Improved constraints on parton distributions using LHCb, ALICE and HERA heavy-flavour measurements and implications for the predictions for prompt atmospheric-neutrino fluxes

TL;DR

This work updates the PROSA PDF analysis by incorporating LHCb and ALICE heavy-flavour measurements together with HERA DIS data to constrain the gluon and sea-quark distributions at very low x. Using NLO QCD in both FFNS and VFNS within xFitter, the study achieves improved low-x gluon constraints (down to x ~ 10^-6) and provides refined predictions for the prompt atmospheric-neutrino flux, with results that align with IceCube limits and other PDF-based predictions. The analysis also assesses systematic and model uncertainties, tests multiple gluon parametrisations, and delivers publicly available PROSA 2019 PDFs for applications in high-energy and astroparticle physics. Overall, the paper demonstrates that forward heavy-flavour data from the LHC substantially enhance our understanding of proton structure at ultra-low x and improve astrophysical flux predictions.

Abstract

The impact of measurements of heavy-flavour production in deep inelastic $ep$ scattering and in $pp$ collisions on parton distribution functions is studied in a QCD analysis at next-to-leading order. Recent combined results of inclusive and heavy-flavour production cross sections in deep inelastic scattering at HERA are investigated together with heavy-flavour production measurements at the LHC. Differential cross sections of charm- and beauty-hadron production measured by the LHCb collaboration at the centre-of-mass energies of 5, 7 and 13 TeV as well as the recent measurements of the ALICE experiment at the centre-of-mass energies of 5 and 7 TeV are explored. These data impose additional constraints on the gluon and the sea-quark distributions at low partonic fractions $x$ of the proton momentum, down to $x\approx10^{-6}$. The impact of the resulting parton distribution function in the predictions for the prompt atmospheric-neutrino fluxes is studied.

Figures (10)

• Figure 1: NLO QCD predictions for $D^{0}$ meson production at LHCb at $\sqrt{s} = 13$ TeV (top row), cross section ratios at $\sqrt{s} = 13$ TeV and $\sqrt{s} = 5$ TeV, denoted as $R_{13/5}$ (middle row), and normalised cross sections, denoted as $R_y$ (bottom row) with their PDF uncertainties obtained using the HERAPDF2.0 PDF set with three active flavours (HERAPDF20_NLO_FF3A_EIG and HERAPDF20_NLO_FF3A_VAR LHAPDF sets) and different scale choices for two representative $p_T$ regions (the cross sections in the top right panel are scaled by a factor of $200$ for presentation purposes). The lower panels indicate the ratio of the predictions to the nominal one.
• Figure 2: Left panel: the gluon PDF with their total uncertainties at the scale $\mu^2_f=10$ GeV$^2$ obtained using different gluon parametrisations, see Eq. (\ref{['eq:gluonpar']}). Right panel: the same PDFs normalised to the distribution obtained using the nominal parametrisation.
• Figure 3: The PROSA 2019 PDF in FFNS with their total uncertainties as a function of $x$ shown at the scale $\mu^2_f=10$ GeV$^2$, compared with the respective distributions from the PROSA 2015 fit.
• Figure 4: Left panel: the ratio of the gluon distributions of PROSA 2019 FFNS and the PROSA 2015, shown as a function of $x$ at the scale $\mu^2_f=10$ GeV$^2$. Right panel: relative total, fit, model and parametrisation uncertainties for the gluon PROSA 2019 PDF at the scale $\mu^2_f=10$ GeV$^2$.
• Figure 5: The gluon distributions of PROSA 2019 FFNS and VFNS fits compared with the NNPDF3.1 Ball:2017nwa PDFs and with the PDFs from Ref. Bertone:2018dse obtained using NLO calculations at the scale $\mu^2_f=10$ GeV$^2$.