Heavy neutral leptons from kaons in effective field theory

TL;DR

This paper investigates the potential of future long-lived-particle detectors at the LHC and DUNE-ND to detect heavy neutral leptons produced in kaon decays within an effective field theory framework, extending current bounds.

Contribution

It provides a comprehensive analysis of kaon decay channels into heavy neutral leptons, including both lepton-number-conserving and violating operators, and assesses detector sensitivities beyond existing experimental limits.

Findings

DUNE-ND can probe parameter space beyond current bounds in most scenarios.

Future LHC detectors have limited reach, only probing certain benchmark scenarios.

Some operators allow probing new physics scales over 3000 TeV.

Abstract

In the framework of the low-energy effective theory containing in addition to the Standard Model fields heavy neutral leptons (HNLs), we compute the decay rates of neutral and charged kaons into HNLs. We consider both lepton-number-conserving and lepton-number-violating four-fermion operators, taking into account also the contribution of active-heavy neutrino mixing. Assuming that the produced HNLs are long-lived, we perform simulations and calculate the sensitivities of future long-lived-particle (LLP) detectors at the high-luminosity LHC as well as the near detector of the Deep Underground Neutrino Experiment (DUNE-ND) to the considered scenario. When applicable, we also recast the existing bounds on the minimal mixing case obtained by NA62, T2K, and PS191. Our findings show that while the future LHC LLP detectors can probe currently allowed parameter space only in certain benchmark scenarios, DUNE-ND should be sensitive to parameter space beyond the current bounds in almost all the benchmark scenarios and for some of the effective operators considered it can even probe new-physics scales in excess of 3000 TeV.