1 / 34

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

aerona
Download Presentation

Di-boson Physics at the Tevatron

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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!

More Related