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Electroweak Measurements at the Tevatron

Comprehensive study on vector bosons and their interactions at the Tevatron collider, including precise tests on the Standard Model, Higgs background, and boson charge asymmetries. Unique experiments performed with high efficiency exploring various decay channels and properties unreachable at the LHC. Crucial insights into fundamental particles and processes.

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Electroweak Measurements at the Tevatron

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  1. Electroweak measurement @ the Tevatron Liang HAN University of Science & Technology of China (USTC)

  2. Tevatron, CDF and DØ • P-Pbar @1.96 TeV, 2x1032cm-2s-1 • Vector boson factor L ~ 30 pb-1/week • ~0.7 million W, • ~0.15 million Z • ~400 WW, ~120 WZ, ~50 ZZ, … • Precise test on Standard Model & understand Higgs background • Two experiments perform with high efficiency L.Han(USTC)@HEP10 2008

  3. Single W and Z production -- Due to large jet background, W and Z events are typically reconstructed in lepton decay l=e,m -- Tools to calibration isolated high pT l=e,m and MET from Wen -- Physics : NNLO QCD test on Z pT, h distribution, Ztt, andMWmeasurement etc; and something that won’t be accessible at LHC… L.Han(USTC)@HEP10 2008

  4. dσ/dy (nb) √s = 1.96 TeV Rapidity y W charge asymmetry -- Up quarks carry more proton momentum than down quarks  more W-in anti-proton direction, and more W+in proton direction -- W charge asymmetry A(y) is sensitive to u(x)/d(x) -- Difficult to measure W boson A(y) directly; instead, convolute A(y) to W± V-A decay  lepton rapidity asymmetry A(hl): L.Han(USTC)@HEP10 2008

  5. Accepted by PRD arXiv 0709.4254 Lepton and W charge asymmetry • DØ, Wl: lepton charge asymmetry • CP folding  -A(-y)==A(y) • CDF, We: W charge asymmetry • Reconstruct yW using MW constraint DØ preliminary: We 1fb-1 -- Experimental uncertainties have already been smaller than orcomparable with the parton distribution function CTEQ uncertainties in most regions L.Han(USTC)@HEP10 2008

  6. Z/g*l+l-Forward/Backward Asymmetry • Standard Model neutral-current couplings of Z bosons to fermions as e- q • Electron charge forward/backward asymmetry AFBin Z e+ (measured as function of Mee) • --  as negatively charged e-relative to the incoming quark L.Han(USTC)@HEP10 2008

  7. Tevatron, the only place of q+qbare-+e+AFB precise measurement • Many systematic uncertainties cancelled • Complementary sensitivity to Z’ model-independently, via Z/g*/Z’ interference 500GeV Z’,Z, Zx AFB Mee(GeV) • Precise test on the SM, especially the weak mixing angle sin2qWmeasurement L.Han(USTC)@HEP10 2008

  8. SM fundamental parameters : a, GF, MZ, MWandsin2qW • The effective weak mixing angle , from Z-pole observables, e.g. AFB 0.23152±0.00014 -- LEP b-quark asymmetry：+2.4s from global EW fit, 3.2sfrom SLC -- NuTeVn-N scattering ：0.2277±0.0016,+3.1s from SM prediction [PRL 88, 091802(02)] L.Han(USTC)@HEP10 2008

  9. @ Tevatron • DØ 1fb-1 analysis: • Select Forward/Backward di-EM events in 50GeV<Mee<500GeV • Subtract background from QCD and SM predictions( Ztt etc) • Reweight Pythia Z/g*ee to, e.g. 1) EM energy scale and resolution calibrated at Z-pole • 2) NLO QCD Z-pT,h,Mee distribution at partonic level • Compare to s of different inputs 0.2327±0.0018±0.0006 (statistic) (systematic) -- uncertainty comparable to LEP and NuTeV -- systematic : + 0.0005CTEQ6 PDF + 0.0003EM scale/resolution 0.2238±0.0040±0.0030 • CDF 72pb-1 analysis: [PRD 71, 052002(2005)] L.Han(USTC)@HEP10 2008

  10. Unfolded AFBdistribution @ Tevatron • Correct detector resolution, acceptance & efficiency etc  comparable to prediction • Detector resolution  Mee migration  unfolding matrix, computed iteratively on rewighted MC • Detector geometric and kinematic cuts  correct acceptance ×efficiency CDF 72pb-1 -- Provide complementary information on heavy Z’ boson search L.Han(USTC)@HEP10 2008

  11. Di-Boson production • Wg (DØ 0.7 fb-1) • Zg(DØ 1 fb-1) • WZ (CDF 2 fb-1, DØ 1 fb-1) • WW/WZ ljj (CDF 1.2 fb-1) • ZZ (CDF 2 fb-1, DØ 1 fb-1) • Precise test of non-Abelian SU(2)L×U(1)Y • --complementary to LEP : higher c.m. energy, new couplings of charged currents • Probe TGC (trilinear gauge couplings) • -- sensitive to “low” energy remnants of new physics @ high scale • Background to hunting Higgs, top and SUSY • Topology : ≥2 isolated high pT(>15 GeV) lepton(l=e,m)/g, MET(>20 GeV) for W L.Han(USTC)@HEP10 2008

  12. WZ production @ Tevatron SM NLO : [ PRD 60, 113006 (1999) ] • Unique measurement on WWZ TGC -- non-SM anomalous as with form factor as -- Enhancement on production + excess at W/Z high pT spectrum • WZllln search channel : -- eee, eem, emm and mmm combined, Br~1.5% -- high pT isolated lepton + MET + di-lepton invariant mass around Z L.Han(USTC)@HEP10 2008

  13. Evidence of WZ3l @ DØ 1fb-1 • 13 candidates with 4.5 background ~ 3 significance (HWZ generator) • Anomalous WWZ TGC =1.5 TeV =2.0 TeV a -0.18<Z<0.22 -0.17<Z<0.21 -0.15<g1Z<0.35 -0.14<g1Z<0.34 -0.14<Z =g1Z<0.31 -0.12<Z =g1Z<0.29 [ PRD 76, 111104(R) (2007) ] L.Han(USTC)@HEP10 2008

  14. Observation of WZ3l @ CDF 2fb-1 • Cross-section measurement: 25 candidates [ PRL 98, 161801 ] • Constraint on anomalous WWZ =1.5 TeV =2.0 TeV a -0.14<Z<0.16 -0.13<Z<0.14 -0.17<g1Z<0.27 -0.15<g1Z<0.24 -0.86<Z<1.36 -0.82<Z<1.27 L.Han(USTC)@HEP10 2008

  15. WW/WZlnjj@ CDF 1.2fb-1 • First measurement of (l+MET+2jets) @Tevatron : • more statistic sensitive to TGC • similar to WHlnbb • huge background from W+jets, ~300pb s(WW+WZ)×Br = 2.09±0.14 pb • Analysis strategy : 2) likelihood fit  signal fraction 1) NN to increase S/B significance S/B<1% 3% xBr < 2.88pb@95%C.L. L.Han(USTC)@HEP10 2008

  16. Radiation-Amplitude Zero in Wg • SM : RAZ(Radiation Amplitude Zero) • Measured as Charge-Sign photon-lepton Rapidity • Difference Q[() - (l)] • Predicted at dip L.Han(USTC)@HEP10 2008

  17. Study of W(ln)g RAZ @ DØ 0.7fb-1 • First indication of RAZ : ET(g)>7GeV, R(l)>0.7, MT(lgn)>90GeV • Full covariance matrix c2/dof=17.0/12 • 2-Bin Statistical analysis : • unimodal hypothesis ruled out @ 2.6s Small Max Bin Dip Bin • Photon pT spectrum  anomalous WWgTGC L.Han(USTC)@HEP10 2008

  18. Precise Z(ll)g measurement @ DØ 1fb-1 • Event selections: ET(g)>7GeV, R(l)>0.9, M(ll)>30GeV ISR : M(llg) ≥ MZ ISR FSR : M(llg) ≤ MZ FSR ( Zgllg ) = 4.96±0.30(stat+syst)±0.30(lumi) pb. SM NLO : 4.74 ± 0.22 pb. [ PRD 57, 2823 (1998) ] L.Han(USTC)@HEP10 2008

  19. Anomalous ZZg/ Zgg TGC@ DØ 1fb-1 • Photon ET spectrum of selected events : [ PLB 653, 378 (2007) ] L.Han(USTC)@HEP10 2008

  20. First measurement of ZZ @ CDF 2fb-1 • Charged 4l channel: • 3 events with 0.1 background 4.2 significance L.Han(USTC)@HEP10 2008

  21. Adding the llnn channel: • leading order Elemental Matrix  likelihood ration • Combined 4l + llnnresult : 4.4 significance SM NLO :1.4 ± 0.1 pb. [ PRD 60, 113006 (1999) ] L.Han(USTC)@HEP10 2008

  22. Search for ZZ @ DØ • SM NLO : • --1.6  0.1pb [ PRD 62, 113011; PRD 60, 072002 ] • -- t-channel only, no tri-linear TGC • Charged4lchannel @1 fb-1: M(ll) > 30 GeV for eeee, eemm, mmmm • 1event observed with 0.13  0.03 background expected • Cross section (ZZ/Z*) < 4.4pb@95%C.L. • The first bounds on ZZZ/ZZg*anomalous couplings from Tevatron [ hep-ex/0712.0599 ] L.Han(USTC)@HEP10 2008

  23. Combined e and mchannel of llnn@2.2 fb-1: • Recoil of Z+X discriminating variable • Physics background  likelihood electron channel electron channel muon channel muon channel • Statistic test : 1.77σ significance predicted → 2.4σ significance observed • Cross section measurement : L.Han(USTC)@HEP10 2008

  24. EW Physics @ Tevatron • Precise measurement from O(104)pb • down to O(1)pb @ up to 2fb-1, • precise agreement to SM is observed (1) (2) (1) W charge asymmetry (2) Zee F/B asymmetry (3) First evidence of Wg RAZ (3) (4) (4) Zg cross-section measurement (5) WW/WZlnjj semi-leptonic (6) WWZ TGC (5) (7) First evidence of ZZ (6) (7) • More data coming, digging hard for Higgs, and something else as precise • measurement of AFB and L.Han(USTC)@HEP10 2008

  25. Backup slides L.Han(USTC)@HEP10 2008

  26. Integral Luminosity -- Collider performance -- Experiment performance L.Han(USTC)@HEP10 2008

  27. L.Han(USTC)@HEP10 2008

  28. Z inclusive cross section • DØ (1 fb-1): Z()(hadron) • 1527 candidates with 20% backgrounds •  (ppZ)xBr(Z) = 247 ± 8(stat.) ± 13(syst.) ± 15(lumi.)pb • Consistent with SM prediction 251.9+5-11.8pb • Experimentally important for all  studies such as H search - L.Han(USTC)@HEP10 2008

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