Jet substructures of boosted polarized top quarks

Abstract

We study jet substructures of a boosted polarized top quark, which undergoes the semileptonic decay $t\to b\ell\nu$, in the perturbative QCD framework. The jet mass distribution (energy profile) is factorized into the convolution of a hard top-quark decay kernel with the bottom-quark jet function (jet energy function). Computing the hard kernel to leading order in QCD and inputting the latter functions from the resummation formalism, we observe that the jet mass distribution is not sensitive to the helicity of the top quark, but the energy profile is: energy is accumulated faster within a left-handed top jet than within a right-handed one, a feature related to the $V-A$ structure of weak interaction. It is pointed out that the energy profile is a simple and useful jet observable for helicity discrimination of a boosted top quark, which helps identification of physics beyond the Standard Model at the Large Hadron Collider. The extension of our analysis to other jet substructures, including those associated with a hadronically decaying polarized top quark, is proposed.Comment: 18 pages, 8 figure

Light dark matter showering under broken dark U(1) — revisited

“…It has been known that jet substructures serve as a powerful tool to explore properties of parent particles which lead jets. For example, it was proposed in [21] are generally too small to be identified in the distributions.…”

Longitudinal top polarisation measurement and anomalous Wtb coupling

“…In such a case observables based on the energy distributions of the decay products rather than their angular distributions are more suitable to probe the polarisation of the top quark [75]. For such highly boosted tops methods based on the jet substructure have been proposed to extract information on the polarisation of the top which then can be used to get information on the production mechanism of top quarks [76][77][78]. Recently a new method for measuring the polarisation of top, when the top decays hadronically, has been proposed [79].…”

Energy profile of b-jet for boosted top quarks

“…00027-p. 5 Besides this discrimination will be helpful not only for the identification of the top helicities, but also for the study of the chiral structure of the top quark through jet observables. The straightforward application of this formalism to the hadronic top-decay is under investigation.…”

“…The decay part M decay 2 is given by the product of leptonic trace and the trace for the decay part. Factorising the b-quark trace from the decay trace by Fierz identity and combining the phase space, the decay part is converted into a part of the top-jet function [5]. The LO top-jet function J (0),s t t specified by the top-spin vector s t is expressed as the convolution with the hard kernels F a , F b and the LO b-jet function J (0) b in the following form:…”

“…In our previous work [5], the helicity dependence in the top-jet substructure is discussed, especially the energy profile (alternatively, jet shape) which expresses a distribution of the sub-jet energy in the top-jet cone for a highly boosted polarised-top is considered. The energy profile is defined in the following: where r ≤ R t is a test radius in the top jet J t , N J t is a number of top jets with the top-jet radius R t , P T i is the transverse momentum of a particle i in the top-jet.…”