Impact of Charm H1-ZEUS Combined data and Determination of the Strong Coupling in Two Different Schemes

TL;DR

This study assesses how recent charm cross section data from H1-ZEUS influences the determination of parton distribution functions and the strong coupling constant, showing improved precision and the importance of charm contributions in different schemes.

Contribution

It provides a comparative analysis of RT and RTOPT schemes at NLO, highlighting the impact of charm data on gluon distribution and strong coupling determination.

Findings

Adding charm data reduces gluon distribution uncertainty.

Improved fit quality with charm data in both schemes.

Significant enhancement in the precision of _s(M^2_Z) with charm contributions.

Abstract

We study the impact of recent measurements of charm cross section H1-ZEUS combined data on simultaneous determination of parton distribution functions (PDFs) and the strong coupling, $\alpha_s(M^2_Z)$, in two different schemes. We perform several fits based on Thorne-Roberts (RT) and Thorne-Roberts optimal (RTOPT) schemes at next-to-leading order (NLO). We show that adding charm cross section H1-ZEUS combined data reduces the uncertainty of the gluon distribution and improves the fit quality up to $\sim 0.4$~\% and $\sim 0.9$~\%~, without and with the charm contribution, from the RT scheme to the RTOPT scheme, respectively. We also emphasise the central role of the strong coupling, $\alpha_s(M^2_Z)$, in revealing the impact of charm flavour contribution, when it is considered as an extra free parameter. We show that in going from the RT scheme to the RT OPT scheme, we get $\sim 0.9$~\% and $\sim 2.0$~\%~improvement in the value of $\alpha_s(M^2_Z)$, without and with the charm flavour contribution respectively.