2021-05-14 11:00  P5A-1

Long-lived sterile neutrinos at the LHC in effective field theory

Zeren Simon Wang

We study the prospects of displaced-vertex searches for sterile neutrinos at the Large Hadron Collider in the framework of the neutrino-extended Standard Model Effective Field Theory (N_R SMEFT). The production and decay of sterile neutrinos can proceed via the standard active-sterile neutrino mixing in the weak current, as well as through higher-dimensional operators arising from decoupled new physics. If sterile neutrinos are long-lived, their decay can lead to displaced vertices which can be reconstructed. We perform Monte-Carlo simulations to investigate the search sensitivities for the ATLAS/CMS detector, the future far-detector experiments: AL3X, ANUBIS, CODEX-b, FASER, MATHUSLA, and MoEDAL-MAPP, and at the proposed fixed-target experiment SHiP. We consider two scenarios: 1) sterile neutrinos are predominantly produced via rare charm and bottom mesons decays through minimal mixing and/or dimension-six operators in the N_R SMEFT Lagrangian, and 2) sterile neutrinos are produced primarily via EFT operators which contain two sterile neutrinos and decay only via the minimal mixing. We find that these experiments are very competitive with other searches, and that in the second scenario the phenomenology can actually differ for masses above roughly 100 GeV between Dirac and Majorana sterile neutrinos.