Jet Substructure

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Back to [[Tools_and_Monte_Carlo_Session_1_(SM)#Jet_Physics Jet Physics]].
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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  
Boosted hadronic decays of massive particles (W,Z,Top,H,BSM..., with session 2) and jet mass/shape studies  
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'''Interested parties (Session 1)'''
'''Interested parties (Session 1)'''
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''Matt Schwartz, Giacinto Piaquadio, Mario Campanelli, Paulo Francvilla, Jon Butterworth, Peter Loch, Ezio Maina, Leif Lonnblad, Keith Hamilton, Simon Dean, ... ''
+
''Matt Schwartz, Giacinto Piacquadio, Mario Campanelli, Paulo Francvilla, Jon Butterworth, Peter Loch, Ezio Maina, Leif Lonnblad, Keith Hamilton, Simon Dean, Rohini Godbole, ... ''
 +
 
 +
'''Interested parties (Session 2)'''
 +
 
 +
''Are Raklev, Gavin Salam, ... ''
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.
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.
-
[http://xxx.soton.ac.uk/abs/0906.1923 Recent preprint on] Zbb and Wbb at NLO.
+
== Types of object one might use substructure on ==
-
+
-
'''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
+
* Substructure tagging minireview. (Schwartz...)
-
POWHEG in Higgs decays. Dead cones etc. ''Keith Hamilton, Giacinto Piacquadio, Matt Schwartz, Leif? to produce a short summary of the effects implemented in different MCs.''
+
* See also section 5.3 of [http://arxiv.org/abs/0906.1833/ arXiv:0906.1833] (Salam)
-
'''How sensitive are the various subjet methods to the above differences?'''
+
=== QCD jets (quark gluon separation) ===
-
'''Detector issues'''
+
* Wjj provides a sample of quark jets at LHC?
-
Pile-up, calorimeter nouse, granularity.
+
* SUSY cascades are rich in quark jets. Could use quark ID to simplify decay chains.
-
Slides from Peter Loch to be linked here.
+
-
Studies from GP, MS.
+
* Experimental papers using substructure to separate q.g jets
 +
** LEP papers.
 +
** [http://lss.fnal.gov/archive/2004/conf/fermilab-conf-04-439-e.pdf CDF conference proceedings (2004).]
 +
** [http://projects.hepforge.org/rivet/analyses#CDF_2005_S6217184 CDF inclusive jet shapes]
 +
** [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0806.1699 CDF b-jet shape paper]. Available in [http://projects.hepforge.org/rivet/analyses#CDF_2008_S7782535 rivet].
 +
** [http://www.slac.stanford.edu/spires/find/hep/www?irn=5883601 ZEUS paper]. Fig.13 p27 of [http://www-spires.dur.ac.uk/cgi-bin/spiface/hep/www?eprint=hep-ex/0509018 this review] shows a comparison of the angular distributions for quark/gluon jets identified using subjet techniques and using charm tagging.
-
'''Incomplete set of jet substructure references'''
+
=== Colour singlet heavy objects, two body decay (W,Z,H...) ===
-
* [http://www.slac.stanford.edu/spires/find/hep/www?irn=7662955 Butterworth+] W/Z+higgs (Cambridge/Aachen)
+
See also the [[List of models]] that produce pairs of high-pt W,Z,H.
-
* [http://www.slac.stanford.edu/spires/find/hep/www?key=7777973 Kaplan+] top tagging
+
-
* [http://www.slac.stanford.edu/spires/find/hep/www?irn=2836785 Seymour+] clustering (kT algorithm)
+
-
* [http://www.slac.stanford.edu/spires/find/hep/www?irn=4825381 Butterworth+] WW (kT y scales)
+
-
* 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].
+
-
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=hep-ph/0702150 Butterworth+] W,Z,H in SUSY cascades (kT y scale again)
+
-
* [http://www.slac.stanford.edu/spires/find/hep/www?irn=3590534 Dokshitzer+] clustering
+
-
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0810.0934 Almeida+] and [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0807.0234 Almeida+] top event shapes
+
-
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0906.0728 Butterworth+] neutralinos (kT yscales and Cambridge/Aachen)
+
-
* ATLAS public note (SUSY09) on [http://cdsweb.cern.ch/record/1177832 neutralinos from subjet structure]
+
-
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0903.5081 S. Ellis+] jet pruning, using top as an example
+
-
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0903.0392 Krohn+] variable R
+
-
* Top ID using kT y scales [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0802.3715 this Les Houches report] (p106)
+
-
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0803.0883 Bahr+] Herwig++ manual (includes heavy particle decays)
+
-
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=hep-ph/0612236 Hamilton+] Showers for top decay
+
-
''' Types of object one might use substructure on '''
+
* [http://www.slac.stanford.edu/spires/find/hep/www?irn=4825381 Butterworth+] WW (kT y scales)
 +
* 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].
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=hep-ph/0702150 Butterworth+] W,Z,H in SUSY cascades (kT y scale again)
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?irn=7662955 Butterworth+] W/Z+higgs (Cambridge/Aachen). For some related discussion on the Wbb background, see [[Wbb in the high pT HW region]].* ttH [http://cms.cern.ch/iCMS/jsp/openfile.jsp?type=TS&year=2007&files=TS2007_001.pdf CMS study] No substructure used yet...
 +
** [http://cms.cern.ch/iCMS/jsp/openfile.jsp?type=TS&year=2007&files=TS2007_001.pdf  CMS PhD thesis]
 +
* ttH [http://cdsweb.cern.ch/record/1178698/files/ATL-PHYS-SLIDE-2009-131.pdf Atlas CSC results] Also no substructure yet.
 +
* See also [[TtH developments]].
-
* QCD jets (quark gluon separation)
+
Plot from Matt showing higgs pT spectrum in ttH events.
-
Wjj provides a sample of quark jets at LHC?
+
[[Image:Pt of higgs.png]]
-
SUSY cascades are rich in quark jets. Could use quark ID to simplify decay chains.
+
Shows that 17% of ttH events contain a Higgs with pT>200 GeV, and ~50% have one with pT>100 GeV. Shows that subjet analyses could have a big impact on ttH.
-
LEP papers.
+
Simon/Jan/Jon to look at using the Higgs substructure analysis on ttH events from Sherpa (particle level).
-
[http://lss.fnal.gov/archive/2004/conf/fermilab-conf-04-439-e.pdf CDF conference proceedings (2004).]  
+
=== Colour singlet heavy objects, three body decay (Neutralino,...) ===
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0906.0728 Butterworth+] neutralinos (kT yscales and Cambridge/Aachen)
 +
* ATLAS public note (SUSY09) on [http://cdsweb.cern.ch/record/1177832 neutralinos from subjet structure]
-
ZEUS paper.
+
=== Coloured heavy objects (top,...) ===
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?key=7777973 Kaplan+] top tagging
 +
* [http://indico.cern.ch/materialDisplay.py?contribId=23&materialId=slides&confId=46139 Schwartz talk] on top-tagging(May 18, 2009)
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0810.0934 Almeida+] and [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0807.0234 Almeida+] top event shapes
 +
* Top ID using kT y scales [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0802.3715 this Les Houches report] (p106)
 +
* [http://cdsweb.cern.ch/record/1177410 ATLAS note] on top reconstruction with substructure, shown in session 2.
-
* Colour singlet heavy objects, two body decay (W,Z,H...)
+
* Comparison of tagging for different jet algorithms on top (Matt Schwartz):
-
* Colour singlet heavy objects, three body decay (Neutralino,...)
+
 
-
* Coloured heavy objects (top,...)
+
[[Image:Minjetmass.gif|600px]]
 +
 
 +
The minimum invariant mass of the sum of any 2 subjets of the top jet (which can contain 4 subjets), as identified by various algorithms. This variable is sensitive to the QCD singularity in the background (solid,red) and has a W mass peak in the signal (blue). Note that anti-KT declustering does not provide strong discrimination, but finding the jets with anti-kT, and then declustering with C/A works well.
 +
 
 +
== 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. Dead cones etc. ''Keith Hamilton, Giacinto Piacquadio, Matt Schwartz, Leif Lonnblad, Jan Winter to produce a short summary of the effects implemented in different MCs.''
 +
 
 +
'''How sensitive are the various subjet methods to the 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. Matt will look into this if people will send him events.
 +
 
 +
Plots from GP showing the difference between PYTHIA and Herwig when applying the subjet clustering technique implemented
 +
for the high pT WH to lnubb analysis:
 +
* H to bb invariant mass distribution at true level
 +
* H to bb invariant mass distribution with expected detector smearing
 +
* pT(third subjet)/(pT(second subjet)+pT(first subjet) looking into two different windows
 +
 
 +
[[Image:FilteredMassJetComp.png]]
 +
[[Image:PlotMassSigSmeared.png]]
 +
[[Image:ThirdSubjet.png]]
 +
 
 +
In the third plot, it can be clearly seen that Herwig fills almost no events with pT(third subjet) > pT(second b-subjet),
 +
while PYTHIA does, due to the ME corrections implemented in the decay. The radiation spectrum is therefore
 +
softer in HERWIG with respect to PYTHIA. This can be a reason for the fact that one sees a degradation in the mass
 +
resolution at hadron level in HERWIG with respect to PYTHIA. However, once the detector smearing is taken into account,
 +
the difference gets essentially smeared out and the mass distributions are again quite comparable.
 +
 
 +
MC references:
 +
* [http://home.thep.lu.se/~torbjorn/pythia/lutp0613man2.pdf Sjostrand et al] Pythia manual.
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=hep-ph/0612236 Hamilton & Richardson] Showers for Top decay.
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0803.0883 Bähr et al] Herwig++ manual (includes heavy particle decays)
 +
Related, non-MC, theoretical activity on resummation and QCD radiation patterns:
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=hep-ph/0110108 Peter Richardson] Spin correlations in the shower for heavy particles.
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=hep-ph/0209204 Cacciari, Corcella, Mitov] Resummation of b-quark energy spectrum in Top decay.
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=hep-ph/0311101 Alex Mitov] Alex Mitov's PhD thesis (more on the above paper).
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=hep-ph/9308359 Khoze, Ohnemus, Stirling] Soft gluons in Top production.  
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=hep-ph/9605369 Masuda, Orr, Stirling] Soft gluons in Top production and decay.
 +
Top mass:
 +
* [http://conference.ippp.dur.ac.uk/getFile.py/access?contribId=7&resId=0&materialId=slides&confId=88 Adrian Signer] Definition of mtop and colour connection effects / non-factorisable contributions (motivation for the multiscale shower).
 +
 
 +
== Detector issues ==
 +
 
 +
Pile-up, calorimeter noise, granularity, acceptance: The reconstruction quality for the various jet shape variables need to be understood. A first look at jet masses and y-scale in ATLAS can be found at [http://www.physics.arizona.edu/~loch/LesHouches2009/Material/JetMass.pdf (transparencies)],
 +
[http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0712.2447 S.D.Ellis+], and at [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0901.0512 ATLAS Collaboration].
 +
 
 +
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
 +
 
 +
 
 +
[http://www.slac.stanford.edu/spires/find/hep/www?key=6925820 Sarah Allwood's thesis] can be found in the [http://www.hep.manchester.ac.uk/theses/2006.html Manchester thesis archive]. 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...
 +
 
 +
[http://www.hep.ucl.ac.uk/~jmb/Talks/LesHouches/pl_summary.pdf Slides] from Peter and Paulo on the effect of pile up on jet mass and substructure variables.
 +
 
 +
== Miscellaneous References ==
 +
 
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?irn=2836785 Seymour+] clustering (kT algorithm)
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?irn=3590534 Dokshitzer+] clustering
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0903.5081 S. Ellis+] jet pruning, using top as an example
 +
* [http://www.slac.stanford.edu/spires/find/hep/www?eprint=arXiv:0903.0392 Krohn+] variable R

Current revision

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, ...

Interested parties (Session 2)

Are Raklev, Gavin Salam, ...

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.

Contents

Types of object one might use substructure on

  • Substructure tagging minireview. (Schwartz...)
  • See also section 5.3 of arXiv:0906.1833 (Salam)

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.

Colour singlet heavy objects, two body decay (W,Z,H...)

See also the List of models that produce pairs of high-pt W,Z,H.

Plot from Matt showing higgs pT spectrum in ttH events.

Image:Pt of higgs.png

Shows that 17% of ttH events contain a Higgs with pT>200 GeV, and ~50% have one with pT>100 GeV. Shows that subjet analyses could have a big impact on ttH.

Simon/Jan/Jon to look at using the Higgs substructure analysis on ttH events from Sherpa (particle level).

Colour singlet heavy objects, three body decay (Neutralino,...)

Coloured heavy objects (top,...)

  • Comparison of tagging for different jet algorithms on top (Matt Schwartz):

The minimum invariant mass of the sum of any 2 subjets of the top jet (which can contain 4 subjets), as identified by various algorithms. This variable is sensitive to the QCD singularity in the background (solid,red) and has a W mass peak in the signal (blue). Note that anti-KT declustering does not provide strong discrimination, but finding the jets with anti-kT, and then declustering with C/A works well.

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. Dead cones etc. Keith Hamilton, Giacinto Piacquadio, Matt Schwartz, Leif Lonnblad, Jan Winter to produce a short summary of the effects implemented in different MCs.

How sensitive are the various subjet methods to the 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. Matt will look into this if people will send him events.

Plots from GP showing the difference between PYTHIA and Herwig when applying the subjet clustering technique implemented for the high pT WH to lnubb analysis:

  • H to bb invariant mass distribution at true level
  • H to bb invariant mass distribution with expected detector smearing
  • pT(third subjet)/(pT(second subjet)+pT(first subjet) looking into two different windows

Image:FilteredMassJetComp.png Image:PlotMassSigSmeared.png Image:ThirdSubjet.png

In the third plot, it can be clearly seen that Herwig fills almost no events with pT(third subjet) > pT(second b-subjet), while PYTHIA does, due to the ME corrections implemented in the decay. The radiation spectrum is therefore softer in HERWIG with respect to PYTHIA. This can be a reason for the fact that one sees a degradation in the mass resolution at hadron level in HERWIG with respect to PYTHIA. However, once the detector smearing is taken into account, the difference gets essentially smeared out and the mass distributions are again quite comparable.

MC references:

Related, non-MC, theoretical activity on resummation and QCD radiation patterns:

Top mass:

  • Adrian Signer Definition of mtop and colour connection effects / non-factorisable contributions (motivation for the multiscale shower).

Detector issues

Pile-up, calorimeter noise, granularity, acceptance: The reconstruction quality for the various jet shape variables need to be understood. A first look at jet masses and y-scale in ATLAS can be found at (transparencies), S.D.Ellis+, and at ATLAS Collaboration.

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


Sarah Allwood's thesis can be found in the Manchester thesis archive. 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...

Slides from Peter and Paulo on the effect of pile up on jet mass and substructure variables.

Miscellaneous References

* Seymour+ clustering (kT algorithm)
* Dokshitzer+ clustering
* S. Ellis+ jet pruning, using top as an example
* Krohn+ variable R
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