Summary of Higgs session: For the Higgs Working group 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.

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

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 non-W QCD false isolated leptons or false missing energy top quark production physics background mistags in W events false b-tags with lepton + MET W + heavy flavor  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.

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

WHlbb searches at Tevatron

ZHbb searches at Tevatron Missing ET b-jet 120o y x 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

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.

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 Mass Window 105GeV [70,120] 115GeV [80,130] 125GeV [90,140] 135GeV [100,150] Data 4 3 2 Acc (%) 0.29  0.07 0.33  0.08 0.35  0.09 0.34  0.09 Total BKG 2.75  0.88 2.19  0.72 1.93  0.66 1.71  0.57 Wjj/Wbb 32%, Zjj/Zbb 31%, Instr. 16%, Top 15%, WZ/ZZ 6%

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)

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

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

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 ?

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

So how do we get there? Start with existing channels, add in ideas CDF Improvement WHlbb ZHbb ZHllbb Mass resolution 1.7 Continuous b-tag (NN) 1.5 Forward b-tag 1.1 Forward leptons 1.3 1.0 1.6 Track-only leptons 1.4 NN Selection 1.75 WH signal in ZH 2.7 Product of above 8.9 13.3 7.2 CDF+DØ combination 2.0 All combined 17.8 26.6 14.4 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

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

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 : IN jet 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

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

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 the H+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

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)