HonexComb meeting #16



Meeting held on zoom with 14-16 participants


News: Jacek Otwinowski

Discussion: None


EW boson production overview: Guillaume Taillepied


Q by JO: Is there any activity to include all available data to constraint nPDFs?

A: Hard to be done because every nPDF group has its own assumptions and selections. Differences in the assumptions lead to differences in results even while working with the same input data sets.

Q by JO: Do we have any comparisons of the state-of-the-art nPDFs to the data?

A: Not yet because the latest nPDS are too new. This is a nice idea and could be done.

Q by FD: slide 10 - CMS provides correlation matrices for systematics to allow the nPDF analysis. Is it done in the same way by ALICE? A: not yet

Any issue in providing correlations between measurements from different collaboration? A: Use common input, generators to estimate correlations. Use this approach for Run 3 measurements. For Run 2 might be hard.

Q by GM: slide 6 - What is the main uncertainty on the theory? How it can be reduced? A: More data is needed to reduce systematics in nPDF. This is a main source of the uncertainty. More data will reduce the nPDF uncertainty.

Q by JO: What would be a first candidate from ALICE and LHCb for combination? A: Perhaps p+Pb collisions with Z bosons

But also we should repeat measurements in Run 3 with the combination in mind (harmonise the selections). Run 2 could serve as feasibility studies.

What about other measurements which could be input to nPDF? A: Drell-Yan, J/psi, etc

Q by FD: Does ATLAS plan to update W/Z boson measurements in the future? A: No update expected soon for 2018 Pb+Pb data.

Q by JO: slide 16 -Do you have any interpretation for the dramatic change to the nucleon-nucleon cross section? A: not really


Action: try to set up a team of people working on combinations for EW bosons. Volunteers needed from LHCb, CMS and ATLAS.


Exclusive ditau production: Yuriy Volkotrub


Q by JO: Do you have a clear plan to get input from CMS? CMS results are shown as preliminary. They have been published. Could somebody clarify? A: Publication accepted.

How do you get input from CMS: A: From a CMS member.

Clarification: a tiny change in the ATLAS result in the updated publication, covered by the tot uncertainty in the previous version.


Total charm cross section - publication status: Jiayin Sun


Q by JO: Do people have questions and comments to the procedure used in the paper draft? A: None

Other measurements to be used, rapidity dependence in the publication? A: It will not be done because we do not have good measurements in rapidity.

Have we decided which theory calculations will be used for comparisons? A: Ongoing discussion


Discussion of interpretation of tails at high absolute rapidity by Christian Bierlich on dedicated slides attached to the agenda

Solution is the beam drag effect (see slides for details)

Q by JO: Should we add anything to systematics to account for this effect in the extrapolation? A: Not really because it is a real physics effect.

Shape variation is a very conservative estimate of the systematics. Perhaps we should remove this variation and use a different approach based on Lambda_c. Ongoing discussion in the analysis team.

Q by GM: slide 4 - Do we have this plot in the paper draft? A: It is not. It is considered a validation plot. No plan to add it.

Perhaps we could add a reference to the discussion of that effect in the paper.



Total charm cross section and Lambda-C / D case: Sandor Lokos


Q by JO: Should we continue with the coalescence model? Not much we can learn from it. A plan is to invite people from the Catania group to discuss details.

What about charm production in PYTHIA? Answer from Christian: bad internet connection, hard to understand. A student is working on it.

Do we have results from LHCb? A: only from pp, different sqrt{s}. Multiplicity dependence is important in the analysis. Only results from ALICE seem to be available.

Discussion will continue offline.


Next meeting: end of January

Merry Christmas!


There are minutes attached to this event. Show them.
    • 3:00 PM 3:10 PM
      News 10m
      Speakers: Alexander Philipp Kalweit (CERN), Christian Bierlich (Lund University (SE)), Giulia Manca (Universita` degli studi di Cagliari and INFN, Cagliari, IT), Iwona Grabowska-Bold (AGH University of Science and Technology (PL)), Jacek Tomasz Otwinowski (Institute of Nuclear Physics Polish Academy of Sciences (PL)), Jacopo Ghiglieri (Centre National de la Recherche Scientifique (FR)), Raphael Granier De Cassagnac (Centre National de la Recherche Scientifique (FR))
    • 3:10 PM 3:45 PM
      EW boson production overview 35m
      Speaker: Guillaume Taillepied (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE))
    • 3:45 PM 4:00 PM
      Exclusive ditau production 15m
      Speaker: Yuriy Volkotrub (AGH University of Science and Technology)
    • 4:00 PM 4:15 PM
      Total charm cross section - publication status 15m
      Speakers: Christian Bierlich, Christian Bierlich (Lund University (SE)), Jeremy Wilkinson (GSI - Helmholtzzentrum fur Schwerionenforschung GmbH (DE)), Jiayin Sun (Universita e INFN, Cagliari)
    • 4:15 PM 4:30 PM
      Total charm cross section and Lambda-C / D case 15m
      Speaker: Sandor Lokos (Institute of Nuclear Physics Polish Academy of Sciences (PL))
    • 4:30 PM 4:45 PM
      AOBs 15m
      • data / analysis preservation strategy