first results on higgs boson searches (sm + mssm) and ... · first results on higgs boson searches...
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First results on Higgs boson searches (SM+ MSSM) and prospects from ATLAS
Johannes Elmsheuser
Ludwig-Maximilians-Universitat Munchen, Germany
on behalf of the ATLAS Collaboration
01 June 2011
23rd Rencontres de Blois, Particle Physics and Cosmology
ATLAS Detector and Datasets
General purpose detector
Magnets: 2T solenoid 3 air-core toroids EM Calo.: sampling LAr technologyTracking: silicon + transition Hadron Calo.: plastic scintillator (barrel)
radiation tracker LAr technology (endcap)Muon: independent system
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 2 / 19
Datasets
2010:
Peak Lumi.: L ≈ 2 · 1032 cm−2s−1
Int. Lumi.:∫Ldt ≈ 45 pb−1
2011:
L ≈ 1.2 · 1033 cm−2s−1∫Ldt & 400 pb−1
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 3 / 19
Search for the Higgs boson
ATLAS measured most of knownStandard Model (SM) processes with∼ 40pb−1 of data collected 2010
SM Higgs boson sensitivity will bereached soon
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 4 / 19
Higgs Productions at the LHC
Gluon fusion:
• known at NNLO (theo. uncert. O(15%))
Vector boson fusion:
• known at NLO (theo. uncert. O(5%))
• distinctive experimental signature: 2forward jets and rapidity gap
Intermediate to high mH range:
• WW and ZZ most sensitive channels
Low to intermediate mH range:
• γγ: very clean but small BR
• ττ : VBF to reduce BG
• bb: huge QCD BG, some potential inassoc. prod.
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 5 / 19
Intermediate mH: H → WW (∗) → `ν `ν
• Most sensitive channel in the mH = 130-190 GeV range
• large event yields and clean signature by lack of mass resolution
• Main backgrounds: WW, di-bosons (WZ/ZZ/Wγ), W/Z+Jets, Drell-Yan, top, QCD
Common pre-selection:
• 2 isolated high pT leptons
• suppress low mass resonances with lowerbound cut on m``
• Z0 veto (|m`` −mZ | > 10 GeV)
• E/T
• transverse plane angle ∆φ`` cut
Exclusive analysis in bins of jet multiplicities:
• 0-jets: optimized for gluon-fusion, purest channels, least affected by top BG
• 1-jet: more affected by top BG
• 2-jets: optimized for VBF (tag jets in opposite hemispheres, rapidity gap), small signalexpected
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 6 / 19
H → WW (∗) → `ν `ν Background estimationData driven techniques to estimate each contribution• Main backgrounds estimated in control regions, extrapolated into signal region• Cross-contamination of different backgrounds in various control regions taken into account
• WW background from side-bands in m`` and mT :
• small mH → high m`` WW dominated
• large mH → low m`` WW dominated
• Top: estimate jet-veto efficiency in enriched sampleswith b-tagging
• W+jets:
• kinematic from control sample with relaxedlepton ID
• lepton fake probability from independent
jet-trigger sample
• Z+jets: background estimated using ABCD method inm`` - MET plane
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Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 7 / 19
H → WW (∗) → `ν `ν Results
• Analysis optimized in each jet-bin and for each mass hypothesis
• final discriminating observable: transverse mass mT =√
(E ``T + EmissT )2 − (P``T + Pmiss
T )2
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PreliminaryATLAS
mH=170 GeV 0-Jets 1-Jet 2-JetsData 3 1 0BG 1.8±0.1 1.2±0.1 0.02±0.01
Higgs 1.26±0.02 0.6±0.01 0.6±0.01
Most sensitive around mH=160 GeV for SM-like Higgs boson
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 8 / 19
H → ZZ ∗ → 4 leptons
Clean unambiguous signature, low background, robust against pileup but small event yield dueto low Z0 leptonic BR, golden channel to measure mH
Simple selection:
• two pairs of opposite sign and same flavor leptons pT>20 GeV
• consistent with 2 Z0 decays
• isolated leptons without significant impact parameter
for mH ≈ 200 GeV sensitivity comparable with other channels due to clean signature
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 9 / 19
High mH: H → ZZ → ``(qq/νν)
Much less clean topologies compared to 4` channel, but a factor ∼27 higher BR (for ``qq)More sensitive than 4` for large mH when background from W/Z+jets get smallBackgrounds:
• Z/W+jets, tt control regions from sidebands in mjj and m`` and reversed cuts,backgrounds estimated with MC and normalization checks from control regions
• Background from QCD multi-jets negligible (checked with data-driven techniques withrelaxed lepton-ID)
• Di-boson background (ZZ/WW/WZ) estimated from MC
Analysis optimized for low and high mH :llqq llqq
mH<360 GeV mH>360 GeVData 216 11BG 226 ±28 9.88 ± 1.75
Higgs 0.60±0.12 0.24±0.05(mH=200 GeV) (mH=400 GeV)
llνν llννmH<280 GeV mH>280 GeV
Data 5 5BG 5.76 ± 1.38 3.45 ± 0.86
Higgs 0.19±0.04 0.30 ± 0.06(mH=200 GeV) (mH=400 GeV)
no excess observed in data
Cross section limits at ∼10 x σSMJohannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 10 / 19
Low mH search: H → γγ
• SM prefers light Higgs Boson, mH<158GeV
• H → γγ has small BR (∼0.2%), butlargest event yield after all cuts at low mH
• Expect 25 events/fb−1 at√s = 7 TeV
(includes all efficiencies)
Backgrounds:
• irreducible: γγ
• reducible: γ-Jet, Jet-Jet ( handles: massresolution, photon-ID, isolation)
Experimental requirements:
• excellent mass resolution
• precise primary vertex reconstruction
• photon pointing and conversions tracks
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 11 / 19
H → γγ results
Backgrounds estimated with data-driven techniques:
Exclusion limits:
• mH=127 GeV: 8 x σSM
• mH=116 GeV: 38 x σSM
• Sensitivity close to currentTevatron limits
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 12 / 19
H → γγ results, 2011 update
2011: 2011:
2010+2011:
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 13 / 19
SUSY Higgs: h/H/A→ ττ
• MSSM Higgs sector: 5 bosons h, H, A, H+, H− with 2 parameters mA, tanβ at LO• Higgs coupling to b, τ enhanced for high tanβ → Search for: h→ ττ (`τhad3ν,eµ4ν)• Backgrounds: Z → ττ , (Z → ``, W+jets (`h), tt(eµ), QCD)• Use of data-driven techniques to predict QCD and W+jets BG from same sign data.• Main background Z → ττ estimated from MC and shape validated with embedding
technique using data
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data
=40β, tanττ→A(120)/H/h
)+Jets(OSSS)ττ→Z(
Others(OSSS)
W+jets (OSSS)
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syst.
channelshad
τµ + hadτe
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Data Total BG h/H/Atan β = 40
mA=120 GeV`τhad 206 206±35 55.3 ±0.9eµ 70 63±7 15.2±0.3
Limits in (mA, tanβ) plane:
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)1
Tevatron (1.82.2 fb
LEP2Observed (CLs)
Observed (CLs+b, PCL)
Expected (95%CL)
σ 1±σ+ 2
extends Tevatron exclusion region
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 14 / 19
Light CP-odd Higgs boson in µµ final state
• In NMSSM: additional singlet complex field leads to additionalCP-even and odd Higgs
• For low CP-odd masses (ma1 < 2mb) lightest CP-even Higgs avoidsLEP limits
• Search for direct production in 6-9 GeV and 11-12 GeV mass range,avoiding Υ resonances
Selection:
• two isolated muons with pT>4 GeV
• Likelihood-ratio selection on primaryvertex χ2/ndf and calorimetric isolation,PDFs derived from data
No significant excess in data, limitson σxBR
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 15 / 19
Combination for SM Higgs boson search (I)
Combination of SM Higgs boson decay channels for mH = 110 - 600 GeV:H → γγ, H → ZZ (∗) → ````, H → ZZ → ``νν, H → ZZ → ``qq,H →WW (∗) → `ν`ν, H →WW → `νqq
Individual limits:
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Limits PCL 95% CL
ATLAS Preliminary
S.M. Expect. Observed
Combination:
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Observed, PCL
Observed, before PCL
Expected, PCL
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ATLAS Preliminary
mH= 160 - 170 GeV expected exclusion 2.3 x σSM
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 16 / 19
Combination for SM Higgs boson search II
CLs limits and other experiments:
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Tevatron exclusion
LEP exclusion
Observed, PCLExpected, PCL
, PCLσ 1±, PCLσ+ 2
SObserved, CL
SExpected, CL
=7 TeVs1
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ATLAS Preliminary
4th generation exclusion:(with 4th generation of high massquarks and leptons with SM-likecouplings to the Higgs boson)
[GeV]Hm
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Observed PCLObserved, before PCL
Expected PCL
PCLσ 1± PCLσ+ 2
Observed CLsExpected CLs
CMS exclusionTevatron exclusion
generation modelth
4
=7 TeVs1
L dt ~ 35 pb∫Excluded
ATLAS Preliminary
Exclusion for m4thH = 140 - 185 GeV
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 17 / 19
Summary and Future perspectives
• ATLAS detector performs very well, but no hint for Higgs at LHCwith ∼40 pb−1 yet: inclusive and simple cut-based selections
• 1-3 fb−1 are expected in 2011 (∼ 1fb−1 until June) and more in 2012→ ATLAS will be able to make a statement about the SM Higgsboson existence over a large mH range
with <4 fb−1 we could exclude down to LEP limit, but hopefully we willnot do so!
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 18 / 19
Documentation
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/
H → γγ ATLAS-CONF-2011-071, ATLAS-CONF-2011-025H → ZZ ATLAS-CONF-2011-048, ATLAS-CONF-2011-026H →WW ATLAS-CONF-2011-052, ATLAS-CONF-2011-005h/H/A→ ττ ATLAS-CONF-2011-024CP-odd Higgs boson in µµ ATLAS-CONF-2011-020Charged Higgs ATLAS-CONF-2011-018, ATLAS-CONF-2011-051
https://twiki.cern.ch/twiki/bin/view/AtlasPublic/WebHome
SM Higgs Combination ATLAS-HIGG-2011-01-002, CERN-PH-EP-2011-076
Johannes Elmsheuser (LMU Munchen) First ATLAS Higgs results 01/06/2011 19 / 19
BACKUP
High mH: H → WW → `νqq
• Most sensitive channel whenmH>400-500 GeV
• Cross section limits at ∼10-20 xσSM
SUSY Higgs: H± → τhν
Hadronic tau, hadronic W:
• bτhadνbqq ie. 1 τ -jet, 2b, 2q,2ν
• largely data driven SM estimates
• good agreement so far
Hadronic tau, leptonic W:
• bτhadνb`ν ie. 1 τ -jet, 2b, 1`, 3ν
• largely data driven SM estimates
• good agreement so far
SUSY Higgs: H± → τe/µν
Leptonic τ , hadronic W:
• bτe/µνbqq ie. 1 ` , 2b, 2q, 3ν
• SM estimates from MC only
• Distributions of discriminatingvariables
• fair agreement with SM
• signal alters the distributions
• more luminosity needed todistinguish
Leptonic τ , leptonic W :
• bτe/µνb`ν ie. 2` , 2b, 4ν
• similar plots (not shown)
• exclusion plots for 1 fb−1 MCstudy