Inhaltszusammenfassung

We present the first measurement at the LHC of exclusive J/ψ photoproduction off protons, in ultra-peripheral proton-lead collisions at sNN‾‾‾‾√=5.02 TeV. Events are selected with a dimuon pair produced either in the rapidity interval, in the laboratory frame, 2.5<y<4 (p-Pb) or −3.6<y<−2.6 (Pb--p), and no other particles observed in the ALICE acceptance. The measured cross sections σ(γ+p→J/ψ+p) are 33.2 ± 2.2 (stat) ± 3.1 (syst) ± 0.7 (theo) nb in p-Pb and 284 ± 36 (stat) +27−32 (syst) ± 26 (...We present the first measurement at the LHC of exclusive J/ψ photoproduction off protons, in ultra-peripheral proton-lead collisions at sNN‾‾‾‾√=5.02 TeV. Events are selected with a dimuon pair produced either in the rapidity interval, in the laboratory frame, 2.5<y<4 (p-Pb) or −3.6<y<−2.6 (Pb--p), and no other particles observed in the ALICE acceptance. The measured cross sections σ(γ+p→J/ψ+p) are 33.2 ± 2.2 (stat) ± 3.1 (syst) ± 0.7 (theo) nb in p-Pb and 284 ± 36 (stat) +27−32 (syst) ± 26 (theo) nb in Pb-p collisions. We measure this process up to about 700 GeV in the γp centre-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 J/ψ photoproduction cross section in γp energies from about 20 to 700 GeV, or equivalently, from Bjorken-x between ∼2×10−2 to ∼2×10−5, thus indicating no significant change in the gluon density behaviour of the proton between HERA and LHC energies. » weiterlesen» einklappen

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DDC Sachgruppe:
Physik