A Reduced basis for CP violation in SMEFT at colliders and its application to Diboson production

TL;DR

This paper identifies a minimal set of CP-odd operators in SMEFT that dominate CP violation effects at colliders, introduces new observables for their detection, and compares their effectiveness.

Contribution

It presents a reduced basis of CP-odd SMEFT operators and proposes new collider observables that enhance sensitivity to CP violation effects.

Findings

10 (17) key CP-odd operators identified for leading contributions.

New observables in diboson production are more efficient across phase space.

Complementary to existing methods, these observables probe different operator combinations.

Abstract

We show that only 10 (17) CP-odd operators of the SMEFT give the leading, i.e. least suppressed by the new physics scale, CP-violating contributions once we assume that all fermions are massless but the top (and bottom) quark(s). We start with a short review of previous analyses focusing on operators of our reduced basis and list different observables probing their CP violating effects by direct measurements at colliders and by indirect measurements in low-energy observables. Since CP-odd operators typically lead to phase space suppressed interferences, we quantify the efficiency to revive the interference for various observables found in the literature but also for new observables in diboson production. Our new observables are found to be more efficient on the whole experimental fiducial phase space and are complementary to those presented so far as they probe different combinations of operators and get their sensitivities from different regions of the phase space.