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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 - PowerPoint PPT Presentation
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LHC signal of the Little Higgs modelwith T-parity, focusing on thetop-partner production at the LHCwith a realistic simulation
Little Higgs Mechanism1. Higgs boson is regarded as Pseudo NG boson2. Pattern of the breaking is specially arranged (Collective symmetry breaking) in order to cancel quadratic divergent contributions to mh at 1-loop level. can be 10 TeV without the fine turning!!
Little Hierarchy Problem LEP experiment requires > 10 TeV ( = new physics scale) On the other hand, fine tuning problem on the Higgs mass mh requires < 1 TeV
Can we investigate the LittleHiggs Mechanism at the LHC?
Solution
Confirmation
Problem
I. Motivation
LH: Due to the Little Higgs mechanism, the Little Higgs partners are introdced.
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.
, W±, Z, h
[Arkani-Hamed, Cohen, Katz and Nelson (2002)]
H, WH±, ZH, Φ
t T
LH
Particle contents
LH
Gauge-Higgs sector Top 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-oddparticle (AH) is stable, can be dark matter!!
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.
, W±, Z, h
[Arkani-Hamed, Cohen, Katz and Nelson (2002)]
H, WH±, ZH, Φ
t T
t– T–
TLHT
Particle contents
LH
Gauge-Higgs sector Top sectorT
III T– pair production at the LHC
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.
Proton Proton
T-
7 TeV 7 TeV
T-– t
AH
t
AH
–
From WMAP: mAH = 80 – 400 GeVFrom EW test: mT- > 600 GeV mT- – mAH > 500 GeV Energetic top quarks with large missing energy
Constraints from WMAP and EW Precision test
WMAP
EW testWMAP
III T– pair production at the LHC
Four representative points
Detector effects AcerDET code
Event generation CompHep and HERWIG codes
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.
Proton Proton
T-
7 TeV 7 TeV
T-– t
AH
t
AH
–
IV. Event Reconstruction
The distribution peaks at the top mass, clearly showing that the analysis can group the jets from correctly
Three jetsinvariant mass
Two separate jet system is expected in the sigma events.
Two separate jet system is expected in the sigma events.By observing m(jjj) in a hemisphere, t is reconstructed.
pp
T–
T–
b-jet
b-jet
tt
DM(AH)DM(AH)
W
W
jetjet
jet
jet
V. Background reduction
m(jjj) < 200 GeV in at least one of the hemisphere
1. kinematic cut
2mT- – 0.2(3) TeV < Meff < 2mT- for Sample I, II(III, IV)
The events have no isolated leptons
Background: pp tt + X(102 – 103 larger than the signal)
2. Top cut
3. Lepton veto
–
Point III
Point III
Each distribution shows the clear excess of events over the background!!
VI. Results (50 fb-1)
BGSignal + BG
Signal
I II
III IV
SummarSummaryy• 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 m
easurements, 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.