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Les Houches

2023 Session

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Les Houches Themes



MC variation II

Project aim:

  • consider 1 case study, pick a selection of 2-3 observables, perform a selection of MC variations
  • for a given setup X=(FO/matching/merging accuracy, PS model, NP model), produce envelope
  • check if the envelope from setup X behaves as expected or not: for instance, it might happen that even in a region that should be dominated by “hard physics”, one has a residual dependence upon the NP model, or a too-large dependence upon some shower parameter, if the variations are not done properly, or if there's an inconsistency.
  • check if envelopes from setup X_i and setup X_j overlap at least partially. If there are very large differences, is this expected (given the kinematic region probed and the perturbative/non-perturbative content of the setups)?


  • to some extent, such a study could be considered a continuation of what can be found in chapter V.1 of . Nowadays we might aim for having higher accuracy in the ME part, and possibly more developed and more efficient frameworks for “PS-reweighting”.

Possible test cases:

  • pth in gluon-fusion (pros: directly related to STXS bins)
  • Drell-Yan (pros: there's data available)
  • ttbar (pros: atlas and cms have already several studies performed with identical or very similar setups)

Meeting on Monday

  • agree first on the utility/need (from the EXP side) of such a study, and then on the best test case
  • →Check


  • Agreement reached points towards ttbar as first choice. Probably as a second choice: gg→H

Next steps

  • Work out a strategy (slack?)

Interested participants (please add your name):

* ttbar  
  * Emanuele Re
  * Helen Brooks (can provide Vincia+POWHEG, maybe Pythia)


  • Carlo Pandini
  • Simone Amoroso
  • Helen Brooks
  • Josh McFayden
  • Philippe Gras
  • Adil Jueid
2019/groups/tools/mcvariation2.txt · Last modified: 2019/06/25 17:12 by adil.jueid