LUXqed provides a model-independent determination of the photon parton distribution function (PDF) inside the proton. It is based on structure function and elastic form factor fits in electron-positron scattering, as described in arXiv:1607.04266.

There is currently one complete PDF set, LUXqed_plus_PDF4LHC15_nnlo_100 in LHAPDF v6 format. It combines QCD partons from PDF4LHC15_nnlo_100 with the LUXqed photon determination. It should only be used at scales μ>10 GeV.

The low Q2 LUXqed photon component is determined from A1, CLAS and Hermes GD11-P fits. The high-Q2 part is determined from the input QCD PDF with standard (massless) NNLO coefficient functions. The photon was generated at scale 100 GeV, and other partons matched at scale 10 GeV. Momentum conservation is enforced by adjusting g(x) → 0.99299 g(x) at scale 10 GeV. The DGLAP evolution includes the O(α αs) splitting functions from arXiv:1512.00612.

PDF members:

  • 0: central
  • 1-100: map to original PDF4LHC15_nnlo_100 members
  • 101: replacement of CLAS resonance fit with Christy-Bosted fit
  • 102: rescale R in low-Q2 region by 1.5
  • 103: rescale R in high-Q2 region with a higher-twist component
  • 104: use an elastic fit result without the two-photon exchange corrections
  • 105: use the lower edge of the elastic fit error band
  • 106: lower the transition from Hermes GD11-P to the PDF-based F2, FL determinations to 5 GeV2
  • 107: change the upper limit of the Q2 integral in Eq.(6) of arXiv:1607.04266 to μ2 (with appropriate change of last term of Eq.(6) to maintain accuracy)

Additional plots:

  • momentum fraction carried by the photon as a function of the factorisation scale (the various pages just show different vertical scales, with and without other photon determinations).
  • validation plots, including a visualisation of the photon distribution and the impact of QED corrections on the various partons.