }_{c2}}\mathcal{B}({\chi }_{c2}\to J/\psi \gamma )/{\sigma }_{{\chi }_{c1}}\mathcal{B}({\chi }_{c1}\to J/\psi \gamma )$, in $1.1{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. This measurement covers the kinematic range $p_T(J/\psi )>4.0\mathrm{GeV}/c$, $|\eta (J/\psi )<1.0$, and $p_T(\gamma )>1.0\mathrm{GeV}/c$. For events due to prompt processes, we find $R_p=0.395\pm 0.016(\mathrm{stat})\pm 0.015(\mathrm{syst})$. This result represents a significant improvement in precision over previous measurements of prompt ${\chi }_{c1,2}$ hadro production.

Figure 1

The $J/\psi \gamma$ mass distribution (points) with the projection of the likelihood fit overlaid on the data. The masses of the ${\chi }_{cJ}$ mesons and the contributions of the signal and background components are indicated.

Figure 2

The $ct$ distribution (points) for events in the ${\chi }_{c1}$ (a) and ${\chi }_{c2}$ (b) mass ranges. The projection of the fit is overlaid on the data, with the contribution of each signal and background component indicated.