The study of q q production at LHC in the l l channel and sensitivity to other models

1. ~ ~ The study of q q production at LHC in the l l channel and sensitivity to other models L L ± ± (hep-ph/0701190) Michihisa Takeuchi Kyoto Univ. (YITP), ＫＥＫ　D2 Collaboration with M. M. Nojiri

2. 1. New Physics at TeV scale Fine tuning prob. • The Standard Model describes interactions among elementary particles well. But, radiative corrections for Higgs mass parameter is quadratic divergent. New Physics at TeV Dark matter prob. • We cannot doubt of the existence of the Dark matter in the universe. But, there is no candidate in the Standard Model. Assuming the DM is WIMP and the mass is TeV mass DM is natural

3. New symmetry Partner particles for the SM particles But, new particles are added in TeV scale. The lightest Z parity odd particle Constraint from ＬＥＰ cannot decay into the SM particles Too heavy (fine tuning problem is reintroduced) Z odd particles are always pair produced in a collider experiment 2. Models beyond the SM ･ Fine tuning problem For example, these models have this structure • ＳＵＳＹ（ＭＳＳＭ） • Littlest Higgs model with T-parity • Universal Extra Dimension model and so on… ・ Existence of stable DM

4. Partners have the same features Models with LHT MSSM 1050 GeV Similar typical partners’ mass spectra 950 GeV 350 GeV The litest Z2 odd particle Is a good candidate of DM 300 GeV 180 GeV All Z2 odd particles decay in cascade to the DM with emitting SM particles This is important feature to distinguish new physics from the SM processes at the LHC

5. At the LHC At the LHC, the SM processes are also produced enormously. We must find out the signal beyond the SM. Strong interacting particles are produced in pair Proton consists mainly of u, d and gluon. p p Once new particles are produced, they decay in cascade. Many hard jets Two lightest Z parity odd particles are finally produced Large To distinguish from SM events Signal ： 、High jets、 High leptons

6. Fine tuning prob. Dark matter Partners Signal ： 、High jets、 high leptons Mass spectrum of new particles are extracted But, what we can see is an evidence of new particles beyond the SM. Mass spectrum determination After selecting events beyond the SM by proper cuts, mass spectrum can be determined by the kinematics of the cascade decay.

7. Sample point 1050 GeV 950 GeV 350 GeV 300 GeV 180 GeV • ＭＳＳＭ • The model with an extended gluino sector • ＬＨＴ Measurement of production cross section separately helps this purpose Distinguish models Mass spectra are extracted by kinematics. (model independent way) Difficult to distinguish models with partners and paity To investigate the own features of the models are needed. We compare production cross section of 3 models with the same mass spectra

8. Sample point 1050 GeV 950 GeV 350 GeV 300 GeV 180 GeV The MSSM In the MSSM, once mass spectrum are determined, we can calculate production cross sections of various processes. ・We focus on Left handed squark < From PDF of proton We can verify the MSSM to measure the production cross sections.

9. Sample point 1050 GeV 950 GeV 350 GeV 300 GeV 180 GeV The model with Extended gluino sector Inspired from N=2 model MSSM + SU(3) adjoint fermion (JHEP 0208:035,2002. P. J. Fox, A. E. Nelson, N. Weiner) Two gluinos Decay pattern is the same as MSSM ・We assume Mass spectrum is completely the same As the MSSM Left handed squark pair productions are suppressed

10. Sample point 1050 GeV 950 GeV 350 GeV 300 GeV 180 GeV Littlest Higgs model with T parity (JHEP 0410:067,2004, I. Low) Higgs is introduced as gold stone boson in this model • This model has T odd partners for SM particles • No gluon partner • Decay pattern of T-odd quark is similar to squark Quark partners production cross section is 4~5 times as large as that of the MSSM. (T-parity would be weakly broken by anomaly, but collider signal doesn’t change)

11. Summary table of production cross sections Few production No prod. Key point is 4 times of ～４：１ (Unit of pb) From u : d ～２：１ in PDF ～２：１ • Measurement of production cross section helps to distinguish these models How to measure? Let’s consider the MSSM case at first.

12. LHC is hadron collider therefore we cannot tell easily what the initial partons are.Identification of the produced particles is difficult. But, background SS2lepton events come from BR=4% We need a method to distinguish the production processes. At 1TeV, is larger than (5 times as) Both contributions are same order ~ ~ In the MSSM, How to Measureσ( q q ) L L Left handed squark decay into lepton BR=46% BR=44% SS2lepton channel easy to distinguish from SM events We can estimate production cross section from number of SS2 lepton events Charge information is conserved BR=20%

13. b-veto Gluino decay into third generation squarks 60% of events with gluino are cut. • Number of jets （We use Hemisphere cuts） 2 jets Originally due to large gluino contribution 1 jet After cutting gluino contribution, we expect Separation of production processes To measure ,we want to cut gluino production contribution

14. 2 jets or more 1 jet Hemisphere analysis Produced two particles decay independently and form two groups. It is useful to reconstruct these two groups. We regard objects with similar momenta have the same parent. hemisphere 1 2 hemispheres We define following variable in each hemisphere We can likely identify the parent particles in each hemisphere. Using only kinematics hemisphere 2 Model independent

15. 2 jets 1 jet vs distribution （major 3 production processes of the MSSM) generated by Herwig 6.5 with AcerDET 1.0 We impose ：3% left to cut gluino contributions ：35% left

16. If we know the efficiency of cuts from MC and branching ratio, we can estimate the production cross sections using SS2l event rate. Numerical results 1. Basic cut ( : for cutting SM events) 2. b-veto ( : for cutting gluino contribution) 3. Hemisphere cuts More than 97 % of events with gluino are cut after .

17. Comparison of the models Unit is pb Few production No prod. Key point is 4 times of Main source of after Hemisphere cuts Ratio of after/before cuts 2573 Absolute value ~4000 ~1000 Gluino contribution is large 2：1 If gluino contribution is large, number of events after the cut are reduced. Squark contribution is large 4：1

18. Summary • The models which describe TeV physics have Ｚ2 parity, and collider signals are similar. 　　　　　　　　　　ＭＳＳＭ、ＬＨＴ、ＵＥＤ、etc. • It is important to measure each production cross section separately for distinguish these models, therefore also important to identify production process. • We investigate SS2l events and propose the method to distinguish between gluino and squark productions based on counting number of jets.