higgs reach through vbf with atlas
DESCRIPTION
Higgs Reach Through VBF with ATLAS. Recontres de Moriond 2004 QCD and High Energy Hadronic Interactions. Bruce Mellado University of Wisconsin-Madison. Outline. Introduction Higgs Discovery Potential SM Higgs Low Mass SM Higgs Intermediate Mass SM Higgs Overall ATLAS potential - PowerPoint PPT PresentationTRANSCRIPT
Higgs Reach Through VBF with ATLAS
Bruce MelladoUniversity of Wisconsin-Madison
Recontres de Moriond 2004QCD and High Energy Hadronic
Interactions
Bruce Mellado, Moriond 2004, 02/04/04 2
OutlineIntroductionHiggs Discovery PotentialSM Higgs
Low Mass SM HiggsIntermediate Mass SM HiggsOverall ATLAS potential
MSSM Higgs
Prospects of Couplings MeasurementConclusions
Bruce Mellado, Moriond 2004, 02/04/04 3
Production:Direct
gg H Dominant Large background
at masses close to LEP limit
qq qqH (VBF) Distinct final state
Associated ttH, WH, ZH
Small cross-section
SM Higgs at LHC
VBFgg H
Associated
Bruce Mellado, Moriond 2004, 02/04/04 4
Low Mass Higgs via VBFWisconsin Phenomenology Institute (D.Rainwater, D.Zeppenfeld et al.):Two high PT jets with
large separationStrong discovery
potential for low Higgs mass
Helps measuring couplings
Feasibility studies CMS Note 2003/033 ATLAS SN-ATLAS-2003-024
Updates in progress
Jet
Jet
Forward jets
Higgs Decay
Bruce Mellado, Moriond 2004, 02/04/04 5
Tagging forward jets:Efficiencies criticalFull simulation usedDouble tag efficiency ~50%
Central jet veto:Pile up effects introduce fake central jets Effect small at low
luminosity Serious concern at high
luminosity
Major Experimental Issues
Major experimental issues addressed with a full detector simulation (Geant3)
Currently ATLAS is assessing feasibility of entire analysis with a full detector simulation
Bruce Mellado, Moriond 2004, 02/04/04 6
Low Mass Higgs via VBF
H->WW*->ll,lqq. Strongest in 125<MH<190 GeVMain background:
tt EW WWjj W + 4 jets
H->->ll,lh (+ptmiss). Strong around LEP limitMain background
QCD and EW Zjj
H->. Contributes around LEP limitMain background
Real and fake non-resonant
Bruce Mellado, Moriond 2004, 02/04/04 7
H->WW*->ll
Background: tt, EW WWjj Understanding of tt production is crucial
Background suppression:Well separated forward jets and central jet veto
b-jet vetoLepton angular correlations
Two neutrinos in final state. No narrow mass peak, transverse mass is used, insteadMay achieve large signal-to-background ratio
ATLAS Preliminary
Used MC@NLO for tt production
Bruce Mellado, Moriond 2004, 02/04/04 8
Perturbative QCD
Parton Shower
H->WW*->ll (cont)
ATLAS updated study with new simulation of ttOld study based on PythiaNew study based on MC@NLO/HERWIG
Strong differences between generatorsPT of tt and jet multiplicity
However, discovery potential does not suffer significantly
Made mass dependent cut optimization
Bruce Mellado, Moriond 2004, 02/04/04 9
H->WW*->ll (cont)
Evidence of Spin-0 resonance in H->WW->ll modesLook into difference in between leptons
MT>175 GeVMT<175 GeV
Signal Region
Outside Signal Region
Bruce Mellado, Moriond 2004, 02/04/04 10
H analyses (->ll,lh):M reconstruction using collinear approximation (mass resolution ~10%) Missing ET and reconstruction, critical
issues Background (Zjj) rejection
Well separated forward jets and central jet veto
H-> Collinear approximation
H-> ->ll30 fb-1
ATLAS
CMS
Bruce Mellado, Moriond 2004, 02/04/04 11
Narrow peak with ~1.4% mass resolutionBackgroundsReal and fake photons
Suppression Well separated forward
jets and central jet veto
Diminished by large fake photon contribution~2 for 30 fb-1
Needs more work
H->
ATLAS
Real
Fake
Bruce Mellado, Moriond 2004, 02/04/04 12
Intermediate Mass Higgs via VBF
Used for first time HWWll and HZZllqq associated with two hard jets for intermediate masses (2MZ<MH<500 GeV)
By using kinematic fits obtain (M/M2.5%) with HZZllqq
Discovery confirmation and direct measurement of couplings ratio
ATLAS Preliminary
HZZ
HWW
ΓΓ
=)qqZZqqH(BR×σ)qqWWqqH(BR×σ
→
→
Bruce Mellado, Moriond 2004, 02/04/04 13
Sensitivity to low mass SM Higgs dominated by VBFVBF studies extended to intermediate masses
ATLAS Preliminary
Bruce Mellado, Moriond 2004, 02/04/04 14
Multivariate Analysis
Signal significance improvement with neural network based analysis: Neural network output
used as a discriminating variable with likelihood techniques
NN applied to H->WW->ll and H->->llSimilar results
Results improve by 45-50%
5 effect for MH>115 GeV with one exp and 10 fb-1 provided nominal detector performance
H->WW->ll
ATLAS
Bruce Mellado, Moriond 2004, 02/04/04 15
MSSM Higgs Discovery Potential
Two Experiments 10 fb-1 (No VBF)
One Experiment 10 fb-1 (With VBF)
Bruce Mellado, Moriond 2004, 02/04/04 16
Couplings MeasurementATLAS attempted a global fit to cross-sections of known channels to extract Higgs couplingsHiggs searches associated with two hard jets play a big role
Bruce Mellado, Moriond 2004, 02/04/04 17
Couplings Measurement (cont)
Relative Branching Ratios
Relative Couplings
Bruce Mellado, Moriond 2004, 02/04/04 18
SummarySearches associated with two hard jets dominate sensitivity for low mass HiggsForward jet tagging efficiency crucial and understanding of central jet veto - crucial issues
With Neural nets and likelihood techniques may reach 5 effect for MH>115 GeV with one experiment and 10 fb-1 assuming expected detector performance
ATLAS has extended these searches to 2MZ<MH<500 GeV
With these searches one experiment may cover all MSSM parameter space with 10 fb-1
Efforts underway to address entire analysis with a full detector simulation wit systematic error studies with “data-like” control samples
SM Higgs Coupling measurements (low mass):Accuracy of relative branching ratios and relative couplings vary from 10% to 60% depending on coupling and mass