Report on LHT at the LHC～ Some results from simulation

study ～

Shigeki Matsumoto(Univ. of Toyama)

1. What kinds of LHT signals are expected,and how accurately the LHC parametersare determined at the LHC?

2. Important to clarify the between theLHT study at the ILC and at the LHC.

S. M., M. M. Nojiri, and D. Nomura, PRD75 (2007)S. M., T. Moroi and K. Tobe (arXiv:0806.3837, will be in

PRD)

Little Higgs Model with T-parity

New particles (will be) playing an important role are Heavy gauge bosons (γH, ZH, WH), Top partners (T±), Triplet Higgs!

- - -

- - -

- - -

- - -Triplet

H

H

H

T+ T–

T-even T-odd except T+

Masses of T-parity partners of quarks and leptons (q–, l–) are assumed to be large!

New physics parameters introduced in the LHC are Breaking Scale ( f ) and Top partner mass (λ2f) and mh!

(DM)

Proton Proton

New Colored Particles

7 TeV 7 TeV

LHC is a “hadron” collider, so that colored new particles are copiously produced!

Productions of top partners, in particular, T+ & T–!

Littlest Higgs model with T-parity at the LHC

Representative Points

~ Signal Processes ~ Pair T+ production, Single T+ production, Pair T– production.

Littlest Higgs model with T-parity at the LHC

~ Strategy to generate events ~

Event generation at the parton level including PDF effects: MadGraph/Event

Fragmentation, initialand final state radiations,hadronization effects: PYTHIA

Detector simulations including Jet reconstruction withcone algorithm, b and t jet tags, isolated leptons andphotons identification, missing momentum fromcalorimater information: PDG4

T+ pair production at the LHC

SM BG: tt–production! (460 pb)-

At the parton levelSignal = bbqqlν- -

Reconstruct Two T+-system: T+(lep) & T–

(had)

using the fact that the missing momentum pT is due to the neutrino emission and (pl + pν)2 = mW

2. There are 6-fold ambiguity in the reconstruction of T+-system.The combination to minimize

~ Output ~Distribution of

~ Strategy to reduce BG ~

T+ pair production at the LHC

The distributions have distinguishable peaks at around the T+ mass. SM BG are well below the signal. From the distribution, we will be able to study the properties of T+.

~ Results ~ ~ Cut used in the analysis ~

~ Discussion ~

T+ pair production at the LHC

We consider the bin

Then, we calculate the # of events in the bin as a function of with being fixed.

The peak of the distribution is determined by maximizing the # of events in the bin. We applied the procedure for

~ Results ~

~ Conclusion ~

~ Accuracy of the mT+ determination ~

The difference between the position of the peak and the input value of mT+ is, typically, 10-20 GeV!

T+ single production at the LHC

SM BG: tt & single t productions!-

At the parton levelSignal = bqlν

Existence of very energetic jet (b from T+)!With the leading jet, reconstruct T+-system.There are 2-fold ambiguity to reconstructneutrino momenta & Reject events unless is small.Jet mass is also used to reduce the BG.

~ Output ~Distribution of

~ Strategy to reduce BG ~

Single T+ production occurs not through a QCD process but through a EW process (e.g. W-exchange). Distributions have distinguishable peaks at around the T+ mass when sin2β is large enough! From the cross section, we will be able to determine sinβ.

~ Results ~ ~ Cut used in the analysis ~

~ Discussion ~

T+ single production at the LHC

We use the side-band method to extract the # of the single production events, (L) (C) (R)after imposing the cuts. Then, cross section for the single T+ production can be obtained from the # of events in the signal region.

~ Results (Point 2) ~

~ Conclusion ~~ Accuracy of sinβ determination ~

The cross section, which is proportional to sin2β, will be determined with 10-20%. Parameter “sinβ”, which is given by a combinationof f & λ2, will be determined with 5-10% accuracy!

T+ single production at the LHC

T– pair production at the LHC

SM BG: tt–production! (460 pb)-

At the parton levelSignal = (bqqAH)×2

1. Large missing momentum is expected in the signal event due to dark matter emissions.2. Use the hemisphere analysis to reconstruct the top quark [S.M., Nojiri, Nomura (2007)].3. Since AH is undetectable, direct masurements of T– & AH are difficult. MT2 variable!

~ Output ~Distribution of MT2

~ Strategy to reduce BG ~

T– decays into t + AH with 100 % branching ratio

H1H2

“MT2 variable” is a powerful tool to determine mT+ and mAH, which is defined by

with being the postulated AH mass. Then, the end point of MT2 distribution is

~ Results (Point 2) ~ ~ Cut used in the analysis ~

~ Discussion ~

T– pair production at the LHC

0 100 200

End-point of the distribution of MT2 is determined by a combination of mT+ , mAH, and the postulate mass . By looking at the position of the end-point with an appropriate value of , it is possible to get information of mAH & mT+! We have also checked that there is no contamination of the BG around End-point!

~ Results (Point 2) ~

~ Conclusion ~~ Accuracy MT2

(max) determination ~

Using the distribution of the MT2 with , the upper end-point will be determined with 10-20 GeV accuracy (at Point 2)!

T– pair production at the LHC

With the use of quadratic function to estimate the end-point,

usingusing

when . Theoretically, the end-point is 664 GeV.

~ Results ~~ Observables ~

Testing the Model

Case 1 (Conservative)

Case 2 (Optimistic)

(pink) T+ pair(black) T+ single(blue) T- pair

(pink) T+ pair(black) T+ single(blue) T- pair

~ Results ~~ Observables ~

Testing the Model

Case 1 (Conservative)

Case 2 (Optimistic) It is also possible to determinethe cosmic abundance of the dark matter (AH) using the LHT data. However, it is also true that, whenf is small enough, the determinationhas a large ambiguities.

Summary• The top partners T+ and T– play an essential role to

discover the deviation from the SM at the LHC.• It is possible to extract the LHT parameters from the data

such as mT+, sinβ, MT2(max), etc.

• It is also possible to test the model by looking at the non-trivial relation between the signal, though the method is rather model dependent.

Discussion• In the cosmological connection, it is important to get

information about mass, spin, quantum numbers, interactions of the dark matter (AH). At the LHC, it may be possible to extract the LHC parameters under the model dependent way, and estimate the cosmic abundance of the dark matter. However, it is very challenging to perform those under the model dependent way.