SciPost Submission Page

Probing proton PDFs at high x with LHCb

by Thomas Boettcher on behalf of the LHCb Collaboration

This is not the current version.

Submission summary

As Contributors: Thomas Boettcher
Preprint link: scipost_202107_00091v1
Date submitted: 2021-07-30 15:13
Submitted by: Boettcher, Thomas
Submitted to: SciPost Physics Proceedings
Proceedings issue: DIS2021
Academic field: Physics
  • High-Energy Physics - Experiment
  • Nuclear Physics - Experiment
Approach: Experimental


LHCb is a forward spectrometer at the LHC covering the pseudorapidity region $2<\eta<5$. Because of this forward coverage, LHCb can probe the proton parton distribution functions (PDFs) in previously unexplored kinematic regimes, in particular at very high and low Bjorken-$x$. This contribution presents LHCb measurements that can be used to constrain the proton PDFs, with a focus on the high-$x$ and high-$Q^2$ regime.

Current status:
Has been resubmitted

Submission & Refereeing History

Resubmission scipost_202107_00091v2 on 14 September 2021

Reports on this Submission

Anonymous Report 1 on 2021-8-9 (Invited Report)


Presents recent LHCb data which can constrain PDFs


Does not really demonstrate these constraints


This is a short conference report on the impact of LHCb data on high-x PDFs. Whereas it is undoubtedly true that these data can have impact this is only explicitly demonstrated in Fig 1. The rest of the time it is asserted with reference to figures which do not actually show this. In the case of top data there is not even a figure.
I have suggested that information could be added to Figs 2 and 3 below. I have also pointed out that PDFs for intrinsic charm have appeared long before the recent NNPF3.1. If these matter are addressed it can be pulished.

Requested changes

Both Fig 2 and Fig 3 present cross section data compared to theory with minimal information as to what the theory is (particularly for Fig 3). As a minimum the PDF used should be specified and its uncertainties quantified, better still predictions using different PDFs should e compared. Otherwise on cannot claim that these data have impact on PDFs.
it is also stated that NNPDF3.1 is the first general purpose PDFset to allow for intrinsic charm. This is not strictly true the older CTEQ66c set (~2006) did this.

  • validity: ok
  • significance: good
  • originality: high
  • clarity: good
  • formatting: good
  • grammar: good

Author:  Thomas Boettcher  on 2021-09-14

(in reply to Report 1 on 2021-08-09)

Thank you for the helpful comments. Additional information about the theory calculations has been added in the captions of Figures 2 and 3.

I disagree characterizing CTEQ66c as a "general purpose" PDF set. The CTEQ authors do not characterize it as a general purpose PDF set (see for example where CTEQ6, 6.1, 6.5, and 6.6 are all explicitly labeled as "general purpose" while 6.5cn and 6.6C are not). In addition, CTEQ6.5cn and CTEQ6.6C were not published with eigenvector PDF sets to allow for uncertainty calculations.

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