title: Precision Determination of the Small-x Gluon from Charm Production at LHCb.
abstract: The small-x gluon in global fits of parton distributions is affected by large uncertainties from the lack of direct experimental constraints. In this Letter, we provide a precision determination of the small-x gluon from the exploitation of forward charm production data provided by LHCb for three different center-of-mass (c.m.) energies: 5 TeV, 7 TeV, and 13 TeV. The LHCb measurements are included in the parton distribution function (PDF) fit by means of normalized distributions and cross-section ratios between data taken at different c.m. values, R_{13/7} and R_{13/5}. We demonstrate that forward charm production leads to a reduction of the PDF uncertainties of the gluon down to x≃10^{-6} by up to an order of magnitude, with implications for high-energy colliders, cosmic ray physics, and neutrino astronomy.
authors.affiliation: Institute for Theoretical Physics, ETH, CH-8093 Zurich, Switzerland.|Institute for Particle Physics Phenomenology, University of Durham, DH1 3LE Durham, United Kingdom.
authors.forename: Rhorry
authors.initials: R
authors.lastname: Gauld
authors.affiliation: Department of Physics and Astronomy, VU University Amsterdam, De Boelelaan 1081, NL-1081 HV Amsterdam, The Netherlands.|Nikhef, Science Park 105, NL-1098 XG Amsterdam, The Netherlands.
authors.forename: Juan
authors.initials: J
authors.lastname: Rojo