An Update of the ABMP16 PDF Fit

TL;DR

This paper updates the ABMP16 nucleon PDFs using recent LHC and HERA data, improving the fit and providing new insights into the strange quark and gluon distributions at small x.

Contribution

The paper introduces an updated ABMP16 PDF set incorporating new experimental data and refined analysis techniques, including photon-initiated processes.

Findings

Strange quark distribution is suppressed relative to non-strange at moderate x.

Small-x gluon distribution is enhanced compared to previous fit.

Good description of non-resonant $oldsymbol{ u}$-production data with photon-initiated processes.

Abstract

We present an updated version of the ABMP16 nucleon PDFs, which is tuned by using recent precise data on $W$- and $Z/\gamma^*$-production at the LHC and the final HERA data on DIS $c$- and $b$-quark production and by imposing a stringent $Q^2$-cut on the inclusive DIS data in order to avoid the impact of higher twist terms at small $x$ at HERA. The new $W$- and $Z$-boson production data, in particular the updated version of the ATLAS data at the c.m.s. energy 7 TeV, are well accommodated into the present fit. The strange sea distribution obtained is consistent with the average of the up and down quark ones at small $x$. However, it is still suppressed with respect to the non-strange one by a factor of $\sim 0.5$ at moderate $x$. The small-$x$ gluon distribution is enhanced as compared to the previous ABMP16 fit, in line with updated data on the DIS $c$-quark production. Finally, a good description of the non-resonant $\gamma^*/Z$-production data, which are included into the ABM analysis for the first time, is achieved provided the photon-initiated lepton pair production is taken into account.