Impact of dijet and D-meson data from 5.02 TeV p+Pb collisions on nuclear PDFs
2021
Abstract We discuss the new constraints on gluon parton distribution function (PDF) in lead nucleus, derivable with the Hessian PDF reweighting method from the 5.02 TeV p+Pb measurements of dijet (CMS) and D0-meson (LHCb) nuclear modification ratios. The impact is found to be significant, placing stringent constraints in the mid- and previously unconstrained small-x regions. The CMS dijet data confirm the existence of gluon anti-shadowing and the onset of small-x shadowing, as well as reduce the gluon PDF uncertainties in the larger-x region. The gluon constraints from the LHCb D0 data, reaching down to x ∼ 10−5 and derived in a NLO perturbative QCD approach, provide a remarkable reduction of the small-x uncertainties with a strong direct evidence of gluon shadowing. Furthermore, we find a good description of the data even down to zero D0-meson transverse momentum within a purely DGLAP-based approach without a need for imposing any non-linear effects. Importantly, the constraints obtained from the dijet and D0 data are mutually fully consistent, supporting the universality of nuclear PDFs in hard-scattering processes.
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