The HERAPDF project aims to extract quark and gluon parton distribution functions (PDFs) of the proton from experimental data. The HERA deep inelastic scattering data provide some of the strongest constraints on PDFs and particularly for the gluon density at low x which is essential for predictions of Higgs boson production rates. In addition the final HERA data have now been published by H1 and ZEUS and provide more flavour discrimination with better precision in the high x region, which is relevant for predicting new physics models at high energy.

The project has developed a statisitical combination method to optimise the averaging of H1 and ZEUS measurements in a model independent way which also accounts for correlated systematic uncertainties allowing allowing cross-calibration to reduce the overall systematic uncertainty on the combined data. The averaged data are then used in a QCD fit to determine the proton PDFs with a complete evaluation of the experimental and theoretical uncertainties.

The next phase of the project will

  • Perform statistical combinations of the final DIS cross section data from HERA
  • Extract proton PDFs with uncertainties corresponding to a Δχ2=1 criterion
  • Evaluate potential PDF uncertainties arising from parameterisation bias
  • Optimise the χ2 definition for use in PDF fits
  • Evaluate experimental uncertainties using toy MC replicas
  • Perform QCD fits at NLO and NNLO
  • Extract the value of αS


Combined Measurement and QCD Analysis of the Inclusive ep Scattering Cross Sections at HERA
H1 and Zeus Collab., Dr Eram Rizvi et.al.,
JHEP 2009 (arXiv:0911.0884)

Combination of Measurements of Inclusive Deep Inelastic ep Scattering Cross Sections and QCD Analysis of HERA Data
H1 and Zeus Collab., Dr Eram Rizvi et.al.,
Eur.Phys.J. C75 (2015) 12, 580