分类： 物理学 >> 基本粒子与场物理学 提交时间： 2017-08-24
摘要： We study the properties of g 1 , the first excited state of the gluon in representative variants of the Randall Sundrum model with the Standard Model fields in the bulk. We find that measurements of the coupling to light quarks (from the inclusive cross-section for pp → g 1 → tt), the coupling to bottom quarks (from the rate of pp → g 1 b), as well as the overall width, can provide powerful discriminants between the models. In models with large brane kinetic terms, the g 1 resonance can even potentially be discovered decaying into dijets against the large QCD background. We also derive bounds based on existing Tevatron searches for resonant tt production and find that they require Mg 1 & 950 GeV. In addition we explore the pattern of interference between the g 1 signal and the non-resonant SM background, defining an asymmetry parameter for the invariant mass distribution. The interference probes the relative signs of the couplings of the g 1 to light quark pairs and to tt, and thus provides an indication that the top is localized on the other side of the extra dimension from the light quarks, as is typical in the RS framework.
分类： 物理学 >> 核物理学 提交时间： 2016-09-14
摘要： Many new physics models predict sizable modifications to the SM Zbb couplings, while the corresponding measurements at LEP and SLC exhibit some discrepancy with the SM predictions. After updating the current results on the Zbb coupling constraints from global fits, we list the observables that are most important for improving the Zbb coupling constraints and estimate the expected precision reach of three proposed future e+e- colliders, CEPC, ILC and FCC-ee. We consider both the case that the results are SM-like and the one that the Zbb couplings deviate significantly from the SM predictions. We show that, if we assume the value of the Zbb couplings to be within 68% CL of the current measurements, any one of the three colliders will be able to rule out the SM with more than 99.9999% CL (5 sigma). We study the implications of the improved Zbb coupling constraints on new physics models, and point out their complementarity with the constraints from the direct search of new physics particles at the LHC, as well as with Higgs precision measurements. Our results provide a further motivation for the construction of future e+e- colliders.
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