Photo-production of psi' Mesons at HERA

TL;DR

This paper reports the observation and measurement of quasi-elastic psi' meson photoproduction at HERA, detailing cross-sections and ratios at high photon-proton energies, advancing understanding of charmonium production in photon-proton interactions.

Contribution

It provides the first measurement of psi' quasi-elastic photoproduction cross-sections and their ratio to J/psi, at high energies, using decay channels at HERA.

Findings

Measured psi' photoproduction cross-section at 80 GeV is 18.0 nb.

The ratio of psi' to J/psi cross-sections is approximately 0.15.

Observation of quasi-elastic psi' production at high energies.

Abstract

Quasi-elastic (z >0.95) photo-production of psi' mesons has been observed at HERA for photon-proton centre-of-mass energies in the range 40 to 160 GeV. The psi' mesons were identified through their decays to l+l- and to J/psi pi+ pi-, where the J/psi subsequently decays to l+l-, the lepton l being either a muon or an electron. The cross-section for quasi-elastic photoproduction was measured to be [18.0 +- 2.8 (stat) +- 3.0(syst)] nb at a photon-proton centre-of-mass energy of 80 GeV. The ratio of the psi' to J/psi quasi-elastic cross-sections is 0.150 +- 0.027 (stat) +- 0.022 (syst).