Searches for High-Mass SM Higgs at the...

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Ralf Bernhard University of Freiburg For the CDF and DØ Collaborations The XLVth Rencontres de Moriond QCD La Thuile, 17. March 2010 Searches for High-Mass SM Higgs at the Tevatron

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Page 1: Searches for High-Mass SM Higgs at the Tevatronmoriond.in2p3.fr/QCD/2010/WednesdayMorning/Bernhard.pdfSearches for High-Mass SM Higgs at the Tevatron. ... 40 50 60 70 W+jets Wa tt

Ralf BernhardUniversity of Freiburg

For the CDF and DØ Collaborations

The XLVth Rencontres de Moriond QCDLa Thuile, 17. March 2010

Searches for High-Mass SM Higgs at the Tevatron

Page 2: Searches for High-Mass SM Higgs at the Tevatronmoriond.in2p3.fr/QCD/2010/WednesdayMorning/Bernhard.pdfSearches for High-Mass SM Higgs at the Tevatron. ... 40 50 60 70 W+jets Wa tt

17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron

Higgs Production at the Tevatron

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(100 < mH < 200 GeV):σ(gg→H) ≈ 2−0.2 pb σ(qq→HW) ≈ 0.3−0.02 pb

Higgs  Boson  mass  mH  [GeV]

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For mH > 135 GeV H → WW dominant- Defines High-mass

Higgs-Boson search- H → ZZ starts also to

be important for mH>180 GeV

17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron

Higgs Decay at the Tevatron

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H → bb̄

H →WW

Higgs  Boson  mass  mH  [GeV]

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Backgrounds & Rates

Di-BosonWW: σ×BR = 13 pbWZ: σ×BR = 4.0 pbZZ: σ×BR = 1.5 pb

Other Backgroundsttbar: σ×BR =7 pbsingle top: σ×BR = 3 pb

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qqH

Associated production(VH) and Vector Boson fusion (qqH) → ~35% more signal

gg →H (H→WW→llνν [~6% of WW decays])σ×BR = 0.04 pb at mH = 160 GeV

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17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron

Background Rejection

Two high pT isolated leptons with η up to 2.5

Missing ET cut to reject a large fraction of Z background

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Missing ET (preselection)

High jet multiplicity region→ veto events with b-tagged jets to reduce ttbar background

S/B ~ 1.5% after all selection cuts with ~68 signal events (CDF + DØ) @mH = 165 GeV

0bar  Events

Page 6: Searches for High-Mass SM Higgs at the Tevatronmoriond.in2p3.fr/QCD/2010/WednesdayMorning/Bernhard.pdfSearches for High-Mass SM Higgs at the Tevatron. ... 40 50 60 70 W+jets Wa tt

Split analysis into several orthogonal channels → optimize separately

Lepton flavor: different efficiency, resolution and kinematics- DØ separate analysis into ee/µµ/eµ pairs- CDF into high and low S/B samples

17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron

Analysis Strategies

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Page 7: Searches for High-Mass SM Higgs at the Tevatronmoriond.in2p3.fr/QCD/2010/WednesdayMorning/Bernhard.pdfSearches for High-Mass SM Higgs at the Tevatron. ... 40 50 60 70 W+jets Wa tt

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17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron

Analysis Strategies

Jet Multiplicity- different background

compositions

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CDF separate samples into dilepton+0 jet, 1 jet and ≥ 2 jets,

DØ uses shape of N jet distribution

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CDF Run II PreliminaryOS 1 Jets

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Discriminating Variables

Variables using kinematics of two leptons- Angular separation: powerful discriminant against WW→ smaller

separation angle for leptons from Higgs decay due to spin correlation- Invariant mass: effective against most of the physics backgrounds - Kinematics of individual leptons and quality information

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Final  SelecBon

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17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron

Discriminating Variables

Variables describing event topology- Relation between lepton and missing ET

• e.g. transverse mass (MT), angular separation, ET sum

Topological variables based on leptons, jets and missing ET

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Matrix Element (ME) calculation ME probability discriminant Powerful discriminant (LR(WW))→

~10% gain in sensitivity

Basic cuts on kinematic variables to reduce dominant backgrounds + multivariate analysis for maximum use of information

Final  SelecBon

Final  SelecBon

Likelihood based on ME

Page 10: Searches for High-Mass SM Higgs at the Tevatronmoriond.in2p3.fr/QCD/2010/WednesdayMorning/Bernhard.pdfSearches for High-Mass SM Higgs at the Tevatron. ... 40 50 60 70 W+jets Wa tt

17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron

Multivariate Technique

S/√B ~0.6: simple counting experiment is not enough

Maximize the power of discriminating variables using combinations in Neural Networks

Trained independently for each Higgs Mass point hypothesis and orthogonal channel

Output classifier is used to extract sensitivity

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S/B = 30/2445

Final  SelecBonee/μμ/eμ  pairs

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CDF Run II Preliminary

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17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron

Multivariate Technique

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NN using LO matrixelements probabilities.transverse energydΦ(l1,l2), dR(l1,l2)

NN adds MET cut, leptonpTs, no LO matrixelement due to extra jet

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17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron

Additional Acceptance

Kinematic regions: high/low dilepton invariant mass (Mll) region- dedicated low (< 16 GeV) Mll

analysis by CDF

Charge configuration:- SS signal from VH production,

physics background very small

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OS Low M(ll)2 = 160 GeV/cHM

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dominatedby  Wγ

S/B =0.9/99

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Same Charge DiLeptons

Suppress Standard Model bkgds → true same sign from WZ and ZZ

Fake leptons from W+jet and multijet

Charge mis-measurement in OS (mostly Z → ll events)

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Not well modeled by simulation Lepton fake rate measured in data Charge mis-measurement

controlled by track quality cuts

Instrumental Backgrounds

Charge  mis-­‐ID

WZ  and  ZZFake

S/B =2.1/81

S/B =1.1/118

Same sign leptons from VH production

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17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron

Trilepton Channels

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17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron

Systematic Uncertainties

Systematics Uncertainties for CDF and DØ- Integrated luminosity (6%) - Theoretical cross sections

(5-10%)- MC acceptance, up to 10%- LeptonID, 2-4%- Jet / missing ET modeling,

4-30% (process dependent)

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Uncertainty on estimated signal & bkgd normalization and shape

Page 16: Searches for High-Mass SM Higgs at the Tevatronmoriond.in2p3.fr/QCD/2010/WednesdayMorning/Bernhard.pdfSearches for High-Mass SM Higgs at the Tevatron. ... 40 50 60 70 W+jets Wa tt

17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron

Results

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Each  single  experiment  not  yet  able  to  reach  SM  sensi6vity  →  Combina6on

σ95 = 1.36 ⋅ σSM(H) at MH = 165 GeV (exp)σ95 = 1.55 ⋅ σSM(H) at MH = 165 GeV (obs)

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1±High Mass

2±High Mass

High Mass Observed

σ95 = 1.03 ⋅ σSM(H) at MH = 165 GeV (exp)σ95 = 1.13 ⋅ σSM(H) at MH = 165 GeV (obs)

PRL 104, 061804 (2010)

CDF Note 9887

Page 17: Searches for High-Mass SM Higgs at the Tevatronmoriond.in2p3.fr/QCD/2010/WednesdayMorning/Bernhard.pdfSearches for High-Mass SM Higgs at the Tevatron. ... 40 50 60 70 W+jets Wa tt

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Conclusions

Rapid incorporation of new data and analysis improvements - Still lots of ideas under-going to improve analyses- Sensitivity continues to improve faster than luminosity scaling

Expect soon exclusion by each experiment alone Expect increase of mass range where Tevatron has SM

sensitivity!

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Page 18: Searches for High-Mass SM Higgs at the Tevatronmoriond.in2p3.fr/QCD/2010/WednesdayMorning/Bernhard.pdfSearches for High-Mass SM Higgs at the Tevatron. ... 40 50 60 70 W+jets Wa tt

Backup starts right here….

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17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron

Combination Results

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Combined dileptonresults published

→ First joint CDF+DØ publication on SM Higgs search

Exclusion region162-166 GeV @95%CL(159-169 GeV expected)

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Progress of Higgs limits

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CDF and D0 at the Tevatron

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Tevatron: ppbar collider at √s = 1.96 TeV, performing really well

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Run II 8 fb-1 7.11 fb-1

August 2009Since April 2002

~89% data taking efficiency

CDF comparable

Analyses use up to 5.4 fb-1 ~14% Loss due to data quality~75% Overall efficiency

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17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron

H→WW final states

W Boson decays- BR(W→ lv) ~ 32%- BR(W→ hadrons) ~ 68%

Hadronic modes have large QCD background: not used at the moment.

Select both W Boson decaying leptonically- Easy and clean triggers on single electron or muon

• Manageable trigger cross section at hadronic colliders• Clean signature, exploiting good tracking and muon

systems of CDF and D0 detectors

Partially includes τ→(e,µ) Overall BR for WW pair to di-lepton (e or µ) ~ 6%

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