# Sensitivity of CLIC at 380 GeV to the top FCNC decay $t\rightarrow cH$

## TL;DR

This study evaluates CLIC's sensitivity to the rare top quark decay $t
ightarrow cH$ within the 2HDM(III) model, considering realistic beam effects and background, and estimates the potential to detect or constrain this flavor-changing neutral current process.

## Contribution

It provides a detailed simulation-based analysis of CLIC's capability to observe or limit the $t
ightarrow cH$ decay, incorporating beam polarization and background effects.

## Key findings

- Signal selection efficiency around 10%.
- Expected limits on $BR(t
ightarrow cH)\times BR(H\rightarrow b\bar{b})$ are established.
- Comparison with previous parton-level results shows realistic sensitivity estimates.

## Abstract

In the Standard Model (SM), flavour changing neutral current (FCNC) top decays, possible at loop level only, are very strongly suppressed. Observation of any such decay would be a direct signature of physics beyond the SM. Large enhancements are possible in many "new physics" scenarios and the largest enhancement is in most cases expected for the $t\rightarrow cH$ decay. A full study for CLIC was based on the WHIZARD simulation of FCNC top decays within the 2HDM(III) model. Beam polarization and beam-induced background were taken into account. Top pair production events with the FCNC decay $t\rightarrow cH$ can be identified based on kinematic constrains and flavour tagging information. Due to a large overlap in the kinematic space with standard top pair events, the final signal selection-efficiency is small, at the 10% level. Expected limits on $BR(t\rightarrow cH)\times BR(H\rightarrow b\bar{b})$ are compared with earlier results based on parton level simulation.