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Higgs Searches at Tevatron

This article discusses the ongoing searches for the Higgs boson at the Tevatron accelerator. It explores both the standard model predictions and extensions, as well as the experimental techniques and results. Additionally, it covers the searches for Higgs bosons in supersymmetric models.

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Higgs Searches at Tevatron

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  1. Higgs Searches at Tevatron Makoto Tomoto 戸本　誠 Fermilab/Nagoya University On behalf of the DØ & CDF Collaborations DIS2006 @ Tsukuba , April 21st, 2006

  2. Higgs boson searches • Mass of fundamental particles are given by Higgs boson • Only particle predicted by SM and NOT discovered yet. • SM cannot predict the exact mass of Higgs boson, but…. • Higgs bosons with extension models have been also looked for • 2HDM  5 physical Higgs bosons, mH(lightest) < 135GeV Experiments tell us: - MH > 114GeV (95% CL) by LEP - MH < 175GeV (95%CL) by global fit ( center value = 89 + 45 – 30 GeV) Theory predict - SM Higgs mass is light - New physics at ~ 1 TeV Not allowed by SM Allowed Not allowed by SM Tevatron has capability to search for Higgs bosons in this mass region

  3. 0. Tevatron/Tools SM Higgs boson Hbb WH  lnbb ZH  nnbb HWWleptonic WH  WWW  lnlnX H  WW  lnln Combination SUSY Higgs boson pp  hb(b) pp  h tt Charged MSSM Higgs boson Outline Many updates and new analysis  Started combination of the Higgs search Important signature of Higgs searches is leptons, b-jets, tau, and ET

  4. Tevatron Status Booster CDF DØ 80-85% Average Efficiency p Delivered ~1.5 fb-1 Recorded ~1.2 fb-1 Tevatron p Main Injector p source • Currently in shutdown: • Silicon and Trigger upgrades 4-8 fb-1 expected by end of 2009

  5. DØ & CDF detectors DØ • Higgs searches rely on • - Jets • Lepton ID for W/Z • b quark jets for Hbb decay • tau ID for htt • missing ET for Wln and Znn CDF • - e/jet ID by Calorimeter • Good muon detector • - b-ID by inner tracking system • muon/electron/jet triggers • tau ID using Neural Network

  6. b tagging • Characteristics of b-quarks • Leptons from semileptonic b decay ( Br(bln)~10%) • Travel some distance from the primary vertex before decaying • ~1mm • With charm cascade decay, about 4.2 charged tracks • 3 main algorithms under development/improvement • Soft-lepton tagging • Secondary Vertex reconstruction • Lxy/s(Lxy) • Impact Parameter based • d0/s(d0) Jet m Secondary Vertex b Lxy/s(Lxy) Primary vertex +d0 d0/s(d0)

  7. 1. Standard Model Higgs boson searches

  8. SM Higgs searches at Tevatron Production • MH < 135GeV : Hbb (di b-jets mass) • ggHbb sink down into deep QCD backgrounds • WHlnbb (lepton + ET) • ZHnnbb, llbb (ET or lepton(s)) • MH > 135GeV : HWW (di-lepton) • ggHWWlnln(opposite charge) • WHWWWlnlnX (same charge) s(pb) Excluded Decay 135GeV Gluon Fusion Br(HX) 1.0 – 0.1 pb 1000-100 events @ 1fb-1 Associated production Excluded 0.2 – 0.02 pb 200-20 events @ 1fb-1 mH (GeV/c2)

  9. b jet b jet n e/m WHlnbb (l=e,m) single b-tagging double b-tagging • e/m + ET restricts QCD backgrounds • Excess due to Higgs from dijet mass? combined single b-tagging

  10. ZHnnbb single b-tagging double b-tagging s(ZHnnbb) || s(WHlnbb) - Large ET rejects lots of QCD bkg - QCD bkg estimated from sideband combined If lepton is missing  WHlnbb combined single b-tagging

  11. WHWWW*lnl’nX (l, l’ = e, m) • Event Selection • Same charge di-lepton from W’s (One from H, the other from WH) suppress SM backgrounds • pT (lepton)> 15 GeV • ET > 20 GeV • Main backgrounds • WZ production MC • Charge flip from Z/g*ll, WW, and ttllX  data • QCD multijet, W+jets data q flip QCD L=363pb-1 CDF Preliminary (L=194pb-1) DØ Preliminary

  12. Event Selection Cannot reconstruct H mass  Angular correlation between e/m Backgrounds Z/g*ll, WW, Wg, WZ, ZZ, tt, and W+jets 95% limits from binned likelihood Df(ll) distribution e+/m+ e-/m-   W+ W- HWW*lnl’n (l, l’ = e, m) MH=160GeV ‘04 MH=160GeV ‘05

  13. HWW*lnln (ee or em) • Full data sets (L=950pb-1) • ee and em channel only • pT(1st)>15GeV, pT(2nd)>10GeV • Z/g*ll, and energetic jets veto • 95% C.L. limits from CLs method • 4th Generation Model starts to be excluded selections MH=160GeV

  14. Combined Higgs boson search • First attempt to see a combined result from DØ • 14 different analysis • decay mode, lepton flavor, b-tag conditions • Combination is done by modified frequentists method (CLs) • So far, a factor of 15 away from SM prediction (MH=115GeV) • with L=2fb-1, CDF/DØ combined, NN b-tagging, NN selections, track-cal jets, increased acceptance, additionally new channels, cross efficiency, and reduced systematic • cross section factor  1

  15. 14 updated analysis combined by DØ !! A factor of 15 away from SM @MH=115GeV

  16. 2. SUSY Higgs boson searches

  17. SUSY Higgs bosons • In two Higgs doublet model, such as MSSM • 5 physical Higgs bosons h, H, A, H±(mh < mH) • tanb = vu/vd : ratio of VEV of 2 Higgs fields • Cross sections for bbh enhanced like tan2b • h is predicted to be light (mh < ~135 GeV) • LEP limit is mh> ~92 GeV @ 95 C.L. • Tevatron is sensitive to large tanb • At high tan b , A is almost degenerate with h/H • s(A) ~ s(h/H), G(A) ~ G(h/H) • Br(Abb) ~ Br(h/Hbb) ~ 90% … hbb • Br(Att) ~ Br(h/Htt) ~ 10% … htt

  18. hb(b) at least 3 b-tagged jets • L=260pb-1 • At least 3 b-tagged jets • pT cuts optimized • b-tag rate estimated from data (~2%) • 2 b-tagged sample  b-tag rate • Z(bb,cc)+jets, tt estimated from MC • No Excess found • 95% C.L. from fit of dijet mass search fit region

  19. htt CDF:L=310pb-1, DØ: 348pb-1 • L = 310(CDF)/325 (DØ) pb-1 • Sample • te/tm+thad • te+tm (DØ only) • Selection • NN for t ID • visible mass pT(e/m/t) and ET tau DØ: hbb+htt combined, CDF: htt only

  20. Charged MSSM Higgs boson search in tt MSSM SM • Look at four tt final states: • di-lepton + jets • lepton + jets (=1 b-tag) • lepton + jets (≥ 2 b-tags) • lepton + tau + jets • Interpret for several MSSM scenarios, tan β, and mH • Search for difference from SM • Major decay modes: • H+→tn • H+→cs • H+→t*b→W+bbb • H+→W+h→W+bb

  21. Charged MSSM Higgs search L = 193 pb-1 Consistent with SM prediction No-mixing benchmark scenario mhmax benchmark scenario

  22. Conclusion • Tevatron is hunting Higgs bosons • SM Higgs boson • with extension like MSSM Higgs boson • CDF and DØ competing and will perform combined result soon • First attempt of SM Higgs combination at DØ • Current results encouraging us. • 3-4 times more data in tape • Learned improved analysis • Sensitivity to MH>114GeV starts at 2 fb-1 • Exclusion up to 180 GeV possible with 8 fb-1

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