Investigation on Diboson Production Ye Li Graduate Student UW - - - PowerPoint PPT Presentation

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
• f 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
• bserved
• More stringent search in NP by the end of

Run II