Yes, BARYON is a Scrabble word!

Letter values in Scrabble US: B 3, A 1, R 1, Y 4, O 1, N 1.

Is it a valid word?

BARYON is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

any of the elementary particles having a mass equal to or greater than that of a proton and that participate in strong interactions; a hadron with a baryon number of +1

Also: heavy particle.