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Exploring the Littlest Higgs Model at the LHC: Phenomenology and Search Strategies

This presentation discusses the Littlest Higgs model and its implications within the framework of particle physics. Presented by Jose E. Garcia from the ATLAS Collaboration, the talk highlights the gauge sector, particle spectrum, and new coupling strategies for searching processes at the LHC. Specific focus is given to the production mechanisms, signatures for identifying Higgs bosons, and the strategies for data analysis including cuts for signal processing in events like T→bW and reconstructing ZH decays. The talk aims to provide insights into the phenomenology and potential discoveries linked to this model.

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Exploring the Littlest Higgs Model at the LHC: Phenomenology and Search Strategies

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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

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