#CMSPaper 1287 looks for undiscovered extra neutrinos, in signatures with many leptons (including taus, see plot, very few events). It is a #nullresult that sets very stringent bounds on heavy neutral leptons and majorana neutrinos https://buff.ly/3U7LYgZ
#CMSPaper 1230: This paper searches for undetectable particles in signatures with quarks, gluons, Higgs bosons and photons. It's a #NullResult, but it is sensitive to #supersymmetry partners of the Higgs boson, W/Z boson (worlds best!) ... and graviton! https://arxiv.org/abs/2307.16216