# Single top polarisation as a window to new physics

## TL;DR

This paper investigates how heavy new physics, modeled by four-fermion operators, affects the polarization of single top quarks in LHC processes, highlighting the enhanced sensitivity of polarization measurements to potential new physics effects.

## Contribution

It demonstrates that top quark polarization is more sensitive than cross section to certain four-fermion operators involving right-handed top quarks, especially at high momenta.

## Key findings

- Polarization effects are twice as sensitive as cross section to specific operators.
- Right-handed top quark operators significantly influence longitudinal polarization.
- Polarization measurements are particularly promising at high momenta for new physics searches.

## Abstract

We discuss the effect of heavy new physics, parameterised in terms of four-fermion operators, in the polarisation of single top (anti-)quarks in the $t$-channel process at the LHC. It is found that for operators involving a right-handed top quark field the relative effect on the longitudinal polarisation is twice larger than the relative effect on the total cross section. This enhanced dependence on possible four-fermion contributions makes the polarisation measurements specially interesting, in particular at high momenta.