Speaker
Alessia Bruni
(Universita e INFN, Bologna (IT))
Description
The exclusive photoproduction reaction $\gamma p \to \psi(2S) p$ has been studied with the ZEUS detector in $ep$ collisions at HERA using an integrated luminosity of 350 pb$^{-1}$, in the kinematic range $30 < W < 180$ GeV, $Q^2 < 1$ GeV$^2$, $|t| < 5$ GeV$^2$, where $W$ is the photon-proton centre-of-mass energy, $Q^2$ - the photon virtuality and $t$ – four-momentum transfer at the proton vertex. The $\psi(2S)$ mesons were identified via the decay channels: $\psi(2S) \to \mu^+\mu^-$ and $J/\psi \pi^+\pi^-$ with $J/\psi \to \mu^+\mu^-$. The ratio of the production cross sections $R = \sigma(\psi(2S) / \sigma(J/\psi)$ was measured as a function of $W$ and compared to predictions of the perturbative QCD.
Primary author
Alessia Bruni
(Universita e INFN, Bologna (IT))
