The Phenomenology Study Of Higgs Physics At The Collider

No matter in the Standard Model(SM) or the new physics, Higgs field plays an important role, for the responsibility of providing mass to the gauge bosons through Higgs mechanism, or to the fermions through Yukawa interaction. In the past decades, the remarkable agreement of experiment with theory testifies the correctness of SM in describing the electro-weak physics, but, the deviation of its prediction from the Higgs data of LHC, and theoretical defects of the SM itself suggest the existence of new physics. Therefore, the research of Higgs in the framework of new physics is still the hot spot of particle physics.In the first part of the series of works, we investigate the Higgs phenomenology in the λ-SUSY, as well as the Higgs pair production process pp �' hh at LHC(?)s=14TeV). As a most natural realization of the Next-to Minimal Supersymmetry Standard Model (NMSSM), λ-SUSY is parameterized by a large λ around one and a low tan β below 10. we find that naturalness plays an important role in selecting the parameter space of λ-SUSY, and that the Higgs χ2 obtained with the latest data is usually significantly smaller than before due to the more consistency of the ATLAS and CMS measurements. We first scan the parameter space of λ-SUSY by considering various experimental constraints, including the limitation from the Higgs data updated by the ATLAS and CMS collaborations in the summer of 2014, then we study the properties of the Higgs bosons. We have following observations:· For the lightest Higgs boson hI, i.e. the SM-like Higgs boson h, current Higgs data still allow for a sizable singlet component in h, which at most reaches 25%, while the non-SM doublet component is forbidden to be larger than 1%; the normalized couplings such as Chγγ/SM, ChZZ/SM and Chtt/SM are limited within 15% deviation from unity at 95% C.L.; the strength of the triple self coupling of h may get enhanced by a factor over 10, and naturalness can limit such a possibility.● For the next-to-lightest CP-even Higgs boson h2, naturalness disfavors a h2 with mass at several TeV regardless its field components. For mh2≤ 500GeV, h2 in most cases is either highly non-SM doublet dominated or highly singlet dominated. For the singlet dominated h2, although it may be as light as 150GeV, its couplings with SM fermions is usually rather weak, so is of less interest in phenomenology study. For the non-SM double dominated h2, it may be as light as 200GeV. As for its coupling, we find|Chtt/SM|≥0.2, and in optimal case the normalized coupling is just slightly below 1. On the other hand,|Chbb/SM|is usually larger than one with its maximum value reaching 6. As a result, the h2gg coupling may be comparable with the SM hgg coupling for a low tanβ. For either the doublet dominated h2 or the singlet dominated h2, the strength of the h2hh interaction may be quite large. Consequently, h2 �' hh can act as the dominant decay channel of h2.● There are three mechanisms to enhance h pair production cross section greatly, i.e. by stop-induced box diagrams, by s-channel resonant h2 effect and by large self coupling of h. With these mechanisms, we conclude that the h pair production rate in λ-SUSY may be enhanced by more than 100 times compared with its SM prediction.In the second part of the series of works, We investigate the Higgs-strahlung production process e+e- �' Zh at the future Higgs factory such as TLEP by including radiative corrections in the Minimal Dilaton Model (MDM), which extends the SM by one singlet scalar called dilaton. We consider various theoretical and experimental constraints on the model, and perform fits to the Higgs data taken from ATLAS, CMS and CDF+DO. Then for the lσ surviving samples, we calculate the MDM predictions on the inclusive production rate σ(e+e- �' Zh) at the 240-GeV Higgs factory, and also the signal rates of e+e- �' Zh with the Higgs boson decaying to bb and γγ. We have following observations:● In the heavy dilaton scenario, the deviation of a(e+e- �' Zh) from its SM prediction can vary from -15% to 85%, which mainly arises from the modification of the tree-level hZZ coupling and also the radiative correction induced by possibly large Higgs self-couplings. The processes e+e- �' Zh at the Higgs factory and pp �' hh at 14-TeV LHC are comple-mentary in limiting the MDM parameter space. Requiring the deviation of a(e+e- �' Zh) from its SM prediction to be less than 1% and that of a(pp �' hh) to be less than 50%, tan θs in the MDM will be limited to be-0.1< tan θs< 0.3, and the deviations of the signal rates are constrained to be|Rbb|< 2% and|Rγγ|< 7%. Especially, the Higgs self-coupling normalized to its SM prediction is now upper bounded by about 4.● In the light dilaton scenario, the deviation of σ(e+e- �' Zh) may reach-7%, and requiring its size to be less than 1% will result in 0< tanθs< 0.1, and -10% < Rbb,Rγγ< 1%.● For the t’-induced radiative correction to the Higgs-strahlung production process e+e- �' Zh at future Higgs factory, we present the analytical calculations in detail and show how to handle the ultraviolet divergence. We find that a large sin θL can enhance the correction, for sinθL= 0.2 and mt’ = 1200GeV, the correction is 0.26% and 2.1% for (?)Se+e-= 240GeV, 1TeV respectively, and a larger value can be achieved as sin θL increases.