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Exploring Little Higgs Model for Particle Searches at LHC

Explore recent developments in Little Higgs model searches at LHC, covering heavy gauge boson searches, leptonic and hadronic decays, and Higgs decays at different masses. Discoveries and implications are summarized with new strategies and insights.

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Exploring Little Higgs Model for Particle 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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