Author/Authors :
ZEUS Collaboration، نويسنده , , M Derrick، نويسنده , , D Krakauer، نويسنده , , S Magill، نويسنده , , D. Mikunas، نويسنده , , B Musgrave، نويسنده , , J. Repond، نويسنده , , R Stanek، نويسنده , , R.L. Talaga، نويسنده , , H Zhang، نويسنده , , R Ayad، نويسنده , , G Bari، نويسنده , , M Basile، نويسنده , , L Bellagamba، نويسنده , , D Boscherini، نويسنده , , A Bruni، نويسنده , , G Bruni، نويسنده , , P Bruni، نويسنده , , G. Cara Romeo، نويسنده , , G Castellini، نويسنده , , et al.، نويسنده ,
Abstract :
This paper reports the cross section measurements for the process ep → e J/ψ p for Q2 < 4 GeV2 at s = 296 GeV, based on an integrated luminosity of about 0.5 pb−1, using the ZEUS detector. The J/ψ was detected in its e+e− and μ+μ− decay modes. The photoproduction cross section was measured to be 52−12+7 ± 10 nb at an average γp centre of mass energy of 67 GeV and 71−20+13±12 nb at 114 GeV. The significant rise of the cross section compared to lower energy measurements is not in agreement with VDM models, but can be described by QCD inspired models if a rise in the gluon momentum density at low x in the proton is assumed.
