Abt, I (reprint author), Max Planck Inst Phys & Astrophys, Werner Heisenberg Inst, D-80805 Munich, Germany.
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 >= 4.5 GeV/c. 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. The psi' to J/psi production ratio is almost constant in the covered x(F) range and shows a slow increase with p(T).