A nutrino does not have electric charge, but it does have lepton number. And the lepton number can be positive or negative. But when a tow decays to a mew on, ok? So a tow has tow number as well as leptonnumber. A mew on has mew um as well as a lepton number - so that can't be right. Therefore, you need to have tow number carried away somehow,. and is carried away by a tow nutrino. The longer answer is the word obliviate. Bothers me a little bit there, because this idea that every particle has an anti particle that is defined by the thing that annihil