HIGGS BOSON SEARCHES AT THE TEVATRON Bárbara Álvarez González On behalf of the CDF and D0 Collaborations LISHEP 2009, Rio de Janeiro, January 19th

V (Φ) = μ2Φ†Φ + λ(Φ†Φ)2 ; μ2<0 λ>0 OUTLINE Fermilab and Tevatron: Introduction. CDF and D0 Detectors. Standard Model (SM) Higgs. SM Analyses Results. Beyond Standard Model. Beyond SM Analyses Results. Conclusions. “MEXICAN HAT” The potential energy of the higgs field has a mexican hat shape. V (Φ) = μ2Φ†Φ + λ(Φ†Φ)2 ; μ2<0 λ>0 Bárbara Álvarez- U. de Oviedo

p p FERMILAB TEVATRON particle accelerator and collider. Chicago CDF D0 TEVATRON MAIN INJECTOR Fermilab is home to the Tevatron, the world's highest-energy particle accelerator and collider. proton-antiproton collisions at √s = 1.96 TeV. Tevatron is performing really well: 6-8 fb-1 expected by the end of 2009. At a center of mass energy of 1.96 GeV p p Bárbara Álvarez- U. de Oviedo

LUMINOSITY AND DATA TAKING Total delivered = 5.5 fb-1 PER EXPERIMENT Total Acquired = 4.58 fb-1 DELIVERED The best initial luminosity: 3.61×1032 cm-2 s-1 ACQUIRED Data Taking Average Efficiency ~82% Bárbara Álvarez- U. de Oviedo

DETECTORS AT FERMILAB Data analyses with 2 multipurpose detectors, CDF and D0: Silicon vertex detectors for b-tagging. Charged particle tracker in magnetic field. EM+HAD calorimeter for e,mu id. Muon detectors for muon id. Bárbara Álvarez- U. de Oviedo

HIGGS BOSON The search for the Higgs boson is one of the most active areas of research at the Tevatron. The Higgs boson is the only SM particle that has not been observed. It requires an exceptionally large amount of energy and beam luminosity to create and observe at high energy colliders due to small cross sections and large backgrounds. Higgs boson is the remaining particle of the SM. It needs a large amount of energy and luminosity to be observed and create. LHC is going to double the Tevatron center of mass energy. One of the LHC goals is to discover the higgs boson. Only ~40 Higgs events are expected to be produced per fb-1 at each experiment in detectable channels Bárbara Álvarez- U. de Oviedo

Indirect EWK constraints: mH < 154 GeV/c2 In the standard model (SM), the Higgs boson is crucial to the understanding of electroweak symmetry breaking and the mass generation of electroweak gauge bosons and fermions. Higher order diagrams involving Higgs Bosons enter as corrections to SM predictions for EWK processes Direct searches at LEP: mH > 114.4 GeV/c2 at 95% C.L. Indirect EWK constraints: mH < 154 GeV/c2 The figure on the left shows the Delta-chi2 curve derived from high-Q2 precision electroweak measurements, performed at LEP and by SLD, CDF, and D0, as a function of the Higgs-boson mass, assuming the Standard Model to be the correct theory of nature. The preferred value for its mass, corresponding to the minimum of the curve, is at 84 GeV, with an experimental uncertainty of +34 and -26 GeV (at 68 percent confidence level derived from Delta chi2 = 1 for the black line, thus not taking the theoretical uncertainty shown as the blue band into account). This result is only little affected by the low-Q2 results such as the NuTeV measurement discussed above. While this is not a proof that the Standard-Model Higgs boson actually exists, it does serve as a guideline in what mass range to look for it. The precision electroweak measurements tell us that the mass of the Standard-Model Higgs boson is lower than about 154 GeV (one-sided 95 percent confidence level upper limit derived from Delta chi2 = 2.7 for the blue band, thus including both the experimental and the theoretical uncertainty). This limit increases to 185 GeV when including the LEP-2 direct search limit of 114 GeV shown in yellow (see below). Bárbara Álvarez- U. de Oviedo

SM HIGGS CROSS SECTIONS AND BR High mass Higgs region (mH>135 GeV/c2): H → WW dominant decay. Gluon fusion production search (gg → H). Low mass Higgs region (mH<135 GeV/c2): H → bb dominant decay. Search for associated W/Z production. We divide the searches in low and high mass region. Low mass is with mh<135 Gev and associated production with Z/W, high mass mh>135GeV and decay to WW. Bárbara Álvarez- U. de Oviedo

ANALYSIS STRUCTURE RESULTS B K G E S T I M A O N DATA & MC SAMPLES EVENT SELECTION SYSTEMATIC UNCERTAINTIES MULTIVARIATE TECHNIQUES Neural Networks (NN) 2 1012 Matrix Element (ME) Boosted Decision Trees (BDT) 109 RESULTS Data and MC samples: we take the samples needed for each analysis. Event selection: we select the events depending on the final state that we are looking for. Bkg estimation: requires really hard work to remove all the event that are background and contanimate our signal and understand all the main bkgs. Because we have really small signal compare with the huge bkgs, we can not use counting experiments, we apply multivariate techquines as ME, BDT, NN... to distinguish signal from bkg. We study all significant systematics and … Results: observing no significant excess in the data we place 95 % c.l. Upper limits. 2 105 2 104 THE CHALLENGE IS TO DISTINGUISH A SMALL SIGNAL FROM ALL THE HUGE BACKGROUNDS 2 102 102 1 Bárbara Álvarez- U. de Oviedo

ANALYSIS TOOLS Multiple b-quark tagging algorithms: SecVtx algorithm Multiple b-quark tagging algorithms: DØ: NN tagger based on b-lifetime information, with multiple operating points. CDF: Secondary Vertex and Jet Probability algorithms. Additional NN flavor separators. Maximize lepton acceptance: Separate into different lepton categories based on S/B. Bárbara Álvarez- U. de Oviedo

/ μ WH → lvbb Low Mass Dedicated trigger: High pT leptons, and MET+jets. Same selection. Same background treatment. Different analysis techniques In CDF, 2 WH analysis are performed ME + BDT NN These two results are combined to have the final WH → lvbb limit (next page). ME+BDT Neural Network One analysis uses the BDT techquine with ME variables as input in the BDT. The other uses NN with 6 studied input variables. Then we combine all this, after the job of matching the event selection, in a new result Into a new NN callled NEAT... Bárbara Álvarez- U. de Oviedo

Parton Distribution Functions lepton and jet 4-vectors Transfer Function EVENT PROBABILITY DENSITIES: P(pl,pj1,pj2) = 1/σ ∫ dρj1dρj2dpν ∑Φ4|M(pi)2| f(q1)f(q2)/|q1||q2| Wjet (Ejet,Epart) Parton Distribution Functions Phase Space Factor Matrix Elements Inputs: lepton and jet 4-vectors – no other information needed! Backgrounds peak to zero and signal peaks higher Single tag region WHx25 Event Probablity Discriminant (EPD) = Ps / Ps + Pbkg Bárbara Álvarez- U. de Oviedo

WH → lvbb Low Mass For Higgs searches, the most sensitive This is the most sensitive production channel at the Tevatron for a mH < ~135 GeV/c2 Low Mass Analysis Lumi (fb-1) Exp. / SM Obs. / SM D0 (115 GeV/c2) 1.7 8.9 10.9 CDF (115 GeV/c2) 2.7 4.8 5.6 Combine ME+BDT & NN Selected using a Neural Network For Higgs searches, the most sensitive production channel at the Tevatron for a mH below ~ 135 GeV/c2 is the associated production of a Higgs boson with a W boson. Neuro-Evolution of Augmenting Topologies Bárbara Álvarez- U. de Oviedo

ZH → lvbb Event Selection: 2 high pT Main Background: Analysis Lumi (fb-1) Exp. / SM Obs. / SM D0, NN & BDT(115 GeV/c2) 2.3 12.3 11.0 CDF, NN (115 GeV/c2) 2.7 9.9 7.1 CDF, ME (120 GeV/c2) 2.0 15.0 14.2 ZH → lvbb Low Mass Event Selection: 2 high pT leptons (ee/μμ) and b-jets. Main Background: Z+jets. Analysis techniques: D0: NN and BDT discriminants. CDF: 2D NN analysis: improved dijet mass resolution with METprojection technique. New ME analysis. Double tag CDF, to maximize signal acceptance we relax the lepton and b jet requirements. To maintain signal efficiency and improve signal discrimination, we employ an additional neural network trained to discriminate event kinematics of $ZH$ compared to the main $Z + jets$ background and the kinematically different $t\bar{t}$ background Bárbara Álvarez- U. de Oviedo

VH → ννbb MET + JETS Low Mass Main background: QCD multijet processes. SIGNATURE MET Main background: QCD multijet processes. In CDF, a data-driven model for QCD background removal is used. Other backgrounds: top, single top, dibosons, W+jets, Z+jets... + Low Mass JETS 3 orthogonal tag categories and 3 jet bin. D0 analysis has a very close sensitive. The scenario is a Higgs production associated with a W/Z boson. H decays to bbbar and W/Z to 2 neutrinos, when the lepton from the W scapes to detection or is reconstracted as a jet. The signature is met+jets. Because for this version of the analysis the jet cuts where relaxed, the main bkg is QCD multijet processes, there is a data-drive QCD model build, NN to remove the not signal like events. An additinal NN is used to discriminate the Higgs signal from the remaining bkg. Both experiments have similar sensitivities. For a Higgs mass of 115 GeV/c2 EXP. Lumi (fb-1) Exp. / SM Obs. / SM D0 2.1 7.0 5.7 CDF 5.6 6.9 Bárbara Álvarez- U. de Oviedo

Most sensitive Higgs search at the Tevatron gg → H → WW(*) → ll'νν (l,l'=e,mu) Most sensitive Higgs search at the Tevatron High Mass Signature: 2 high pT leptons + MET. Leptons in same directions due to spin correlation. Different background composition: WW, Drell-Yan, tt... / μ+ Final states: e+e-, eμ, or μ+μ- and 2 ν. / μ- W´s decay leptonically. There are several production mechanisms besides gluon fusion: WH → WWW, ZH → WWW, V.B.F H → WW New dedicated analyses in different 0, 1, 2 jet bins. Analyses optimized for each jet bin. Both experiments approaching SM sensitivity Bárbara Álvarez- U. de Oviedo

gg → H → WW(*) → ll'νν (l,l'=e,mu) CDF, H → WW, 0 jets Process # of events ttbar 0.96 ± 0.19 Drell-Yan 66.88 ± 15.20 WW 280.42 ± 38.99 WZ 12.17 ± 1.93 ZZ 17.29 ± 2.74 W+jets 83.61 ± 20.09 Wγ 79.15 ± 21.12 Total bkg 540.48 ± 64.81 gg → H 8.38 ± 1.29 Total Signal Data 552 ΔΦ between the leptons is the most discriminating variable for the 0 jet bin. WW background distinguish by the spin correlation of the leptons. CDF, H → WW, 0, 1, ≥2 jets Bárbara Álvarez- U. de Oviedo

H → WW(*) → ll'νν, ∫ L = 3.0 fb-1 High Mass EXPERIMENT EXP. Limit/SM CDF Search for Higgs to WW* Production using a Combined Matrix Element and NN Technique NN is used in each of the three di-lepton channels High Mass EXPERIMENT EXP. Limit/SM mH=165 GeV/c2 OBS. Limit/SM 1.9 2.0 1.6 1.7 Bárbara Álvarez- U. de Oviedo

ADDITIONAL CHANNELS Four signal processes considered: Many other SM Higgs searches, not as sensitive but contribute in combination. Analysis Lumi (fb-1) Exp. / SM Obs. / SM D0, ttH → lvbbbbqq 2.1 45.3 63.9 D0, H → γγ 2.7 23.2 30.8 CDF, H → ττ 2.0 24.8 30.5 Signature: 1 lepton + MET + 4 jets. 12 channels (4, ≥5 jets) x (1, 2, ≥3 b-tags). Scalar sum of jets (HT ) to extract signal. Four signal processes considered: W(→ qq') H(→ τ+τ-) Z(→ qq) H(→ τ+τ-) VBF qHq'→ q' τ+τ-q gg → H → τ+τ- Bárbara Álvarez- U. de Oviedo

INDIVIDUAL EXPERIMENTS COMBINATION 100 < mH < 200 GeV/c2 Contributing production processes: Associated production (W/Z). Gluon fusion. Vector boson fusion. Analyses are conducted with integrated luminosities from 1.1 to 3.0 fb-1 EXPERIMENT EXP.(OBS)/SM mH=115 GeV/c2 mH=165 GeV/c2 D0 4.6 (5.3) 1.9 (2.0) CDF 3.1 (3.7) 1.6 (1.8) Bayesian and modied frequentist approaches used We have calculated combined upper limits on the ratio of Higgs boson cross section times the branching ratio to its Standard Model prediction(R95) for Higgs boson masses between 100 and 200 Bárbara Álvarez- U. de Oviedo

Tevatron Run II Preliminary, L= 3fb-1 SM TEVATRON HIGH MASS COMBINATION Tevatron Run II Preliminary, L= 3fb-1 Combine results from CDF and D0 searches for SM Higgs boson. Systematics and their correlation between channels and experiments taken into account. Results presented at ICHEP 2008, Philadelphia Tevatron high mass combination: We exclude at 95% C.L. the production of a SM Higgs boson of 170 GeV/c2. First direct exclusion since LEP! We combine results from CDF and DO searches for a standard model Higgs boson in ppbar collisions at the Fermilab Tevatron, at sqrt{s}=1.96 TeV. With 3.0 fb-1 of data analyzed at CDF, and at DO, the 95% C.L. upper limits on Higgs boson production are a factor of 1.2, 1.0 and 1.3 higher than the SM cross section for a Higgs boson mass of m_{H}=$165, 170 and 175 GeV, respectively. We exclude at 95% C.L. a standard model Higgs boson of m_H=170 GeV. Based on simulation, the ratios of the corresponding median expected upper limit to the Standard Model cross section are 1.2, 1.4 and 1.7. Compared to the previous Higgs Tevatron combination, more data and refined analysis techniques have been used. These results extend significantly the individual limits of each experiment and provide new knowledge on the mass of the standard model Higgs boson beyond the LEP direct searches. RESULT 3 fb-1 EXP.(OBS.)/SM mH=165 GeV/c2 D0 + CDF 1.2 (1.2) Bárbara Álvarez- U. de Oviedo

We are sensitive to a Higgs The low mass region is challenging, but in the next Tevatron combination the expected limit should fall below: ~3 x SM for mH = 115 GeV/c2 Achieved & Projected There is still room for improvements: Increase in acceptance. Sophisticated analysis tools. B-tagging. jet/MET resolutions. The top of the yellow band corresponds to the Summer 2007 performance expected limit divided by 1.5, and the bottom of the yellow band corresponds to the Summer 2007 performance expected limit divided by 2.25. This plot is shown for mH=115 GeV/c2 Achieved and projected median expected upper limits on the SM Higgs boson cross section, by date. We are sensitive to a Higgs of 160 GeV/c2 Bárbara Álvarez- U. de Oviedo

"Beyond the Standard Model" The Minimal Supersymmetric Standard Model (MSSM) is the minimal extension to the SM that realizes supersymmetry. In the MSSM, 5 Higgs bosons remain after EW symmetry breaking: 3 neutral: h, H, and A - denoted as Φ. 2 charged: H±. MSSM MSSM processes (next pages): bΦ → bbb bΦ → bττ Φ → ττ In physics, the Standard Model of particle physics is currently the best description of all experimental data.[1] Nevertheless, there are reasons to believe that there are phenomena that are not accurately described by this theory and "Beyond the Standard Model" physics studies possible extensions to the Standard Model that will be probed in up-coming experiments. At tree level the Higgs sector can be parameterized by tan β, the ratio of the two Higgs doublet vacuum expectation values, and mA, the mass of the pseudo-scalar Higgs boson A. Bárbara Álvarez- U. de Oviedo

MSSM bΦ → bbb (multi-b-jets) This process could be observable in supersymmetric models with high values of tanβ. Event signature: at least 3 b-jets. Data required (trigger): 2 central clusters with ET>15 GeV, the third jet ET>10 GeV. Offline: three jets with ET>20 GeV, |η| < 2. This final state suffers from a large multijet background. The dijet mass of the 2 leading jets in the events (m12) used , in triple tag events, to separate Higgs signal from background events. RESULTS The production rate of light Higgs bosons in association with b-quarks can be significantly enhanced in supersymmetric extensions of the standard model. This occurs for large values of tan , the ratio of the Higgs coupling to down-type versus up-type quarks In this analysis we search for Higgs decays into b¯b, accompanied by an additional highpT b, giving an event signature of at least three b-jets. We study the dijet mass spectrum of the two leading jets in three-jet events with all three jets identified as b-jet candidates using a displaced vertex algorithm EXP. LUMI EXP. (OBS.) pb mH = 90GeV/c2 mH= 200GeV/c2 CDF 1.9 fb-1 77 (57) 6.1 (4.1) D0 1.6 fb-1 149 (201) 7.7 (6.2) Bárbara Álvarez- U. de Oviedo

MSSM Φ (=H; h;A)+b → b τ τ Φ (=H; h;A) → τ+ τ- Search requires the tau pairs to decay into τeτhad, τμτhad, or τeτμ Backgrounds: W+jets Top Z → τ+ τ- Others... Φ (=H; h;A)+b → b τ τ The final state includes a μ candidate, a τhadronic candidate, and a jet tagged as a b-quark jet. bΦ → bbb (multi-b-jets) 95% CL exclusion limit in the (mA; tan β) plane obtained with the current analysis for the mhmax , μ=-200 GeV scenario. The exclusion limit obtained from the LEP experiments is also shown. The bττ channel offers a much cleaner final state than the bbb channel, giving the two channels similar sensitivities. Exclusion limits are set at the 95% C.L. for several supersymmetric scenarios. Bárbara Álvarez- U. de Oviedo

H → γγ WH → WWW FERMIOPHOBIC HIGGS Photon energy resolution better than jets. Look for peak in di-photon mass. SM-like search but branching ratio is enhanced in fermiophobic model. WH → WWW Look for same-sign leptons. Also sensitive to SM at high mass. At low mass more sensitive if H is fermiophobic. The mass resolution of the diphoton channel is extremely good compared to dijet decay modes. Limits are set on the production cross section and branching fraction using a Bayesian binned likelihood approach. The fermiophobic Higgs boson has no coupling to the fermions. Existence of the fermiophobic Higgs could be an indication that the origin of particle mass would be different for the bosons and the fermions. Bárbara Álvarez- U. de Oviedo

CONCLUSIONS The Higgs boson search is in its most exciting era ever. Tevatron is running really well. The Higgs boson search is in its most exciting era ever. Reaching sensitivity to SM Higgs over full mass range and beyond SM Higgs boson. NO evidence for signal found yet. We exclude at 95% C.L. a SM Higgs boson of 170 GeV/c2 We are sensitive to a Higgs of 160 GeV/c2 Stay tuned for further improvements! Bárbara Álvarez- U. de Oviedo

THANK YOU!!! Extremely sophisticated analyses. Tevatron performing really well, almost every week. THANK YOU!!! Bárbara Álvarez- U. de Oviedo

BACK UP SLIDES Bárbara Álvarez- U. de Oviedo

Only ~40 Higgs events are expected to be produced per fb-1 at each experiment in detectable channels TOTAL WH → lvbb H → WW ZH → vvbb ZH → llbb Bárbara Álvarez- U. de Oviedo