Jerry Blazey / April 16, 2007 / APS 1 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

Jerry Blazey / April 16, 2007 / APS 2 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- Chilton, Julien Donini, Wade Fisher, Krisztian Peters, Ashutosh Kotwal, & Martin Gruenwald for plots and figures

Jerry Blazey / April 16, 2007 / APS 3 (Select) Electroweak Physics at the Tevatron Precision physics with Ws & Zs:Precision physics with Ws & Zs: –Tests of higher order calculations –Constrain PDFs –Properties of the boson: W mass Completing the spectrum of di-boson cross sectionsCompleting the spectrum of di-boson cross sections –Study the structure of the theory –Backgrounds to Higgs, top, SUSY –Probe new physics w/ anomalous couplings

Jerry Blazey / April 16, 2007 / APS 4 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.

Jerry Blazey / April 16, 2007 / APS 5 Basic* Event Characteristics ElectronsElectrons –ET > ~ 20 GeV –Shower Shapes – Isolation –|  | coverage CDF: 0-2.5CDF: DZero: 0-3.2DZero: PhotonsPhotons –ET > ~ 7 GeV –Shower Shapes –Lepton Isolation –|  | coverage CDF: 0-1.1CDF: DZero: 0-2.5DZero: Muons –pT > ~ 20 GeV –Isolation –|  | coverage CDF: 0-2 DZero: 0-2 Neutrinos –Missing ET > ~ 20GeV –Angular Isolation * Tight and loose selections are employed to improve efficiency or rejection as needed

Jerry Blazey / April 16, 2007 / APS 6 Z  e + e - Rapidity Z rapidity related to parton momentum fractions byZ rapidity related to parton momentum fractions by Acceptance at large rapidities opens full range of parton xAcceptance at large rapidities opens full range of parton x σ Tot = 265.9±1.0±1.1 pb NNLO w/ NLO CTEQ6.1 most consistent with data

Jerry Blazey / April 16, 2007 / APS 7 Z  e + e - Transverse Momentum Tests higher order descriptions of Z P TTests higher order descriptions of Z P T Reduces uncertainty on W mass by improving modeling of E T.Reduces uncertainty on W mass by improving modeling of E T. Improves understanding of backgrounds for new phenomena searchesImproves understanding of backgrounds for new phenomena searches 1fb -1 Resbos +Photos

Jerry Blazey / April 16, 2007 / APS 8 W  Production Sensitive to W  couplingSensitive to W  coupling Variation in W  production would be sign of new physicsVariation in W  production would be sign of new physics Particularly changes in P T (  ) spectrum at high M T (W  )Particularly changes in P T (  ) spectrum at high M T (W  ) DØ preliminary M T (l  ) > 90 GeVDØ preliminary M T (l  ) > 90 GeV  channel:  (   X) = / pb  channel:  (   X) = / pb e channel:  ( e  X) = / pb theory:  ( l  X) = / pb CDF preliminary 30 < M T (  ) < 120 GeV:CDF preliminary 30 < M T (  ) < 120 GeV: e+  channel:  ( l  X) = / pbe+  channel:  ( l  X) = / pb theory:  (  X)= /- 1.4 pb Measured Cross Sections and  spectra in good agreement with SM.

Jerry Blazey / April 16, 2007 / APS 9 W  : Radiation Zero SM couplings at LO produce amplitude zero in the center-of- mass production angleSM couplings at LO produce amplitude zero in the center-of- mass production angle Correlations lead to a dip in Q*(   -  l )= Q* Correlations lead to a dip in Q*(   -  l )= Q*  Discrimination against anomalous coupling evident!Discrimination against anomalous coupling evident! Background-subtracted data Q* 

Jerry Blazey / April 16, 2007 / APS 10  (WZ)  Observation Sensitive to WWZ vertexSensitive to WWZ vertex SM NNL cross section: 3.7 +/- 0.3 pbSM NNL cross section: 3.7 +/- 0.3 pb WZ  l l + l - modeWZ  l l + l - mode Main Backgrounds: Z*/  +jet, ZZ, DYMain Backgrounds: Z*/  +jet, ZZ, DY 12 observed 7.5 expected 3.6 background 3.3  16 observed 12.5 expected 2.7 background 6.0  Z Z Z CDF: pb DZero: pb

Jerry Blazey / April 16, 2007 / APS 11 No self coupling of Z bosons in the standard model.No self coupling of Z bosons in the standard model. Produced in t channelProduced in t channel SM  : 1.4 +/- 0.1pbSM  : 1.4 +/- 0.1pb StrategiesStrategies –ZZ  4 charged leptons Very clean signaturesVery clean signatures Low background from Z+jLow background from Z+j Small BFSmall BF –ZZ  2 charged leptons+ 2 neutrinos Six times productionSix times production High Background WW, DYHigh Background WW, DY Event Likelihood using WW, ZZ Matrix elmentsEvent Likelihood using WW, ZZ Matrix elments  (ZZ) Evidence DZero 4 lepton (1.0 fb -1 )DZero 4 lepton (1.0 fb -1 ) –Observed: 1 Event –Signal: / –Background: / CDF 4 lepton (1.4 fb -1 )CDF 4 lepton (1.4 fb -1 ) –Observed: 1 Event –Signal: / –Background: / –2.2  significance DZero ee  event

Jerry Blazey / April 16, 2007 / APS 12  (ZZ) Adding the ll+ Channel Signal Extraction:Signal Extraction: –Calculate LO event probability or LRatio= P(ZZ)/(P(ZZ)+P(WW)) –Fit to extract signal –1.9  significance Combination with 4lCombination with 4l –Use binned-likelihood –3.0  combined significance

Jerry Blazey / April 16, 2007 / APS 13 ? Boson and Di-boson Status Evidence(3  ) Observation(5  ) EW Single Top 4.9+/-1.4 pb

Jerry Blazey / April 16, 2007 / APS 14 Run II W Mass CDF for ~200pb -1 (Feb’02- Sep’03)CDF for ~200pb -1 (Feb’02- Sep’03) Event RequirementsEvent Requirements –One selected lepton Electron cluster E T > 30 GeV, track p T > 18 GeVElectron cluster E T > 30 GeV, track p T > 18 GeV Muon track p T > 30 GeVMuon track p T > 30 GeV –Hadronic Recoil < 15 GeV –p T ( ) > 30 GeV Derive mass directly from EW quantities Radiative corrections are dominated by t, H loops: W mass indirect measures of Higgs mass.

Jerry Blazey / April 16, 2007 / APS 15 Results: Data, Fits, & Systematics Electron Transverse Mass Transverse Mass Fits Combined fits 3 e: /- 62 MeV 3  : /- 60 MeV All: /- 48 MeV m T (e ) Basic Technique: Fit e,  transverse mass, momentum, & missing energy to Monte Carlo templates to extract mass

Jerry Blazey / April 16, 2007 / APS 16 Best Single Measurement! New Tevatron Average: /- 39 MeV New World Average: /- 25 MeV

Jerry Blazey / April 16, 2007 / APS 17 Constraints on Higgs Mass Direct e + e -  HZ LEP searchDirect e + e -  HZ LEP search m H > % C.L. New Winter 2007 EW fits including new m W and m top measurements:New Winter 2007 EW fits including new m W and m top measurements: m H = GeV m H <144 95% C.L. Combination of the EW fit and LEP2 limit:Combination of the EW fit and LEP2 limit: m H <182 95% C.L. m H <182 95% C.L. See previous talk by Kevin Lannon, OSU for new results on top mass M t =170.9+/-1.8 GeV

Jerry Blazey / April 16, 2007 / APS % C.L. m W (GeV) m t (GeV) We’re looking for a light Higgs!

Jerry Blazey / April 16, 2007 / APS 19 Tevatron Searches: SM Higgs Production and Decay Mass Dependent StrategyMass Dependent Strategy M H <135 GeVM H <135 GeV –gg  H  bb overwhelmed by huge multi-jet (QCD) background. –Use leptons from associated W and Z production along with H  bb decay to “tag” event –Complement with H  WW* –Backgrounds: Wbb, Zbb, W/Zjj, top, diboson, QCD… M H >135 GeVM H >135 GeV –gg  H  WW production –Multi-lepton final states distinctive. –Background: WW, DY, WZ, ZZ, tt, tW, .. Excluded pb BF 200GeV80GeV

Jerry Blazey / April 16, 2007 / APS 20 Combined Tevatron Higgs Limits (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 m H =115 GeV –A factor of 3.8 above SM at m H =160 GeV Recent progressRecent progress –Both CDF & DZero completed low & high mass 1fb -1 analyses. –Improvements in analysis techniques & systematic uncertainties.

Jerry Blazey / April 16, 2007 / APS 21 Associated Higgs Production Experimental Signature Leptonic decay of W/Z bosons provides “handle” for event Higgs decay to two bottom-quarks helps reduce SM backgrounds

Jerry Blazey / April 16, 2007 / APS 22 WH  l bb, l = e,  CDF/DØ box cut analysesCDF/DØ box cut analyses –isolated e or  –missing E T –jets>15 GeV (CDF)/20 GeV (DØ) Backgrounds: Wbb, top, di- boson, QCDBackgrounds: Wbb, top, di- boson, QCD Analyzed one “tight” b-tag and 2 “loose” b-tag channels, later combinedAnalyzed one “tight” b-tag and 2 “loose” b-tag channels, later combined Cross section limits are derived from invariant mass distributionsCross section limits are derived from invariant mass distributions 95% CL upper limits (pb) for m H =115 GeV (SM expected: 0.13 pb)95% CL upper limits (pb) for m H =115 GeV (SM expected: 0.13 pb) –CDF: 3.4 (2.2) observed (expected) –DØ: 1.3 (1.1) observed (expected) Best Expected:  excl /  SM =9

Jerry Blazey / April 16, 2007 / APS 23 Use LO ME to compute event probability densities for signal and backgroundUse LO ME to compute event probability densities for signal and background Selection criteria based on single top search (will be optimized in the future)Selection criteria based on single top search (will be optimized in the future) Cross section limits are derived from the discriminant distributionsCross section limits are derived from the discriminant distributions 95% CL upper limit for m H =115 GeV is 1.7(1.2) pb observed (expected)95% CL upper limit for m H =115 GeV is 1.7(1.2) pb observed (expected) Similar sensitivity to cut-based analysis, with optimization ~30% increase in sensitivity.Similar sensitivity to cut-based analysis, with optimization ~30% increase in sensitivity. New Technique: WH  l bb, l = e, 

Jerry Blazey / April 16, 2007 / APS 24 Selection:Selection: –ee or  with dilepton mass ~ M Z –opposite charge and isolated from jets –Jets > 15 GeV (DØ), > 25(15) GeV (CDF) Dominant backgrounds: Z+jets (Zbb irreducible), top, WZ, ZZ, QCD multijetDominant backgrounds: Z+jets (Zbb irreducible), top, WZ, ZZ, QCD multijet DØ:DØ: –Require at least two b-tagged jets. –Cross section limit derived from dijet invariant mass distribution within a search window CDF:CDF: –Require 1 b-tagged jet. –2-D Neural Network to discriminate against the two largest backgrounds (tt vs. ZH and Z+jets vs. ZH) –Limits derived from the neural network distribution 95% CL upper limits (pb) for m H =115 GeV (SM expected: 0.08 pb)95% CL upper limits (pb) for m H =115 GeV (SM expected: 0.08 pb) –DØ: 2.7 (2.8) observed (expected) –CDF: 2.2 (1.9) observed (expected) ZH  l l bb, l = e,  Best Expected:  excl /  SM =24 Mjj(GeV)

Jerry Blazey / April 16, 2007 / APS 25 New: ZH  l l bb, l = e,  using NN 2 Loosen Event SelectionLoosen Event Selection NN One:NN One: –Improves jet resolution –Assign missing Et to jets based on position and azimuthal separation NN Two:NN Two: –Train on single tags and double tags –Two dimensional ZH+ ZjetZH+ Zjet ZH+ Top-antitopZH+ Top-antitop Expected:  excl /  SM = 16

Jerry Blazey / April 16, 2007 / APS 26 Selection:Selection: –Separate analysis for 1 and 2 b-tag sample –Exactly Two Jets –Large missing E T, not aligned in  with jets Backgrounds:Backgrounds: –Physics: Z/W+jets, top –Instrumental: mis-measured E T together with QCD jets At 115 GeV:At 115 GeV: ZH  bb, WH  l bb Best Expected:  excl /  SM =10 2tags

Jerry Blazey / April 16, 2007 / APS 27 H  WW *  l + l - H  WW *  l + l - Search strategy:Search strategy: –2 high p T isolated, opposite signed leptons –Require missing E T, veto near jets –Choose di-lepton opening angle  ll to discriminate against dominant WW background –WW comes from spin-0 Higgs & leptons prefer to point in the same direction Sensitivity at m H ~ 160 GeV:Sensitivity at m H ~ 160 GeV: Best Expected:  excl /  SM =4

Jerry Blazey / April 16, 2007 / APS 28 New: H  WW*  l + l – New: H  WW*  l + l – Event SelectionEvent Selection –Exactly 2 Leptons –Lepton Isolation –Missing Et –Less than 2 jets (>15 GeV) Limit Extraction:Limit Extraction: –Using ME calculate P(H)/(P(H)+k i B i ) –Perform binned maximum likelihood fit over discriminator –At 160 GeV  <1.3pb at 95% C.L. An additional NN analysis just approved has similar sensitivityAn additional NN analysis just approved has similar sensitivity Expected:  excl /  SM = 5

Jerry Blazey / April 16, 2007 / APS 29 Updated DZero Combined Higgs Limits Updated DZero Combined Higgs Limits Single Experiment Limit competitive or better than 2006 combinationSingle Experiment Limit competitive or better than 2006 combination Observed combined limits:Observed combined limits: –At m H =115 GeV a factor of 8.4 (5.9 expected) above SM –At m H =160 GeV afactor of 3.7 (4.2 expected) above SM and select observed CDF measurements H  WW Three analyses!

Jerry Blazey / April 16, 2007 / APS 30 Final Comments & Conclusions EWEW –Precision studies continue –Nearly completed the di-boson spectrum –Improved techniques/backgrounds for Higgs Search HiggsHiggs –EW fits + LEP: m H <182 95% C.L. –Closing in on exclusion near 160 GeV! –Prospects Steady progress on improved techniques, sensitivity & limitsSteady progress on improved techniques, sensitivity & limits New combined Tevatron limit this summer.New combined Tevatron limit this summer.

Jerry Blazey / April 16, 2007 / APS 31 top