Electroweak Physics and Higgs Searches with 1fb -1 at the Tevatron Collider

Jerry Blazey / April 16, 2007 / APS

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Electroweak Physics and Higgs Electroweak Physics and Higgs Searches with Searches with 1fb1fb-1-1 at the Tevatron at the Tevatron

ColliderCollider

Gerald C. BlazeyGerald C. BlazeyNICADD/Northern Illinois UniversityNICADD/Northern Illinois University

(for the CDF and DZero Collaborations)(for the CDF and DZero Collaborations)

APS 2007 April MeetingAPS 2007 April MeetingApril 16, 2007April 16, 2007


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Talk Outline• Context• Electroweak

Physics– Z Production– Di-Bosons– W mass

• Standard Model Higgs – Indirect Constraints

– Direct Searches• Low Mass• High Mass

– Conclusions

Thanks to Gregorio Bernardi, Jan Stark, Oliver Stelzer-Thanks to Gregorio Bernardi, Jan Stark, Oliver Stelzer-Chilton, Julien Donini, Wade Fisher, Krisztian Peters, Chilton, Julien Donini, Wade Fisher, Krisztian Peters,

Ashutosh Kotwal, & Martin Gruenwald for plots and figuresAshutosh Kotwal, & Martin Gruenwald for plots and figures


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(Select) Electroweak Physics at the (Select) Electroweak Physics at the TevatronTevatron

• Precision physics with Ws & Zs: Precision physics with Ws & Zs: – Tests of higher order calculations Tests of higher order calculations – Constrain PDFsConstrain PDFs– Properties of the boson: W massProperties of the boson: W mass

• Completing the spectrum of di-boson Completing the spectrum of di-boson cross sectionscross sections– Study the structure Study the structure of the theory of the theory

– Backgrounds to Higgs, Backgrounds to Higgs, top, SUSY top, SUSY

– Probe new physics w/ anomalous Probe new physics w/ anomalous couplingscouplings


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EW Symmetry Breaking The Higgs

• To explain quark, lepton, and gauge boson mass, the symmetry of the EW theory must be broken.

• The simplest model for symmetry breaking involves the addition of a doublet of complex scalar fields.– These fundamental Higgs scalar fields acquire non-

zero vacuum expectation values when symmetry breaks down• Three d.o.f “give their mass” to the W+, W-,Z • The remaining d.o.f corresponds to a fundamental scalar or the Higgs boson

– Fermions gain mass by interacting with the Higgs fields

– The observation of the single massive scalar would be the smoking gun!

• There are indirect limits on the mass of the Higgs and a number of direct searches for the particle.

• More complex models for symmetry breaking will be covered in the next talk by Ulrich Heintz, BU.


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Basic* Event CharacteristicsBasic* Event Characteristics

• ElectronsElectrons– ET > ~ 20 GeVET > ~ 20 GeV– Shower ShapesShower Shapes– IsolationIsolation– ||| coverage| coverage

• CDF: 0-2.5CDF: 0-2.5• DZero: 0-3.2DZero: 0-3.2

• PhotonsPhotons– ET > ~ 7 GeVET > ~ 7 GeV– Shower ShapesShower Shapes– Lepton Isolation Lepton Isolation – ||| coverage| coverage

• CDF: 0-1.1CDF: 0-1.1• DZero: 0-2.5DZero: 0-2.5

• MuonsMuons– pT > ~ 20 GeVpT > ~ 20 GeV– IsolationIsolation– ||| coverage| coverage

• CDF: 0-2 CDF: 0-2 • DZero: 0-2DZero: 0-2

• NeutrinosNeutrinos– Missing ET > ~ 20GeVMissing ET > ~ 20GeV– Angular IsolationAngular Isolation

**Tight and loose selections Tight and loose selections are employed to improve are employed to improve efficiency or rejection as efficiency or rejection as neededneeded


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ZZee++ee-- Rapidity Rapidity

• Z rapidity related to Z rapidity related to parton momentum fractions parton momentum fractions byby

• Acceptance at large Acceptance at large rapidities opens full rapidities opens full range of parton xrange of parton x

• σTot = 265.9±1.0±1.1 pb

• NNLO w/ NLO CTEQ6.1 NNLO w/ NLO CTEQ6.1 most consistent with most consistent with datadata


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ZZee++ee-- Transverse Momentum Transverse Momentum

• Tests higher order Tests higher order descriptions of Z Pdescriptions of Z PTT

• Reduces uncertainty on Reduces uncertainty on W mass by improving W mass by improving modeling of Emodeling of ETT..

• Improves understanding Improves understanding of backgrounds for new of backgrounds for new phenomena searchesphenomena searches

1fb1fb-1-1

Resbos +Photos


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WWProductionProduction

• Sensitive to WSensitive to W coupling coupling• Variation in WVariation in W production production would be sign of new physicswould be sign of new physics

• Particularly changes in PParticularly changes in PTT(() ) spectrum at high Mspectrum at high MTT(W(W))

• DØ preliminary DØ preliminary MMTT(l(l) > 90 GeV) > 90 GeV channel: channel: ( ( X) = 3.21 +/- X) = 3.21 +/-

0.52 pb0.52 pbe channel: e channel: ( e ( e X) = 3.12 +/- 0.42 pb X) = 3.12 +/- 0.42 pbtheory: theory: ( l ( l X) = 3.21 +/- 0.08 X) = 3.21 +/- 0.08 pbpb

• CDF preliminary 30 < MCDF preliminary 30 < MTT(() < 120 GeV:) < 120 GeV:• e+e+ channel: channel: ( l( l X) = 18.03+/- 2.83 pb X) = 18.03+/- 2.83 pb

theory: theory: ( ( X)= 19.3 +/- 1.4 X)= 19.3 +/- 1.4 pb pb

Measured Cross Sections and Measured Cross Sections and spectra spectra in good agreement with SM.in good agreement with SM.


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WW: Radiation Zero: Radiation Zero

• SM couplings at LO produce SM couplings at LO produce amplitude zero in the amplitude zero in the center-of-mass production center-of-mass production angleangle

• Correlations lead to a dip Correlations lead to a dip in Q*(in Q*(--ll)= )= Q*Q*

• Discrimination against Discrimination against anomalous coupling evident!anomalous coupling evident!

Background-subtracted dataBackground-subtracted data

Q*


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(WZ)(WZ)ObservationObservation• Sensitive to WWZ vertexSensitive to WWZ vertex• SM NNL cross section: SM NNL cross section: 3.7 +/- 0.3 pb 3.7 +/- 0.3 pb

• WZWZ l lll++ll-- mode mode • Main Backgrounds: Main Backgrounds: Z*/Z*/+jet, ZZ, DY+jet, ZZ, DY

12 observed12 observed7.5 expected7.5 expected3.6 background3.6 background

3.33.3

16 observed16 observed12.5 expected12.5 expected

2.7 2.7 backgroundbackground

6.06.0

Z

Z

Z

CDF: 5.0 CDF: 5.0 +1.8+1.8 -1.6-1.6 pb pbDZero: 4.0 DZero: 4.0 +1.9 +1.9

-1.5-1.5 pb pb


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• No self coupling of Z No self coupling of Z bosons in the standard bosons in the standard model.model.

• Produced in t channelProduced in t channel

• SM SM : 1.4 +/- 0.1pb: 1.4 +/- 0.1pb• StrategiesStrategies

– ZZ ZZ 4 charged leptons 4 charged leptons• Very clean signaturesVery clean signatures• Low background from Z+jLow background from Z+j• Small BFSmall BF

– ZZ ZZ 2 charged leptons+ 2 charged leptons+ 2 neutrinos 2 neutrinos• Six times productionSix times production• High Background WW, DYHigh Background WW, DY• Event Likelihood using Event Likelihood using

WW, ZZ Matrix elments WW, ZZ Matrix elments

(ZZ) Evidence(ZZ) Evidence

• DZero 4 lepton (1.0 fbDZero 4 lepton (1.0 fb-1-1))– Observed: 1 EventObserved: 1 Event– Signal: 1.71 +/- 0.10Signal: 1.71 +/- 0.10– Background: 0.17 +/- 0.04Background: 0.17 +/- 0.04

• CDF 4 lepton (1.4 fbCDF 4 lepton (1.4 fb-1-1))– Observed: 1 EventObserved: 1 Event– Signal: 2.54 +/- 0.15Signal: 2.54 +/- 0.15– Background: 0.03 +/- 0.02Background: 0.03 +/- 0.02– 2.22.2 significance significance

DZero ee event


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(ZZ) Adding the ll+(ZZ) Adding the ll+ Channel Channel

• Signal Extraction:Signal Extraction:– Calculate LO event Calculate LO event probability or probability or LRatio= LRatio= P(ZZ)/(P(ZZ)P(ZZ)/(P(ZZ)+P(WW))+P(WW))

– Fit to extract signalFit to extract signal– 1.9 1.9 significance significance

• Combination with 4lCombination with 4l– Use binned-likelihoodUse binned-likelihood– 3.0 3.0 combined combined significancesignificance


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?

Boson and Di-boson StatusBoson and Di-boson Status

Evidence(3Evidence(3))Observation(5Observation(5))

EW Single EW Single TopTop

4.9+/-1.4 pb4.9+/-1.4 pb


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Run II W MassRun II W Mass

• CDF for ~200pbCDF for ~200pb-1-1 (Feb’02- (Feb’02-Sep’03)Sep’03)

• Event RequirementsEvent Requirements– One selected leptonOne selected lepton

• Electron cluster EElectron cluster ETT > >

30 GeV, track p30 GeV, track pTT > 18 > 18

GeVGeV• Muon track pMuon track p

TT > 30 GeV > 30 GeV

– Hadronic Recoil < 15 Hadronic Recoil < 15 GeVGeV

– ppTT(() > 30 GeV) > 30 GeV

• Derive mass directly Derive mass directly from EW quantitiesfrom EW quantities

• Radiative corrections Radiative corrections are dominated by t, H are dominated by t, H loops:loops:

• W mass indirect W mass indirect measures of Higgs measures of Higgs mass.mass.

)1(sin2 2

2

rGm

WF

emW −

=θ

πα


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Results: Data, Fits, & Results: Data, Fits, & SystematicsSystematics

ElectronTransverseMass

Transverse Mass Fits

Combined fitsCombined fits

3 e: 80477+/- 62 MeV3 e: 80477+/- 62 MeV

3 3 : 80352+/- 60 MeV: 80352+/- 60 MeV

All: 80413+/- 48 MeVAll: 80413+/- 48 MeV

mT(e)

Basic Technique: Fit Basic Technique: Fit e, e, transverse mass, transverse mass, momentum, & missing momentum, & missing energy to Monte Carlo energy to Monte Carlo templates to extract templates to extract massmass


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Best Single Measurement!Best Single Measurement!New Tevatron Average: 80428+/- 39 MeVNew Tevatron Average: 80428+/- 39 MeVNew World Average: 80398 +/- 25 MeVNew World Average: 80398 +/- 25 MeV


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Constraints on Higgs Mass Constraints on Higgs Mass

• Direct eDirect e++ee--HZ LEP HZ LEP searchsearch

mmHH>114.4 GeV @ 95% C.L.>114.4 GeV @ 95% C.L.

• New Winter 2007 EW fits New Winter 2007 EW fits including new mincluding new mWW and m and mtoptop measurements:measurements:

mmHH=76=76+33+33-25-25 GeV GeV

mmHH<144 GeV @ 95% C.L.<144 GeV @ 95% C.L.

• Combination of the EW Combination of the EW fit and LEP2 limit:fit and LEP2 limit:

mmHH<182 GeV @ 95% C.L.<182 GeV @ 95% C.L.See previous talk by Kevin Lannon, OSU

for new results on top mass

Mt=170.9+/-1.8 GeV


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68 % C.L.

mW

(G

eV)

mt (GeV)

We’re looking forWe’re looking fora light Higgs!a light Higgs!


19Tevatron Searches: SM Higgs Production and Tevatron Searches: SM Higgs Production and DecayDecay

• Mass Dependent StrategyMass Dependent Strategy• MMHH<135 GeV<135 GeV

– gg gg H H bb overwhelmed bb overwhelmed by huge multi-jet (QCD) by huge multi-jet (QCD) background. background.

– Use leptons from Use leptons from associated W and Z associated W and Z production along with production along with HHbb decay to “tag” eventbb decay to “tag” event

– Complement with HComplement with HWW*WW*– Backgrounds: Wbb, Zbb, Backgrounds: Wbb, Zbb,

W/Zjj, top, diboson, QCD…W/Zjj, top, diboson, QCD…

• MMHH>135 GeV>135 GeV– gg gg H H WW production WW production– Multi-lepton final states Multi-lepton final states

distinctive.distinctive.– Background: WW, DY, WZ, Background: WW, DY, WZ,

ZZ, tt, tW, ZZ, tt, tW, .. ..

Excluded

pb

BF

200GeV80GeV H bb→H WW→


20Combined Tevatron Higgs LimitsCombined Tevatron Higgs Limits(Summer 2006)(Summer 2006)

• Sixteen mutually exclusive final states for WH, ZH, WWSixteen mutually exclusive final states for WH, ZH, WW• Observed combined limits:Observed combined limits:

– A factor of 10.4 above SM at mA factor of 10.4 above SM at mHH=115 GeV=115 GeV– A factor of 3.8 above SM at mA factor of 3.8 above SM at mHH=160 GeV=160 GeV

• Recent progressRecent progress– Both CDF & DZero completed low & high mass 1fbBoth CDF & DZero completed low & high mass 1fb-1-1 analyses. analyses.– Improvements in analysis techniques & systematic Improvements in analysis techniques & systematic

uncertainties.uncertainties.


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Associated Higgs ProductionAssociated Higgs Production

Experimental Signature• Leptonic decay of W/Z bosons provides “handle” for event

• Higgs decay to two bottom-quarks helps reduce SM backgrounds


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WHWHl l bb, bb, l l ==ee,,• CDF/DCDF/DØØ box cut analyses box cut analyses

– isolated e or isolated e or – missing Emissing ETT – jets>15 GeV (CDF)/jets>15 GeV (CDF)/20 GeV 20 GeV

(DØ)(DØ)• Backgrounds: Wbb, top, di-Backgrounds: Wbb, top, di-

boson, QCDboson, QCD• Analyzed one “tight” b-tag Analyzed one “tight” b-tag

and 2 “loose” b-tag and 2 “loose” b-tag channels, later combinedchannels, later combined

• Cross section limits are Cross section limits are derived from invariant mass derived from invariant mass distributions distributions

• 95% CL upper limits (pb) 95% CL upper limits (pb) for mfor mHH=115 GeV (SM expected: =115 GeV (SM expected: 0.13 pb)0.13 pb)– CDF: 3.4 (2.2) observed CDF: 3.4 (2.2) observed

(expected)(expected)– DDØ: 1.3 (1.1) Ø: 1.3 (1.1) observed observed

(expected)(expected)

Best Expected:excl/SM=9


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• Use LO ME to compute event Use LO ME to compute event probability densities for probability densities for signal and backgroundsignal and background

• Selection criteria based on Selection criteria based on single top search (will be single top search (will be optimized in the future)optimized in the future)

• Cross section limits are Cross section limits are derived from the derived from the discriminant distributions discriminant distributions

• 95% CL upper limit for 95% CL upper limit for mmHH=115 GeV is 1.7(1.2) pb =115 GeV is 1.7(1.2) pb observed (expected)observed (expected)

• Similar sensitivity to cut-Similar sensitivity to cut-based analysis, with based analysis, with optimization ~30% increase optimization ~30% increase in sensitivity.in sensitivity.

( ) ( )( ) ( )

WH

WH i Bii

P xD x

P x c P x=

+∑

rr

r r

New Technique: WHNew Technique: WHl l bb, bb, l l ==ee,,


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• Selection:Selection:– ee or ee or with dilepton mass ~ M with dilepton mass ~ MZZ

– opposite charge and isolated from opposite charge and isolated from jetsjets

– Jets > 15 GeV (DJets > 15 GeV (DØ)Ø), > 25(15) GeV , > 25(15) GeV (CDF)(CDF)

• Dominant backgrounds: Z+jets (Zbb Dominant backgrounds: Z+jets (Zbb irreducible), top, WZ, ZZ, QCD multijetirreducible), top, WZ, ZZ, QCD multijet

• DDØ: Ø: – Require at least two b-tagged jets. Require at least two b-tagged jets. – Cross section limit derived from Cross section limit derived from

dijet invariant mass distribution dijet invariant mass distribution within a search windowwithin a search window

• CDF: CDF: – Require 1 b-tagged jet. Require 1 b-tagged jet. – 2-D Neural Network to discriminate 2-D Neural Network to discriminate

against the two largest backgrounds against the two largest backgrounds (tt vs. ZH and Z+jets vs. ZH)(tt vs. ZH and Z+jets vs. ZH)

– Limits derived from the neural Limits derived from the neural network distribution network distribution

• 95% CL upper limits (pb) for m95% CL upper limits (pb) for mHH=115 GeV =115 GeV (SM expected: 0.08 pb)(SM expected: 0.08 pb)– DDØ: 2.7 (2.8) Ø: 2.7 (2.8) observed (expected)observed (expected)– CDF: 2.2 (1.9) observed (expected)CDF: 2.2 (1.9) observed (expected)

ZHZHl l l l bb, bb, l l ==ee,,

Best Expected: excl/SM=24

Mjj(GeV)


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New: ZHNew: ZHl l l l bb, bb, l l ==ee,, using NN using NN22

• Loosen Event Loosen Event SelectionSelection

• NN One: NN One: – Improves jet Improves jet resolution resolution

– Assign missing Et to Assign missing Et to jets based on jets based on position and position and azimuthal separationazimuthal separation

• NN Two:NN Two:– Train on single tags Train on single tags and double tagsand double tags

– Two dimensional Two dimensional • ZH+ ZjetZH+ Zjet• ZH+ Top-antitopZH+ Top-antitopExpected: excl/SM=

16


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• Selection:Selection:– Separate analysis for 1 and 2 b-tag sampleSeparate analysis for 1 and 2 b-tag sample– Exactly Two JetsExactly Two Jets– Large missing Large missing EET T , not aligned in , not aligned in with jets with jets

• Backgrounds:Backgrounds:– Physics: Z/W+jets, topPhysics: Z/W+jets, top– Instrumental: mis-measured Instrumental: mis-measured EET T together with QCD jetstogether with QCD jets

• At 115 GeV: At 115 GeV:

ZHZHbb, WHbb, WHl l bbbb

Best Expected: excl/SM=10

2tags


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HHWWWW**l l ++l l - - • Search strategy:Search strategy:

– 2 high p2 high pT T isolated, isolated, opposite signed leptonsopposite signed leptons

– Require missing ERequire missing ET T , veto , veto near jetsnear jets

– Choose di-lepton opening Choose di-lepton opening angle angle llll to to discriminate against discriminate against dominant WW backgrounddominant WW background

– WW comes from spin-0 WW comes from spin-0 Higgs & leptons prefer Higgs & leptons prefer to point in the same to point in the same directiondirection

• Sensitivity at mSensitivity at mH H ~ 160 GeV:~ 160 GeV:Best Expected: excl/SM=4


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New: HNew: HWW*WW*l l ++l l ––

• Event SelectionEvent Selection– Exactly 2 LeptonsExactly 2 Leptons– Lepton IsolationLepton Isolation– Missing Et Missing Et – Less than 2 jets Less than 2 jets (>15 GeV)(>15 GeV)

• Limit Extraction:Limit Extraction:– Using ME calculate Using ME calculate P(H)/(P(H)+kP(H)/(P(H)+kiiBBii))

– Perform binned Perform binned maximum likelihood maximum likelihood fit over fit over discriminatordiscriminator

– At 160 GeV At 160 GeV <1.3pb <1.3pb at 95% C.L.at 95% C.L.

• An additional NN An additional NN analysis just approved analysis just approved has similar sensitivityhas similar sensitivity

Expected: excl/SM= 5


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Updated DZero Combined Higgs Limits Updated DZero Combined Higgs Limits

• Single Experiment Limit competitive or better than 2006 Single Experiment Limit competitive or better than 2006 combinationcombination

• Observed combined limits:Observed combined limits:– At mAt mHH=115 GeV a factor of 8.4 (5.9 expected) above SM =115 GeV a factor of 8.4 (5.9 expected) above SM – At mAt mHH=160 GeV afactor of 3.7 (4.2 expected) above SM=160 GeV afactor of 3.7 (4.2 expected) above SM

and select observed CDF measurementsand select observed CDF measurements

HWW

Three analyses!


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Final Comments & ConclusionsFinal Comments & Conclusions

• EWEW– Precision studies continuePrecision studies continue– Nearly completed the di-boson Nearly completed the di-boson spectrumspectrum

– Improved techniques/backgrounds for Improved techniques/backgrounds for Higgs SearchHiggs Search

• HiggsHiggs– EW fits + LEP: mEW fits + LEP: mHH<182 GeV @ 95% C.L.<182 GeV @ 95% C.L.– Closing in on exclusion near 160 GeV!Closing in on exclusion near 160 GeV!– ProspectsProspects

• Steady progress on improved techniques, Steady progress on improved techniques, sensitivity & limitssensitivity & limits

• New combined Tevatron limit this summer. New combined Tevatron limit this summer.


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Electroweak Physics and Higgs Searches with 1fb -1 at the Tevatron Collider

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