Les Houches

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====MC, Tools and ML====

===Systematic uncertainties [Thurs 14h00-16h00 Auditorium]===
Slack channel: #np-ps-syst-uncs

Possible projects:
  * Shower accuracy and benchmarks
  * Amplitude evolution, if people are interested
  * Role and impact of the infrared cutoff, tuning, and uncertainties
  * A practical approach for experiments
    * What comparisons make sense - what is available?
    * Generators wishlist?
  * Including systematic uncertainties in ML based analysis 
Interested people: Josh, Simon, Stefan, Vinny, Axel, Aishik, Saptaparna, Andrzej, Ana, Maria V., Gianna, Chris G, Christian P, Max, Peter M

**Agreed projects:**
  - Perturbative benchmarks of showers [Simon, James, Daniel]
    - NLL, Numerical impacts 
  - Interplay between shower and hadronisation [Simon]
    - Extending study from LH17 [[https://arxiv.org/abs/1803.07977|arXiv:1803.07977]]
    - Effective/comprehensive uncertainty band
  - Uncertainty recommendation using available tools [Josh, Gianna]
    - Setup 4-point variations of all combinations of shower and hadronisation model
    - Tune these in a consistent way to get an uncertainty envelope 
  - Tuning strategies [Stefan K]
    - What is currently done?
    - Common framework?
    - Better documentation of existing framework
    - Benchmark sets of data


===Generator software and computing considerations [Friday 11h00-12h30 Auditorium]===
Slack channel: #gen-soft-comp

Possible projects:
  * Efficiencies
  * MC reweighting/unweighting
  * GPU/Vectorisation
  * Event format/sharing
  * Containerisation/preservation/reproducibility
  * Use of ML
  * Common frameworks
Interested people: Josh, Vinny, Andrea, Stefan, Saptaparna, Maria V., Sergio, Chris G, Christian P, Ana, Max, Peter M, Simon, Sudeepan

**Agreed projects:**
  - GPU/Vectorisation/HPC [Josh]
    - Experience porting codes
    - Workflows in experiments 
      - How would code be run in practise
      - How to get/confirm allocations
      - Sharing of resources between EXP and TH
  - Computing performance [Josh]
    - Benchmarking current code
      - Also with examples from EXP
    - Accounting in experiments
    - Projections for future N(2,3)LO calculations
  - Updates to interfaces [Josh]
    - Interoperability of models
    - Modular framework
    - Multi-event API in MC generators
      - Resampling
  - Accessibility of tools [Josh]
    - Containerisation and reproducibility 
      - Docker images, run cards, Rivet routines, Yoda files -> HepData
      - Use these tools to make LH studies reproducible
      - Can at Docker-based workflow on e.g. lxplus be documented to lower barrier to entry for MC studies?
      - Make sure cards actually used by EXP are uploaded with TH prediction Yoda files.
      - Make available for benchmarking (c.f. point 2.), including full chain in EXP
    - MC Generation generic tool/interface
      - Like MCPlots
  - Event formats [Josh]
    - New HDF5 standard <- LHEF/HepMC 
      - Easier event sharing, smaller disk footprint
    - Need for more information in intermediate stages of generation?
    - Sample sharing between experiments
      - Joint/cross validation
  - ML for MC []
    - Interoperability link to point 3. (swapping out parts of generation in modular framework)
    - Discussion of exact vs approximate use of ML
  - Resampling/reweighting [Josh]
    - Reweighting and derivative-based optimisation
    - Resampling to eliminate negative weights
      - NN and cell-based tools
      - Stress tests of these tools?
        - Problem areas from TH PoV
        - Validation at scale in EXP

===ttW modelling studies [TBC]===
Slack channel: #ttw

Possible projects:
  * Understanding differences between Sherpa MEPS@NLO and aMC+Py8 FxFx?
  * Modelling uncertainties?
Interested people: Josh, Sergio, Stefan, Gianna

===Issues with EW evolution, identification of EW final states [Thurs 16h00-17h30 QCD room]===
Slack channel: #ew-evo-id
  * Possibly connecting to ttW?
Interested people: Simon, Axel, Andrzej

=== Interplay between showers and hadronization ===

  * Hadronization model should respond to shower IR cut variations
  * Study IR ctuoff dependence, map out how purely perturbative variations compare
  * goal is to update the LH 17 study on retuning with a more solid theory framework

Interested: Simon, Andrzej, Stefan K.


===Tuning Accord and Strategies===
  * What is currently done:
    - Common framework for tuning exist, but no single script to run
      - Nice to have a script, which automatically prints exactly what is done and with which flags
    - Every generator team does tuning on their own
    - Almost no documentation on the tunes provided
      - Rarely publicly available weights
      - Rarely publicly available tuning options (samples, interpolation order, flags used, ...)
      - Often post-processing tune by eye
  * Goals of the project:
    - Coordination among generator authors of Herwig, Pythia and Sherpa (mattermost channel?)
    - Common framework for tuning exist, but no single reproducible script:
      - Stefan K. trying to provide this in Professor, which automatically documents what version, options, flags, etc. are being run 
      - Someone could do something similar in Apprentice
    - Les Houches Accord on some Benchmark observable+weight sets:
      - Observable quality & quantity requirements:
        - No ratio Rivets if full information is available?
        - Reduce double counting of observables:
          - No gaps in histogram (see e.g. some ALEPH identified particle momentum distribution)
          - Smaller bin-width is preferred
          - Enough statistics:
            - NOTE: If the errors of the data are to small a theory uncertainty should be provided to the tuning framework otherwise the minimization will likely over-fit this data
      - Benchmark sets:
        - Conservative set of selected (IRC safe?) Event Shapes:
          - Input from perturbative experts needed
          - Only close to the peak, where hadronization is not dominant
        - Provide global sets from each generator to gather information
        - Ultimate goals:
          - Minimal set of accorded observables+weights among all generators for comparability
            - Tune using $\chi^2$ (more strict) and $\chi^2/(1+\chi^2)$ (less strict)
          - Maximal set of accorded observables+weights among all generators for comparability
            - Tune using $\chi^2$ (more strict) and $\chi^2/(1+\chi^2)$ (less strict)
    - Provide recommendations to experiments on tuning?
      - ...

Interested: Simon, Andrzej, Stefan K., ....


===Status of q/g discrimination [Weds 14h00-15h30 Library]===
  * Linked to Jets and Higgs
Interested people: Simon, Andrzej


===Fiducial multiboson cross sections (VBF/VBS) [Thurs 11h00-12h30 QCD room]===
  * Linked to Higgs
Interested people: Simon, Josh, Stefan, Axel, Saptaparna

===Possible HF review [TBC]===
  * Linked with Higgs and Jets
Interested people: Josh, Davide?, Stefan


===ML-focused [TBC]===

Possible projects:
  * New unfolding observables
  * Interoperability/practical considerations
Interested people: Vinny,Josh, Aishik, Andrzej, Maria V., Peter M


===Overlaps between FPF and LHC [TBC]===
Slack channel: #lhc-fpf

(Possibly the same for DUNE and EIC if enough people are here?)

Possible projects:
  * Impact of NNPDF + FPF data on LHC precision, e.g. W-mass

Interested people: Josh, Maria V., Stefan, Peter M (EIC)
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