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Higgs Searches at Tevatron

Higgs Searches at Tevatron. Makoto Tomoto 戸本　誠 Fermilab/Nagoya University On behalf of the DØ & CDF Collaborations. DIS2006 @ Tsukuba , April 21 st , 2006. Higgs boson searches. Mass of fundamental particles are given by Higgs boson Only particle predicted by SM and NOT discovered yet.

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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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