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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

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

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  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

  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

  3. (Select) Electroweak Physics at the Tevatron • 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 sections • Study the structure of the theory • Backgrounds to Higgs, top, SUSY • Probe new physics w/ anomalous couplings

  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.

  5. Electrons ET > ~ 20 GeV Shower Shapes Isolation |h| coverage CDF: 0-2.5 DZero: 0-3.2 Photons ET > ~ 7 GeV Shower Shapes Lepton Isolation |h| coverage CDF: 0-1.1 DZero: 0-2.5 Muons pT > ~ 20 GeV Isolation |h| 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 Basic* Event Characteristics

  6. Z rapidity related to parton momentum fractions by Acceptance at large rapidities opens full range of parton x σTot = 265.9±1.0±1.1 pb NNLO w/ NLO CTEQ6.1 most consistent with data Ze+e- Rapidity

  7. Ze+e- Transverse Momentum • Tests higher order descriptions of Z PT • Reduces uncertainty on W mass by improving modeling of ET. • Improves understanding of backgrounds for new phenomena searches Resbos +Photos 1fb-1

  8. Sensitive to Wg coupling Variation in Wg production would be sign of new physics Particularly changes in PT(g) spectrum at high MT(Wg) Wg Production • DØ preliminary MT(lgn) > 90 GeV m channel: s( mn g X) = 3.21 +/- 0.52 pb e channel: s( e n g X) = 3.12 +/- 0.42 pb theory: s( l n g X) = 3.21 +/- 0.08 pb • CDF preliminary 30 < MT(mn) < 120 GeV: • e+m channel: s( l n g X) = 18.03+/- 2.83 pb theory: s( m n g X)= 19.3 +/- 1.4 pb Measured Cross Sections and g spectra in good agreement with SM.

  9. Wg: Radiation Zero • SM couplings at LO produce amplitude zero in the center-of-mass production angle • Correlations lead to a dip in Q*(hg-hl)= Q*Dh • Discrimination against anomalous coupling evident! Background-subtracted data Q*Dh

  10. Sensitive to WWZ vertex SM NNL cross section: 3.7 +/- 0.3 pb WZ lnl+l- mode Main Backgrounds: Z*/g+jet, ZZ, DY Z Z Z s(WZ)Observation 16 observed 12.5 expected 2.7 background 6.0s 12 observed 7.5 expected 3.6 background 3.3s CDF: 5.0 +1.8-1.6 pb DZero: 4.0 +1.9 -1.5 pb

  11. No self coupling of Z bosons in the standard model. Produced in t channel SM s: 1.4 +/- 0.1pb Strategies ZZ  4 charged leptons Very clean signatures Low background from Z+j Small BF ZZ  2 charged leptons+ 2 neutrinos Six times production High Background WW, DY Event Likelihood using WW, ZZ Matrix elments s(ZZ) Evidence DZero eemm event • DZero 4 lepton (1.0 fb-1) • Observed: 1 Event • Signal: 1.71 +/- 0.10 • Background: 0.17 +/- 0.04 • CDF 4 lepton (1.4 fb-1) • Observed: 1 Event • Signal: 2.54 +/- 0.15 • Background: 0.03 +/- 0.02 • 2.2s significance

  12. s(ZZ) Adding the ll+nn Channel • Signal Extraction: • Calculate LO event probability or LRatio= P(ZZ)/(P(ZZ)+P(WW)) • Fit to extract signal • 1.9 s significance • Combination with 4l • Use binned-likelihood • 3.0 s combined significance

  13. EW Single Top 4.9+/-1.4 pb Evidence(3s) Observation(5s) ? Boson and Di-boson Status

  14. CDF for ~200pb-1 (Feb’02-Sep’03) Event Requirements One selected lepton Electron cluster ET > 30 GeV, track pT > 18 GeV Muon track pT > 30 GeV Hadronic Recoil < 15 GeV pT(n) > 30 GeV Derive mass directly from EW quantities Radiative corrections are dominated by t, H loops: W mass indirect measures of Higgs mass. Run II W Mass

  15. Results: Data, Fits, & Systematics Transverse Mass Fits Basic Technique: Fit e, m transverse mass, momentum, & missing energy to Monte Carlo templates to extract mass Combined fits 3 e: 80477+/- 62 MeV 3 m: 80352+/- 60 MeV All: 80413+/- 48 MeV Electron Transverse Mass mT(en)

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

  17. Constraints on Higgs Mass • Direct e+e-HZ LEP search mH>114.4 GeV @ 95% C.L. • New Winter 2007 EW fits including new mW and mtop measurements: mH=76+33-25 GeV mH<144 GeV @ 95% C.L. • Combination of the EW fit and LEP2 limit: mH<182 GeV @ 95% C.L. See previous talk by Kevin Lannon, OSU for new results on top mass Mt=170.9+/-1.8 GeV

  18. 68 % C.L. mW (GeV) mt (GeV) We’re looking for a light Higgs!

  19. Excluded Tevatron Searches: SM Higgs Production and Decay pb • Mass Dependent Strategy • MH<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… • MH>135 GeV • gg  H  WW production • Multi-lepton final states distinctive. • Background: WW, DY, WZ, ZZ, tt, tW, tt.. BF 80GeV 200GeV

  20. Combined Tevatron Higgs Limits(Summer 2006) • Sixteen mutually exclusive final states for WH, ZH, WW • Observed combined limits: • A factor of 10.4 above SM at mH=115 GeV • A factor of 3.8 above SM at mH=160 GeV • Recent progress • Both CDF & DZero completed low & high mass 1fb-1 analyses. • Improvements in analysis techniques & systematic uncertainties.

  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

  22. WHl nbb, l =e,m • CDF/DØ box cut analyses • isolated e or m • missing ET • jets>15 GeV (CDF)/20 GeV (DØ) • Backgrounds: Wbb, top, di-boson, QCD • Analyzed one “tight” b-tag and 2 “loose” b-tag channels, later combined • Cross section limits are derived from invariant mass distributions • 95% CL upper limits (pb) for mH=115 GeV (SM expected: 0.13 pb) • CDF: 3.4 (2.2) observed (expected) • DØ: 1.3 (1.1) observed (expected) Best Expected: sexcl/sSM=9

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

  24. Selection: ee or mm with dilepton mass ~ MZ opposite charge and isolated from jets Jets > 15 GeV (DØ), > 25(15) GeV (CDF) Dominant backgrounds: Z+jets (Zbb irreducible), top, WZ, ZZ, QCD multijet DØ: Require at least two b-tagged jets. Cross section limit derived from dijet invariant mass distribution within a search window 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 mH=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,m Mjj(GeV) Best Expected: sexcl/sSM=24

  25. New: ZHl l bb, l =e,m using NN2 • Loosen Event Selection • NN One: • Improves jet resolution • Assign missing Et to jets based on position and azimuthal separation • NN Two: • Train on single tags and double tags • Two dimensional • ZH+ Zjet • ZH+ Top-antitop Expected: sexcl/sSM= 16

  26. ZHnnbb, WHl nbb • Selection: • Separate analysis for 1 and 2 b-tag sample • Exactly Two Jets • Large missing ET , not aligned in f with jets • Backgrounds: • Physics: Z/W+jets, top • Instrumental: mis-measured ET together with QCD jets • At 115 GeV: Best Expected: sexcl/sSM=10 2tags

  27. HWW*l +l - nn • Search strategy: • 2 high pT isolated, opposite signed leptons • Require missing ET , veto near jets • Choose di-lepton opening angle Dfll to discriminate against dominant WW background • WW comes from spin-0 Higgs & leptons prefer to point in the same direction • Sensitivity at mH ~ 160 GeV: Best Expected: sexcl/sSM=4

  28. New: HWW*l +l –nn • Event Selection • Exactly 2 Leptons • Lepton Isolation • Missing Et • Less than 2 jets (>15 GeV) • Limit Extraction: • Using ME calculate P(H)/(P(H)+kiBi) • Perform binned maximum likelihood fit over discriminator • At 160 GeV s<1.3pb at 95% C.L. • An additional NN analysis just approved has similar sensitivity Expected: sexcl/sSM= 5

  29. and select observed CDF measurements Three analyses! HWW Updated DZero Combined Higgs Limits • Single Experiment Limit competitive or better than 2006 combination • Observed combined limits: • At mH=115 GeV a factor of 8.4 (5.9 expected) above SM • At mH=160 GeV afactor of 3.7 (4.2 expected) above SM

  30. Final Comments & Conclusions • EW • Precision studies continue • Nearly completed the di-boson spectrum • Improved techniques/backgrounds for Higgs Search • Higgs • EW fits + LEP: mH<182 GeV @ 95% C.L. • Closing in on exclusion near 160 GeV! • Prospects • Steady progress on improved techniques, sensitivity & limits • New combined Tevatron limit this summer.

  31. Accelerator Higgs top

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