Heavy neutral leptons in effective field theory and the high-luminosity LHC
Giovanna Cottin (Departamento de Ciencias, Facultad de Artes Liberales, Universidad Adolfo Ibáñez, Diagonal Las Torres, Santiago, 2640, Chile, Millennium Institute for Subatomic Physics at High Energy Frontier (SAPHIR), Fernández Concha, Santiago, 700, Chile); Juan Helo (Departamento de Física, Facultad de Ciencias, Universidad de La Serena, Avenida Cisternas, La Serena, 1200, Chile, Millennium Institute for Subatomic Physics at High Energy Frontier (SAPHIR), Fernández Concha, Santiago, 700, Chile); Martin Hirsch (AHEP Group, Instituto de Física Corpuscular — CSIC/Universitat de València, Apartado 22085, València, E-46071, Spain); Arsenii Titov (Departament de Física Teòrica, Universitat de València, Instituto de Física Corpuscular — CSIC/Universitat de València, Dr. Moliner 50, Burjassot, E-46100, Spain); Zeren Wang (Department of Physics, National Tsing Hua University, Hsinchu, 300, Taiwan, Center for Theory and Computation, National Tsing Hua University, Hsinchu, 300, Taiwan)
Heavy neutral leptons (HNLs) with masses around the electroweak scale are expected to be rather long-lived particles, as a result of the observed smallness of the active neutrino masses. In this work, we study long-lived HNLs in N R SMEFT, a Standard Model (SM) extension with singlet fermions to which we add non-renormalizable operators up to dimension-6. Operators which contain two HNLs can lead to a sizable enhancement of the production cross sections, compared to the minimal case where HNLs are produced only via their mixing with the SM neutrinos. We calculate the expected sensitivities for the ATLAS detector and the future far-detector experiments: AL3X, ANUBIS, CODEX-b, FASER, MATHUSLA, and MoEDAL-MAPP in this setup. The sensitive ranges of the HNL mass and of the active-heavy mixing angle are much larger than those in the minimal case. We study both, Dirac and Majorana, HNLs and discuss how the two cases actually differ phenomenologically, for HNL masses above roughly 100 GeV.
