Measuring $|V_{ts}|$ directly using strange-quark tagging at the LHC

TL;DR

This paper proposes a method to directly measure the CKM matrix element |V_{ts}| at the LHC by tagging strange quarks in top quark decays, using detailed detector simulations and $K_S$ reconstruction.

Contribution

It introduces a detailed analysis and simulation strategy for measuring |V_{ts}| directly from top quark decays at the LHC, extending previous proposals.

Findings

Potential to exclude |V_{ts}|=0 at 6.0σ with HL-LHC data

Demonstrates feasibility of strange-quark tagging in top decays

Uses $K_S$ reconstruction for improved tagging accuracy

Abstract

The Cabibbo-Kobayashi-Maskawa (CKM) element $V_{ts}$, representing the coupling between the top and strange quarks, is currently best determined through fits based on the unitarity of the CKM matrix, and measured indirectly through box-diagram oscillations, and loop-mediated rare decays of the $B$ or $K$ mesons. It has been previously proposed to use the tree level decay of the $t$ quark to the $s$ quark to determine $|V_{ts}|$ at the LHC, which has become a top factory. In this paper, we extend the proposal by performing a detailed analysis of measuring $t \to sW$ in dileptonic $t\bar{t}$ events. In particular, we perform detector response simulation, including the reconstruction of $K_S$, which are used for tagging jets produced by $s$ quarks against the dominant $t \to bW$ decay. We show that it should be possible to exclude $|V_{ts}| = 0$ at 6.0$\sigma$ with the expected High Luminosity LHC luminosity of 3000 fb$^{-1}$.