Minutes of Meeting

Participants

Amanda Cooper Sarkar, Bogdan Malaescu, Daniel Reichelt, David d'Enterria, Deniz Sunar Cerci, Federico Sforza, Francesco Giuli, Garwita Agarwal, Jeff Dandoy, Joey Huston, Klaus Rabbertz, Lucian Hard Lang, Mario Campanelli, Mikko Voutillainen, Ota Zaplatilek, Patrick Connor, Petr Jacka, Robert Thorne, Stanislav Polacek, Thomas Cridge, Valentina Guglielmi, and Zdenek Hubacek.

1. Introduction and General Discussion

Federico Sforza’s Introduction Slides

• The next PDF4LHC meeting is expected to take place around November.
• A dedicated session slot may be possible during that meeting, although not for the June meeting.
• Participants agreed to stay informed about future developments and scheduling opportunities.

Related Links

• Robert Thorne shared the Indico page for the meeting:
  https://indico.cern.ch/event/1675595/

Possible Joint Meeting

• A suggestion was made to organize a common meeting involving both LHCEWWG2 and PDF4LHC in November.
• Bogdan Malaescu suggested that technical discussions should first be carried out before broader organizational discussions.

Previous Work and Publications

• Two publication notes exist for 7 TeV and 8 TeV analyses for a single observable.
• This work was originally triggered by the Top LHC Working Group.
• The existing studies do not yet address fully differential cross-section measurements.

2. Patrick Connor’s Presentation

Reference

• Joey Huston shared the following recent paper:
  https://arxiv.org/abs/2604.25490

xFitter Developments

• Francesco Giuli mentioned that the “errors-on-errors” implementation will soon be available in xFitter.
• This will allow testing the impact on PDF determination studies.

3. Technical Discussion

Scope and Ambition

• Bogdan Malaescu commented that the goals presented on Slide 2 appear very ambitious and extend significantly beyond previous work.

Unfolding Uncertainties

• Discussions between ATLAS and CMS have so far mainly focused on statistical aspects.
• Current understanding indicates that unfolding uncertainties are relatively small.
• Therefore, unfolding uncertainties are not considered a critical issue, provided each experiment uses its established methodology.
• Model uncertainties are partially covered by unfolding uncertainties.
• However, modelling uncertainties are still not fully under control and require further discussion.

Physics-Driven Method

• Additional discussion was requested regarding the “physics-driven method” mentioned on Slide 8.

4. JES (Jet Energy Scale) Discussion

Key Topics

• Amanda Cooper Sarkar suggested reviewing the most important recent developments in Jet Energy Calibration.
• It was proposed to involve relevant experts, depending on available time and manpower, to move toward a more practical and detailed description.

JES Uncertainty Sources

• A detailed list of JES uncertainty sources should be compiled for both ATLAS and CMS.
• Bogdan Malaescu suggested starting from the existing 7 TeV and 8 TeV publication notes and then evaluating what has changed since then.
• The goal is to identify modifications introduced separately by CMS and ATLAS.

Comments from Jeff Dandoy

• Jeff Dandoy emphasized that the previous work remains highly valid.
• According to him, not much has changed on the ATLAS side since the earlier studies.
• Small differences between current and previous approaches can be reviewed systematically.
• Regarding Slide 6 and relative FSR effects, he noted that calibration procedures have evolved even if the purpose of the systematic uncertainty treatment has remained the same.

5. Next Steps

• Organize a dedicated meeting with ATLAS and CMS experts within the next month.
• Plan a follow-up discussion involving PDF experts toward the end of the year.
• Continue technical discussions on modelling uncertainties and JES uncertainty harmonization between experiments.