Tools and Monte Carlo Session 1 (SM)

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(Jet Physics)
(Standard Processes for Early LHC Data (Joint with NLO/Multileg))
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* ttbar (Kajari Mazumdar, Rohini Godbole...)
* ttbar (Kajari Mazumdar, Rohini Godbole...)
* W/Z ratios etc (Bruce Mellado...)
* W/Z ratios etc (Bruce Mellado...)
 +
 +
= Study of radiation between jets, for colour singlet and colour octet exchange =
 +
 +
The idea is to study the difference between the exchange of colour singlets and coloure objects in events with jets separated by large rapidity intervals, to be validated by early LHC data.
 +
From the theory point of view, we plan to use an FKL approach to very high-order processes where a gluon
 +
ladder is emitted between the two main jets.
 +
Experimentally, we will study observables to distinguish the two cases, also in the presence of the underlying event, so developing techniques to subtract it and distinguish it from the hard QCD radiation.
 +
 +
* theory: J.Andersen, P.Skands, ...
 +
* experiment: M.Campanelli, P.Loch, Joanna

Revision as of 15:11, 12 June 2009

Conveners present: Peter Skands, Fabio Maltoni, Jon Butterworth
(Click here for Tools and Monte Carlo Session 2 (BSM))

Contents

Tuning

Validity of tunes and Uncertainty Bands

Automated Tuning: Rivet & Professor

Toolkit for validation of Monte Carlo event generators. Using an computationally efficient model for observable computations, Rivet provides a set of experimental analyses useful for generator sanity checks, as well as a convenient infrastructure for adding your own analyses. Rivet's design emphasises the separation between HepMC records and where they came from, allowing it to be a completely cross-generator validation platform. Rivet 1.1.3 was just released (9 June).

A rivet tutorial (Andy Buckley) is scheduled for 16:00 Thursday in the QCD room.

Project: identify important data sets which are not in rivet but should be. Maybe implement some of them this week if possible. We will try & collect names on this after the tutorial, or sign yourself up here if interested.

Professor is a MC tuning tool, developed in Python as a set of command line programs and an underlying library. The Rivet toolkit is used to generate MC data and retrieve experimental reference data.

  • Can we define regions of validity for the physics implemented in the MC? e.g. What about small x, high rapidity effects
  • Can we obtain credible uncertainty bands with existing tools, or are new methods needed

Project: Take an example, probably the energy extrapolation of underlying event, and evaluate the uncertainty band. Maybe examine the effect of (pseudo) LHC data. Peter Skands, Andy Buckley, +....

  • Impact of tunes on new physics searches (with Session 2)

Project: Maybe we can produce "Demystifying Tuning: A Les Houches Guide to Tuning?"

Multiple Parton Interactions

  • W+jets from MPI (E. Maina, R. Chierici, S. Plaetzer, P. Skands, K. Mazumdar)

Tuning in the presence of matching

  • Chart the problem. Determine some Classic Examples.

TODO: Summary of study by Giulio Lenzi http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0903.3918

  • How dependent on matching strategy?
  • Are there ways of revamping pre-matched tunes?
  • Influence of UE on matching

Model (in)dependence in Data/Theory Comparisons

Detector Simulation

This is joint with Session 2; for details follow this link: Tools_and_Monte_Carlo_Session_2_(BSM)#Detector_simulation_.28with_Session_1.29

Data Correction and Unfolding

At what "truth" level should data and theory generally be compared? What corrections are optimal for data to be used in MC tuning?

Issues include:

  • Jet calibration: what truth do we calibrate to? (see last Les Houches for accord on final states)
  • What is an electron? How to treat/correct for photon radiation.
  • Resonances: e.g. do we measure a Z or a lepton mass distribution?
  • Photon isolation at the truth level
  • Role of detector simulation (see Tools_and_Monte_Carlo_Session_2_(BSM)#Detector_simulation_.28with_Session_1.29 for related discussions)
  • ...



Matching

Projects at Les Houches

  • A Collection of Matching Benchmarks
    • So far declared interest: F. Maltoni, P. Skands, S. Hoeche, K. Hamilton, S. Plaetzer, S. Mrenna, L. Lonnblad, P. Francavilla, J. Winter, M. Schwarz, P. Lenzi...
    • Overview of systematic studies so far (Z/W+jets, ttbar, Z->qqbar)
    • Why it's not a complete set
      • gg initial states (Higgs, with NLM Higgs)
      • gluon splitting (Zbbbar, Wbbbar) (G. Piacquadio)
      • distinguish between W+ and W- at LHC
      • QCD n-jets (P. Francavilla)
      • New Physics Benchmarks?
    • Comparison of NLO (e.g., MCFM, MC@NLO, POWHEG) with tree-level calculations (e.g., Madgraph, Alpgen, with and without showers) (e.g., for Higgs) (J. Winter, P. Lenzi)
    • Pathological Observables / Theory Tests : (P. Skands, S. Weinzierl, S. Plaetzer, K. Hamilton, M. Schwarz, ...)
      • To test Higher-Order/Higher-Log properties of matching
      • To test Coherence/Subleadling-Logs dependence on Shower Model (new PS models)
    • Complete set of observables? (not only pT and rapidity, but jet-jet correlations, jet masses, jet-jet Delta(R), etc)
    • Sensitivity to tuning (with Tuning subgroup)
  • QED/EW ME/PS Matching
    • So far declared interest: S. Gascon, F. Piccinini, C. Baty, S. Ferrag, K. Mazumdar...
  • LHEF for Matching
    • So far declared interest: L. Lonnblad, T. Sjostrand, F. Maltoni, S. Platzer, S. Hoeche, K. Hamilton, A. Buckley, J. Huston...
    • Possible to agree on Standard for describing, in Les Houches Event Files, properties and cuts used in ME generation that subsequent matching steps based on jet clustering would need to know about?
    • Possibly including NLO
  • Automated ME/PS merging
    • So far declared interest: S. Mrenna, P. Skands, S. Hoeche, K. Hamilton, S. Plaetzer
    • Automating 1st-order correction factors for showers from automatic evaluation of |M(X+1)|^2/|M(X)|^2 from an ME generator.
    • Automated merging for BSM (with session 2)
  • Discussion on MC Uncertainties (with EX/TH and tuning subgroups)
    • Theoretical: uncertainty bands, errors
    • Specifically for matching and matching procedures
    • Experimental: contraints, validation, tuning uncertainties
    • Technical: usage and design
    • Uncertainty bands for Monte Carlos
    • So far declared interest: S. Mrenna, R. Chierici, F. Maltoni, P. Skands
  • NLO Matching Discussion
    • Multileg matching at NLO, state of the field
    • What is needed for automating NLO matching?
  • Matching Beyond Fixed Orders
    • Matching in High-Energy Limit (Andersen, Campanelli, Skands)
    • Tuning in the presence of matching (see Tuning above)
  • ...

Parton Densities

PDFs in Monte Carlos

  • Exploring the LO* PDFs, are we ready to use them for production?
  • Uncertainty Bands for the LO* PDFs
  • PDFs and their interaction with MC tuning
  • Pythia 8 - Advantages/disadvantages of using one PDF for hard scattering ME (best cross section?) and another for evolution (universal tuning?)

Beyond LO*

  • Are PDFs ready for NLO/Multileg WG?
  • Electroweak and QCD in PDFs
  • BSM effects in PDFs (with Session 2)

Heavy quark PDF's

  • HQ initiated processes vis-a-vis latest implementation of HQ PDF's(Session 1)

Jet Physics

For discussion of calibration and truth level, see the session on Data/Theory comparison Tools_and_Monte_Carlo_Session_1_(SM)#Data_Correction_and_Unfolding

A very recent pedagogical review of jets, new algorithms and substructure.

Jet Substructure

Boosted hadronic decays of massive particles (W,Z,Top,H,BSM..., with session 2) and jet mass/shape studies with QCD jets in early data.

The title above is a link.

Standard Processes for Early LHC Data (Joint with NLO/Multileg)

In the introduction session, the proposal was made that some standard processes should be listed, and in additona a subset of these should followed through the various MC and NLM sessions, to review the impact of the various issues ((N)NLO, Matching, PDFs, jet definition, EW corrections...) on the process. This is probably a cross-group activity which should be migrated to a separate page but is here for now as a reminder.

List based on my poor memory, to be amended...

  • Drell-Yan (Samir Ferrag...)
  • ttbar (Kajari Mazumdar, Rohini Godbole...)
  • W/Z ratios etc (Bruce Mellado...)

Study of radiation between jets, for colour singlet and colour octet exchange

The idea is to study the difference between the exchange of colour singlets and coloure objects in events with jets separated by large rapidity intervals, to be validated by early LHC data. From the theory point of view, we plan to use an FKL approach to very high-order processes where a gluon ladder is emitted between the two main jets. Experimentally, we will study observables to distinguish the two cases, also in the presence of the underlying event, so developing techniques to subtract it and distinguish it from the hard QCD radiation.

  • theory: J.Andersen, P.Skands, ...
  • experiment: M.Campanelli, P.Loch, Joanna
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