1 / 19

Summary of Higgs session: Experimental part Ia Iashvili SUNY at Buffalo

TeV4LHC Workshop Fermilab, 22 October 2005. Summary of Higgs session: Experimental part Ia Iashvili SUNY at Buffalo For the Higgs Working group. Outline Tevatron Higgs searches Experience gained

mariko-phillips
Download Presentation

Summary of Higgs session: Experimental part Ia Iashvili SUNY at Buffalo

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. TeV4LHC Workshop Fermilab, 22 October 2005 Summary of Higgs session: Experimental part Ia Iashvili SUNY at Buffalo For the Higgs Working group Outline • Tevatron Higgs searches • Experience gained • What can Tevatron achieve before LHC • Example of Tevatron data being used for testing LHC predictions • Some LHC Higgs studies • Summary and outlook Only selected topics. Contributions at earlier TeV4LHC meetings won’t be covered. These will be documented in the workshop write-up.

  2. Introduction s(pp H + X) [pb] √s = 2 TeV ggH HW Hqq HZ Hbb Htt MH [GeV] H bb H  WW(*) Dominant decay modes • Goal: • Achieve above • Help to achieve this (similar sensitivity in Atlas)

  3. WHlbb searches at Tevatron • WH/ZH, Hbb is best for light Higgs search • At MH=115GeV • ZHnnbb … 15 events/fb-1 • ZHllbb … 2 events/fb-1 • WHlnbb … 14 events/fb–1 • WHlbb:high pT isolated lepton, missing ET and two b-jets Background  Should be estimated entirely from data Strong motivation for measuring top production cross section precisely! Mistagging rate estimated in data Flavor composition from MC (Alpgen) and cross checked in data Each background estimate is a miniature analysis unto itself. Techniques can be spun off to measure other physics processes.

  4. WHlbb searches at Tevatron Checking event kinematics Checking event counts B-tagging performance Check efficiency in data events vs. efficiency in simulation: need scale factor of 0.91±0.06

  5. WHlbb searches at Tevatron

  6. ZHbb searches at Tevatron b-jet Missing ET 120o 110o y x b-jet • Signal has a distinctive topology • Large missing transverse energy • two high pT b-jets • No isolated leptons • Jets are acoplanar • But diffical to trigger – no high-pT lepton in the event • trigger on missing ET and jets • Suffers from large background • “physics” backgrounds W+jets, Z+jets, top, ZZ, and WZ •  Can be estimated from MC • “instrumental” backgrounds QCD multijet events with mismeasurement of jets Estimated from data • Need to find smart variable to separate signal from background

  7. ZHbb searches at Tevatron • Control Region 2– EWK • Require min. 1 lepton • Missing ET and 2nd leading jets are not parallel • Optimized cuts are tested in this region before looking at the real data in the Signal Region • Extended Signal Region (no optimization) • Veto events with leptons • Missing ET and 2nd leading jet are not parallel • Cut optimization is performed in this region based on MC simulation before looking at the data • Control Region 1 – QCD h.f. • Veto events with identified leptons • Missing ET and 2nd leading jet are parallel • For the 120 GeV Higgs mass in ±20 GeV mass window around the expected reconstructed peak value (Dijet mass resolution is ~17 %): • SM background prediction: 4.36  1.02 events • QCD (11.4%), Top (20.5%), EWK (18.2%), Light flavor mistag(50%) • Observed: 6 events.

  8. ZHbb searches at Tevatron Instrumental bkgd from sidebands sideband signal sideband • Asym = (ET-HT)/(ET+HT) • Rtrk = |PTtrk-PT,2trk|/PTtrk Physics bkgd from MC Wjj/Wbb 32%, Zjj/Zbb 31%, Instr. 16%, Top 15%, WZ/ZZ 6%

  9. HW+W-ll searches at Tevatron • Two high pT isolated lepton and large missing ET and no hard jets • Clean and easily triggerable signature • Sensitive to tau channels with leptonic decay • One of the most promissing channels at LHC as well • Backgrounds: • WW, WZ, ZZ, DY, ttbar estimated from PYTHIA and normalized NLO cross section calculations. • W+jets(jete/m) estimated (at least partially) from data • multijets events estimated from data Efficiencies: • Lepton triggering, reconstruction and identification efficiencies all have to be determined in data and factorized in MC for signal rate estimation • Precise estimation is importrant since no “bump” can be observed from Higgs WW production is the dominant backgroundcompulsory to first measure the WW production cross-section (W+W-)=13.8 +4.3(stat)+1.2 (sys)±0.9(lumi) pb -3.8 -0.9 [PRL 94, 151801 (2005)] (DØ) (W+W-)=14.6 +5.8(stat)+1.8 (sys)±0.9(lumi) pb -5.1 -3.0 [PRL 94, 211801 (2005)] (CDF) Consistent with thepry prediction of12-13.5 pb (J.Ohnemus, J.M. Campbell, R.K.Ellis)

  10. HW+W-ll searches at Tevatron W+  e+  e- W- Exploit spin correlations • Leptons tend to be parallel -- small (ℓ, ℓ) • Neutrinos go parallel -- typically larger missing energy than WW • Small di-lepton invariant mass

  11. Tevatron SM Higgs Sensitivity: expectations two years ago Prospects updated in 2003 in the low Higgs mass region W(Z) H ln(nn,ll) bb  better detector understanding  optimization of analysis Sensitivity in the mass region above LEP limit (114.4 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  understanding detectors better, optimizing analysis techniques  measuring SM backgrounds (Zb, WW, Wbb) Placing first Higgs limits which can be compared to the prospects

  12. Sensitivity with existing Tevatron analyses Cross-Section times branching fraction limit as a multiple of the SM rate CDF DØ Work in progress Work in progress the “kink” at around 140 GeV goes away We should be around 6 at low masses, not around 12-20 with the current lumi (0.3 fb-1). Where can we gain ?

  13. So how do we get there? DØ • Step 1 (for early 2006) • WH/ZH: • Optimize b-tagging (Looser) • Combine single and double tag • S/sqrt(B) is 40-50% in single tag compared to double tag. Equivalent to 20% more lumi than double tag alone. • WH(e): include Phi-cracks • WH(): combine single- and +jets trigger • ZH : optimize Selection • Step 2 • WH/ZH: • include WHWWW and Z l+l- channel ! (*1.3) • use Neural Net Tagger (*1.34*1.34) • use Neural Net Selection (*1.8) • use TrackCalJets mass resolution (*1.3) • WH(e): include End-Cap calorimeter • WH(): improve QCD rejection  loosen b-tag • WH : include W   (*1.4) All these improvements will bring us to the expected level of sensitivity

  14. So how do we get there? CDF • Start with existing channels, add in ideas • with latest knowledge • of how well they work. Expect a factor of ~10 luminosity improvement per channel, and a factor of 2 from CDF+DØ Combination

  15. Expected Signal Significance CDF+DØ vs Luminosity Work in progress Work in progress per experiment per experiment mH=115 GeV assumed

  16. Improving Jet Energy Resolution Using Tracks • Idea • Reconstruct calorimeter-based jets (0.5 cone) • Use track momentum measurements to set an accurate scale for hadron response for each hadron in the jet. • Proposed in CMS • CMS Note 2004/015, O.Kodolova et al. “Jet energy correction with charged particle tracks in CMS” • Tevatron provides an excellent opportunity to test and optimize this technique on real collider data. Propagate tracks to the calorimeter surface. dca(xy) < 0.5cm, dca(z) < 1.0 cm. Classify tracks: DR(vtx)<0.5, DR(cal)<0.5 : INjet DR(vtx)<0.5, DR(cal)>0.5 : Out-of-cone For each IN-jet track: Etrkjet=Ecaljet +(1-F)Etrk For each Out-of-cone track: Etrkjet=Ecaljet +Etrk where F is a single pion calorimeter response Out-Jet In-Jet

  17. Improving Jet Energy Resolution Using Tracks 12% improvement in mass resolution. 12%  20% by optimization of the TrackCalJet algorithm Performance in Zbbbar MC events 10-20% jet resolution improvement in data at 40 GeV. Higher improvement at lower pT. In CMS MC studies: ~40% improvement at the same energies Performance in +jet data events

  18. QCD Higher Order Corrections in H + 1jet at the LHC • Low mass Higgs searches with H in association with high PT jets are crucial at the LHC • NLO QCD corrections for VBF signal and Z+jets in H+2jet analysis have been considered in the past • QCD Higher order corrections have not been evaluated within theH+1jet analysis neither for signal nor for the Z+jets background • NLO corrections are evaluated here with MCFM • Also address the impact of Z+2-3jet tree level ME on Z+jets using ALPGEN/SHERPA • QCD HO corrections are large in the region of the phase space where the signal-to-background is optimal for searches • QCD Z+1j is enhanced by a factor of 2 • Signal, H+1j is enhanced by a factor 1.75 • Need to re-optimize the analysis • Signal significance does not decrease Tag jet Not Tagged Large PTH & MHJ Tag jet

  19. Summary and outlook • Much has been learned from Tevatron Higgs searches on various challenges and issues faced at hadron collider environment • We have also learned how important current experience is • to actually achieve expected performance • Tevatron will provide important information on Higgs sector before LHC. For low mass Higgs searched Tevatron is complementary to LHC. • We are able to test LHC predictions using Tevatron data and provide important feadback • The plan is to document our experience and findings in the Workshop proceeding (beginning of next year)

More Related