A Measurement of the Polarization of $J/\psi$ Mesons Produced in High-Energy $p\bar{p}$ Collisions

Abstract

This dissertation presents an analysis of the polarization of $J/\psi$ mesons produced in $p\overline{p}$ collisions at a centre-of-mass energy of 1.8 TeV. The collisions were produced by the Fermilab Tevatron collider, the world's highest energy particle accelerator. The data were recorded by the Collider Detector at Fermilab during Run 1 of the Tevatron in 1992-1995. The $J/\psi$ meson consists of a charm quark and its antiquark, and is the best-known type of quarkonium, the bound state of a heavy quark-antiquark pair. The measurement of the production polarization of $J/\psi$ mesons and other quarkonia provides a test of quarkonium production models. The study of quarkonium production is important for understanding the strong nuclear force between quarks. The strong force is one of the four known fundamental forces, being responsible for binding quarks into hadrons and holding atomic nuclei together. The polarization of centrally produced $J/\psi$ mesons has been measured over the transverse momentum range 4 - 20 GeV=c , using an analysis of the angular distribution of their decays to $\mu^+ \mu^-$. Decay length measurements made by CDF's silicon vertex detector allowed the promptly produced $J/\psi$ mesons to be separated from those produced in B hadron decays. The prompt and B- decay polarization parameters, $\alpha_P$ and $\alpha_B$, have both been measured. The measured value of $\alpha_P$ is positive at intermediate $P_{\tau}$ , but is consistent with zero above 12 GeV=c , in apparent disagreement with predictions of the NRQCD factorization formalism. iii