HonexComb kick-off meeting

160/1-009 (CERN)



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1/ Reviews of the four original topics that were put forward in the proposal (nPDF, light-by-light, open HF and quarkonia), to gauge the need for combinations.

2/ Gather the tons of (other) ideas you will propose!

HonexComb minutes 28/01/20

Attendance: about 35 connections on vidyo, 13 people in the room 

Next meetings: Feb 25th, Mar 31st, Apr 28th...


  • Any theorist interested in joining?

  • Do we also foresee publications for technical aspects? We could, if the added value is worth being published… 

  • Should we define similar binning? Depends if we can anticipate, or not. 

  • It would help to have similar definitions for basic quantities and try to provide measurements in function of the same observables...

  • Possible: Would be nice to provide summary plots of key published measurements with the four LHC experiments covering the different areas of momentum and rapidity, as done in the past by the QWG. 

Message: Overall, it is difficult to provide a unified answer to these generic questions, TBD on a case by case basis, with agility… 

nPDF (talk by André Stahl) 

  • Fact: nPDF makers already have tools to combine different measurements

  • Action: ask them if they want something from us?

  • Action: should first compare quantitatively the existing results, in particular the high statistics?

  • Possible: would we gain in combining the lower statistics signals, e.g. Z or W bosons in the forward region from LHCb and Alice? 

Open heavy flavour (talk by Jiayin Sun) 

  • Large kinematical overlap between experiments 

  • Possible: Total cross section of charm 

  • Possible: Pseudo-rapidty dependences 

  • Possible: Baryon/meson ratio, would be nice from LHCb 

  • Possible: Open beauty > LUT from the theory? 

  • Action: Review the multiplicity definition (more generic) 

Quarkonia (talk by Michael Winn) 

  • Possible: Upsilons, a nice combination paper for run 3? Intriguing comparison btw ATLAS and CMS, to be followed up…

Message: Make the comparison or combination on yields and cross-sections, not RAA. 

Iwona, post meeting: some comparisons on yields are available as part of the ATLAS preliminary analysis (e.g. Fig. 5a, 5b): https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2019-054/

Rare processes, light-by-light and top quarks (talk by Iwona) 

  • Possible: Light-by-light, ATLAS+CMS, TBD… 

  • Action: help to popularize the top quark studies  

Other ideas (to be followed)

  • Possible: X(3872) ? 

  • Possible: Jets ? 

  • Possible: nPDF from UPC ?  

There are minutes attached to this event. Show them.
    • 15:00 15:15
      Welcome 15m
      Speaker: Raphael Granier De Cassagnac (Centre National de la Recherche Scientifique (FR))
    • 15:15 15:45
      Constraining nPDF 30m
      Speaker: Andre Govinda Stahl Leiton (Rice University (US))
    • 15:45 16:15
      Heavy flavours 30m
      Speaker: Jiayin Sun (Tsinghua University)
    • 16:15 16:45
      Quarkonia 30m
      Speaker: Michael Andreas Winn (Université Paris-Saclay (FR))
    • 16:45 17:15
      Light-by-light scattering (and other rare processes) 30m
      Speaker: Iwona Grabowska-Bold (AGH University of Science and Technology (PL))
    • 17:15 18:00
      Other ideas ? 45m
      - It could be interesting to add to the list of observable groups UPC measurements gamma-pomeron measurements (exclusive heavy Quarkonia and light vector mesons (rho, phi)). One would need to see up to which point this makes sense since a good fraction of the activity is in the US and what in that respect is already covered by the forward physics group of LHC. (M. Winn)