Dark matter is believed to be part of the missing mass.

暗物质也被认为是遗失质量的一部分。

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The leading theory to explain the missing neutrinos was that neutrinos had a little mass, which it turns out would allow them to transform themselves as they traveled from one neutrino type to another.

NPR: Neutrinos: A Cursed Subatomic Particle?

For a few months in 2010 it looked as though the Tevatron might get a reprieve in order to find the last (and heaviest) missing bit of the model the Higgs boson, which is thought to give other particles their mass.

ECONOMIST: The future of physics (1)