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Generator Study of W(mn)g @ Tevatron collider
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2 vs. 3 body W(mn)gamma and CSRD
Motivation: precise test of RAZ of SM, and probe ATGC in both photon pT and RAZ Both call for on-shell W, cascade decaying leptonically, i.e. 22 2body final states. This is what Pythia does; but experimentally, what observed in m+n+g, and under on-shell W assumption predicted by Pythia Radiation Amplitude Zero (RAZ) Charge Signed Lepton Photon Rapidity Difference (CSRD) in Tevatron Lab frame in Wg rest frame Blue stands for Pythia in all slides
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Distort of CSRD and dphi
The correct treatment of m+n+g 3-body final states, including lepton FSR and interference, as CompHep (here I assume Baur-LO gives the same results as CompHep) On-shell W Events by Pythia8 FSR-inclusive Events by Comphep Significant difference of 2- and 3-body treatment M(mn) CSRD off-shell effects in 23 Distort of CSRD and dphi M(mng) dphi(mg)
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Photon PT >10, Muon PT > 20, Neutrino PT > 20,
Kinematic cuts to “restore” Pythia? Photon PT >10, Muon PT > 20, Neutrino PT > 20, dR > 0.7, MT(lng)>110GeV W- Events by Pythia8 W- Events by Comphep Photon pT Muon pT Neutrino pT dR(mg)
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Photon PT >10, Muon PT > 20, Neutrino PT > 20,
dR > 0.7, MT >110GeV W- Events by Pythia8 W- Events by Comphep M(mn) M(mng) MT(mng)
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Photon PT >10, Muon PT > 20, Neutrino PT > 20,
dR > 0.7, MT >110GeV W- Events by Pythia8 W- Events by Comphep Photon eta Muon eta dphi(mg) CSRD This CSRD plot is in consistent with previous result, where a plain instead of peak in the right was seen, see next slide
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Charge Signed Lepton Photon Rapidity Difference
Plots of Different Cut On-shell W Events MT3 >110GeV Events MT3 >100GeV Events MT3 >90GeV Events Photon PT >10GeV Lepton PT >20GeV Missing ET >20GeV dR>0.7 Charge Signed Lepton Photon Rapidity Difference
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Conclusion 1 + 3-body FRS and interference differs from on-shell Wgamma production and lepton decay + Cuts as MT>110GeV will suppress off-shell effect, and give good photon pT agreement, but dphi and CSRD of lepton and photon + Question: we see dphi and CSRD difference of Wgamma-LO and Pythia, how can we trust a 2-body NLO QCD Wgamma-NLO?
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Parameters used in Comphep vs. WGAMMA
3 body consistency: CompHep vs BaurLO Parameters used in Comphep vs. WGAMMA Beam type ppbar Energy (TeV) 1.96 PDF CTEQ6L αem 1/132.43 M(W) 80.41 M(Z) 91.188 sin2θw Гw 2.103
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Photon PT >5GeV, dR(l,γ) > 0.7
W- Events by Comphep W- Events by WGAMMA Photon PT >5GeV, dR(l,γ) > 0.7 Photon Pt Muon Pt Neutrino Pt dR(muon,photon)
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Photon PT >5GeV, dR(l,γ) > 0.7
W- Events by Comphep W- Events by WGAMMA M(mn) M(mng) MT(mng)
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Photon PT >5GeV, dR(l,γ) > 0.7
W- Events by Comphep W- Events by WGAMMA Photon Eta Muon Eta Dphi(mg) CSRD
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