Abstract
We present the first measurement at the LHC of exclusive photoproduction off protons, in ultraperipheral proton-lead collisions at . Events are selected with a dimuon pair produced either in the rapidity interval, in the laboratory frame, () or (), and no other particles observed in the ALICE acceptance. The measured cross sections are in and in collisions. We measure this process up to about 700 GeV in the center of mass, which is a factor of two larger than the highest energy studied at HERA. The data are consistent with a power law dependence of the photoproduction cross section in energies from about 20 to 700 GeV, or equivalently, from Bjorken scaling variable between and , thus indicating no significant change in the gluon density behavior of the proton between HERA and LHC energies.
- Received 1 July 2014
DOI:https://doi.org/10.1103/PhysRevLett.113.232504
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© 2014 CERN, for the The ALICE Collaboration