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g g s. High Mass Higgs at the Tevatron Matthew Herndon, University of Wisconsin Madison Higgs Days 2012. The Higgs Boson. SM postulates a mechanism of electroweak symmetry breaking via the Higgs mechanism Interaction with the Higgs field results in masses for the W and Z vector bosons, - PowerPoint PPT Presentation
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M. Herndon, H Days 2012 1
High Mass Higgs at the Tevatron
Matthew Herndon, University of Wisconsin Madison
Higgs Days 2012
g g s
M. Herndon, H Days 2012 2
The Higgs BosonSM postulates a mechanism of electroweak symmetry breaking via the Higgs mechanism
Interaction with the Higgs field results in masses for the W and Z vector bosons,
Possible mass terms for the fermions
Also expect and observable quanta of the field: Higgs boson
Directly testable hypothesis by searching for the Higgs boson
A primary goal of the Tevatron and LHC
Now directly testable by measuring Higgs properties!
M. Herndon, H Days 2012 3
The Higgs BosonWhere to concentrate you searchOne answer: where your experiment excels
Higgs decay to pairs of mass vector bosons with leptonic decays
Where the data says to look(just before final analyses)
SM LEP Direct search: mH > 114GeV
SM (Tevatron) indirect constraint: mH < 152GeV
LHC: 115.5 < mH < 129
LHC: Look around 125 GeV
Some Hints that optimizing the analysis at low mass was called for.
M. Herndon, H Days 2012 4
Tevatron Performance
9.7/fb used in analysis
Over 10 fb-1!
Enough data to make an impact at low mass
M. Herndon, H Days 2012 5
Tevatron Higgs HistoryAfter LP 2007 we had predicted expected preface enhancements and extrapolated to 10fb-1
Improvement factors based on studies in data
Expectation: 3σ evidence for Higgs possible at 115GeV
125 was a harder mass.
Needed to exceed the expectations
M. Herndon, H Days 2012 6
High mass: HWWll decay available (ZZ used - contribution small)
Takes advantage of large ggH production cross section
Alternative production mechanismsWHWWW, ZHZWW, VBF: qqHqq->WWjj
Significant contribution in events with 1, 2 or more jets and same sign leptons, three leptons events. Helps at low mass
SM Higgs Production and Decay
M. Herndon, H Days 2012 7
Analysis Technique Expanded acceptance
Expanded lepton acceptance in areas with weak/no dedicated lepton IdMultiple analysis channels beyond HWW: HZZ, HWW (lepton + jets), VH (same sign, trilepton, extra jets) and VBF (extra jets)
Analyze specific event topologiesIsolate subsets of signal/background processes for optimal discrimination Optimize inputs to discriminants as a function of massUse of jet kinematics to find vector bosons and identify VBF events
Control regions Check modeling of primary backgroundsMeasure background cross sections where possible: Z, WW, WZ, ttbar
Apply advanced techniquesAdd only order 10-20% sensitivity to the analysis but needed in regions where the spin correlation is not enough such as at low mass
M. Herndon, H Days 2012 8
SM Higgs: HWW HWWll - signature: Two high pT leptons and MET
The most powerful analysis channel
Primary backgrounds: WW and top in di-lepton decay channel
Excellent physics based discriminantsH
μ+
ν
W-
W+
e-
ν
W-
W+
Spin correlation: Charged leptons go in the same direction
M. Herndon, H Days 2012 9
SignalsVHVWWl+l- MET jj analysis, VHB HWW + forward jets, ggHWW jj
Analysis improvementsImplementation of MCs with good 2+ jets modeling for backgrounds
Use of jets kinematics:
Energy and rapidity
Use of dijet variables
mass, delta rapidity
Optimization of variables
as a function of mH
CDF WW 2+ Jet Analysis
25% imrpvement
M. Herndon, H Days 2012 10
As sensitive as individual Hbb searches as low mass
Combination of CDF H WW searches
CDF HWW Search
most sensitive analysis for mH > 128GeV
HWW Channels:
Exp. Limit σ/σH per
channel and combined
Exp. Limit125
Exp. Limit 165
ggH: 0 Jets 6.68 1.41
ggH, VH, VBF: 2+ Jets 7.83 1.89
ggH: 1 Jet 9.11 1.83
Low mll 11.1 2.86
SS 11.7 3.93
Trilepton 11.6 4.07
Combined 3.08 0.69
Observed limit 2.98
UW contribution
M. Herndon, H Days 2012 11
ll – signature subdivided by jet topology & lepton charge
Further subdivided by lepton flavor
BDT for DY suppression
Example: HWWeμ + MET High purity channel
DØ HWWll Search
Exp limit 1.19@165 – most powerful single Tevatron channel
M. Herndon, H Days 2012 12
ljj(jj): lepton + jets signatureHWWljj, VHljjjj, WHlnubb
High and low mass analysis at once
At high mass takes advantage of large Wjj branching ratio
Classifies events by number and type of b tag
BDT based discriminant
DØ H: ljj
M. Herndon, H Days 2012 13
hWW combined sensitivity more powerful that any of the low mass H analysisObserved limit 4.56
Combination of DØ H WW searches
DØ HWW Search
HWW Channels:
Exp. Limit σ/σH per
channel and combined
Exp. Limit125
Exp. Limit 165
H: eμ 5.22 1.19
H: ee, μμ 6.89
6.76
1.59
1.64
gg->H Combined 3.59 0.81
VH: SS leptons 11.6 5.89
VH: tri leptons 11.1 6.64
H: l+jets ---- 4.56
Combined 0.72
M. Herndon, H Days 2012 14
Tevatron Higgs Combination
Obs. Exclusion 147-180 GeV
Exclusion driven by HWWNo interesting WW signal observed
M. Herndon, H Days 2012 15
Conclusions
We exclude at 95% C.L. the production of a SM Higgs boson of 147-180 GeV
The observed data in HWW is compatible with a SM Higgs boson but not constraining
LHC has observed a boson with mass ~125 GeV!What we have measured so far almost certainly means it plays a part in electroweak symmetry breaking.
The Tevatron experiments have achieved sensitivity to the SM Higgs boson production cross section at high and low mass
The sensitivity of the CDF and DØ high mass searches make them a primary element of the Tevatron search at mass around 125 GeV