Jerry Blazey / April 16, 2007 / APS 1 Electroweak Physics and Higgs Electroweak Physics and Higgs Searches with Searches with 1fb 1fb -1 -1 at the Tevatron at the Tevatron Collider Collider Gerald C. Blazey Gerald C. Blazey NICADD/Northern Illinois University NICADD/Northern Illinois University (for the CDF and DZero Collaborations) (for the CDF and DZero Collaborations) APS 2007 April Meeting APS 2007 April Meeting April 16, 2007 April 16, 2007
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Electroweak Physics and Higgs Searches with 1fb -1 at the Tevatron Collider
Electroweak Physics and Higgs Searches with 1fb -1 at the Tevatron Collider. Gerald C. Blazey NICADD/Northern Illinois University (for the CDF and DZero Collaborations) APS 2007 April Meeting April 16, 2007. Talk Outline Context Electroweak Physics Z Production Di-Bosons W mass - PowerPoint PPT Presentation
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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
Jerry Blazey / April 16, 2007 / APS
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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.
• 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
• 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))
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
(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
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!
Jerry Blazey / April 16, 2007 / APS
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• 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,
• 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
• 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
• 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
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
• 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.