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Recent Developments in Little Higgs Searches at LHC

SUSY 06, Newport Beach. Recent Developments in Little Higgs Searches at LHC. on behalf of the ATLAS collaboration. presented by: F. Ledroit. Outline. The model Heavy gauge boson searches Leptonic decays ( Eur. Phys. J. C39S2 , 13 (2005) ) Hadronic decays Higgs decays, m h =200 GeV

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Recent Developments in Little Higgs Searches at LHC

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  1. SUSY 06, Newport Beach Recent Developments in Little Higgs Searches at LHC on behalf of theATLAScollaboration presented by:F. Ledroit

  2. Outline • The model • Heavy gauge boson searches • Leptonic decays (Eur. Phys. J. C39S2, 13 (2005)) • Hadronic decays • Higgs decays, mh=200 GeV • Higgs decays, mh=120 GeV (Eur. Phys. J. C39S2, 13 (2005)) • Summary NEW! NEW!

  3. 2 æ ö mh ç ÷ 200 GeV è ø • Effective model adressing hierarchy problem • larger symmetry, broken at high scale • introduce heavy top T, heavy Higgses f andheavy gauge bosons ZH,WH, AH Little Higgs model Littlest Higgs model[Arkani-Hamed et al., JHEP 207(2002)34] SU(5)  SO(5), scale ~10TeVGauge sector [SU(2)U(1)]2SM Higgs PhenomenologyHan et al., Phys.Rev.D67(2003)95004 Gauge sector: parameterq: mixing anglebetween W triplets WH , ZHmassdegenerate M < 6 TeV· EW fits  strong constraints Little Higgs realized in several models. Similar particle content.

  4. qq anihilation q ZH,WH q 12% All l+l- or qq BR(ZH) BR( ZHqq) = 1/8 BR(WHqq’) = 1/4   (cot ) 2 Zh+W+W- (ZH) (fb) Br(WHtb)=3xBr(WHen) cot  cot  = 1 GW (Wh+WZ) = GZ (Zh+WW) H H Fermionic channels: Bosonic channels: ZH,WH production and decays ZHl+l-,qq ZH Zh, W+W- WH l ,qq’ WHW±h, W±Z ± ± (WH) = 2 (ZH)

  5. Outline • The model • Heavy gauge boson searches • Leptonic decays (Eur. Phys. J. C39S2, 13 (2005)) • Hadronic decays • Higgs decays, mh=200 GeV • Higgs decays, mh=120 GeV (Eur. Phys. J. C39S2, 13 (2005)) • Summary NEW! NEW!

  6. Discovery channel ZH WH VH= ZH, WH ZH  e+e- WH e n LeptonicVH decays With 300 fb-1 = 3 years of LHC high luminosity: All analyses performed using a parameterized simulation of the ATLAS detector (ATLFAST) Poisson significance (~S/√B) > 5+ S  10 in the mass windowdiscovery • (lepton tag) = 90%

  7. Outline • The model • Heavy gauge boson searches • Leptonic decays (Eur. Phys. J. C39S2, 13 (2005)) • Hadronic decays • Higgs decays, mh=200 GeV • Higgs decays, mh=120 GeV (Eur. Phys. J. C39S2, 13 (2005)) • Summary NEW! NEW!

  8. Cuts: • 1 isol. lepton, pT>25 GeV • ET > 25 GeV • 2 b-jets, pT>25 GeV, • DR(b1 l )<2, DR(b2 l )>2 • t1 = b1 + l1 + ET (with n // l) • t2 = b2 + all jets DR<2 • pT(b2+j) > 0.25 M j Signature: 2 b-jets + 1 lepton + ET j W t2 ZH b l W t1  ZH b Hadronic VH decays NEW! VH= ZH, WH (DR)2 = (Dh)2 + (Df)2 h=pseudo-rapidity, f=azimuthal angle ZH t1t2, t1 bln, t2bjj (l=e,m) e(b tag) = 50 (20)% Ru = 100 (130) M = 1 (2)TeV validated with full simulation ZH Background: tt, W+jets,… ekine= 27 (21)%, M=1 (2) TeV

  9. ZHtt M=1 TeV Hadronic VH decays Mass reco. bias: <1% Mass resolution: ~12% >> natural width: G/M = 2% cotq 30 fb-1 Two other modes: ZH bb WH tbb ln b 30 fb-1 300 fb-1 M=2 TeV cot = 1

  10. Hadronic VH decays • The ZH to tt and bb decays are difficult to detect 300 fb-1 • The WH to tb decay might yield a signal • clearly separable from background • Possible improvement by optimizing • b-tagging at very high pT

  11. Outline • The model • Heavy gauge boson searches • Leptonic decays (Eur. Phys. J. C39S2, 13 (2005)) • Hadronic decays • Higgs decays, mh=200 GeV • Higgs decays, mh=120 GeV (Eur. Phys. J. C39S2, 13 (2005)) • Summary NEW! NEW!

  12. VH decays to Higgs (mh=200 GeV) NEW! Assume Higgs discovered • mh=200 GeVBR(hW+W-) = 74 % SM Higgsusual BR • BR(hZZ) = 26 % • VH V1h  V1V2V3V = Z,W • Studied channels:  VH 3 leptonic V ( leptons only) •  VH 2 leptonic V + 1 V  jj • “A” modes:  (V1jj) andisolated leptons • “B” modes:  (V2 or V3 jj) lepton in jet • Branching fractions = 4 10-5 – 7 10-4 (cotq=0.5)

  13. VH decays to Higgs (mh=200 GeV) j l + j V VH l- l Z h l Z Signature: 4 leptons + jet(s) A modes VH Vh  jjZZ  jjl+l-l+l-(l=e,m)very clean • Cuts: • 2 isol. leptons (1,2) M12= MZ±15 GeV • 2 isol. leptons (3,4) DR1,2-3,4<1.5 • pT(1+2+3+4)>0.25 M • 1 or 2 jets, pT> 0.25 M (DR1-2<1) • m(4l+j)=M ± 15% VH VH VH cot=0.5 Background: ~ none

  14. VH decays to Higgs (mh=200 GeV) S= 76.7 eS≈12% A modes Two other modes: ZH Zh  l+l-W+W-l+l-l+nl-n WH Wh  lnW+W-lnl+nl-n VH Vh  jjZZ  jjl+l-l+l- 300 fb-1 ZH+WH 300 fb-1 1 TeV 1 TeV S= 28.7 cot = 0.5 eS≈26% Mass reco. bias: 1% Mass resolution: 4%   Assume p = pT bias, poor resolution

  15. VH decays to Higgs (mh=200 GeV) l + l- Signature: 3 leptons + jet(s) + ET B modes ZH Zh l+l-WWl+l-jjln (l=e,m) • Cuts: • 2 isol. leptons (1,2) M12= MZ±15 GeV • 1 isol. lepton, W1=l3+ET, pT>50 GeV • apply MW constraint or assume n // l3 • 1 or 2 jets, Mj= MW±15 GeV • pT(l1+l2+W1+j)>100 GeV Z j ZH W j h l W n cot=0.5 Background: tt, Zh, WZ, ZZ, h s.BR (fb)= 3376, 2, … Lack of statistics on background  extrapolated

  16. VH decays to Higgs (mh=200 GeV) B modes ZHZhl+l-WW l+l-jjln Two other modes: ZH Zh l+l-ZZl+l-jjl+l- WH Wh lnZZ ln jjl+l- 300 fb-1 1.5 TeV 9.2  S= 31 300 fb-1 eS≈24% eB<1% 18.6  S= 92 1 TeV eS≈21% eB<1% cot = 0.5 Mass reco. bias: 1% Mass resolution: 4% ~same all modes

  17. VH decays to Higgs (mh=200 GeV) 12% BR(ZH) All l+l- or qq Zh+WW cot  M < 6 TeV for mh = 200 GeV (avoid fine tuning) VH Ldt = 300 fb-1 Mass reach about 2 TeV, except when cotq ~ 1 Although ATLFAST lepton isolation criteria were especially tuned (B modes), needs validation with full simulation

  18. Outline • The model • Heavy gauge boson searches • Leptonic decays (Eur. Phys. J. C39S2, 13 (2005)) • Hadronic decays • Higgs decays, mh=200 GeV • Higgs decays, mh=120 GeV (Eur. Phys. J. C39S2, 13 (2005)) • Summary NEW! NEW!

  19. VH decays to Higgs (mh=120 GeV) • BR(hbb) = 66 % • BR(h) = 0.2 % 300 fb-1 excluded ZH  Zh  jjgg, ll bb WH Wh jjgg, ln bb (l=e,m) M < 2.2 TeV for mh=120 GeV m (GeV) VH Earlier results: e(b tag) = 40-50% Ru = 100 e(g tag) = 80%

  20. The ZH, WH can be discoveredup to5-6 TeV if cotq large • It may be possible to probe the modelup to ~ 2 TeV • using the WHtbdecay (cotq > 0.25) • usingthe VHVh decay (cotq [0.8,1.2]) Summary Fermionic decays Bosonic decays

  21. Many thanks to References: G. Azuelos et al., Eur. Phys. J. C39S2, 13 (2005) S. Gonzales de la Hoz et al., ATL-PHYS-PUB-2006-003 E. Ros and D. Rousseau, ATL-COM-PHYS-2006-031 the authors of these analyses, and especially David Rousseau and Matthieu Lechowski Eduardo Ros and Jose E. Garcia

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