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Di-boson Physics at the Tevatron

Di-boson Physics at the Tevatron. Fourth Workshop on Mass Origin and Supersymmetry Physics Tsukuba, Japan March 6, 2006 Al Goshaw , Duke University (with thanks to CDF and D0 Colleagues). Outline. Introduction Survey of recent measurements W( l n ) g and Z( l l ) g

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Di-boson Physics at the Tevatron

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  1. Di-boson Physics at the Tevatron Fourth Workshop on Mass Origin and Supersymmetry Physics Tsukuba, Japan March 6, 2006 Al Goshaw , Duke University (with thanks to CDF and D0 Colleagues)

  2. Outline • Introduction • Survey of recent measurements • W(ln) g and Z(l l) g • WW and W Z studies using leptonic decays • Search for W/Z -> q q signals in di-boson events • Summary and outlook

  3. Di-boson physics at the Tevatron • Measurements of di-boson production provide a rich source of electroweak Standard Model tests and are a natural avenue into searches for the Higgs boson. • Vector boson pair production includes (this talk): g gW W W H W g W Z Z H Z g Z Z • The CDF and DØ experiments have completed the first analysis phase based upon ~ 400 pb-1 of p p integrated luminosity. • Ultimate sensitivity will be based upon 4-8 fb-1 • And of course continuation at the LHC …

  4. p p production of W and Z bosons at √s = 1.96 TeVThe general landscape High statistics W/Z inclusive and W mass Lower statistics di-bosons ET(g) > 10 GeV DR(lg) > 0.7 Limits on H production

  5. Approach to di-boson studies • 1. Compare production properties to Standard Model predictions and measure agreement/deviations. • 2. Use anomalous coupling parameters as the metric for evaluating the sensitivity to new physics. This assumes the new physics appears as deviations of the W and Z boson from Standard Model point particles. There are of course other sources of new physics that would appear in di-boson production -- perhaps the most likely sources of a discovery. • 3. Use the advantage of having both q q and q q ’ collisions to separate out specific triple gauge couplings where possible: • q q ’ -> W* -> W g WWg coupling only • q q ’ -> W* -> W Z WWZ coupling only • q q -> Z/g -> W W mix of WWg and WWZ couplings • q q -> Z/g -> Z g mix of ZZg and Zgg couplings • q q -> Z/g -> Z Z mix of ZZg and ZZZ couplings absent in SM

  6. Approach to di-boson studies • 4. For the triple gauge coupling studies use leptonic decays of the W and Z: • W g -> l ng • Z g -> l+ l-g • W+ W- -> l+nl-n • W Z -> l’nl+ l- • Z Z -> l+ l- l’ + l’ - and l+ l-n n • where l = e or m • 5. Extend measurements to W/Z hadronic decay channels • Specific channels: W/Z(jet-jet) + g and W/Z(jet-jet) + W(ln) • Useful for calibration/improvement of di-jet mass resolution • Prototypes for WH and ZH searches

  7. Photon probes of W and Z bosons Wg studies using p p -> lng + x Zg studies using p p -> l+ l-g + x g CDF p p -> m ng + x candidate m n

  8. p p -> lng+ x Production • The lng final states have contributions from quark and lepton bremsstrahlung processes and the direct production Wg -> lng • The first two diagrams involve W boson coupling only to fermions, and are assumed to be described by the Standard Model . • The third diagram depends on the WWg coupling • Therefore the production p p -> lng + x can be used to measure this coupling. W WWg triple gauge coupling initial state radiation final state radiation

  9. p p -> l+ l-g+ x Production • Within the confines of the SM, the ZZg and Zgg couplings are zero at tree level. • Destructive interference of the Wg -> lng process with the initial state bremsstrahlung process suppresses the lng cross section. For p p collisions at √s = 1.96 TeV the SM expectations are: s[W(ln)] / s [Z(ll)] ~ 10.7 for ET(g) > 0 s[lng] / s[llg] ~ 4.3 (1.5) for ET(g) > 10 (100) GeV with DR(lg) > 0.7 Absent in SM Z/g Z/g Z l Z/g l l initial state radiation triple gauge coupling final state radiation

  10. Data selection for lng and l+ l-g events • Events triggered on high ET/PT central electron/muon • Selection of leptons similar to inclusive W/Z measurements • Selection of photons • central: |h| < ~ 1.0 photon • energy: ET > ~ 8 GeV • isolated: DR(lg) > 0.7 • Dominate background from W(ln)+jets and Z/g(l l)+jets with jet -> fake photon • Use jet data samples to measure the jet -> g fake rates • Correct for real photon content • Apply this to jets in W/Z + jet data to get W/Z + fake photons

  11. Data corrections for lng and l+ l-g events • Electron and muon ID efficiencies are evaluated from data using Z -> ee and mm inclusive decays. • Photon ID efficiencies are determined from a combination of data (use electrons as proxies for photons) and GEANT-based detector simulations. • Geometric acceptances determined from SM event generators and detector simulations. • Quote cross sections corrected for: • full W -> ln decay phase space • full Z/g*-> l l decay phase space for M(ll) > 30 (40) GeV/c2 D0 (CDF) • Photon phase space for DR(lg) > 0.7 and ET(g) > 7 (8) GeV CDF (D0)

  12. Comparison of lngand l+ l-gdata to Standard Model predictions s(p p -> lng + X) (pb) with DR(lg) > 0.7 PRL 94, 041803 (2005) PRD 71, 091108 (2005) p p at √s = 1.96 TeV s(p p -> l lg + X) (pb) with DR(lg) > 0.7 PRL 94, 041803 (2005) PRL 95, 051802 (2005)

  13. Comparison of lng signal to Standard Model predictions DØ W + g CDF CDF final state radiation

  14. Comparison of l+ l-g signal to Standard Model predictions CDF Z+ g DY + g DØ DØ final state radiation

  15. Introduction of anomalous couplingsparameters • Under the assumption of Lorentz and electromagnetic gauge invariance, for massless fermions, the WWg coupling can be described in terms of four parameters. • The effective Lagrangian is [ Baur and Berger PRD 41, 1476 (1990) ] LWWg= -ie [(Wmn Wm An - Wm An Wmn ) + kg Wm Wn Fmn + lg/MW2 Wlm Wmn Fnl + 2 more CP violating terms • The magnetic dipole and electric quadrapole moments of the W boson are given by: mW = (1 + kg + lg)e/2MW and QW = -(kg- lg)e/MW2 • In the SM at tree level Dkg= kg - 1 = lg= 0. Estimates of loop corrections are small: |Dkg| = 0.008 and |lg| = 0.002 . - - Strong constraints from limits on the neutron’s electric dipole moment - -

  16. Introduction of anomalous couplingsparameters • The anomalous coupling parameters must be suppressed at high energies to avoid unitarity violations. • For the WWg vertex these are assumed to be of the form: Dkg= Dkog /(1 + s/L2)2 lg = log/(1 + s/L2)2 where L is the scale of the new physics and √s is the Wg invariant mass. • Similarly, under the assumptions of Lorentz and electromagnetic gauge invariance, the anomalous coupling parameters for the ZVg vertex are: hiV = hioV /(1 + s/L2) n where V = s-channel g or Z √s = Zg invariant mass i = 1,2 (CP violating), 3,4 (CP conserving) ==> 8 parameters [see e.g. Baur and Berger PRD 47, 4889 (1993)]

  17. Using lng events to put limits on WWg couplings (DØ) • Non-zero Dkg or lglead to enhancement of high ET photons above the SM prediction. • Suppress event with FSR by selecting events with MT(lng ) > 90 GeV/c2 • Use binned-likelihood fitting ET(g) on Dkog vs loggrid 2D 95% C.L. 1D 95% C.L. -0.88 < Dkog < 0.96 -0.20 < log< 0.20 log Dkog L = 2 TeV

  18. Using l+ l-g events to put limits on ZZg and Zgg couplings (DØ) • No deviations from SM predictions, but very clean data samples can be used to put limits on anomalous couplings. • Form factors imposed to preserve unitarity with n= 3 for i = 1,3 and n = 4 for i = 2,4 (see form on page 17). • Use binned-likelihood fitting to ET(g) on 2D grid of (h10V vs h20V) and (h30V vs h40V). Set 95% C/L. for L = 1 TeV. (D0 PRL and hep-ex/0502036).

  19. WWZ probes of W and Z bosons WZ studies using p p -> l’nl+ l- + x W+ W- studies using p p -> l+nl’-n + x DØ p p -> m nm m + x candidate CDF p p -> m n e n + x candidate m n ‘s n m m m e

  20. p p -> W+ W- + x Production • W+ W- pair production is sensitive to both the WWg and WWZ) couplings. • The SM expectation for p p - > W+ W- +X at √s = 1.96 TeV is ~ 12.4 pb • To date CDF and DØ have used channels.: • ln l‘ n with l, l‘ = e or m BR ~ 4.6% small BR, good S/B • q q’ ln with l= e or m BR ~ 29% good BR, poor S/B destructive interference causes WW cross section suppression WWZ and WWg

  21. Comparison of W+W- to Standard Model predictions using l+nl’-n decays • Measurement of p p -> W+ W- +X at √s = 1.96 TeV with BR corrections • SM theory predictions at NLO with MCFM • Experimental details can be found at: • DO hep-ex/ ( Published in PRL) • CDF hep-ex/ (Published in PRL) DØ Run II: PRL 94, 151801 (2005) CDF Run II: PRL 94, 211801 (2005) SM s(WW) = 12.4 + 0.8 pb

  22. New measurement from CDF (Feb. 2006)An Inclusive Di-lepton Analysis (AIDA) • This analysis is used to simultaneously extract event channels leading to opposite sign di-lepton events: • t t -> l+ l- + MET + high ET jets • W+ W- -> l+ l- + MET + soft jets • Z -> t+ t- -> l+ l- + low MET + soft jets • X+ X- -> l+ l- + ? (search for new physics) • Select events with opposite sign di-leptons using standard cuts: • e+ e- • m+ m- • e+m- e-m+ • Fit these events for signals in a 2 dimensional phase space of MET vs number of jets with ET > 15 GeV and | h | < 2.5 • Minimal selection cuts => maximum sensitivity to signals ET (PT) > 20 GeV (GeV/c)

  23. New measurement from CDF (Feb. 2006)An Inclusive Di-lepton Analysis (AIDA) • Backgrounds • Drell-Yan Z/g - > ee/mm use PYTHIA MC cross checked with data • Wg , WZ and ZZ use SM predictions • Fake leptons in W + jets obtain jet -> lepton fake rate from data

  24. New measurement from CDF (Feb. 2006)An Inclusive Di-lepton Analysis (AIDA)

  25. New measurement from CDF (Feb. 2006)An Inclusive Di-lepton Analysis (AIDA) New CDF s(WW) = 16.7 pb +5.1 -4.3

  26. Comparison of WZ (and ZZ) to Standard Model predictions using all leptonic decays s[p p -> WZ (ZZ) + x ] at √s = 1.96 TeV corrected for W/Z branching ratios • SM theory predictions at NLO with MCFM • Experimental details can be found at: • DØ hep-ex/0504019 (Submitted to PRL) • CDF PRD 71, 091105 (2005) • Bottom line: consistent with the SM Integrated Luminosity ~ 300 pb-1 (DØ) ~ 200 pb-1 (CDF)

  27. Search for W/Z boson hadronic decays Searches for W/Z-> q qusing W/Z + W(ln) events

  28. Searches for p p -> W/Z(q q) + XMotivation • New physics searches using dijets depend critically on a good understanding of the jet-jet invariant mass resolution. • One calibration source is W/Z -> q q -> jet jet • This requires a trigger that does not bias the W/Z mass peak, and allows low mass side bands for background subtraction. • Using diboson events of the type W/Z(q q) g and W/Z(q q) W(ln) allows a trigger selection based upon the a high Et photon or lepton, and provides an unbiased look at the jet-jet spectrum for extraction of W/Z -> q q . • Also, the W/Z(q q) W(ln) channels are very similar to those used for Higgs searches in H(b b) W(ln) and provide a SM calibration line.

  29. Search for p p -> W/Z(q q) + W(ln) • The channel p p -> W(ln) + W/Z (q q ) has been studied by CDF • Advantages: larger branching ratio • Disadvantages: much higher backgrounds • BUT anomalous signals appear at high ET of the W where backgrounds lower • W + jet jet QCD background is constrained by fitting to dijet mass spectrum around MW plus MZ peak. • Fit to data: Ndata = 109 + 110 + 54 events sdata(WW + WZ) < 36 pb • With the SM expectation NSM ~ 160 events sSM(WW + WZ) = 16.5 pb New CDF March 2006

  30. Search for p p -> W/Z(q q) + W(ln) • Fits to anomalous couplings require assumptions here since 5 parameters contribute to WW plus WZ production: Dg1z , Dkz , lz, Dkg , and lg • Assume Dg01z= 0 and let Dko = Dkoz = Dkog and lo= loz= log • The PT of the W(ln ) is found to be the most sensitive distribution since anomalous VV pairs are produced at high PT . • Limits set: - 0.51 < Dk o < + 0.45 - 0.29 < lo< + 0.29 New CDF March 2006

  31. Summary and Outlook

  32. SUMMARY: Comparison of diboson production to SM predictions All rates and kinematic distributions are consistent with SM predictions (table uses nominal SM predictions with no theory uncertainties) Tevatron Run II p p at √s = 1.96 TeV 200-400 pb-1

  33. SUMMARY: Limits on anomalous couplings Analyses just starting on individual channels Need to combine channels and CDF+D0 measurements

  34. SUMMARY: Physics beyond the SM • New physics sources (anomalous couplings, new fermions or gauge bosons) contribute to the high PT tails of W/Z/g production. • At high PT most sources of background (jets faking photons and leptons) fall rapidly. • Therefore the sensitivity to new physics is almost entirely statistics driven. • The Tevatron is ramping up according to its design plan, and the CDF and DØ detectors are operating with good efficiency. • The data sets presented here represent 5-10% of the potential of the Tevatron. • Di-boson channels will be some of the first measurements at the LHC where there is good hope that the SM signals will be badly polluted with new physics!

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