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Higgs Searches at Tevatron

Higgs Searches at Tevatron

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Higgs Searches at Tevatron

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  1. Higgs Searches at Tevatron • Motivation • Experimental strategy (and detector) • Higgs search status • Prospects • Conclusions 花垣和則 (Kazunori Hanagaki) / Fermilab for the CDF & DØ collaborations Kazu Hanagaki

  2. Motivation

  3. Electroweak Symmetry Breaking • Gauge invariant  no mass term • Higgs mechanism [with U(1) vector field] • L = (Dmf)*(Dmf)– V(f) - ¼ FmnFmn Dm ∂m+ieAm, Fmn ∂nAm - ∂mAn V(f) = m2f*f + |l|(f*f)2 • f is complex scalar doublet: Higgs field • e2AmAmf*fin (Dmf)*(Dmf) (e2v2)/2·AmAm  mass term!! • One Higgs doublet in SM • 4 degree of freedom – 3 x (gauge boson)  one Higgs boson Spontaneous symmetry breaking m2>0 (hot) potential minimum at f=0 m2<0 (cold=present world) at f0 <f> = v/sqrt(2) Kazu Hanagaki

  4. W- W+ W- W+ g Z e- e+ e- e+ W- W+ W- W+ H n e- e+ e- e+ Why is Higgs Preferred? • Unitarity: individual diagram diverges with sqrt(s) • gauge cancellation • spin 1 intermediate state • spin 0 component due to wrong helicity state of e+e- must be canceled by spin 0 particle proportional to mass Higgs coupling! Kazu Hanagaki

  5. Higgs Mass • MH > 114.4 GeV @95% CL search by LEP2 • MH < 175 (207) GeV @95% CL global EW fitting Higgs self-coupling diverges unstable vacuum energy scale (GeV) • Needs to be light (160-180 GeV) for a theory valid up to Plank scale • Finding a Higgs at MH ~ 120 GeV would be an evidence of new physics  115-200 GeV is our target mass range Kazu Hanagaki

  6. If the symmetry is not broken…? • Fermion remains massless • Nucleon mass almost unchanged, but proton would be heavier than neutron • Spontaneous symmetry breaking by QCD  W/Z mass ~1/2500 (W,Z vs p)  very rapid inversed beta decay (pn+e++n) • Unstable proton  no hydrogen atom  Completely different world !! Mechanism of electroweak symmetry breaking is the mystery relevant for existence of ourselves Kazu Hanagaki

  7. Experimental Strategy and Detector

  8. Search Strategy • MH < 135 GeV • H  b b-bar dominant • too much BG in gg  H  b b-bar • qqW/Z+H(bb) • For high MH range • H  WW dominant  gg  H  WW • For medium MH range • W/Z+H(WW) helps Kazu Hanagaki

  9. The Detector h = -ln[tan(q/2)] Kazu Hanagaki

  10. Silicon Tracker for b-jets Identification • New silicon detector in DØ for improvement of b-jet ID • installed and tested in this shutdown period Silicon micro-strip detector for precise measurement of charged particle trajectory Kazu Hanagaki

  11. Identification of b-jets • ctb-hadron ~ 400-500 mm  travel by a few mm from primary vertex • S(Lxy) = Lxy/s(Lxy) or S(IP) = d0/sd0with V0 (Ks etc.) removal secondary vertex Lxy primary vertex DØ sec.vertex base d0 CDF Kazu Hanagaki

  12. Higgs Search Status Standard Model MSSM

  13. q H W*/Z* q(’) W/Z Standard Model – Low Mass Higgs b • sxBr(W/Zff) = 0.015-0.003 pb • Backgrounds • W/Z+bb/cc/jj, top, W/Z+Z(bb), QCD… • b-jet ID, jet energy resolution are important • W/Z identification • Wln: high pT isolated lepton + missing ET W mass • Znn: large missing ET • Zll: high pT isolated dilepton  Z mass • High pT dijets with b-ID  dijet mass b f f Z(nn)H(bb) Lint = 261 pb-1 Kazu Hanagaki

  14. W(ln)H(bb) • pT(e or m) > 20 GeV • Missing ET > 20 GeV (CDF) > 25 GeV (DØ) • CDF: jet ET>15 GeV, |h|<2 • DØ: jet ET>20 GeV, |h|<2.5 • b-jet tagging • Consistent with SM background expectations • backgrounds well understood Kazu Hanagaki

  15. e+ n W+ n W- e- Standard Model – High Mass • Two isolated high pT leptons + missing ET • Dominant background is qqWW • different decay angular correlation with Higgs signal DØ Run II Preliminary Lint = 950 pb-1 Kazu Hanagaki

  16. The Other Analyses • WH(WW)  l±nl±nX • high pT isolated like sign dilepton (ee,mm,em) • large missing ET • diboson production is the main background due to charge mis-identification • t(bW)t(bW)H(bb) • exactly one e or m • missing ET • 5 or more jets • 3 or more b-jets Kazu Hanagaki

  17. Standard Model Higgs Summary ~15 • First DØ combined result • Z(ll)H not yet included Kazu Hanagaki

  18. 0 0 t b MSSM Higgs • Two Higgs doublet in MSSM to avoid anomaly • 8 degrees of freedom – 3 x (longitudinal polarization of W± and Z)  5 scalars (h, H, A, H±) • tanb = <Hu>/<Hd> • At high tanb, s(h or H, A) is enhanced • Br(Abb)~90%, Br(Att)~10%  f0 b + 0 b Amplitude  tan Amplitude  1/tan Amplitude  tan Kazu Hanagaki

  19. MSSM Higgs Search Status • CDF: f0tt; DØ: b(b)f0b(b)bb, f0tt Kazu Hanagaki

  20. Prospects

  21. 200E30 100E30 Luminosity • Improvement by the recycler as a storage ring of p-bar • Electron cooling at the recycler • 4-8 fb-1 by 2009 Kazu Hanagaki

  22. Improvement of b-tag at DØ correlation coefficient QCD data (fake rate) • Three b-tag algorithms in DØ; SVT, JLIP, and CSIP • correlated in efficiency • small correlation for fake  significant improvement by combination by Neural Network (~30% per jet) m+ jet data (efficiency) SVT JLIP CSIP SVT JLIP CSIP SVT JLIP CSIP SVT JLIP CSIP Kazu Hanagaki

  23. The Future of SM Higgs Search • Comparison w.r.t. old sensitivity study • For MH=115GeV: Limit/s =15 @~330pb-1by DØ alone vs 95% CL exclusion @2fb-1 • We can reach very close to the sensitivity study Kazu Hanagaki

  24. Conclusions

  25. Conclusions • Mechanism of electroweak symmetry breaking is a profound mystery • Searches have been carried out with 194-950 pb-1 of data • Remaining events consistent with SM backgrounds • If the (SM) Higgs exists and is light, there is a great potential to find the Higgs Now is the Time to Search for Higgs at Tevatron Kazu Hanagaki

  26. Backup

  27. Projection of MSSM Higgs Search • Tevatron will probe below Kazu Hanagaki

  28. A h H MSSM Parameters radiative correction depending on many parameters Kazu Hanagaki

  29. New Technique of Jet Reconstruction • Charged track information in jet reconstruction • Ecal = E(e/g) + E(neutral hadron) + E(chrgd had) • Etrkcal = Ecal – Eexpect(chrgd had) + Etrk(chrgd had) resolution measured in g+jet data DØ Run II Preliminary similar improvement at CDF as well Kazu Hanagaki

  30. b-tag efficiency measurement at DØ • Solve 8 equations for 8 unknowns example to measure JLIP efficiency with the combination of muon tag m+jet m+jet && opposite tag before b-tag b-tag by muon unknowns b-tag by tagger under testing b-tag by both tagger number of events Kazu Hanagaki

  31. Low Mass Higgs Search at DØ • W(e/m+n)H(bb): sxBR = 0.015 pb • Z(ee/mm)H(bb): sxBR = 0.003 pb • Z(nn)H(bb): sxBR = 0.015 pb Kazu Hanagaki