The study of q q production at LHC in the l l channel and sensitivity to other models Michihisa Takeuchi ~~ LL ± ± (hep-ph/ ) Kyoto Univ. (YITP), ＫＥＫ D1 Collaboration with M. M. Nojiri

Partners and Z 2 are key points, ＳＵＳＹ（ＭＳＳＭ） Littlest Higgs model with T-parity Universal Extra Dimension model and so on… ・ DM problem ･ Fine tuning problem New symmetry is introduced Partners for the SM particles from ＬＥＰ constraint Too heavy But, new particles are added in TeV scale. (fine tuning problem is reintroduced) The model beyond the SM should solve two problems Z 2 odd particles are always pair produced The lightest Z 2 parity odd particle cannot decay into the SM particles in a collider experiment SM: even, New particles: odd

Typical mass spectra are similar All Z 2 odd particles decay in cascade with SM particles and finally decay into DM GeV 950 GeV 350 GeV 300 GeV 180 GeV Ex.) mSUGRA point MSSM Littlest Higgs with T-parity Such models have similar features. 950 GeV 350 GeV 180 GeV 300 GeV Decay patterns are similar.

p p Strong interacting particles are produced Once new particles are produced, they decay in cascade with SM particles. Two lightest Z 2 parity odd particles are finally produced. They cannot be detected. High jets 、 high leptons Large At LHC, new particles can be produced, but the SM processes are also produced copiously. We must find out the signal beyond the SM. Proton consists of u, d and gluon. 7 TeV These signals are common for models which have SM partners and Z 2 parity. ex.) gluino, squark in SUSY

we cannot distinguish these models only by the mass spectrum MSSM, UED, LHT, beyond the MSSM, etc. mass spectrum can be determined by the kinematics of cascade decay. spin, coupling relations, majorana nature of gaugino, etc. investigate the special features of the models. Once these signals are observed, Measurement of the production cross sections. Ex.) depends strongly on the majorana nature of gluino. This process needs chirality flip. If gluino is dirac, this process is forbidden.

1. Introduction 2. Cross sections of various models 3. Measurement of σ( q q ) 4. Numerical results 5. Summary Plan ~~ LL

2. Cross section of various models ＭＳＳ Ｍ The model with an extended gluino sector ＬＨＴ LHC is hadron collider therefore we cannot tell easily what the initial partons are. Identification of the produced particles is difficult. If we can measure the and separately, we can distinguish these models. We consider how we can measure the production cross section separately in the MSSM at first. Mass spectra are the same.

3. Measurement of σ( q q ) To measure, we use same-sign two lepton channel. BR=46% BR=44% BR=20% ~~ L L Let’s consider the MSSM. This gives a clean signal. BR=4% This also produce We need a method to separate production processes. However, there is a big background from

Separation of production processes We want to cut gluino contribution b-veto Cut the events with b-jet Gluino partly decay into third generation squarks. b-quark are always accompanied 2 jets 1 jet additional jet We want to separate these two kinds of production processes

Hemisphere cuts Produced two particles decay independently and form two groups. 2 jets 1 jet The largest invariant mass of jet pair in the hemisphere. If there is 1 or 0 jet in the hemisphere, we define as 0. It is useful to reconstruct these two groups. This method is using only kinematics Model independent hemisphere 2 hemisphere 1 We can identify each hemisphere’s parent particle

To cut gluino contributions, we impose the cut vs distribution for three production processes 2 jets 1 jet From these figure, you can see this method works well generated by Herwig 6.5

4. Numerical results for SS2l events 1. Basic cut ( : for cutting SM events) 2. b-veto ( : for cutting gluino contribution) 3. Hemisphere cuts Calculated with Herwig 6.5 Total number of events contribution from number of generated events number of events after Basic cut number of events after Basic cut & b-veto number of events after Basic cut & b-veto & Hemisphere cuts

Gluino 60% off More than 97 % of events with gluino are cut after. 40% from If gluino contribution is larger, the ratio approaches If there is no gluino contribution, the ratio approaches % from Calculated with Herwig 6.5 More than 30 % of events from survive after.

Comparison of models Main sources of ＭＳＳ Ｍ The model with an extended gluino sector ＬＨＴ These cut efficiency is model independent, so we can apply them to other models,

5. Summary New particles probably exist at TeV scale. Promising models: MSSM, LHT, UED, … If mass spectrum can be determined, to distinguish these models is important. Production cross sections help to distinguish the models. We proposed a method to distinguish production processes based on the number of jets in a hemisphere. (hep-ph/ , M. T. and M. M. Nojiri.)