Measurement of elastic J/upsilon photoproduction at HERA

The reaction a p --> J/psi p has been studied in epsilon p interactions using the ZEUS detector at HERA. The cross section for elastic J/psi photoproduction has been measured as a function of the photon-proton centre of mass energy W in the range 40 < W < 140 GeV at a median photon virtuality Q(2) of 5 x 10(-5) GEV(2). The photoproduction cross section, sigma(ap-->J/psi p), is observed to rise steeply with W. A fit to the data presented in this paper to determine the parameter delta in the form sigma(ap-->J/psi p) proportional to W-delta yields the value delta=0.92+/-0.14+/-0.10. The differential cross section d sigma/d\t\ is presented over the range \t\ < 1.0 GEV(2) where t is the square of the four-momentum exchanged at the proton vertex. d sigma/d\t\ falls exponentially with a slope parameter of 4.6+/-0.4(-0.6)(+0.4) GEV(-2). The measured decay angular distrubitions are consistent with 8-channel helicity conservation. RI Bashkirov, Vladimir/A-4818-2008; De Pasquale, Salvatore/B-9165-2008; Lancaster, Mark/C-1693-2008; Gladilin, Leonid/B-5226-2011; Golubkov, Yury/E-1643-2012

The reaction a p --> J/psi p has been studied in epsilon p interactions using the ZEUS detector at HERA. The cross section for elastic J/psi photoproduction has been measured as a function of the photon-proton centre of mass energy W in the range 40 < W < 140 GeV at a median photon virtuality Q(2) of 5 x 10(-5) GEV(2). The photoproduction cross section, sigma(ap-->J/psi p), is observed to rise steeply with W. A fit to the data presented in this paper to determine the parameter delta in the form sigma(ap-->J/psi p) proportional to W-delta yields the value delta=0.92+/-0.14+/-0.10. The differential cross section d sigma/d\t\ is presented over the range \t\ < 1.0 GEV(2) where t is the square of the four-momentum exchanged at the proton vertex. d sigma/d\t\ falls exponentially with a slope parameter of 4.6+/-0.4(-0.6)(+0.4) GEV(-2). The measured decay angular distrubitions are consistent with 8-channel helicity conservation.