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presented by: Jose E. Garcia (IFIC-Valencia) PowerPoint Presentation
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presented by: Jose E. Garcia (IFIC-Valencia)

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  1. XXXIXth Rencontres de Moriond on behalf of ATLAS Collaboration presented by: Jose E. Garcia(IFIC-Valencia)

  2. 2 • Littlest Higgs model • SU(5)  SO(5) • Gauge sector  [SU2U1]2 • SM Higgs • Arkani-Hamed et al., JHEP 207 (2002) 34 • Phenomenology • Han et al., Phys. Rev. D67 (2003) 95004 • Burdman et al., hep-ph/0212228 M Particle Spectrum 0,+,++ T WH ,ZH 1 TeV AH t Z ,W h  scalar sector top sector gauge sector v’ ’ 1/2 new couplings (+ scale f) Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  3. q q’ VH q’ 1 W q1 W+ ++ T b W+ q2 q’ 2 3 ++ T Strategies at LHC q VH q’ qq annihilation   (cot)2 Wide range in cot  possible. ZH e+e- & WH lVH  V h(V is Z or W) • Wb fusion •  (1)2 1/ 2  1 suppressed by b-quark PDF. T bW, tZ, th • VBF mechanism •  (v’)2 v’ should be small ++  W+W+ Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  4. q q’ W T b 1 2 ( )2 T bW 50 % T tZ 25 % T th 25 % BR  1 M 16  2 % 4 • Production mechanism = Wb fusion heavy top T 1/2 = 1 (T) (fb) T T T 1 , 2 Yukawa couplings of T and t Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  5. 5 T  Wb b-jet + lepton + ET T Wb L = 3·105 pb-1 1/2=1 • Cuts: • pT(jet) > 200 GeV • pT(lepton) > 100 GeV • ET > 100 GeV • 1 b-tag required Backgrounds:tt,t, Wbb Signal with 5 for MT< 2000 GeV Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  6. l+ l- b Signature: 3 leptons + 1 b-jet + ETmiss 6 Signature: T  Zt and T  ht 3 b-jets + 1 lepton + ETmiss b h Z T T l W l W 1 TeV 1 TeV t t   b b BKG BKG tbZ, tZ,WZ tt,Wbb Not distinguishable peak clear peak but poor statistics Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  7. 7 MT= 1 TeV T  tZ 3 leptons + b-jet + ET T Zt signal L = 3·105 pb-1 1/2=1 • Cuts: • 3 isolated leptons • (2 of them with Ml l = MZ) • 1 b –jet • ET > 100 GeV + - Signal with 5 for MT< 1050 GeV Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  8. 8 MT= 1 TeV T  ht 3 b-jets + lepton + ET T ht signal L = 3·105 pb-1 1/2=1 • Cuts: • pT(3-jets) > 130 GeV • pT(lepton) > 100 GeV • 110 < Mh < 130 GeV • At least 1 b-tag MT= 1.0 Bkg M(T) (GeV) Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  9. q 9 Gauge Boson ZH 12%   (cot ) 2 e+e- + +- + +- q BR ZH (ZH) (fb) Zh cot  = 1 cot  Once a mass is given, the only free parameter in the model is, . (ll) ~ (cot ) 2 (Zh) ~ (cot 2) 2 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  10. S  5000 B  20 cot  = 1.0 S  100 B  8 cot  = 0.2 10 M(ZH) =2 TeV L=3·105 pb-1 Search for ZH qq ZHe+e- slight improvement is reached using also +- • Selection cuts: • 2 isolated electrons with • pT > 20 GeV and || < 2.5 • minimum invariant mass • equal to 800 GeV • Background: • Drell-Yan (qq  Z/  e+e- ) N(e+e-) bkg subtracted M(e+e-) (GeV) Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  11. M MZ (TeV) H 11 L=3·105 pb-1 Discovery region for ZH • (ZH) decreases as M increases • (ZH)  (cot )2 • BR(ZH e+e-) drops for cot   0 • If ZH is found, cot  can be • extracted from (ZH) and (ZH) cot  S B > 5 = [ 3.4(cot )2 +0.071 (cot 2)2] % 6 2 4 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  12. Z ZH q h 12 q ZH  Zh   (cot  cot 2) 2 cot 2 cot  (cot ) (cot  = 0.5) • mh = 120 GeV • BR(h bb) = 66 % • BR(h ) = 0.2 % Ratio • mh = 200 GeV • BR(h W+W-) = 74 % • BR(h ZZ) = 26 % 0.5 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  13. l+ l- b b b 13 l+ ZH  Zh with h  bb l- Z Z ZH ZH 2 TeV 1 TeV h h b Cuts Cuts || < 2.5(jets and leptons) PT(Z) > 250 GeV PT(h) > 250 GeV b-tagging || < 2.5(jets and leptons) PT(Z) > 500 GeV PT(h) > 500 GeV b-tagging Background: Z + jets Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  14. MZ = 1 TeV H L = 3·105 pb-1 cot  = 0.5 L = 3·105 pb-1 cot  = 0.5 14 MZ = 2 TeV H ZH  Zh signal Events Events M(ZH) (GeV) M(ZH) (GeV) b-tag: b = 40%, Ru = 100 Inside mass window: S = 15 S B = 8 B b-tag: b = 50%, Ru = 100 Inside mass window: S = 195 S B = 16 B = 5 = 50 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  15. Cuts |()| < 2.5 PT() > 25 GeV PT(h) > 400 GeV -tagging, ()= 80% 15 MZ = MW = 1 TeV j H H WH / ZHW/Z h with h  L = 3·105 pb-1 cot  = 0.5 j W+Z WH + ZH WH  1 TeV h ZH Bkg  S(WH  Wh) = 64 S(ZH  Zh) = 33 B(h inclusive) = 8 B( inclusive) = 5 97 S B = 27 13 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  16. VH to leptons ZHl+ l- WHl  h(120)  bb ZH Zh l+ l-bb WH Wh l  bb h(120)   ZH Zh jets WH Wh jets 16 Discovery region for VH L = 3·105 pb-1 S/B > 5 N > 10 M(VH) (TeV) Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  17. 17 • Production: VBF mechanism • (vector boson fusion) L= 3·105 pb-1 New Higgs ++ W+W+ ++ W+W+ q’ 1 q1 M() = 1.5 TeV W+ M() = 2 TeV ++ W+ Events q2 q’ 2 v’ = 25 GeV   (v’)2 Decay: ++W+W+ SM Decay of ++to leptonsis suppressed in this model Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  18. 18 ++ W+W+ l+l+ ++  W+W+ L = 3·105 pb-1 • Bkg: WWqq, WZ • WZqq, Wtt • 2 forward jets (E > 100 GeV) • 2 leptons (charge +) • PT(lepton 1) > 150 GeV • PT(lepton 2) > 20 GeV • ET > 50 GeV • mT > 500 GeV Main cuts: mT () (GeV) mT =(E(l1) + E(l2) + |pT|)2 + (p(l1) + p(l2) + pT)2 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  19. 19 Outlook and Summary • Searches for the new particles predicted by Littlest Higgs model at LHC have been performed. HeavyTopand new Gauge boson sector are observable over a large range of parameter. • “Toy” model used for the study severely constrained by electro-weak measurements • Little Higgs idea is realized in several different models: SU(5)/SO(5),SU(6)/SP(6), Minimal moose SU(3)2/SU(3) and general mooses SU(3)n/SU(3)k, etc. They have similar particle content and are less constrained. • More detailed information on the ATLAS searches can be found inG. Azuelos et al., hep-ph/0402037 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  20. XXXIXth Rencontres de Moriond on behalf of ATLAS Collaboration presented by: Jose E. Garcia(IFIC-Valencia)

  21. 21 broken at scale   1 TeV The Littlest Higgs model 0 , + , ++ 10 GB 6 GB 24 - 10= 14massless Goldstone bosons mass through radiative corrections 4 GB used to give mass to ZH, WH, AH 4 GB used to give mass to Z,W, and h   broken at scale   1 TeV broken at scale   244 GeV Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  22. hierarchy and fine-tuning problems electroweak Planck cancellations SUSY : Little Higgs : bosons fermions new gauge bosons gauge bosons quarks new quarks electroweak Planck symmetry breaking pseudo-Goldstone bosons Goldstone bosons "light" mass massless 22 • Motivation : • Quadratic divergences : • Higgs fields : The Littlest Higgs model Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  23. 2 2 2 2 2 mh = (4mt – 2Mw – 4Mz – mh ) 2 3  2 2 8   t t t 23 Corrections Minimum needed to cancel all loops T heavy top new EW singlet WH, ZH heavy gauge bosonsnew SU(2)U(1) symmetry  heavy higgs bosons many new Goldstone bosons EW triplet (0 , + , ++) Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  24. 24 Upper limits:to avoid fine tuning scale f < 1 TeV· Mass Range T M < 2 TeV· mh = 120 GeV M < 0.2 TeV mh = 200 GeV M < 2 TeV WH , ZH, AHM < 6 TeV· mh = 120 GeV M < 2.2 TeV mh = 200 GeV M < 6 TeV M < 10 TeV ± Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  25. 25 Little Higgst and  will mix  standard top t, heavy topT Top quark sector • v = electroweak scale = 244 GeV • = heavy scale  1 TeV 1, 2= Yukawa couplingsO(1) 2 can be eliminated using SM top mass • = 1 TeV  2 new free parameters, , 1 • > 1 TeV (EW data!) but if MT is too large  finetuning Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  26. 26 new particles couplings mass Littlest Higgs: particle content and couplings Newconstants: scale  and 1, , ’,’ • No relations between these new constants • AH couplings not fixed by the model • EW data  ƒ  fine tuning • 2 TeV < ƒ < 4 TeV weakness of the model Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  27. 27 f = scale for new physics v = Fermi scale (244 GeV) M(ZH)  mW (f/v) [cot  + 1/cot ] Expectations for ZH Avoid fine tuning  M < 2.2 TeV (assuming mh = 120 GeV) M expected in 1-2 TeV region with wide range of cot  parameter. Agree with EW data  f > 2 TeV Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  28. MZ = 1 TeV MZ = 2 TeV H H 115 28 b-tagging < pT (bb)> = 800 GeV < pT (b)> = 220 GeV ~ 100 0.5 0.4 Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  29. MW = 1 TeV H b ± ± 29 ± l n WH W h with h bb ± W ± WH 1 TeV h 120 GeV b Cuts || < 2.5(jets and leptons) assume n colinear to l for WH reconstruction PT(Z) > 250 GeV PT(h) > 250 GeV b-tagging b-tag: b = 50%, Ru = 100 Inside mass window: S = 1499 S B = 471 B = 69 Background: W + jet , tt Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04

  30. 30 • theorical uncertainties (strong model-dependency) for AH • can deduce limits on s.BR(AH Z h) from results for ZH(same decays) • hypothesis : favorable cases where M(WH/ZH) and M(AH) are distant for each M(AH) (resolution of M(WH/ZH) being 45  80 GeV) Deductions for AH  WH/ZH not background for AH fb region excluded at 95 % CL if we see nothing s.BR(AH Z h) min. • deduced only from study • ZHZ h with h  • can combine other studies M(AH) (GeV) Little Higgs searches at LHC J. E. Garcia Rencontres de Moriond – March 04