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Multi boson production Paolo Mastrandrea PIC 2009 Kobe 8/31/2009 - 9/2/2009

Explore the production of 2 vector bosons and associated couplings at the Tevatron collider. Learn about Triple Gauge Couplings (TGC), anomalous couplings, and analysis techniques for probing new physics phenomena.

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Multi boson production Paolo Mastrandrea PIC 2009 Kobe 8/31/2009 - 9/2/2009

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  1. Multi boson productionPaolo MastrandreaPIC 2009Kobe 8/31/2009 - 9/2/2009

  2. Diboson production • Associated production of 2 vector bosons (g, W, Z) can occur via: • particle-antiparticle annihilation (t-channel) • boson self-interactions or Triple Gauge Coupling (TGC) (s-channel) s-channel t-channel Paolo Mastrandrea - FNAL

  3. Why is diboson interesting? • Measure coupling between W,Z and g to test SM prediction; • unique probe for Triple Gauge Coupling (TGC); • observing TGCs not permitted in the SM or anomalous TGCs would be a sign of new physics; • signature similar to Higgs (not in this presentation). • All presented analysis from Tevatron: • most updated; • highest q2 available; • techniques in LHC perspective. Paolo Mastrandrea - FNAL

  4. Triple Gauge Couplings • anomalous Triple Gauge Couplings (aTGCs): • can affect cross-section and kinematics observables (i.e. lepton or boson pT distributions); • can depend on q2. Paolo Mastrandrea - FNAL

  5. Triple Gauge Couplings • VWW: 14 independent couplings (7 each for ZWW and gWW); can be reduced to 5 assuming C and P conservation and electromagnetic gauge invariance. • Common set (kg, kZ, lg, lZ, gZ1); • gauge invariance: kZ = gZ1 - (kg - 1)tan2qW and lZ = lg; • in SM at the tree level kg = kZ = gZ1 = 1 and lg = lZ = 0; • Dk = k - 1 ;Dg = g - 1. [ LEP2 arXiv:hep-ex/0612034v2] Paolo Mastrandrea - FNAL

  6. Triple Gauge Couplings • Zgg* and ZgZ* : deviations from SM couplings may be described by 8 parameters hVi (i = 1,..4; V = g, Z) • ZZg* and ZZZ* : deviations from SM couplings may be described by 4 parameters f Vi (i = 4, 5; V = g, Z) [ LEP2 arXiv:hep-ex/0612034v2] Paolo Mastrandrea - FNAL

  7. Analysis techniques • Leptons for clear signatures; • now start using jets; • increasing statistics is pushing close/beyond LEP limits on aTCGs parameters. Paolo Mastrandrea - FNAL

  8. Zg D0 3.6fb-1 • Zgnng • Copious non-collision background: • a pointing alghoritm which exploits the transverse and longitudinal energy distributions in the EM calorimeter and central preshower detector is used to evaluate zEM; • reject events with |zEM - zV| > 10 cm. • 5.1 s.d. significance -First Tevatron observation Paolo Mastrandrea - FNAL

  9. (hg30 = 0.09 and hg40 = 0.005) Zg - aTGC • Photon ET spectrum in data compared to MC signal + background expectation for a grid of pairs of anomalous coupling parameters; • 1 and 2-dimensional bounds obtained setting all other parameters to SM prediction; • limits on Zgg* and ZgZ* aTGC. World's best Paolo Mastrandrea - FNAL

  10. Wg CDF 1fb-1 • Wglng • Sensitive to WWg aTGC Paolo Mastrandrea - FNAL

  11. Wg D0 162pb-1 • Wg+Xlng+X, (l=e,m) • Limits on WWg aTGC Paolo Mastrandrea - FNAL

  12. WW CDF 3.6fb-1 • W+W-l+nl'-nl' , events selection: • high-pTe and m trigger paths; • 2 opposite charge leptons (e, m). • Background reduction: • no jets with ET>15GeV and |h|<2.5; • missing ET not alligned with leptons or jets - reduces DY background; • Mll > 16 GeV to suppress h.f. contribution. • Event-by-event matrix element probability density functions are used to build a likelihood ratio discriminant. • Binned likelihood fit to extract s(ppWW). Paolo Mastrandrea - FNAL

  13. WW • Matrix element probability density functions pdf: • xobs - This represents the observed lepton momenta vectors as well as the two transverse components of the missing ET. • 1/<s> - This is a normalization factor based on the total leading order cross section and detector acceptances. • s - This refers to the leading-order cross section. • y - The true lepton 4-momenta which are integrated over. • e - Detector efficiencies and acceptances. • G - A generalized detector resolution function. • Likelihood ratio: • where i are the background processes modeled and ki is the relative fraction of the i-th mode such that the sum over all ki equals 1. [All distributons in backup] Paolo Mastrandrea - FNAL

  14. WW • Cross section extracted using a binned likelihood fit which includes gaussian constraints for systematics. • Correlation between systematics taken into account. Paolo Mastrandrea - FNAL

  15. WW - aTGC • The efficiency at a given leading lepton pT is similar for any given coupling - allow to avoid full simulation for every possible coupling • The resulting efficiency curve is then applied to MCFM NLO matrix element simulations for a grid of values of the couplings parameters • The measured leading lepton pT distribution is fitted to extract limits on lZ, DgZ1 and Dkg Paolo Mastrandrea - FNAL

  16. WW D0 1.0 fb-1 • W+W-l+nl'-nl' • aTGC limits extracted comparing the lepton pT distributions with MC simulations for different sets of (Dkg, lg, DgZ1) Paolo Mastrandrea - FNAL

  17. WZ CDF 1.9fb-1 • WZl'nl'l+l- • extended categories of charged leptons to increase acceptance Paolo Mastrandrea - FNAL

  18. WZ - aTGC • Z pT distribution is sensitive to aTGC • Efficiency independent from aTGC couplings • Z pT distribution fitted to for every combination of simulated parameters to extract limits Paolo Mastrandrea - FNAL

  19. ZZ CDF 4.8fb-1 • Zl+l-l'+l-'; • extended categories of charged leptons to increase acceptance. Paolo Mastrandrea - FNAL

  20. ZZ D0 1.7 fb-1 • ZZl+l-l'+l'- • 5.4 s.d. significance Paolo Mastrandrea - FNAL

  21. ZW, ZZ CDF 1.9fb-1 aTGC • ZW/ZZl+l-jj; • extended categories of charged leptons to increase acceptance; • signal fraction extracted by an unbinned fit to dijet mass distribution. control region SM pT(Zl+l-) GeV/c Paolo Mastrandrea - FNAL

  22. ZW, ZZ - aTGC • ZW/ZZl+l-jj . • aTGC limits extracted comparing Mjj distribution to MC simulation. Paolo Mastrandrea - FNAL

  23. WZ, WW CDF 3.9fb-1 • WW/WZlnjj , l = e,m. • Event selection: • 1 lepton with ET>20GeV and |h|<1.2; • missing ET>25GeV; • ≥ 2 jet with ET>20GeV, |h|<2.4, Dh<2.5; • MTW>30GeV/c2; • pT(jj)>40GeV/c. • Diboson fraction extracted by a binned fit to Mjj distribution. • 4.6 s.d.significance (expected 4.9 s.d.) Paolo Mastrandrea - FNAL

  24. WZ, WW CDF 2.7fb-1 • WW/WZlnjj , l = e,m. • Matrix element technique to maximize the use of collected information in signal-background discrimination. • 5.4 s.d. significance (expected 5.1 s.d.). Paolo Mastrandrea - FNAL

  25. n j j n, lep VV->Missing ET+jj CDF 3.5fb-1 • Search for nn and ln final states. • Acceptance for WW, WZ and ZZ events. • Event selection: • Missing ET > 60 GeV; • 2 jets ET > 25 GeV, |h| < 2.0; • Missing ET significance > 4; • Missing ET-jet Df > 0.4. • Missing ET model to enanche QCD rejection. • Sysytematic uncertaintiy on V+jj background shape checked with g+jj events. Paolo Mastrandrea - FNAL

  26. … and what about LHC ? • LHC: • proton-proton • s = 14 TeV • L = 1034 cm-2s-1 • Tevatron: • proton-antiproton • s = 1.96 TeV • L = 31032 cm-2s-1 [arXiv:0901.0512 ; CERN-OPEN-2008-020] Paolo Mastrandrea - FNAL

  27. … and what about LHC ? • Example on WW, L=2TeV [arXiv:0901.0512 ; CERN-OPEN-2008-020] Paolo Mastrandrea - FNAL

  28. Conclusions • Diboson program is wide and exciting • Tevatron is producing mature results • … even more in the next LHC era! Paolo Mastrandrea - FNAL

  29. Backup Paolo Mastrandrea - FNAL

  30. WW • Matrix element probability density functions pdf: Paolo Mastrandrea - FNAL

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