# Les Houches

## 2019 Session

• Working Groups Pages
• Use of wiki. Wifi access/set-up. Printing
• Important info about lodging. Bus. Facilites
• Bulletins.

## Wikis of Previous sessions

#### Les Houches Themes

(Lyrics and Music)

## Help

2019:groups:tools:mcvariation2

# 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)?

Disclaimer

• to some extent, such a study could be considered a continuation of what can be found in chapter V.1 of https://arxiv.org/abs/1605.04692 . 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

Decisions

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

Next steps

• Work out a strategy (slack?)

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

=========

• Carlo Pandini
• Simone Amoroso
• Helen Brooks
• Josh McFayden
• Philippe Gras