Measurement of $σ_{χ_{c2}} {\cal B}(χ_{c2} \to J/ψγ)/ σ_{χ_{c1}} {\cal B}(χ_{c1} \to J/ψγ)$ in $p\bar{p}$ Collisions at $\sqrt{s} =$ 1.96 TeV

Abstract

We measure the ratio of cross section times branching fraction, $R_p \equiv σ_{χ_{c2}} {\cal B}(χ_{c2} \to J/ψγ)/ σ_{χ_{c1}} {\cal B}(χ_{c1} \to J/ψγ)$, in 1.1 fb$^{-1}$ of $p\bar{p}$ collisions at $\sqrt{s} =$ 1.96 TeV. This measurement covers the kinematic range $p_T(J/ψ)>4.0$ GeV/$c$, $|η(J/ψ)| < 1.0$, and $p_T(γ)>1.0$ 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 $χ_{c1,2}$ hadroproduction.

Figures (2)

• 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.