Report on LHT at the LHC ～ Some results from simulation study ～

1. Report on LHTat the LHC～Some results from simulation study～ Shigeki Matsumoto(Univ. of Toyama) S. M., M. M. Nojiri, and D. Nomura, PRD75 (2007) S. M., T. Moroi and K. Tobe(arXiv:0806.3837, will be in PRD) • What kinds of LHT signals are expected,and how accurately the LHC parametersare determined at the LHC? • Important to clarify the between theLHT study at the ILC and at the LHC.

2. - - - H (DM) - - - H Little Higgs Model with T-parity H - - - - - - Triplet 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 particles (will be) playing an important role areHeavy gauge bosons (γH, ZH, WH),Top partners (T±),Triplet Higgs! New physics parameters introduced in the LHC areBreaking Scale ( f ) and Top partner mass (λ2f) and mh!

3. Littlest Higgs model with T-parity at the LHC 7 TeV 7 TeV Proton Proton New Colored Particles LHC is a “hadron” collider, so that colored new particles are copiously produced! Representative Points Productions of top partners, in particular, T+ & T–!

4. Littlest Higgs model with T-parity at the LHC ~ Signal Processes ~ Pair T+ production, Single T+ production, Pair T– production. ~ Strategy to generate events ~ Fragmentation, initialand final state radiations,hadronization effects: PYTHIA Event generation at the parton level including PDF effects: MadGraph/Event Detector simulations including Jet reconstruction withcone algorithm, b and t jet tags, isolated leptons and photons identification, missing momentum from calorimater information: PDG4

5. T+ pair production at the LHC - SM BG: tt–production! (460 pb) At the parton levelSignal = bbqqlν ~ Strategy to reduce BG ~ - - • 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 = mW2. There are 6-fold ambiguity in the reconstruction of T+-system. • The combination to minimize ~ Output ~ Distribution of

6. T+ pair production at the LHC ~ Cut used in the analysis ~ ~ Results ~ ~ Discussion ~ 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+.

7. T+ pair production at the LHC ~ Accuracy of the mT+ determination ~ 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 ~ Conclusion ~ The difference between the position of the peak and the input value of mT+ is, typically, 10-20 GeV! ~ Results ~

8. T+ single production at the LHC - SM BG: tt & single t productions! At the parton levelSignal = bqlν ~ Strategy to reduce BG ~ 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

9. T+ single production at the LHC ~ Cut used in the analysis ~ ~ Results ~ ~ Discussion ~ 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 sin2βis large enough!  From the cross section, we will be able to determine sinβ.

10. T+ single production at the LHC ~ Accuracy of sinβ determination ~ ~ Conclusion ~ 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. 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! ~ Results (Point 2) ~

11. T– pair production at the LHC H1 H2 T– decays into t + AH with 100 % branching ratio - SM BG: tt–production! (460 pb) At the parton levelSignal = (bqqAH)×2 ~ Strategy to reduce BG ~ 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

12. T– pair production at the LHC ~ Cut used in the analysis ~ ~ Results (Point 2) ~ 0 100 200 ~ Discussion ~ “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

13. T– pair production at the LHC ~ Accuracy MT2(max) determination ~ ~ Conclusion ~ 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! Using the distribution of the MT2 with , the upper end-point will be determined with 10-20 GeV accuracy (at Point 2)! ~ Results (Point 2) ~ With the use of quadratic function to estimate the end-point, using using when . Theoretically, the end-point is 664 GeV.

14. Testing the Model ~ Observables ~ ~ Results ~ (pink) T+ pair (black) T+ single (blue) T- pair Case 1 (Conservative) (pink) T+ pair (black) T+ single (blue) T- pair Case 2 (Optimistic)

15. Testing the Model ~ Observables ~ ~ Results ~ Case 1 (Conservative) 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. Case 2 (Optimistic)

16. 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.