Measurement of the cross-section ratio ${\sigma }_{\psi (2S)}/{\sigma }_{J/\psi (1S)}$ in exclusive photoproduction at HERA

Abstract

The exclusive photoproduction reactions $\gamma p\to J/\psi (1S)p$ and $\gamma p\to \psi (2S)p$ have been measured at an $ep$ centre-of-mass energy of 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 373 pb${}^{-1}$. The measurement was made in the kinematic range $30<W<180$ GeV, $Q^2<1$ GeV${}^2$ and $|t|<1$ GeV${}^2$, where $W$ is the photon--proton centre-of-mass energy, $Q^2$ is the photon virtuality and $t$ is the squared four-momentum transfer at the proton vertex. The decay channels used were $J/\psi (1S)\to {\mu }^{+}{\mu }^{-}$, $\psi (2S)\to {\mu }^{+}{\mu }^{-}$ and $\psi (2S)\to J/\psi (1S){\pi }^{+}{\pi }^{-}$ with subsequent decay $J/\psi (1S)\to {\mu }^{+}{\mu }^{-}$. The ratio of the production cross sections, $R={\sigma }_{\psi (2S)}/{\sigma }_{J/\psi (1S)}$, has been measured as a function of $W$ and $|t|$ and compared to previous data in photoproduction and deep inelastic scattering and with predictions of QCD-inspired models of exclusive vector-meson production, which are in reasonable agreement with the data.

arXiv comment31 pages, 9 figures. Updated according to comments from journal referee including a new table. Added full collaboration author list

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Cited by in corpus (3)

• First measurement of the $|t|$-dependence of incoherent J/$\psi$ photonuclear production
• Vector meson photoproduction in UPCs with FoCal
• Exclusive diffractive J/psi and Psi(2S) production in dipole model using a holographic AdS/QCD light front wavefunction with longitudinal confinement