A Measurement of the Psi' to J/psi Production Ratio in 920 GeV Proton-Nucleus Interactions

Abstract

Ratios of the Psi&#39; over the J/psi production cross sections in the dilepton channel for C, Ti and W targets have been measured in 920 GeV proton-nucleus interactions with the HERA-B detector at the HERA storage ring. The Psi&#39; and J/psi states were reconstructed in both the mu+mu- and the e+e- decay modes. The measurements covered the kinematic range -0.35 < x_F < 0.1 with transverse momentum p_T < 4.5 GeV/c. The Psi&#39; to J/psi production ratio is almost constant in the covered x_F range and shows a slow increase with p_T. The angular dependence of the ratio has been used to measure the difference of the Psi&#39; and J/psi polarization. All results for the muon and electron decay channels are in good agreement: their ratio, averaged over all events, is R_psi&#39;(mu)/R_psi&#39;(e)=1.00+-0.08+-0.04. This result constitutes a new, direct experimental constraint on the double ratio of branching fractions, (B&#39;(mu)*B(e))/(B(mu)*B&#39;(e)), of Psi&#39; and J/psi in the two channels.