Jet Substructure

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** The above analysis was carried out with a full detector simulation in the WW scattering chapter (p1769) of [http://www.slac.stanford.edu/spires/find/hep/www?irn=8103593 this big ATLAS paper].
** The above analysis was carried out with a full detector simulation in the WW scattering chapter (p1769) of [http://www.slac.stanford.edu/spires/find/hep/www?irn=8103593 this big ATLAS paper].
** ttH [http://cms.cern.ch/iCMS/jsp/openfile.jsp?type=TS&year=2007&files=TS2007_001.pdf CMS study] No substructure used yet...
** ttH [http://cms.cern.ch/iCMS/jsp/openfile.jsp?type=TS&year=2007&files=TS2007_001.pdf CMS study] No substructure used yet...
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** ttH Atlas (Reference, Simon?)
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** ttH [http://cdsweb.cern.ch/record/1178698/files/ATL-PHYS-SLIDE-2009-131.pdf Atlas CSC results] Also no substructure yet.
* Colour singlet heavy objects, three body decay (Neutralino,...) ===
* Colour singlet heavy objects, three body decay (Neutralino,...) ===

Revision as of 12:30, 12 June 2009

Back to Tools_and_Monte_Carlo_Session_1_(SM)#Jet_Physics.

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.

Interested parties (Session 1)

Matt Schwartz, Giacinto Piacquadio, Mario Campanelli, Paulo Francvilla, Jon Butterworth, Peter Loch, Ezio Maina, Leif Lonnblad, Keith Hamilton, Simon Dean, Rohini Godbole, ...

Examine/discuss the different regions of validity for calculations of variables like jet mass, jet width, subjet multiplicity, using e.g. (N)LO ME, PS, matched and resummed calculations etc... (see also A Collection of Matching Benchmarks). Review, compare, critique literature, think about future ideas.

Recent preprint on Zbb and Wbb at NLO.

Contents

Types of object one might use substructure on

QCD jets (quark gluon separation)

  • Wjj provides a sample of quark jets at LHC?
  • SUSY cascades are rich in quark jets. Could use quark ID to simplify decay chains.

Heavy objects

  • Substructure tagging minireview. (Schwartz...)
  • Colour singlet heavy objects, two body decay (W,Z,H...) ===

MC issues

Differences in heavy object decays; different parton showers, matrix element corrections in some MC, not in others; in Herwig, Herwig++, pythia, sherpa. POWHEG improvement soon. See talk from Carlo Oleari Friday afternoon for some discussion of MC@NLO and POWHEG in Higgs decays. Dead cones etc. Keith Hamilton, Giacinto Piacquadio, Matt Schwartz, Leif Lonnblad to produce a short summary of the effects implemented in different MCs.

  • Keith's slides on Dead Zones to link here.
  • Hamilton+ Showers for top decay

How sensitive are the various subjet methods to the above differences?

Would be nice to have some truth level comparisons, of simple variables (jet mass etc) and also of some of the various boosted decay methods (esp top?) if possible.

Detector issues

Pile-up, calorimeter noise, granularity.

Slides from Peter Loch to be linked here.

Studies from GP.

Proposed cuts for studying this (highest priority ones in bold):

  • pT cut on constituents (MeV) 0,100,500,1000,2000.
  • QCD jets in pT bins between 17,35,70,140,280,560,1120 GeV. Look at the leading jet. Radipity +/- 5.
  • Pile-up. 0,4,8,16-20 interactions per signal event (Poisson). (Think about doing this as a function of number vertices in full sim).
  • Jet algorithms. Use Anti-kT R=0.4, R=0.6. And also C/A, kT etc where appropriate, and also studies of using e.g. C/A to recluster anti-kT jets


This includes studies of the effect of pile-up on W reconstruction using the y-scale method (e.g. p103).



Find the jet first, then cut on constituents, or cut on constituents first then find the jet?

Constituents = final state particles, or pre-clustered final state particles, or towers, or topoclusters...

Miscellaneous References

* Seymour+ clustering (kT algorithm)
* Dokshitzer+ clustering
* S. Ellis+ jet pruning, using top as an example
* Krohn+ variable R
* Top ID using kT y scales this Les Houches report (p106)
* Bahr+ Herwig++ manual (includes heavy particle decays)
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