Long-lived heavy neutral leptons from mesons in effective field theory

TL;DR

This paper investigates the production and detection of long-lived heavy neutral leptons from meson decays within an effective field theory framework, exploring the potential of future LHC detectors to probe new physics at very high scales.

Contribution

It provides the first detailed analysis of HNL production via dimension-six operators in effective field theory and assesses the sensitivity of future detectors to these processes.

Findings

Scales above hundreds of TeV can be probed.

Active-heavy neutrino mixing squared as low as 10^{-15} is detectable.

Future detectors can explore new physics beyond current limits.

Abstract

In the framework of the low-energy effective field theory of the Standard Model extended with heavy neutral leptons (HNLs), we calculate the production rates of HNLs from meson decays triggered by dimension-six operators. We consider both lepton-number-conserving and lepton-number-violating four-fermion operators involving either a pair of HNLs or a single HNL. Assuming that HNLs are long-lived, we perform simulations and investigate the reach of the proposed far detectors at the high-luminosity LHC to (i) active-heavy neutrino mixing and (ii) the Wilson coefficients associated with the effective operators, for HNL masses below the mass of the $B$-meson. We further convert the latter to the associated new-physics scales. Our results show that scales in excess of hundreds of TeV and the active-heavy mixing squared as small as $10^{-15}$ can be probed by these experiments.