Search for Anomalous Couplings in Top Decay at Hadron Colliders

TL;DR

This paper investigates the sensitivity of detecting anomalous top decay couplings at Tevatron and LHC using advanced angular distribution analysis and novel reconstruction techniques, providing bounds on coupling ratios with realistic data.

Contribution

It introduces a new effective spin reconstruction method and applies likelihood fitting to improve sensitivity to anomalous top decay couplings in collider experiments.

Findings

95% CL bounds on coupling ratios at Tevatron and LHC

Development of a new spin reconstruction method

Quantitative sensitivity estimates with realistic event numbers

Abstract

We present a quantitative study on sensitivities to the top-decay anomalous couplings, taking into account realistic experimental conditions expected at Tevatron and LHC. A double angular distribution of W and charged lepton in the top decay is analyzed, using ttbar events in the lepton+jets channel. In order to improve sensitivities to the anomalous couplings, we apply two techniques: (1) We use a likelihood fitting method for full kinematical reconstruction of each top event. (2) We develop a new effective spin reconstruction method for leptonically-decayed top quarks; this method does not require spin information of the antitop side. For simplicity, we neglect couplings of right-handed bottom quark as well as CP violating couplings. The 95% C.L. estimated bound on a ratio of anomalous couplings reads -0.81 < f_2/f_1 < -0.70, -0.12<f_2/f_1<0.14 using 1000 reconstructed top events at Tevatron, while -0.74<f_2/f_1<-0.72, -0.01<f_2/f_1<0.01 is expected with 100k reconstructed top events at LHC, where only statistical errors are taken into account. A two-fold ambiguity in the allowed range remains when the number of events exceeds a few hundred.