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

TL;DR

This paper measures the ratio of Psi' to J/psi production in proton-nucleus collisions at 920 GeV, providing new experimental data on their production and polarization across different targets and decay channels.

Contribution

It presents the first comprehensive measurement of the Psi' to J/psi production ratio in proton-nucleus interactions at this energy, including polarization and decay channel comparisons.

Findings

The Psi' to J/psi production ratio is nearly constant across x_F and increases slowly with p_T.

The ratio is consistent between muon and electron decay channels, with a ratio of 1.00±0.08±0.04.

Results provide new constraints on the branching fraction ratios of Psi' and J/psi decays.

Abstract

Ratios of the Psi' 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' 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' 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' 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'(mu)/R_psi'(e)=1.00+-0.08+-0.04. This result constitutes a new, direct experimental constraint on the double ratio of branching fractions, (B'(mu)*B(e))/(B(mu)*B'(e)), of Psi' and J/psi in the two channels.