Jet Substructure - UC Santa Barbara
Transcript of Jet Substructure - UC Santa Barbara
Jet SubstructureNick Amin
08/29/14
N-subjettiness
โข Given N subjet axes in a fat jet, N-subjettiness, ๐๐ , is given by
โข ๐๐ =1
๐0 ๐ ๐๐,๐min{โ๐ 1,๐ , โ๐ 2,๐ , โฆ , โ๐ ๐,๐}
โข โ๐ ๐,๐ is the angular separation between constituent k and candidate subjet N
โข ๐0 is a normalization factor given by ๐0 = ๐ ๐๐,๐๐ 0 , so 0 โค ๐๐ โค 1
โข ๐ 0 = 0.8 for AK8 clustering
Low ๐๐ (constituents close to subjet axes)
High ๐๐ (consitutents spread out)
Clusters with exactly Nsubjets will have small ๐๐
If ๐๐ โ 1, cluster most likely has more than Nsubjets
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N-subjettiness
โข When comparing N-subjetiness with (N+1)-subjettiness, adding extra candidate subjet allows minimum angular separation to decrease
โข Thus, in most cases, ๐1 > ๐2 > ๐3.
โข Ratio ๐๐๐ = ๐๐/๐๐, where N=M+1, is useful
๐๐๐๐ >
Clusters with small ๐๐๐ most likely have N subjets.
We can use this quantity for cuts.
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Q-jets Volatility
โข Associate clustering history (โtreeโ) with jetsโข Depending on the route (AK8-like, CA8-like, etc.)
taken to get a jet, the mass can change, so you get a mass distribution for a jet when considering the space of possible trees
โข For a pruned jet mass distribution, define
volatility as ๐ =๐2 โ ๐ 2
โจ๐โฉโข Physically, dependence of jet mass on clustering
method governs volatility (large mass fluctuations over different algorithms/routes means the jet is volatile/fuzzy)
A. Hornig
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Jet Toolbox
โข Jet toolbox available at https://twiki.cern.ch/twiki/bin/viewauth/CMS/JetToolboxโข Takes miniAOD (or AODSIM) and adds various substructure branches
โข ~0.1 Hz for miniAODminiAOD+substructure
โข For AK8, it includes:โข Q-jets Volatility
โข N-subjettiness (๐1, ๐2, ๐3)
โข Masses of pruned, trimmed, filtered jets
โข Top-tagged jet massโข If an ungroomed jet is matched to top-tagged jet, this branch is filled with the jet mass
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Current Setup
โข Have 10k-event T2tt sample from Alex (mstop = 850, mLSP = 100)
โข Added โSubJetMakerโ to CMS3 makers, which adds substructure variables from toolboxed miniAOD
โข Preliminary distributions of substructure variables followโข Working on meaningful distributions in my previous framework, along with
same plots with AK8 instead of AK5
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Q-jets Volatility
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N-subjettiness๐3/๐2
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N-subjettiness
๐2
๐3 9
N-subjettiness
๐1
๐2 10
Pruning
Unpruned AK8 Masses
Pru
ne
d A
K8
Mas
ses
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Pruning
Unpruned AK8 Masses Pruned AK8 Masses
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Top-tagged Jet Mass
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Links
โข A. Hornig: https://indico.cern.ch/event/179612/session/2/contribution/39/material/slides/0.pdf
โข H. K. Lou: http://indico.cern.ch/event/215704/session/2/contribution/31/material/slides/0.pdf
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