28/4/2006chris collins-tooth tth, (h bb) with eventviews chris collins-tooth, christian shaw...

28/4/2006 Chris Collins-Tooth

tth, (h→bb) with EventViews

Chris Collins-Tooth, Christian Shaw03-May-2006


Introduction• Report from UK Higgs mtg. in London last Friday• Accessing the tth (h→bb) channel.• Some output (for 20k Mh=130 GeV) MC Sample:

• Sim,Dig:9.0.4• Reco:10.0.4

• Soon: CSC...– These are not even simulated yet.


Report from UK Higgs mtg• Lots of interest in ttH H→bb.

– WM,PTD,RG,NK,SD,CT

• If you are interested, join [email protected]• Made TWiki page for use by ttH H→bb, linked from:

– https://uimon.cern.ch/twiki/bin/view/Atlas/HiggsWorkingGroup

• I Decided to make code available on this page for 11.0.3 EventView-based ttH (H→bb) analysis.

• Focus for next meeting will be work for CSC. – We will undoubtedly need to re-make AOD, since no truth info.– I aim to concentrate on jet algorithms and muon purity..

https://uimon.cern.ch/twiki/bin/view/Atlas/HiggsWorkingGroup


The tth (h→bb) channel• Event trigger is a high Pt lepton.


The tth (h→bb) channel• Event trigger is a high Pt lepton.• Aim: throw away most of the

event leaving the correct two b-jets, allowing Mh reconstruction.


The tth (h→bb) channel• Event trigger is a high Pt lepton.• Aim: throw away most of the

event leaving the correct two b-jets, allowing Mh reconstruction.

• Many combinatorical possibilities! • Must keep them in the list of

possible “Event Views” until we can judge which is the most accurate combination (from comparison to truth, t-mass reco.)•EventView software tools suited to this..


Some Output: tth Trigger Lepton• When only a trigger electron..• “Trigger electrons” are:

– Pt>25 GeV– no soft electrons– IsEM applied– Isolation: no more than 15 GeV in cone 0.45

• When there’s only a trigger muon..• “Trigger muons” are:

– Pt> 20 GeV– Muon track Chi2NdofCut < 20– We intend to implement an isolation cut.

deltaR (electron only)

deltaR (muon only)


Electron or Muon?

• When there’s a trigger electron and some muons which qualify as trigger candidates.. – use the electron!!!

• NB: events with >1 trigger electron candidate are very rare.


b-jet Energy• Look at Ebjet/Ebquark• Adding soft ’s back in to

the jet helps.• Using Kt alg. also helps..• Kt R-param=0.45.

– BEWARE there’s a bug!– Value actually given in

JobOpts=0.2 (=0.45**2).• Seems like a small effect,

but b-jet combinatorics sensitive to small energy shifts!

Add Muons

Cone

Kt


b-jet Energy• Look at Ebjet/Ebquark• Adding soft ’s back in to

the jet helps.• Using Kt alg. also helps..• Kt R-param=0.45.

– BEWARE there’s a bug!– Value actually given in

JobOpts=0.2 (=0.45**2).• Seems like a small effect,

but b-jet combinatorics sensitive to small energy shifts!

Add Muons

Cone

Kt

better mean, m

ore

symm

etric


Higgs Masses

• Cone 0.7 simply not applicable to this channel..too many jets!

• Cone 0.4 not calibrated.• Input Mh=130 GeV.• Use Kt with ’s added.• Mass peaks:

– Cone4, no ’s ~118 GeV– Kt4, with ’s ~125 GeV

Cone

Kt

Add Muons


More detail...• With Kt 0.4, and soft

muons resummed into the b-jets, we see an improvement in the reco’d higgs mass.

• If you want to see exactly how the tth (h→bb) analysis is run, you can see my online log at:

Mh

Fit Mean 1.25e+05





Finally

• Looking at TruthJet energies... – Ebjet/Ebquark has many effects folded in.– Where there is a good match, Interesting to look at

Ebjet/Etruthjet and Etruthjet/Ebquark. • Backgrounds

– We simulated gg->ttbb with AcerMC– Other Backgrounds tbd with Atlfast.– Significances to follow soon – haven’t had time yet!

28/4/2006chris collins-tooth tth, (h bb) with eventviews chris collins-tooth, christian shaw...

Documents