As more types of mesons were discovered in accelerator experiments later, it was eventually found that the mu meson significantly differed not only from the pi meson (of about the same mass), but also from all other types of mesons. The difference, in part, was that mu mesons did not interact with the nuclear force, as pi mesons did (and were required to do, in Yukawa's theory). Newer mesons also showed evidence of behaving like the pi meson in nuclear interactions, but not like the mu meson. Also, the mu meson's decay products included both a neutrino and an antineutrino, rather than just one or the other, as was observed in the decay of other charged mesons.
As more types of mesons were discovered in accelerator experiments later, it was eventually found that the mu meson significantly differed not o,nly from the pi meson (of about the same mass), but also from all other types of mesons. The difference, in .part, was that mu mesons did not interact with the nuclear force, as pi mesons did (and were required to do, in Yukawa's theory) Newer mesons also showed evidence of behaving like t,he pi meson in nuclear interactions but not like the mu meson. Also, the mu meson's decay products included both a neutrino and an antineutrino rather than just one or the other, as was observed in the decay of other charged mesons.