Photoproduction of Jψ mesons at HERA

Abstract

We present a study of $\text{J}\text{ψ}$ meson production in collisions of 26.7 GeV electrons with 820 GeV protons, performed with the H1-detector at the HERA collider at DESY. The $\text{J}\text{ψ}$ mesons are detected via their leptonic decays both to electrons and muons. Requiring exactly two particles in the detector, a cross section of $\text{σ(ep →}\text{J}\text{ψ}\text{X) = (8.8±2.0±2.2)}\text{nb}$ is determined for 30 GeV ≤ W_γp ≤ 180 GeV and Q² ≲ 4 GeV². Using the flux of quasi-real photons with Q² ≲ 4 GeV², a total production cross section of σ(γp → J/ψX) = (56±13±14) nb is derived at an average W_γp=90 GeV. The distribution of the squared momentum transfer t from the proton to the $\text{J}\text{ψ}$ can be fitted using an exponential exp(−b∥t∥) below a ∥t∥ of 0.75 GeV² yielding a slope parameter of b = (4.7±1.9) GeV⁻².