IANAPhysicist, but "shape" strikes me as a particularly inapt metaphor for the property of neutrinos under discussion. "Lepton number" or "mass eigenstate" are unfamiliar terms, but at least they don't mislead the reader into imagining that leptons have shapes. Since the offending term occurs only in the headline and at the beginning and end of this article, this is probably the work of a clumsy linkbaiting editor. I hadn't previously noticed that at Nautilus.