Murray Gell-Mann - The parity revolution: accounting for the tau theta puzzle (76/200)

To listen to more of Murray Gell-Mann’s stories, go to the playlist: • Murray Gell-Mann (Scie...
New York-born physicist Murray Gell-Mann (1929-2019) was a theoretical physicist. His considerable contributions to physics include the theory of quantum chromodynamics. He was awarded the 1969 Nobel Prize in Physics for his work on the theory of elementary particles. [Listener: Geoffrey West; date recorded:1997]
TRANSCRIPT: There was an idea which I had had actually for a number of years and which I had mentioned to Pais and other people back in… in ’54 for accounting for what was called 'the tau theta puzzle'. The tau decayed into three pions; it was i = 1, it was a rather flat spectrum and it looked very much like a zero minus particle. But exactly at the same mass there was a decay into two pions which looked very much like a zero plus particle. And how could this happen? Well, one way it could happen, I thought, was through parity doubling. And I worked out this idea that if the pion was... if the K particle was parity doubled, then probably the lambda was parity doubled also, and so on and so forth. And then the psi could either be a singlet or a triplet under this, and so forth: it would be a new variable. The psi wouldn't have to be parity doubled but the lambda and the sigma would, and the K would and so on. I didn't publish that but I talked about it a lot of places. And then Yang and Lee came up with this same idea and they did publish it and made a huge fuss about it. I was a little upset. I was sorry that I hadn't put it forward under my own name. Feynman said, ‘Well, don't worry, we don't know it's true, so what do you care?’ And I thought, well, maybe he's right, but then what is the explanation? And I didn't know. Then at the Rochester meeting in ’56… ’56? Yeah, ’56; the same one I guess where I spoke about the dispersion theory program. Marty Block, the experimentalist, was rooming with Feynman, and Marty Block said, ‘Well, what if parity isn't conserved?’ Presumably meaning in the weak interaction. ‘Then couldn't the tau and theta be the same thing?’ And Luis Alvarez had been suggesting--without understanding anything about parity--he had been suggesting that somehow the tau and theta could be the same particle, maybe. But anyway Marty posed this question to Feynman instead of posing it to the meeting and so Feynman thought about it and he couldn't think of any real reason why you couldn't have a parity of non-conserving weak interaction. And in fact, although neither of us had paid much attention, we had actually discussed such a thing together in connection with this 'one plus gamma five' idea. So he said to Marty, ‘Well, I don't know of any reason why not. Let me ask Murray.’ So he grabbed hold of me and he said, ‘Murray, what if the weak interaction violates parity?’ Well, he didn't say it that way, he said, ‘What if parity isn't conserved, and the tau and theta are the same particle?’ I said ‘Well, in the weak interaction, it could be that parity isn't conserved. Nobody knows really, nobody has ever proved it one way or the other. Could be true. I don't know of any reason why not.’ I was still interested in my parity doubling hypothesis which Yang and Lee had then put forward, but I had to admit this was a perfectly possible hypothesis. And so Feynman announced it to the meeting. He said, ‘My roommate, Marty Block is suggesting that parity is not conserved in the weak interaction.’ Well, he didn't say, in the weak interaction, but he said ‘is not conserved’. What he meant was in the weak interaction. And maybe that's the explanation and the tau and the theta are the same thing.

[@drbonesshow1]

Block suggested to Feynman that parity is not conserved in weak interactions. Feynman then raised the question with the experts in the field.

[@ARBB1]

Never heard of this particular anecdote.