Phenomenological Study Of New Physics At LHC

With the running of Large Hadron Collider at the European Organization for Nuclear Research, particle physics and high-energy physics have achieved great progress in experiments, especially the discovery of SM-like Higgs and direct searches of SUSY. We did a sires of researches around these experimental results and predictions of LHC:â‘ We consider the natural supersymmetry scenario in the framework of the R-parity con-serving minimal supersymmetric standard model(called natural MSSM) and examine the observability of stop pair production at the LHC. We first scan the parameters of this scenario under various experimental constraints, including the SM-like Higgs boson mass, the indirect limits from precision electroweak data and B-decays. Then in the allowed parameter space we study the stop pair production at the LHC followed by the stop decay into a top quark plus a lightest neutralino or into a bottom quark plus a chargino. From detailed Monte Carlo simulations of the signals and backgrounds, we find the two decay modes are complementary to each other in probing the stop pair production, and the LHC with (?)s=14TeV and100fb-1luminosity is capable of discovering the stop predicted in natural MSSM up to450GeV. If no excess events were observed at the LHC, the95%C.L. exclusion limits of the stop masses can reach around537GeV.Motivated by the new progress of direct search for the productions of stop pair and sbottom pair at the LHC, we further examine the constraints of the search results on the stop mass in natural SUSY. We first scan the parameter space of natural SUSY in the framework of MSSM, considering the constraints from the Higgs mass, B-physics and electroweak precision measurements. Then in the allowed parameter space we perform a Monte Carlo simulation for stop pair production followed by t1â†'tχ10or t1â†'bχ1+and sbottom pair production followed by b1â†'bχ01or b1â†'tχ1â†'tχ1+Using the combined results of ATLAS with20.1fb-1from the search of (?)+jets+ETmiss, hadronic tt+ETmiss and2b+ETmiss, we find that a stop lighter than600GeV can be excluded at95%CL in this scenario.â‘¡The excess of top quark forward-backward asymmetry (AtFB) reported by the Tevatron and the enhancement of the Higgs decay to diphoton observed by the LHC may point to a same origin of new physics. In this note we examined such anomalies in the two-Higgs-doublet model with a color-triplet scalar. We found that under current experimental constraints this model can simultaneously explain both anomalies at la level. Also, we examined the Higgs decay hâ†'Zγ and displayed its correlation with hâ†'γγ. We found that unlike other models, this model predicts a special correlation between hâ†'Zγ and hâ†'γγ, i.e., the Zγ rate is highly suppressed while the γγ rate is enhanced. This behavior may help to distinguish this model in the future high luminosity run of the LHC.â‘¢We presented a Bayesian analysis of CMSSM including the latest LUX constraints, the ATLAS and CMS experiments on Higgs and SUSY, the LHCb measurement of B physics, the dark matter constraints from Planck Data, and other low-energy observable constrains. Firstly we explore the favoured regions of the SUSY parameter spaces with a Markov Chain Monte Carlo method. Then we present the properties of the parameter spaces and predictions with Bayesian analysis. Furthermore we study the SM-like Higgs via the program HiggsSingnal. We find that the CMSSM have the tensions between the anomalous magnetic moment of the muon, the SM-like Higgs mass, which could not satisfy the experimental constrains in2a at the same time while the other experiments were perfectly matched. The best fit point had χ2=13.459, corresponding to a p-value of0.0194.