Proton-Antiproton Correlations in Hadronic Z Decays

Abstract Protons and antiprotons in hadronic events are identified by their rate of ionization energy loss $dE/dx$. Two-particle proton-antiproton correlations are studied in rapidity, azimuth and $\cos\theta^{\star}$, the angle between proton and sphericity axis in the proton-antiproton rest frame. A strong local compensation of baryon number in rapidity is observed, an antiproton being found within 1.0 units of the tagging proton with probability 70\%. No evidence for an anticorrelation in azimuth is seen. A strong peak at $|\cos\theta^{\star}|=1$ is observed, in contrast to the expectation for isotropic cluster decays.