1 / 26

Tev4LHC@CERN, April 2005, Gregorio Bernardi, Paris/FNAL CDF and D Ø Collaborations Results

Results on Higgs Searches @Tevatron. Tevatron/ Luminosity b-tagging SM Higgs Searches Summary. Tev4LHC@CERN, April 2005, Gregorio Bernardi, Paris/FNAL CDF and D Ø Collaborations Results. Tevatron Run II Performance. Design for 2005. Base for 2005. 2005 : so far along Design. 2004.

keane-garrison
Download Presentation

Tev4LHC@CERN, April 2005, Gregorio Bernardi, Paris/FNAL CDF and D Ø Collaborations Results

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. Results on Higgs Searches @Tevatron Tevatron/ Luminosity b-tagging SM Higgs Searches Summary Tev4LHC@CERN, April 2005, Gregorio Bernardi, Paris/FNAL CDF and DØ Collaborations Results

  2. Tevatron Run II Performance Design for 2005 Base for 2005 2005 : so far along Design 2004 2003 2002 1.1032 cm-2sec-1 0.9 fb-1 Peak luminosity is above 1.2.1032 cm-2sec-1 Total ~0.9 fb-1 delivered in Run II 2004 : above Design !

  3. Tevatron Long Term Luminosity Plan Currently expecting delivered luminosity to each experiment  4 - 8 fb-1 by the end of 2009 Increase in number of antiprotons  key for higher luminosity Expected peak luminosity  3.1032 cm-2sec-1 by 2007 Today

  4. SM Higgs Production and Decays Decays Production Excluded mH (GeV/c2) Production cross section  in the 1.0-0.2 pb range for gg  H  in the 0.2-0.03 pb range for associated vector boson production Dominant Decays  bb for MH < 135 GeV  WW* for MH > 135 GeV Search strategy: MH <135 GeV associated production WH and ZH with Hbb decay Backgrounds: top, Wbb, Zbb… MH >135 GeV gg H production with decay to WW* Backgrounds: electroweak WW production…

  5. Experimental Limits on Higgs Mass • direct searches at LEP MH >114 GeV at 95% C.L. • precision EW fits (winter 2005) MH= 126+73-48 GeV MH  280 GeV @ 95% C.L.  Light Higgs favored LEP Tevatron provides: Precision measurements of mtop& Mw and Direct searches:  SM Higgs  non-SM Higgs

  6. Tevatron SM Higgs Search: Outlook Ldt (fb-1) Prospects updated in 2003 in the low Higgs mass region W(Z) H ln(nn,ll) bb  better detector understanding  optimization of analysis Tevatron8 fb-1 LEP Excluded • Sensitivity in the mass region above LEP limit (114 GeV ) starts at ~2 fb-1 • With 8 fb-1: exclusion 115-135 GeV & 145-180 GeV, • 5 - 3 sigma discovery/evidence @ 115 – 130 GeV • Meanwhile •  optimizing analysis techniques, understanding detectors better • measuring SM backgrounds (Zb, Wbb, WW) • Placing first Higgs limits which can be compared to the prospects

  7. SM “Heavy” Higgs: H  WW*  lnln e+ n W+ n W- e- Search strategy:  2 high Pt leptons and missing Et  WW comes from spin 0 Higgs: leptons prefer to point in the same direction H Main Background: WW Production Good agreement with NLO theory: 12.0-13.5 pb Now Measured at the Tevatron by both Experiments Ohnemus, Campbell, R.K.Ellis DØ: PRL/ hep-ex/0410062

  8. Data Selection: two isolated leptons with opposite charges with pT > 20 GeV, >25 GeV, ( , l or j) , veto on jets, light (<MH/2) invariant dilepton mass Search for H  WW* Search in 3 channels: HWW*ll with l = ee,,einclusive high pT lepton triggers: integrated luminosity 184 pb-1 (CDF), 147-177 pb-1(D0) 95% CL for the 3 channels s*BR(H→WW) < 5.7pb For MH=160 GeV D: Obs: 9 evts; Bkgnd:11.1  3.2 Signal: 0.27  0.004(mH=160 GeV) *BR(H→WW)< 5.6pb For MH=160 GeV CDF: Obs: 8 evts; Bkgnd: 8.9  1 Signal: 0.17  0.02(mH=180 GeV) Maximum likelihood limit from the ll distributions

  9. Search for WH  WWW* Search of high-pT isolated like-sign (LS) dilepton events in 193.5 pb-1 data. leading lepton pT,1 > 20 GeV,2nd lepton pT2 > 16 GeV, pT12=|vect.sum of 1,2| > 35 GeV. Search in the (pT,2,pT,12) plane: - 0 events found - total exp. Backgnd: 0.95 +- 0.61(stat) +- 0.18(syst) - bosophilic Higgs (110 GeV)exp. to be about 0.06 evts . (assuming same production x-section as SM Higgs) - SM Higgs (160 GeV) expected to be about 0.03 evts.

  10. Also difficult at LHC (combination of several channels) At Tevatron need to fully exploit associated productions: WH and Z (l+l- or ) H with H  bbb-tagging Understand intrumental and SM backgrounds W,Z+heavy flavor are backgrounds to leptonic WH,ZH instrumental background (QCD) is difficult for  H Here after, b-tagging, WH, ZH and SM Higgs prospects Low Mass (<135 GeV) Higgs Search

  11. Tagging b-quarks (B-hadrons) • Top, Higgs have b-quark jets •  contains a B hadron • Has finite life time • Travels some distance from the vertex before decaying • ~ 1mm • With charm cascade decay, about 4.2 charged tracks •  can have leptons from B meson Vertex Tagging a B (transverse plane) B (Signed) Track Impact Parameter (dca) Decay Lengh (Lxy) Hard Scatter Several algorithms under development/improvement: 3 main categories: - Soft-lepton tagging - Impact Parameter based - Secondary Vertex reconstruction Impact Parameter Resolution tt l+jets ~ 56% Single Top ~ 52% Wbb ~ 52% Wj ~ 0.3% Decay Length Resolution

  12. 3 views of a high dijet mass (220 GeV) Wbb (WH) candidate ETmiss Vertex view of a low mass candidate Clean Events! Mass Reconstruction? ETmiss b-tags dijet mass (48 GeV) electron ETmiss

  13. Search for Wbb/WH Production 162pb-1 sample with one electron or muon and (single-tag search) Electron or muon: pT > 20 GeV/c Missing ET > 20 GeV 2 Jets: pT > 15 GeV/c, ||<2.0 Total systematic error ~ 11% 2540 evts before tagging No significant peak from Higgs W+2jets, 1b-tag 62 evts (66.5  9 expected)

  14. Search for Wbb/WH Production 174pb-1 sample e + 2 jets and Wbb dominant backgd for WH Compared to ALPGEN,PYTHIA showering, and full detector simulation. Normalized to NLO x-section (MCFM for W+jets) Electron: pT > 20 GeV, ||<1.1 Missing ET > 25 GeV 2 Jets: pT > 20 GeV/c, ||<2.5 2540 evts (2580  630 expected)  1 tag: 76 evts (72.6  20 exp.) Data well described by simulation Total experimentalsyst. Error ~15 %

  15. Wbb / WH Search For 115 GeV Higgs, in a +-25 GeV mass window: 0 data, 0.05 exp Higgs, 1.07 bckgd 95% CL upper limit on WH production of 9.0 - 12.2 pb for Higgs masses of 105-135GeV Published Run II limit better than Run I  detector improvements 6 evts (4.4  1.17 expected) 95% CL upper limit of 6.6 pb on production for b with pTb > 20 GeV and >0.75 published (PRL) - hep-ex/0410062

  16. Comparison of WH Results with Prospective Study We are currently missing a factor 2.4 in sensitivity Prospective Study assumed: Larger ECAL coverage (+30%), improved em-id (+40%), extended b-tag efficiency (+50%, 2 tags) and 30% less backgd (better dijet mass resolution)  Factor 2 in S/B  2.4/ 2 = 1.2 difference (only) in sensitivity Apply Advanced techniques Missing Factors can be recovered

  17. SM Higgs Status/Prospects • Future improvements: • Extend b-tagging acceptance • Improve efficiencies • - Use Additional kinematic variables • Better Mbb resolution • Add Zbb channels

  18. ZHnnbb searches n Z Z n b H b ET Jet1 Jet2 • Missing ET from Znn and 2 b jets from Hbb • Large missing ET > 25 GeV • 2 acoplanar b-jets with ET > 20 GeV, |h| < 2.5 • Backgrounds • “physics” • W+jets, Z+jets, top, ZZ and WZ • “instrumental” • QCD multijet events with mismeasured jets • Huge cross section & small acceptance • Strategy • Trigger on events with large missing HT • HT defined as a vector sum of jets’ ET • Estimate “instrumental” background from data • Search for an event excess in di-b-jet mass distribution

  19. More selection variables ET HT PTtrk PT.2trk Jet1 Jet2 • Suppress “physics” background • In addition to missing ET > 25 GeV and two jets with ET > 20 GeV • Veto evts. with isolated tracks  reject leptons from W/Z • HT = S|pT(jets)| < 200 GeV  for tt rejection • Reduce “instrumental” background • Jet acoplanarity Df(dijet) < 165 • Various missing energy/momentum variables • ET calculated using calorimeter cells • HT = – |SpT(jet)| … jets • PTtrk = – |SpT(trk)| … tracks • PT,2trk = – |SpT(trk in dijet)| … tracks in jets • Form various asymmetries • Asym(ET,HT) = (ET – HT)/(ET+HT) • Rtrk = |PTtrk – PT,2trk|/PTtrk  In signal like events they all peak at ~ 0 and are aligned signal sideband sideband Data

  20. Cross Check on W+jets • Cross-checked variables used by selections, using W+jetsmn+jets • Same data sets without isolated track veto • Very small instrumental backgrounds • If ignore muon, the final state is ET + jets  same as ZHnnbb • Muon pT is removed from ET, PTtrk calculations Variables are well modeled by simulation, indeed peak at 0 !!

  21. Instrumental background estimation Instrumental background from MC sideband signal sideband uniform, no peak Physics background from MC Instrumental background from sideband (data) Physics … 1579 from fit 1600 from MC Instrumental … 524 from fit Double Gaussian Exponential

  22. Distributions of ET + 2 jets (with-w/o tagging) Before Tagging Data : 2140 Expect : 2125 1 b-tag Data : 132 Expect : 145

  23. Distributions after double b-tagging 2 b-tags Data : 9 Expect : 6.4 Dijet Mass Window @ 115 GeV Data : 3 Expect : 2.2

  24. First Run II Results for ZH  bb (261 pb-1) Systematic Uncertainty

  25. Run I Combination / Sensitivities Expected “sensitivity” similar for WH and ZH channels (@ mH=110 GeV limit of11 pb for 106 pb-1 e+mu, SingleTag+DoubleTag) Combination of all channels allows to go from 19 pbin a single channel (WH-DT) down to 6 pb Run II vs Run I:expected limit 12 pb@ D0-RunII for WH-DTinstead of 19 pb @CDF-Run I, withequivalent lumi(174 pb-1 e-chan. vs. 106 pb-1 e+mu-chan.) - For WH-ST, expected limit 8 pb @ CDF-Run II vs. 15 pb @ CDF-Run I PROGRESS PRL - hep-ex/0503039

  26. Summary No deviations from SM observed (yet) • Higgs search is in progress: • For the SM Higgs • Most of the channels (WH, ZH, single/double tag) have already been studied with Run II data  no showstoppers, but we have to keep improving efficiencies. •  sensitivity (mH >114 GeV) starts at ~2 fb-1 ( 2007 ) •  Expect exclusion or evidence for a low mass Higgs when LHC produces its first results For non SM Higgs sensitivity could be higher, see A. Haas talk Expect soon substantial improvements in Higgs hunting with ~0.8 fb-1 already on tape …..and with ~8 fb-1 expected in Run II

More Related