Accessing CKM suppressed top decays at the LHC

TL;DR

This paper proposes an enhanced experimental method for measuring rare top quark decays involving light quarks at the LHC, improving statistical sensitivity and enabling precise tests of the CKM matrix elements.

Contribution

The paper introduces a novel analysis strategy combining orthogonal $b$- and $q$-taggers with a new observable, increasing the ability to measure suppressed top decays.

Findings

Potential to exclude $|V_{tb}|=1$ at 95% C.L. at HL-LHC

Enhanced statistical power in top decay measurements

Direct access to $|V_{td}|^2+|V_{ts}|^2$ in the Standard Model

Abstract

We propose an extension of the existing experimental strategy for measuring branching fractions of top quark decays, targeting specifically $t\to j_q W$, where $j_q$ is a light quark jet. The improved strategy uses orthogonal $b$- and $q$-taggers, and adds a new observable, the number of light-quark-tagged jets, to the already commonly used observable, the fraction of $b$-tagged jets in an event. Careful inclusion of the additional complementary observable significantly increases the expected statistical power of the analysis, with the possibility of excluding $|V_{tb}|=1$ at $95\%$ C.L. at the HL-LHC, and accessing directly the standard model value of $|V_{td}|^2+|V_{ts}|^2$.