Investigation on Diboson Production Ye Li Graduate Student UW - Madison
Diboson physics at tevatron • Provide a stringent test for SM TGC (Trilinear Gauge Coupling) • TGC is sensitive to NP (New Physics) • Involve 5 C- and P-conserving coupling parameters • Probe the deviation of some parameters • Effective Lagrangian (SM: g = κ = 1, λ = 0) • V = Z, γ
W γ production • Test of WW γ TGC • Anomalous Coupling leads to and enhancement of the Cross Section and an excess of High Energy Photon • Identify W by leptonic decay (W → l ν ) • Dominant background: jet mimics isolated Photon • Separation Requirement: Δ R > 0.7
Result • Luminosity: 200 pb -1 (CDF) and 162 pb -1 (DO) • W γ Cross Section × BR (Leptonic decay of W): – CDF: 18.1 ± 1.6(stat) ± 2.4(syst.) ± 1.2(lum.) pb; NLO expectation: 19.3 ± 1.4 pb) – DO: 14.8 ± 1.6(stat) ± 1.0(syst.) ± 1.0(lum.) pb; CDF NLO expectation: 16.0 ± 0.4 pb) • Consistent with SM; Not evident for NP
Z γ production • Combination of ZZ γ and Z γγ TGC • Identify Z by leptonic decay (W → l l ) • Dominant background: jet mimics isolated Photon (the same as W γ ) • Separation Requirement: Δ R > 0.7
Result • Luminosity: 200 pb -1 (CDF) and 300 pb -1 (DO) • Z γ Cross Section × BR (Leptonic decay of Z): – CDF: 4.6 ± 0.5(stat) ± 0.2(syst.) ± 0.3(lum.) pb; NLO expectation: 4.5 ± 0.3 pb) – DO: 4.2 ± 0.4(stat + syst.) ± 0.3(lum.) pb; CDF NLO expectation: 3.9 ± 0.2 pb) • Still Consistent with SM
WW production • WW final state: a promising channel for Higgs boson • WW γ and WWZ coupling involved • Higher invariant mass probed in CDF compared to LEP • Signature: leptonic decay of W • Contamination: t t-bar events • Dominant Background after Selection Cut: Drell-Yan, other diboson decay and Jet faking isolated lepton
Result • Luminosity: 240 pb -1 (DO published) and 825 pb -1 (CDF preliminary) • σ (p p-bar → WW + X): – DO published: 13.8 +4.3-3.8 (stat) +1.2-0.9 (syst.) ± 0.9(lum.) pb – CDF preliminary: 13.6 ± 2.3(stat) ± 1.6(syst.) ± 1.2(lum.) pb – NLO expectation: 12.4 ± 0.8 pb) • Also Consistent with SM
WZ / ZZ production • WWZ TGC, WW γ not involved here • Sum of WZ and ZZ production (p p-bar → WZ + ZZ) searched in 2, 3 and 4 lepton channels • Direct search of WZ production in trilepton + MET channel • Dominant background in WZ direct search: Z + X where X = Z, γ or jet faking a lepton
Result • σ (p p-bar → WZ + ZZ) • Luminosity: 194 pb -1 • SM expectation: 5.0 ± 0.4 pb -1.4 (stat) ± 0.4 (syst.) • Measurement: 5.0 +1.8 pb • CDF: σ < 15.2 pb @ 95% CL
Result • NLO σ (p p-bar → WZ) = 3.7 ± 0.3pb (CDF) • DO published – Luminosity: 300 pb -1 – < 13.3 pb @ 95% CL – 4.5 +3.8-2.6 (stat + syst.) • CDF preliminary – Luminosity: 825 pb -1 – < 6.34 pb @ 95% CL
WW + WZ in l ν jj • Search in channel l ν jj • Advantage than pure lepton channel: larger branching fraction • The result shows no statistically significant evidence for this event • σ (p p-bar → WW + WZ) < 36 pb @ 95% CL
Summary • No deviation from the Standard Model is observed • More stringent search in NP by the end of Run II
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