Measurements of J/psi --> p \bar{p}

TL;DR

This paper reports precise measurements of the J/psi decay to proton-antiproton pairs, including the branching ratio and angular distribution, confirming QCD predictions with high accuracy.

Contribution

First detailed measurement of J/psi --> p pbar decay parameters using a large data sample, validating QCD angular distribution predictions.

Findings

Branching ratio Br(J/psi --> p pbar) = (2.26 +- 0.01 +- 0.14) x 10^{-3}

Angular distribution parameter alpha = 0.676 +- 0.036 +- 0.042

Results agree with first-order QCD predictions

Abstract

The process J/\psi --> p \bar{p} is studied using 57.7 X 10^6 J/\psi events collected with the BESII detector at the Beijing Electron Positron Collider. The branching ratio is determined to be Br(J/\psi --> p \bar{p})=(2.26 +- 0.01 +- 0.14) X 10^{-3}, and the angular distribution is well described by \frac{dN}{d cos\theta_p}=1+\alpha\cos^2\theta_p with \alpha = 0.676 +- 0.036 +- 0.042, where \theta_p is the angle between the proton and beam directions. The value of \alpha obtained is in good agreement with the predictions of first-order QCD.