Exclusive photoproduction of J/psi mesons at HERA

The exclusive photoproduction of J/psi mesons, gammap --> J/psip, has been studied in ep collisions with the ZEUS detector at HERA, in the kinematic range 20 < W < 290 GeV, where W is the photon-proton centre-of-mass energy. The J/psi mesons were reconstructed in the union and the electron decay channels using integrated luminosities of 38 pb(-1) and 55 pb(-1), respectively. The helicity structure of J/psi production shows that the hypothesis of s-channel helicity conservation is satisfied within two standard deviations. The total cross section and the differential cross-section dsigma/dt, where t is the squared four-momentum transfer at the proton vertex, are presented as a function of W, for \t\ < 1.8 GeV(2). The t distribution exhibits an exponential shape with a slope parameter increasing logarithmically with W with a value b = 4.15 +/- 0.05(stat.)(-0.18)(+0.30)(syst.) GeV(-2) at W = 90 GeV. The effective parameters of the Pomeron trajectory are alpha(P)(0) = 1.200 +/- 0.009(stat.)(-0.010)(+0.004) (syst.) and alpha(P)' = 0.115 +/- 0.018(stat.)(-0.015)(+0.008) (syst.) GeV(-2). RI De Pasquale, Salvatore/B-9165-2008; Wing, Matthew/C-2169-2008; Bashkirov, Vladimir/A-4818-2008; Doyle, Anthony/C-5889-2009; collins-tooth, christopher/A-9201-2012; Ferrando, James/A-9192-2012; Gladilin, Leonid/B-5226-2011; Golubkov, Yury/E-1643-2012

The exclusive photoproduction of J/psi mesons, gammap --> J/psip, has been studied in ep collisions with the ZEUS detector at HERA, in the kinematic range 20 < W < 290 GeV, where W is the photon-proton centre-of-mass energy. The J/psi mesons were reconstructed in the union and the electron decay channels using integrated luminosities of 38 pb(-1) and 55 pb(-1), respectively. The helicity structure of J/psi production shows that the hypothesis of s-channel helicity conservation is satisfied within two standard deviations. The total cross section and the differential cross-section dsigma/dt, where t is the squared four-momentum transfer at the proton vertex, are presented as a function of W, for \t\ < 1.8 GeV(2). The t distribution exhibits an exponential shape with a slope parameter increasing logarithmically with W with a value b = 4.15 +/- 0.05(stat.)(-0.18)(+0.30)(syst.) GeV(-2) at W = 90 GeV. The effective parameters of the Pomeron trajectory are alpha(P)(0) = 1.200 +/- 0.009(stat.)(-0.010)(+0.004) (syst.) and alpha(P)' = 0.115 +/- 0.018(stat.)(-0.015)(+0.008) (syst.) GeV(-2).