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
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]
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]
17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron
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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WZZZDYWW
10×HWW Data
CDF Run II PreliminaryOS 2+ Jets
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-1 L = 5.3 fb
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
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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(GeV)TH0 100 200 300 400 500 600
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10×HWW Data
CDF Run II PreliminaryOS 0 Jets
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-1 L = 5.3 fb
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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Z Events
WW Events
HT = scalar sum of pT and missing ET
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10×HWW Data
CDF Run II PreliminaryOS 2+ Jets
2 = 160 GeV/cHM
-1 L = 5.3 fb
0bar Events
17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron
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
Final SelecBonee/μμ/eμ pairs
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10×HWW Data
CDF Run II PreliminaryOS 0 Jets
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-1 L = 5.3 fb
WW Events
Signal x 10
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CDF Run II PreliminaryOS 0 Jets
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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
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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10×HWW Data
NN Output
CDF Run II Preliminary
OS 0 Jets, High S/B2 = 160 GeV/cHM
-1 L = 5.3 fb
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
0J
NN adds in pt of dijet system
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10×HWW Data
NN Output
CDF Run II PreliminaryOS 2+ Jets
2 = 160 GeV/cHM
-1 L = 5.3 fb
2J
S/B = 32/1840
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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10×HWW Data
CDF Run II Preliminary
OS Low M(ll)2 = 160 GeV/cHM
-1 L = 5.3 fb
dominatedby Wγ
S/B =0.9/99
17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron
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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ttWH160(x10)ZH160(x10)data
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/10.
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CDF Run II Preliminary -1 L = 5.3 fb2=165 GeV/cH>20, Z-Peak Removed): mT EWH Signal Region (
17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron
Trilepton Channels
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Signal WH x 10
Signal ZH x 10
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Data
NN Output
CDF Run II Preliminary
Trilepton ZH Signal (Z Peak)2 = 160 GeV/cHM
-1 L = 5.3 fb
Signal x 10
S/B =0.6/24.2S/B =0.8/14.6
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
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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Higgs Mass (GeV)
SM95
% C
.L./
CDF Run II Preliminary -1 L = 5.3 fb
Standard Model
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High Mass Expected
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
17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron
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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Backup starts right here….
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)
17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron
Progress of Higgs limits
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17/03/2010 Ralf Bernhard - High Mass Higgs Search at the Tevatron
CDF and D0 at the Tevatron
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Tevatron: ppbar collider at √s = 1.96 TeV, performing really well
Inte
grat
ed L
umin
osity
delivered recorded
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
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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