M. Herndon, H Days 2012 1

High Mass Higgs at the Tevatron

Matthew Herndon, University of Wisconsin Madison

Higgs Days 2012

g g s

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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!

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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.

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Tevatron Performance

9.7/fb used in analysis

Over 10 fb-1!

Enough data to make an impact at low mass

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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

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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

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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

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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

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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

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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

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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

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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

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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

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Tevatron Higgs Combination

Obs. Exclusion 147-180 GeV

Exclusion driven by HWWNo interesting WW signal observed

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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