beta decay

[ythaaa]

for beta decay
n --> p + e- + antineutrino

since neutron has quarks udd while proton has uud, only the d changes to u. is it correct to guess that it is the down quark inside the neutron which "transform" into up quark?

ie d --> u + e- + antineutrino

[AlphaNumeric]

Yes, though there is an intermediate state, in that the process is actually :

d \to u + W^{-} \to u + e^{-} + \bar{\nu}_{e}

The intermediate step was not known about when the weak force was first being modeled because it only exists for a tiny amount of time because the W boson is so massive and unstable.