Higgs Searches at the Tevatron

Outline Introduction Standard Model (SM) Higgs Non-SM Higgs Tevatron Standard Model (SM) Higgs Results Low & high mass Combination Non-SM Higgs Prospects & Conclusions (See parallel sessions for full details) [ Thanks to all my Tevatron colleagues ] Gavin Davies – SUSY08

Many thanks to Accelerator Division Tevatron Performance Over 4fb-1 delivered per experiment. Over 0.2fb-1 recorded last month. Expect ~6fb-1 by Apr 2009, and 8fb-1 by Oct 2010. Average data-taking efficiency > 85% Results presented here use up to 2.4fb-1 (3fb-1 results at ICHEP) Many thanks to Accelerator Division 05/02 05/04 05/06 05/08 Gavin Davies – SUSY08

Standard Model Higgs Higgs mechanism Direct searches at LEP2 Additional scalar field in SM Lagrangian  mass to W,Z & fermions Predicts neutral, spin 0 boson But not its mass Direct searches at LEP2 mH > 114.4 GeV Improved mt & mw tighten indirect constraints: mH < 160 GeV (EW fit) mH < 190 GeV if LEP2 limit included  A light (SUSY?) Higgs is favoured Gavin Davies – SUSY08

SM Higgs Production & Decay Small production cross-sections 0.1 -1 pb Branching ratio dictates search mH < 135 GeV gg → H → bb overwhelmed by multijet (QCD) background Associated WH & ZH production with H → bb decay Main backgrounds: W+bb, Z+bb, W/Z jj, top, di-boson, QCD mH > 135 GeV gg → H → WW Main background: WW Excluded Gavin Davies – SUSY08

SM Higgs Topologies Low mass: Intermediate mass: High mass: Leptonic decay of W / Z boson provides ‘handle’ for event. H  bb reduce SM background High PT opposite sign leptons. Missing ET Gavin Davies – SUSY08

SM Higgs - snapshot Higgs searches at a hadron machine challenging Requires Efficient triggering, lepton ID, b-tagging, jet resolution.. Sizeable data-sets Well established Analyses use multivariate techniques Neural net (NN), matrix element (ME).. Regular Tevatron combinations Approaching the SM expectation Rapid improvement well beyond √L gain Even better to come Gavin Davies – SUSY08

Highest associated production cross-section Selection Backgrounds Use electron and muon channels Selection Isolated lepton, missing ET (MET), 2 jets Backgrounds W+jets, QCD, top, di-boson Analyses Separate channels: 1 & 2 b-tags, e or m, central or forward NN (and ME) based analyses using kinematic variables Gavin Davies – SUSY08

Cross section limits derived from NN distributions Compare observed (obs) or expected (exp) limit to SM prediction Recent CDF analysis Including isolated tracks Increases acceptance by 25% mH=115GeV Lum Obs/SM Exp/SM DØ 1.7 fb-1 10.9 8.9 CDF 1.9 fb-1 8.2 7.3 Exp/SM = 6.4 (14% improvement) Gavin Davies – SUSY08

Large cross-section & acceptance but hard Selection Backgrounds Two jets, MET (not aligned in f with jets) Backgrounds Physics: W/Z + jets, di-boson, top – from Monte Carlo Instrumental: Mis-measured MET with QCD jets – from data Analyses Optimised b-tagging, NN or decision tree (DT) discriminant Exp/SM ~8 (both expts.) Gavin Davies – SUSY08

And…. Not forgetting .. ZH → llbb 1 and 2 b-tags, NN event selection Exp/SM ~ 16-20 at 115GeV (1fb-1) Sensitivity of existing channels rapidly improving Add additional channels DØ Exp/SM ~ 45 at 120GeV CDF Exp/SM ~ 40 at 120GeV Exp/SM ~ 25 at 115GeV Adds 10% to CDF combination (≡ 20% more data) Gavin Davies – SUSY08

Intermediate mass range Selection Backgrounds Analyses 2 like-sign high PT leptons (ee, em, mm) Backgrounds WW,WZ, charge flips (from data) Analyses DØ 1fb-1 and CDF 1.9fb-1 Exp /SM ~25 at 140GeV Exp /SM ~20 at 160GeV Gavin Davies – SUSY08

Dominant for mH >135GeV Selection Backgrounds Analyses: 2 isolated, opposite sign leptons, MET Backgrounds Drell-Yan, W+jets/QCD, tt, SM WW Analyses: WW from spin 0 Higgs Leptons prefer to point in same direction Use NN, using kinematic variables and ME as inputs Gavin Davies – SUSY08

Input ME information to NN Matrix element Use observed leptons & missing ET (xobs) Integrate over LO theory predictions for WW, ZZ, W+g, W+jet, Higgs Construct LR discriminant from probabilities Input ME information to NN CDF – 4 ME’s and 6 kinematic variables DØ – 1 ME and more kinematic variables Cross section limit derived from NN output distribution LR (H  WW)  Gavin Davies – SUSY08

Closing in on the SM Expected Limit / SM ~ 2.5 Observed Limit / SM ~ 2.1 Expected Limit / SM ~ 2.5 Observed Limit / SM ~ 1.6 Closing in on the SM Gavin Davies – SUSY08

Combination Compare background and signal plus background hypotheses using Poisson likelihoods Systematics included in likelihoods Combine across channels within an experiment Combine across experiments Since 2005 sensitivity improved by a factor of 1.7 beyond √L gain Obs/SM Exp/SM 115GeV 3.7 3.3 160GeV 1.1 1.6 Gavin Davies – SUSY08

Non-SM Higgs MSSM f → tt and bf → bbb or bf → btt topologies 2 Higgs doublets, ratio of vev’s = tanb 2 charged (H) and 3 neutral Higgs particles: f = h, H, A At large tan b Coupling to d-type fermions enhanced by tanb → s α tan2b sf  2 sA For low & intermediate masses Br (f → bb) ~90%, Br (f → tt) ~10% f b f f → tt and bf → bbb or bf → btt topologies Gavin Davies – SUSY08

Neutral MSSM Higgs  tt Smaller BR but cleaner Signal: (eτhad) (μτhad) (eμ) pairs + MET Background: Z→tt, jet fakes Use visible mass: No significant excess in visible mass, so proceed to set limits Initially on s x Br then interpret in MSSM (FeynHiggs – arXiv:0705.0746v2) arXiv:0805.2491 Gavin Davies – SUSY08

Neutral MSSM Higgs  tt MSSM interpretation Width included Limits very similar for m<0 Expect to reach tanb~20 at low mA by end 2010 Most powerful constraints on tanb Gavin Davies – SUSY08

Neutral MSSM Higgs  bb + b[b] Signal At least 3 b-tagged jets Look for peak in dijet mass Challenge - Large multijet background Estimate from 2 b-tagged data and simulation Composition: Sec. vertex mass (CDF) & fit to multiple b-tagging criteria (DØ) No significant excess, so set limits, initially on s x Br then interpret in MSSM arXiv:0805.3556 Gavin Davies – SUSY08

Neutral MSSM Higgs  bb + b[b] MSSM interpretation Width included Gavin Davies – SUSY08

Going further… Charged Higgs And beyond MSSM Separate t  W+b & t  H+b (H+  cs) via mass templates And beyond MSSM Fermiophobic Higgs Doubly charged Higgs arXiv:0803.1514 arXiv:0805.1534 HR > 127 GeV HL > 150 GeV CDF also looked for e/t final states Gavin Davies – SUSY08

Prospects – SM Higgs Rapid evolution For 2010 expect, beyond √L gain Significantly better than √L Increased trigger efficiency, lepton acceptance, improved b-tagging, NN discriminants For 2010 expect, beyond √L gain x 1.4 improvement at high mass and x 2.0 improvement at low mass mH =160GeV mH =115GeV Gavin Davies – SUSY08

Prospects – SM Higgs (cont) End 2009 Very limited allowed range End 2010 Full exclusion 3 evidence possible over almost entire range Assumes two experiments Gavin Davies – SUSY08

Conclusions New SM analyses keep coming in ICHEP08? Tevatron and CDF/ DØ experiments performing very well Over 4fb-1 delivered, with 8fb-1 expected by end of 2010 New SM analyses keep coming in Sensitivity almost improving linearly with luminosity Well established, common effort across the Collaborations Closing in on the SM 2008 - go beyond at 160GeV ? Have a clear roadmap to reach desired sensitivity Wide range of BSM searches, ready for discovery Expect to reach tanb ~20 at low mA Exciting times ahead – will only get better! ICHEP08? Gavin Davies – SUSY08

And… Thank you for your attention Please see the parallel sessions for full details Search for the SM Higgs Boson at DØ - Suyong Choi Search for Charged Higgs Bosons at DØ - Yvonne Peters Search for Charged Higgs in Top Quark Decays at CDF - Geumbong Yu Search for BSM Higgs Bosons at DØ - Ingo Torchiani Gavin Davies – SUSY08

Backup slides Gavin Davies – SUSY08

CDF and DØ experiments Both detectors extensively upgraded for Run IIa New silicon vertex detector New tracking system Upgraded muon chambers CDF: New plug calorimeter & ToF DØ New solenoid & preshowers Run IIb: New inner tracking layer & L1 trigger Gavin Davies – SUSY08

DØ data taking Gavin Davies – SUSY08

ZH → llbb WH → lnbb H → WW → lvlv Total Gavin Davies – SUSY08

B-tagging Critical for low mass H bb Use lifetime information Improves S/B by > 10 Use lifetime information Correct for MC / data differences Measured at given operating points Analyse separately (“tight”) single & (“loose”) double tags CDF: Secondary vertex reconstruction Neural Net - improves purity Inputs: track multiplicity, pT, vertex decay length, mass, fit Loose = 50% eff, 1.5 % mistag Tight = 40% eff, 0.5 % mistag DØ: Neural Net tagger Secondary vertex & dca based inputs, derived from basic taggers High efficiency, purity Loose = 70% eff, 4.5% mistag Tight = 50% eff, 0.3% mistag Gavin Davies – SUSY08

DØ B-tagging Several mature algorithms used: 3 main categories: - Soft-lepton tagging - Impact Parameter based - Secondary Vertex reconstruction Gavin Davies – SUSY08

B-tagging – (DØ) Certification Have MC / data differences – particularly at a hadron machine Measure performance on data Tag Rate Function (TRF) Parameterized efficiency & fake-rate as function of pT and η Use to correct MC b-tagging rate b and c-efficiencies Measured using a b-enriched data sample Fake-rate Measured using QCD data Gavin Davies – SUSY08

Tau ID CDF: Isolation based Require 1 or 3 tracks, pT > 1GeV in the isolation cone For 3 tracks total charge must be ±1 pThad > 15 (20) GeV for 1 (3) prongs Mhad < 1.8 (2.2) GeV Reject electrons via E/p cut Validated via W/Z measurements Performance Efficiency ~ 40-50% Jet to tau fake rate ~0.001-0.005 DØ: 3 NN’s for each tau type Validated via Z’s Efficiency (NN>0.9): t ~0.65, jets ~0.02 Gavin Davies – SUSY08

Cleanest channel, but low cross section Selection: Backgrounds: Loose lepton ID, 2 jets Backgrounds: Z+jets, top, WZ, ZZ, QCD Analyses Constrain dijet mass NN event selection Exp/SM ~ 16 Gavin Davies – SUSY08

Limit Setting LEP: Low background, small systematics Tevatron/LHC: High background, large systematics Systematics, including correlations, taken into account Main systematics (depending on channel): - Luminosity and normalisation - QCD background estimates - Input background cross-sections - Jet energy scale and b-tagging - Lepton identification - K-factors on W/Z + heavy flavour Systematic uncertainties included in likelihood via gaussian smearing of expectation (‘profile likelihood’) Background constrained by maximising profile likelihood (‘sideband fitting’) Tevatron experiments use LEP CLs (modified frequentist) and Bayesian methods Limit setting approaches agree to within 10% Gavin Davies – SUSY08

Spring 08 SM Combination Channel Lumi /Technique Final state WH→lbb 1.9 + 1.7 fb—1 / NN+NN e/, 1b/2b ZH→ll bb 1.0 + 1.1 fb—1 / NN+NN ZH→ bb 1.7 + 2.1 fb—1 / NN+DT Z→, W→ł (1b/2b) H→ (gg,VBF,WH,ZH) 2.1 + ….. fb-1 / NN . t + 2 jets H→ …... + 2.3 fb-1 / Di- mass  H→WW* 2.4 + 2.3 fb—1 / NN&ME ee, e,  WH→WWW* ….. + 1.1 fb—1 /2D LHood Total of 28 CDF + DØ channels combined Gavin Davies – SUSY08

Spring 08 SM Combination Channel CDF Obs (exp) DØ Obs (exp WH→lbb 8.2 (7.3) 10.9 (8.9) ZH→ll bb 16 (16) 17.8 (20.4) ZH→ bb 8.0 (8.3) 7.5 (8.4) H→ 30.5 (24.8) - H→ ~45 H→WW* 1.6 (2.5) 2.1 (2.4) WH→WWW* 24 (18) Gavin Davies – SUSY08

Spring 08 SM Combination Gavin Davies – SUSY08

MSSM benchmarks Five additional parameters due to radiative correction MSUSY (parameterizes squark, gaugino masses) Xt (related to the trilinear coupling At → stop mixing) M2 (gaugino mass term)  (Higgs mass parameter) Mgluino (comes in via loops) Two common benchmarks Max-mixing - Higgs boson mass mh close to max possible value for a given tan No-mixing - vanishing mixing in stop sector → small mass for h Gavin Davies – SUSY08

Neutral MSSM Higgs  tt Limits: s x Br (f tt) Evolution: Width: Full 2010 dataset (2 expts.) Width: Gavin Davies – SUSY08