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Hunting for the Top Partner in the Littlest Higgs Model with T-parity at the LHC

Hunting for the Top Partner in the Littlest Higgs Model with T-parity at the LHC. Shigeki Matsumoto (KEK). Collaborated with M.M.Nojiri (KEK) D.Nomura (KEK) hep-ph/0612249 (to be published in PRD). LHC signal of the Little Higgs model with T-parity, focusing on the

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Hunting for the Top Partner in the Littlest Higgs Model with T-parity at the LHC

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  1. Hunting for the Top Partner in the Littlest Higgs Model with T-parity at the LHC Shigeki Matsumoto (KEK) Collaborated with M.M.Nojiri (KEK) D.Nomura (KEK) hep-ph/0612249 (to be published in PRD) LHC signal of the Little Higgs model with T-parity, focusing on the top-partner production at the LHC with a realistic simulation

  2. I. Motivation Problem Little Hierarchy Problem LEP experiment requires L > 10 TeV (L = new physics scale) On the other hand, fine tuning problem on the Higgs mass mh requires L < 1 TeV Solution Little Higgs Mechanism 1. Higgs boson is regarded as Pseudo NG boson 2. Pattern of the breaking is specially arranged (Collective symmetry breaking) in order to cancel quadratic divergent contributions to mh at 1-loop level. L can be 10 TeV without the fine turning!! Confirmation Can we investigate the Little Higgs Mechanism at the LHC?

  3. II. The model The Littlest Higgs model with T-parity (described based on the non-linear sigma model under SU(5)/SO(5) breaking. The subgroup [SU(2)×U(1)]2 in SU(5) is gauged, and broken into the SM gauge under the breaking. [Arkani-Hamed, Cohen, Katz and Nelson (2002)] Particle contents t T A, W±, Z, h LH LH AH, WH±, ZH, Φ Top sector Gauge-Higgs sector LH: Due to the Little Higgs mechanism, the Little Higgs partners are introdced.

  4. II. The model The Littlest Higgs model with T-parity (described based on the non-linear sigma model under SU(5)/SO(5) breaking. The subgroup [SU(2)×U(1)]2 in SU(5) is gauged, and broken into the SM gauge under the breaking. [Arkani-Hamed, Cohen, Katz and Nelson (2002)] Particle contents t T A, W±, Z, h LH T T T LH t–T– AH, WH±, ZH, Φ Top sector Gauge-Higgs sector LH: Due to the Little Higgs mechanism, the Little Higgs partners are introdced. T: LH partners in the gauge Higgs sector can be T-odd partners at the same time. T-odd partners are introduced in the top sector Thanks to the T-parity, the Lightest T-odd particle (AH) is stable, can be dark matter!!

  5. III T– pair production at the LHC 7 TeV 7 TeV Proton Proton – – t t T- T- AH AH T– quark is the lightest colored T-odd particle, and SU(2) singlet. Thus it decays into top quark and dark matter at almost 100% branching ratio. Constraints from WMAP and EW Precision test EW test WMAP WMAP From WMAP: mAH = 80 – 400 GeV From EW test: mT- > 600 GeV mT- – mAH > 500 GeV Energetic top quarks with large missing energy

  6. III T– pair production at the LHC 7 TeV 7 TeV Proton Proton – – t t T- T- AH AH T– quark is the lightest colored T-odd particle, and SU(2) singlet. Thus it decays into top quark and dark matter at almost 100% branching ratio. Four representative points Event generation CompHep and HERWIG codes Detector effects AcerDET code

  7. IV. Event Reconstruction Two separate jet system is expected in the sigma events. jet jet b-jet jet b-jet W jet T– W t t p p T– DM(AH) DM(AH) Two separate jet system is expected in the sigma events. By observing m(jjj) in a hemisphere, t is reconstructed. Three jets invariant mass The distribution peaks at thetop mass, clearly showing that the analysis can group the jets from correctly

  8. V. Background reduction – Background: pp  tt + X (102 – 103 larger than the signal) 1. kinematic cut Point III 2mT- – 0.2(3) TeV < Meff < 2mT- for Sample I, II(III, IV) 2. Top cut Point III m(jjj) < 200 GeV in at least one of the hemisphere 3. Lepton veto The events have no isolated leptons

  9. VI. Results (50 fb-1) Signal + BG BG Signal II I III IV Each distribution shows the clear excess of events over the background!!

  10. Summary • Littlest Higgs model with T-parity is one of interesting model for physics beyond the Standard model. • The T- quark is the key particle at the LHC. • From WMAP and electroweak precision measurements, it turns out that mT- > 600 GeV, and mT- - mAH > 500 GeV. aaa • T- quark can be discovered using the hemi-sphere analysis at the LHC! Discussion • The study has been performed through the tree-level calculation. Thus, the result should be regarded as an order of magnitude estimate. • In addition to the 1-loop level calculations, more realistic detector simulations are needed in order to estimate the reliable significance.

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