Abstract
The recent observation by the IceCube experiment of cosmic neutrinos at energies up to a few PeV heralds the beginning of neutrino astronomy. At such high energies, the conventional neutrino flux is suppressed and the prompt component from charm meson decays is expected to become the dominant background to astrophysical neutrinos. Charm production at high energies is however theoretically uncertain, both since the charm mass is at the boundary of applicability of perturbative QCD, and also because the calculations are sensitive to the poorly-known gluon PDF at small-x. In this work we provide detailed perturbative QCD predictions for charm and bottom production in the forward region, and validate them by comparing with recent data from the LHCb experiment at 7 TeV. Finding good agreement between data and theory, we use the LHCb measurements to constrain the small-x gluon PDF, achieving a substantial reduction in its uncertainties. Using these improved PDFs, we provide predictions for charm and bottom production at LHCb at 13 TeV, as well as for the ratio of cross-sections between 13 and 7 TeV. The same calculations are used to compute the energy distribution of neutrinos from charm decays in pA collisions, a key ingredient towards achieving a theoretically robust estimate of charm-induced backgrounds at neutrino telescopes.
Highlights
Our calculations are based both on the semi-analytical FONLL approach [28], as well as the fully exclusive description of the final state provided by the MadGraph5 aMC@next-to-leading order (NLO) [29] and POWHEG Monte Carlo programs, where the NLO result is matched to the Pythia8 [30, 31] parton shower
Throughout this work, the NNPDF3.0 NLO PDF set will be used as a baseline for our predictions, and we study the dependence of our predictions on the choice of input PDF set
In this work we have performed a detailed study of charm and bottom production in the forward region, based on state-of-the-art perturbative QCD (pQCD) with NLO calculations matched to parton showers
Summary
In pQCD, the NLO calculation of heavy quark pair production in hadronic collisions has been available for a long time, both at the level of total inclusive cross-sections [41], and of differential distributions [42,43,44,45]. Improved with the resummation of soft gluons at NLL [46, 47] and NNLL [48, 49] accuracy Another way of refining the fixed-order result is by matching it to the massless calculation, valid in the limit where the heavy quark transverse momentum (phT ) greatly exceeds the heavy quark mass (mh), obtaining a result which is valid both at small and at large values of phT [28, 50, 51], and has the benefit of reduced of scale uncertainties as compared to the NLO calculation. Throughout this work, the NNPDF3.0 NLO PDF set will be used as a baseline for our predictions, and we study the dependence of our predictions on the choice of input PDF set
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