Evidence for nuclear gluon shadowing from the ALICE measurements of PbPb ultraperipheral exclusive $J/{\psi}$ production

We show that the recent ALICE measurements of exclusive J/ψ production in ultraperipheral PbPb collisions at 2.76 TeV provide the first direct experimental evidence for the strong nuclear gluon shadowing in lead at x∼10−3 . The evidence is based on the comparison of the nuclear suppression factor S(x≈0.001)=0.61−0.04+0.05 found in the analysis of the coherent J/ψ photoproduction cross sections measured by ALICE with the nuclear gluon shadowing predicted by the global fits of nuclear parton distributions and by the leading twist theory of nuclear shadowing.

Note:

14 pages, 3 figures. The final version matching the published paper

ultraperiphereal collisions
nuclear shadowing
parton distributions in nuclei
Ultraperipheral collisions
Nuclear shadowing
Parton distributions in nuclei
gluon: shadowing
parton: distribution function
ALICE
peripheral

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