Phenomenology Study Of Higgs Physics At LHC And ILC

During the past40years, the Standard Model(SM) of elementary particle successfully uni-fed strong and electroweak interaction, and it has been tested by the precise experimental data.We can say that the SM is one of the best theories to describe the interaction of fundamentalparticles. The SM is a good theory but not a perfect one. Because there are several problemsthat have not been solved, for example,fne-tuning problem, candidate for dark matter problemand gravity problem. So, the SM is generally considered to be an efective theory at a low scale,leaving room for developing new physics beyond SM, i.e. there should been some more basictheory at a higher scale. In so many new physics, one of the most popular new physics is lowenergy supersymmetric model, which can solve the problems in the SM. So, the phenomenologystudy of supersymmetric model has attracted more and more attention.Higgs plays a very important role in SM and new physics beyond SM――the mass origina-tion. On the one hand, Higgs give the boson particles mass through mechanism of spontaneoussymmetry breaking–Higgs mechanism；on the other hand, Higgs give fermion mass throughY ukawa coupling. So, Higgs is considered to be“god particle”. The study of Higgs bosonis always hot. From the frst appearance of Higgs concept in1964, to Higgs may exist in July2012, fnally to Higgs announced to be found by CERN in March2013, almost half century havepassed. The study of Higgs is not end, but going on. We do not know the founded Higgs isunder which model, i.e. there is no robust evidence to say the Higgs is in SM. We hope theseproblems will be solved together with the second running of LHC.In this thesis, we focus on Higgs and Higgs pair production in diferent colliders underlow energy efective theory such as minimal supersymmetric standard model(NMSSM), nextto minimal supersymmetric standard model(NMSSM). The diferent colliders are mainly LargeHadron Collider (LHC) and International Linear Collider (ILC). Our work is as follows:(1) In light of the signifcant progress of the LHC to determine the properties of the Higgsboson, we investigate the capability of the Manohar-Wise model to explain the Higgs data. Thismodel extends the SM by one family of color-octet and isospin-doublet scalars, and it can sizablyalter the coupling strengths of the Higgs boson with gluons and photons. We frst examine thecurrent constraints on the model, which are from unitarity, the LHC searches for the scalars and the electroweak precision data (EWPD).In implementing the unitarity constraint, we usethe properties of the SU(3) group to simplify the calculation. Then in the allowed parameterspace we perform a ft of the model using the latest ATLAS and CMS data. We fnd thatthe Manohar-Wise model is able to explain the data with χ2signifcantly smaller than the SMvalue.For elaborate details see chapter4.(2)In MSSM and NMSSM, we focus on Higgs pair production at LHC. This work is helpfulfor studying Higgs self-coupling while Higgs self-coupling can be used to reconstruct the Higgspotential。After125GeV Higgs discovered,the Higgs self-coupling in SM is fxed while in SUSYis not fxed,yet.In SM, the mainly contribution of Higgs pair production is from one loop topquark diagram; in SUSY, the mainly contribution is also from one loop diagram. They arethe same order, so the production of Higgs pair in SUSY may greatly alter the productionin SM. And in this process,the non-decoupling efect may be strong, we could not ignore itsefect. Based on our research, we found that the the dominant contribution to the Higgs pairproduction comes from the gluon fusion process and the production rate can be greatly enhanced,maximally10times larger than SM prediction (even for a TeV-scale stop the production ratecan still be enhanced by a factor of1.3). Such large enhancement may help people to use thisprocess research Higgs.For elaborate details see chapter5.(3)It is the same with (2), we also study the production of Higgs pair at ILC. We found thatthe large enhancement of the cross section in the MSSM is mainly due to the contributions fromthe loops mediated by the stau, while in the NMSSM it is mainly due to the contributions fromthe top-squark loops. The normalized production rate σSUSY/σSMcan reach18in MSSM whilecan reach2in NMSSM. Such enhancement may be detected in the future collider to researchthe property of Higgs boson.For elaborate details see chapter6.