分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-09
摘要： In light of the Higgs discovery and the nonobservation of sparticles at the LHC, we revisit the supersymmetric theory (SUSY) induced top quark flavor-changing decay into the Higgs boson. We perform a scan over the relevant SUSY parameter space by considering the constraints from the Higgs mass measurement, the LHC search for SUSY, the vacuum stability, the precision electroweak observables as well as B -> X-s gamma. We make the following observations: (1) In the Minimal Supersymmetric Standard Model (MSSM), the branching ratio of t -> ch can only reach 3.0 x 10(-6), which is about one order smaller than previous results obtained before the advent of the LHC. Among the considered constraints, the Higgs mass and the LHC search for sparticles are found to play an important role in limiting the prediction. (2) In the singlet extension of the MSSM, since the squark sector is less constrained by the Higgs mass, the branching ratio of t -> ch can reach the order of 10(-5) in the allowed parameter space. (3) The chiral-conserving mixings delta(LL) and delta(RR) may have remanent effects on t -> ch in the heavy SUSY limit. In the MSSM with squarks above 3 TeV and gluino above 4 TeV and meanwhile the CP-odd Higgs boson mass around 1 TeV, the branching ratio of t -> ch can still reach the order of 10(-8) under the constraints.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-09
摘要： In some supersymmetric models like split supersymmetry or models with nonuniversal gaugino mass, 'bino [lightest sparticle (LSP)] and wino [next-to-lightest sparticle (NLSP)] may have rather small mass splitting in order to provide the correct dark matter relic density through bino/wino coannihilation. Such a scenario with the compressed bino/wino is difficult to explore at the LHC. In this work we propose to probe this scenario from pp -> j (chi) over tilde (0)(2)(chi) over tilde (+/-)(1) followed by (chi) over tilde (0)(2) -> gamma(chi) over tilde (0)(1) and (chi) over tilde (+/-)(1) -> W*(chi) over tilde (0)(1) -> l(+/-)nu(chi) over tilde (0)(1) (this method is also applicable to the compressed bino/Higgsino scenario). Through a detailed Monte Carlo simulation for both the signal and the backgrounds, we find that for a mass splitting Delta M similar to 10-15 GeV between bino (LSP) and wino (NLSP), the 14 TeV LHC with a luminosity of 1000 fb(-1) can probe the wino up to 150 GeV (the sensitivity can reach 3.4 sigma for Delta M = 10 GeV and 2 sigma for Delta M = 15 GeV). We also investigate the dark matter detection sensitivities for this scenario and find that the planned XENON-1T (2017) cannot fully cover the parameter space with a wino below 150 GeV allowed by relic density and the LUX limits.
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