1 / 28

Little Higgs Searches with ATLAS

Little Higgs Searches with ATLAS. The Little Higgs task force. S. Asai, G. Azuelos, K. Benslama, D. Costanzo, G. Couture, J. E. Garcia, F. Gianotti, I. Hinchliffe, N. Kanaya, M. Lechowski, R. Mehdiyev, G. Polesello, E. Ros, D. Rousseau.

ila-farrell
Download Presentation

Little Higgs Searches with ATLAS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Little Higgs Searches with ATLAS The Little Higgs task force S. Asai,G. Azuelos,K. Benslama,D. Costanzo, G. Couture,J. E. Garcia,F. Gianotti, I. Hinchliffe, N. Kanaya, M. Lechowski,R. Mehdiyev, G. Polesello, E. Ros, D. Rousseau presented by:M. LECHOWSKI(LAL-Orsay)

  2. 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 • Motivation : • Quadratic divergences : • Higgs fields : Little Higgs model

  3. heavy W± heavy Z heavy  heavy Higgs bosons We have to look for the following particles: Particles • T heavy top • WH ZH AH • Higgs triplet 0 , + , ++ ± described in : arXiv:hep-ph/0301040Phenomenology of the Little Higgs Model

  4. 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 ± ± M(WH)  M(ZH)

  5. discovery channel • TtZ, bW • th • ZH, AH l + l -, qq, … • Zh • WHl, qq’, … • W±h • ++ W+ W+, l + l -, … Decays test of the model ± very heavy particles very high pT final state The modesth, Zh, W±h, …may be difficult to see but are necessary to test the model

  6. We have used the following software for the analysis: Generation • Generation: Pythia 6.2 • new top: 4th generation quarks (T = t’) MSUB(83) • new heavy bosons: generated via MSUB(141), MSUB(142) • new Higgs sector: generated via MSUB(351) • Decays: modify Pythia decay tables to match Little Higgs model • Analysis: fast simulation

  7. q q’ W T b 1 2 ( )2 T bW 50 % T tZ 25 % T th 25 % BR  1 M 16  2 % T • Production mechanism = Wb fusion Heavy top T 1 = 2  1 (T) (fb) T T T 1 , 2 Yukawa couplings

  8. l + l - b Signature: 3 leptons + 1 b-jet + ETmiss T Signature: T searches 3 b-jets + 1 lepton + ETmiss b h Z T T 120 GeV l W l W 1 TeV 1 TeV t t   b b Background: pp  tt pp  Wbb Background: pp  tZ pp  WZ

  9. T T  tZ 3 leptons + b-jet + ET T Zt signal MT= 1 TeV L=3·105 pb-1 1 = 2 S = 10 B = 11 • Cuts: • 3 isolated leptons, pT >30 GeV • (2 of them with Mll= MZ) • 1 b –jet • ET > 100 GeV + - Signal Bkg Bkg Signal S/B > 5(S  10) in the window mass discovery

  10. T T  ht 3 b-jets + lepton + ET MT= 700, 1000, 1300 GeV T ht signal L=3·105 pb-1 • Cuts: • pT(3-jets) > 80 GeV • pT(lepton) > 70 GeV • in window mass of H • At least 1 b-tag MT= 700 Events / 30GeV Bkg using cross-sections to achieve 3 observations : MT= 1000 MT= 700 at3 s.BR(Tht) >525 fb MT= 1000at3 s.BR(Tht) >220 fb MT= 1300 at3 s.BR(Tht) >210 fb MT= 1300 M(T) (GeV) MT (GeV)

  11.   (cot ) 2 q ZH (ZH) (fb) q cot  = 1 (ll ) ~ (cot ) 2 (Zh) ~ (cot 2) 2 ZH, WH, AH Gauge Boson ZH 12% e+e- + +- + +- BR Zh cot  Once a mass is given, the only free parameter in the model is  . NB: (WH) = 2 (ZH) NB: (Wh) for WH=(Zh) for ZH

  12. S  5000 B  20 cot  = 1.0 S  100 B  8 cot  = 0.2 ZH, WH, AH L=3·105 pb-1 Search for ZH qq ZHe+e- MZ = 2 TeV H • 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- ) • other bkg’s are under evaluation N(e+e-) bkg subtracted M(e+e-) (GeV)

  13. cot  S B > 5  M 4 6 2 ZH, WH, AH L=3·105 pb-1 Discovery region for ZH low (ZH) If ZH is found, cot  can be extracted from (ZH) and (ZH) = [ 3.4(cot )2 +0.071 (cot 2)2] % MZ (TeV) H low .BR(ZH e+e)

  14. Z ZH q h ZH, WH, AH q ZH Zh   (cot  cot 2) 2 cot 2 cot  (cot ) • mh = 120 GeV • BR(h bb) = 66 % • BR(h ) = 0.2 % (cot  = 0.5) Ratio • mh = 200 GeV • BR(h W+W-) = 74 % • BR(h ZZ) = 26 % 0.5

  15. l + l - b b b ZH, WH, AH l + ZH Zh with h bb l - Z Z ZH ZH 2 TeV 1 TeV h h 120 GeV 120 GeV 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

  16. MZ = 1 TeV H L = 3·105 pb-1 cot  = 0.5 L = 3·105 pb-1 cot  = 0.5 ZH, WH, AH MZ = 2 TeV H Signal and background 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 * from full sim.

  17. MW = 1 TeV H b ± ± ZH, WH, AH ± l n WH W h with h bb ± W ± Events 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 M(WH) (GeV) b-tag: b = 50%, Ru = 100 Inside mass window: S = 1499 S B = 471 B = 69 Background: W + jet , tt

  18. MZ = MW = 1 TeV H H ZH, WH, AH WH / ZHW/Z h with h  j big jet W+Z or WH +ZH j WH  1 TeV L = 3·105 pb-1 cot  = 0.5 Events h  120 GeV ZH Bkg Cuts |()| < 2.5PT() > 25 GeV m(h) 120 GeV PT(h) > 400 GeV -tagging, ()= 80% PT(W/Z) > 200 GeV inside mass window M(WH/ ZH) (GeV) S(WH  Wh) = 64 S(ZH  Zh) = 33 B(h inclusive) = 8 B( inclusive) = 5 97 S B * = 27 13 Background: h(gg) inclusive gg inclusive *23 without reconstructing W/Z

  19. ZH, WH, AH Regions with S/B > 5 and S > 10 Combined results cot  L=3·105 pb-1 ZH/WH  j j gg excluded ZH l l bb WH l nbb M < 2.2 TeV for mh = 120 GeV M(ZH/WH) (TeV)

  20. ZH, WH, AH • 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)

  21. ++ L=3·105 pb-1 • Production: VBF mechanism • (vector boson fusion) 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 ++W+W+ +++  +, e+e+, … Decays SM might be suppressed

  22. ++ L=3·105 pb-1 ++ W+W+ l +l + ++  W+W+ M(++) = 1.5 TeV PRELIMINARY (theorical uncertainties) Background: WWqq, WZ WZqq, Wtt Bkg S = 3.2 B = 20 Main cuts: Events • 2 forward jets • PT(lepton 1) > 100 GeV • PT(lepton 2) > 50 GeV • ET > 50 GeV • MT > 600 GeV Signal (v’ = 25 GeV) Parameter v’ > 67 GeV to achieve 5 MT () (GeV)

  23. ++ ( Couplings might be suppressed in the little Higgs model ) ++ ++  lepton + jet ++  + + Background: WWjj, tt Required s.BR(++++) (fb) for 5s discovery : Main cuts : 1) Forward jet tag PT(j1) > 40 GeV PT(j2) > 20 GeV | | < 3.8 Mjj > 600 GeV M(++) = 0.3 TeV M(++) = 0.7 TeV Events (arbitrary units) 2) Central jet veto 3)  selection cuts 4) Same charge for -jet and lepton M(++) = 1.5 TeV M(++) (GeV) M(++) (GeV)

  24. TtZ M=1 TeV : S/B >5 (1 = 2) • th M=0.7, 11.3 TeV : visible at 3s • ZHe +e -easily visible for M < 2TeV • Zh • WHW±h • ++ W+ W+ M=1.5 TeV :visible at 5s for v' > 67GeV • t+ t+M=0.71.5 TeV : visible at 5s 3l b Summary 3b l  for s.BR(Tth)> 525, 220 fb discovery channel M=1 (2) TeV : S/B=50 (5) l+l-bb (cot=0.5) test of the model qqgg M=1 (2) TeV : S/B=27 (5) L=3·105pb-1 ± (cot=0.5) qqgg M=1 TeV : S/B=69 l ±nbb (cot=0.5) l +l + 3b l + for s.BR(++++)> 2fb

  25. Conclusions • Work also done on following channels:(but no time to show) • Tth and ZH Zh with M(h) = 200 GeV • ++ W+W+ljjand++ e+e+, ++ The search for particles predicted by the Little Higgs models using the ATLAS detector has started . A large part of parameter space will be covered .

  26. Additionnal slides • b-tagging for ZH  Zh with h  bb • without reconstructing W/Z for WH / ZH W/Z h with h  

  27. MZ = 1 TeV MZ = 2 TeV H H WH(400) from DC1 data bb ZH, WH, AH < pT (bb)> = 800 GeV b-tagging < pT (b)> = 220 GeV 115 ~ 100 0.5 0.4 Full simulation of double b-jets

  28. MZ = MW = 1 TeV H H ZH, WH, AH WH / ZHW/Z h with h  X W+Z WH +ZH L = 3·105 pb-1 cot  = 0.5  1 TeV Bkg Events h WH 120 GeV  ZH Cuts pT(WH/ZH) (GeV) |()| < 2.5 PT() > 25 GeV m(h) 120 GeV PT(h) > 400 GeV -tagging, ()= 80% S(WH  Wh) = 107 S(ZH  Zh) = 53 B(h inclusive) = 31 B( inclusive) = 17 160 S B = 23 48 Background: h(gg) inclusive gg inclusive

More Related