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

Wγ production Test of WWγ TGC Anomalous Coupling leads to and enhancement of the Cross Section and an excess of High Energy Photon Identify W by leptonic decay (W →lν ) Dominant background: jet mimics isolated Photon Separation Requirement: Δ R > 0.7

Result Luminosity: 200 pb-1 (CDF) and 162 pb-1 (DO) Wγ 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

Zγ production Combination of ZZγ and Zγγ TGC Identify Z by leptonic decay (W →l l ) Dominant background: jet mimics isolated Photon (the same as Wγ) Separation Requirement: Δ R > 0.7

Result Luminosity: 200 pb-1 (CDF) and 300 pb-1 (DO) Zγ 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 WWγ 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, WWγ 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, γor jet faking a lepton

Result σ (p p-bar → WZ + ZZ) Luminosity: 194 pb-1 SM expectation: 5.0 ± 0.4 pb Measurement: 5.0 +1.8-1.4(stat)± 0.4 (syst.) 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 lνjj Search in channel lνjj 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