Probing lepton number violation at FCC-ee

Abstract

We propose high-multiplicity final-state signatures, such as $e^{+}{e}^{-}\to N\overline{N}\to {\ell }^{+}{\ell }^{+}4j$ with $\ell$ denoting $e,\mu$, $\tau$, as probes of lepton number violation (LNV) at FCC-ee, featuring negligible Standard Model background. In contrast to conventional searches such as $pp\to {\ell }^{+}N\to {\ell }^{+}{\ell }^{+}jj$ or the process $e^{+}{e}^{-}\to \nu N$, which are suppressed by the small neutrino masses in conventional seesaw scenarios, the minimal linear seesaw picture avoids this suppression. This enables a direct LNV probe from final-state topology, with over $\mathcal{O}(10^3)$ events expected at FCC-ee. Besides probing the Majorana nature of neutrinos, this offers a novel avenue to test the neutrino mass ordering established by oscillation experiments in a high-energy collider setting.

8 pages, 4 figures. Comments are welcome