Probing the Weinberg Operator at Colliders

Abstract

Motivated by searches for $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ decay in nuclear experiments and collider probes of lepton number violation at dimension $d\ge 7$, we investigate the sensitivity to the $d=5$ Weinberg operator using the non-resonant signature $pp\to {\ell }^{\pm }{\ell }^{\prime \pm }jj$ at the LHC. We develop a prescription for the operator that is applicable in collisions and decays, and focus on the $\ell {\ell }^{\prime }=\hat{I}¼\hat{I}¼$ channel, which is beyond the reach of nuclear decays. For a Wilson coefficient $C_5^{\hat{I}¼\hat{I}¼}=1$, scales as heavy as $\hat{I}›\sim 8.3(11)$~TeV can be probed with $\mathcal{L}=300{\mathrm{fb}}^{-1}(3{\mathrm{ab}}^{-1})$. This translates to an effective $\hat{I}¼\hat{I}¼$ Majorana mass of $|m_{\hat{I}¼\hat{I}¼}|\sim 7.3(5.4)$~GeV, and establishes a road map for testing the Weinberg operator at accelerators.

Journal version. 9 pages including an extended technical appendix; 4 figures; 4 tables; UFO models available from https://feynrules.irmp.ucl.ac.be/wiki/SMWeinberg