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Hera Precision Measurements and Impact for LHC Predictions

V. Radescu

TL;DR

The paper demonstrates how a QCD fit to the combined HERA $ep$ DIS cross sections yields HERAPDF proton PDFs, extended by HERA II data to improve high-$x$ precision and NNLO consistency. It shows that including jet data allows precise determination of the strong coupling, and preliminary charm data constrain the charm mass within various heavy-quark schemes. The resulting HERAPDF1.5/1.6 sets provide robust predictions for Tevatron and LHC processes, with high-$x$ gluon and valence distributions notably refined. Overall, the study highlights the consistency of $ep$-based PDFs with collider data and the value of incorporating jet and charm measurements to constrain fundamental QCD parameters.

Abstract

A QCD fit analysis to the combined HERA inclusive deep inelastic cross sections measured by the H1 and ZEUS collaborations for $e^\pm p$ scattering to extract HERAPDF sets is presented. The results are used for predictions of $ p\bar{p}$ processes at Tevatron and $pp$ processes at the LHC. The QCD analysis has been extended to include the combined HERA II measurements at high $Q^2$ resulting in the HERAPDF1.5 sets, with full estimation of uncertainties. The precision of the new PDFs at high $x$ is considerably improved, particularly in the valence sector. In addition, inclusion of the HERA jet data allows for a precise determination of the strong coupling. Moreover, inclusion of the preliminary combined HERA charm data provides constraints for the optimal value of the charm mass used in QCD theory models which may account for some of the differences among global PDF fits.

Hera Precision Measurements and Impact for LHC Predictions

TL;DR

The paper demonstrates how a QCD fit to the combined HERA DIS cross sections yields HERAPDF proton PDFs, extended by HERA II data to improve high- precision and NNLO consistency. It shows that including jet data allows precise determination of the strong coupling, and preliminary charm data constrain the charm mass within various heavy-quark schemes. The resulting HERAPDF1.5/1.6 sets provide robust predictions for Tevatron and LHC processes, with high- gluon and valence distributions notably refined. Overall, the study highlights the consistency of -based PDFs with collider data and the value of incorporating jet and charm measurements to constrain fundamental QCD parameters.

Abstract

A QCD fit analysis to the combined HERA inclusive deep inelastic cross sections measured by the H1 and ZEUS collaborations for scattering to extract HERAPDF sets is presented. The results are used for predictions of processes at Tevatron and processes at the LHC. The QCD analysis has been extended to include the combined HERA II measurements at high resulting in the HERAPDF1.5 sets, with full estimation of uncertainties. The precision of the new PDFs at high is considerably improved, particularly in the valence sector. In addition, inclusion of the HERA jet data allows for a precise determination of the strong coupling. Moreover, inclusion of the preliminary combined HERA charm data provides constraints for the optimal value of the charm mass used in QCD theory models which may account for some of the differences among global PDF fits.

Paper Structure

This paper contains 4 sections, 4 figures.

Table of Contents

  1. Combined H1 and ZEUS Cross Section Measurements
  2. QCD Analysis settings
  3. Results and Comparisons
  4. Summary

Figures (4)

  • Figure 1: On the left hand side: the comparison between HERAPDF1.0 (light colour) based on the HERA I data and HERAPDF1.5 (dark colour) based on the HERA I and II data, using the total uncertainty band at $Q^2=10$ GeV$^2$ with gluon, sea (which are scaled by a factor of 0.05) and valence distributions. On the right hand side: the summary plot for HERAPDF1.5 at $Q^2=10$ GeV$^2$ at NNLO with the uncertainties including the experimental (red), model (yellow) and the PDF parametrisation (green), compared to the central fit for HERAPDF1.0 at NNLO.
  • Figure 2: On the left hand side: the gluon distribution from the HERAPDF sets (based on HERA I only - HERAPDF1.0, and based on HERA I+II, HERAPDF1.5) to MSTW08 at NNLO in the high $x$ region. On the right hand side: the $\Delta\chi^2$ distribution as a function of the value of $\alpha_S(M_Z)$ in the PDF fits for HERAPDF1.5f (dashed line) without jet data and HERAPDF1.6 (solid line) with jet data.
  • Figure 3: Summary plot for HERAPDF1.5f (left) and HERAPDF1.6 (right) as a function of $x$ for $Q^2 = 10$ GeV$^2$. The strong coupling constant $\alpha_S(M_Z)$ is a free parameter in both fits. The central values of the PDFs (solid lines) are shown together with the experimental, model and parametrisation uncertainties represented by the red, yellow and green shaded bands, respectively.
  • Figure :