Search for Flavor Changing Neutral Currents in $t\to H c, H\to \tau\tau$ Decay at the LHC

TL;DR

This paper investigates the potential to detect flavor changing neutral currents in top quark decays to Higgs and charm quarks at the LHC, using simulated data and advanced analysis techniques to improve sensitivity.

Contribution

It introduces a novel analysis method combining mass constraints and boosted decision trees to enhance detection sensitivity for FCNC top decays at the LHC.

Findings

Expected upper limit of 0.25% on the branching ratio of t→Hc at 95% CL

Improved Higgs and top mass reconstruction techniques

Demonstrated sensitivity with 100 fb^{-1} data at 13 TeV

Abstract

The prospects of searching for the flavor changing neutral current effect in the decay of $t\to H c, H\to \tau\tau$ are investigated with the simulated $p-p$ collision data for the ATLAS detector at the LHC, where the Higgs mass is assumed to be 125~GeV. A fit based on the constraints from the Higgs mass and the tau decay kinematics is performed for each event, which improves significantly the Higgs and top mass reconstruction and helps the signal-background separation. Boosted Decision Trees discriminants are developed to achieve an optimal sensitivity of searching for the FCNC signal. An expected upper limit of the branching ratio $\mathcal{B}(t\to H c)$ at $95\%$ confidence level of 0.25\% is obtained with a data set of 100~fb$^{-1}$ at $\sqrt{s}=13$ TeV during the LHC Run-2 period.