What is the plural for magnetic moments/momenta?

The plural of "moment" is definitely "moments," in all senses.

There are only two plausible reasons why the plural of "moment" might possibly be anything other than "moments," and neither reason holds up:

1. A handful of native English words have irregular plurals inherited from centuries ago, such as mouse (mice) and goose (geese). However, "moment" is not one of those words.
2. When we borrow a noun from another language into English, we often borrow both the singular and the plural from the original language. However, there is no possible origin language where the singular is "moment" and the plural is something other than "moment," so this situation can't have happened either.

Also, I checked a couple of dictionaries and all of them list "moments" as the only plural form of "moment."

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This is a bit of a digression, but I'm guessing that there are no nouns at all in English where

• the English plural form is borrowed from some other language, but
• the English singular form is not the singular form from that other language, and
• the English singular form is not a backformation from the plural form, either. (An example of such a backformation is "tamale," which is back-formed from the English plural, "tamales," which is borrowed from the Spanish plural. The Spanish singular is tamal.)

If the plural of "moment" were "momenta," then it would be a counterexample to my guess.