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arXiv 1902.08096hep-phhep-ex
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提升顶夸克极化

Boosted Top quark polarization

Rohini Godbole, Monoranjan Guchait, Charanjit K. Khosa, Jayita Lahiri, Seema Sharma, Aravind H. Vijay

备注：
19 pages, 12 figures, Substantially revised text, results remain unchanged. Added few references. To be published in Physical Review D
发表信息：
Phys. Rev. D 100, 056010 (2019)
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摘要：

在顶夸克产生中，由耦合的手征结构决定的顶夸克的极化很可能在任何新的物理贡献的存在下被修改。因此，这对于那些耦合具有不同于标准模型（SM）中的手性结构的新物理模型是一个很好的解释。在本说明中，我们构建探针的极化顶夸克衰变强子，使用容易获得的运动学变量，如能量分数或角相关的衰变产物。利用通常的喷注子结构技术标记助推顶夸克，我们研究了这些观测值对基准过程$W^{\prime} \to tb$的鲁棒性。我们证明了实验室框架中的b喷注能量分数和我们在顶静止框架中构造的一个新的角变量都是区分左、右极化顶夸克的有力工具。基于偏振敏感的角度变量，我们构造了反映偏振的不对称性。我们研究了两个新的物理过程中这些变量的效率，这两个新的物理过程产生了推升顶夸克：（i）超对称搜索背景下的顶夸克衰变，和（ii）Kaluza-Klein（KK）引力子和KK胶子的衰变，在Randall Sundrum（RS）模型。值得注意的是，发现不对称性可以在大约+20\%到-20\%的宽范围内变化。还详细研究了这些模型中存在的新粒子的不对称性对顶夸克耦合的依赖性。

英文摘要：

In top quark production, the polarization of top quarks, decided by the chiral structure of couplings, is likely to be modified in the presence of any new physics contribution to the production. Hence the same is a good discriminator for those new physics models wherein the couplings have a chiral structure different than that in the Standard Model (SM). In this note we construct probes of the polarization of a top quark decaying hadronically, using easily accessible kinematic variables such as the energy fraction or angular correlations of the decay products. Tagging the boosted top quark using the usual jet sub structure technique we study robustness of these observables for a benchmark process, $W^{\prime} \to tb$. We demonstrate that the energy fraction of b-jet in the laboratory frame and a new angular variable, constructed by us in the top rest frame, are both very powerful tools to discriminate between the left and right polarized top quarks. Based on the polarization sensitive angular variables, we construct asymmetries which reflect the polarization. We study the efficiency of these variables for two new physics processes where which give rise to boosted top quarks: (i) decay of the top squark in the context of supersymmetry searches, and (ii) decays of the Kaluza-Klein(KK) graviton and KK gluon, in Randall Sundrum(RS) model. Remarkably, it is found that the asymmetry can vary over a wide range about +20\% to -20\%. The dependence of asymmetry on top quark couplings of the new particles present in these models beyond the SM (BSM) is also investigated in detail.

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