Selected Citation

The Pain and Joy of a Major Scientific Discovery

Authors(s):R. E. Marshak Publication:Current Science Publication Date:July 25, 1992 Publisher: Current Science Association Citation: Current Science Vol. 63, No. 2 Link:

This three-day workshop is being held on the occasion of George Sudarshan’s 60th birthday to do honor to his significant and many-faceted contributions to theoretical physics. The nature and extent of these contributions are being covered by a host of distinguished speaker and, hence, I shall limit my banquet remarks to George Sudarshan’a early scientific career in particle physics which culminated in his remarkable doctoral dissertation on the nature of the four-fermion interaction, otherwise known as the universal V–A theory of weak interactions.

But more than conferences and associates influenced Sudarshan’s early career; a major turning point came in December 1956 with the discover of parity violation Sudarshan listened with rapt attention when the θ-τ meson puzzle was discussed earlier at the Sixth Rochester Conference (in April 1956)—he even joined me in proposing a more conservative resolution of the θ-τ puzzle than parity violation. I am sure that Sudarshan was as eager as I was to reexamine weak interaction theory when Madame Wu and her collaborators announced the large parity violation effect in the ß decay of Co0. I had been more than a casual participant in weak interaction developments even since 1939—when in my thesis, I invoke the Gamow-Teller selection rule for the proton - proton reaction in order to pin down the internal temperature-density distribution in white dwarf stars. Moreover, I was cognizant of the attempts by Tiomno and Wheeler and others during the period 1947-49…to ascertain whether a universal Fermi interaction (UFI) was operative among the weak interactions then known.

It was therefore completely natural—after the Wu et al. announcement—to suggest to Sudarshan that he might take a fresh look as to whether a common Lorentz structure and strength could be assigned to all weak interactions. Sudarshan plunged into this problem with alacrity and exceeding good taste; he made a comprehensive analysis, within the framework of the UFI hypothesis, of the published and unpublished experiments in ß decay µ decay, π decay and K decay. I must remind you that during 1957 new parity-violating experiments were undertaken and old parity-conserving experiments were restudied at an incredible pace.

By the time of the Seventh Rochester Conference in April 1957, it was clear to both Sudarshan and myself that the only possible UFI for weak processes was V–A (with a left-handed neutrino), as was widely believed. While the ß-decay data were confusing, muon decay mandated the V–A choice and, moreover, an elegant chirality invariance argument applied to all hadron and lepton currents—patterned after the two-component neutrino hypothesis—uniquely predicted the universal V–A theory. We were aware of four experiments contradicting V–A: the two published parity-conserving experiments on the electron-neutrino angular correlation in He6 (favoring the T interaction) and the substantial disagreement of the measured branching ratio in pain decay (to e and µ) with the sharp V-A prediction of 1.3 x 10-4. By April 1957, there were also two preliminary parity-violating experiments (one reported in preprint form and the second a private communication to me)—on the electron polarization from muon decay and the asymmetry from polarized neutron decay—that disagreed with the V–A theory. We realized that if any one of these four experiments prevailed, one would have to abandon UFI or the underlying assumptions of a two-component neutrino and/or the law of conservation of leptons.

All this was interesting stuff and in a rational world, it should have been reported at the Rochester conference in April 1957. Here I must confess to my first ‘cardinal blunder’: the failure to arrange for a report on the V–A theory during the course of the Seventh Rochester Conference. ….


So far, these two excuses seem plausible to me dirty four yes after the act but I must still explain why I did not speak up when Matthews failed to intervene during two splendid opportunities provided by the review talks of T. D. Lee and C. S. Wu. The strong message of Lee and Wu at the Seventh Rochester Conference was threefold: (!) the Columbia He6 experiment had settled the question of the Gamow-Teller part of the ß interaction in favor of T (rather than A); (2) since the muon interaction is V (and A), UFI, according to Lee, ‘cannot be realized in the way we have expressed it’; and (3) a new experiment by Wu on the positron asymmetry from Co58 raised doubts about the presence of S rather than V (in addition to T) in the ß interaction. The basic conclusion to be drawn from the Lee and Wu talks was that the ß interaction was probably V and T so that one would be forced to assign opposite helictites to the neutrinos emitted in the Fermi- and Gamow-Teller-type ß transitions, a very splashing prospect indeed.

To add to the confusion, the possibility of a V, T ß interaction was reinforced by two tumors circulating at the Seventh Rochester Conference: one rumor was that Felix Boehm at CalTech had obtained a similar result to that of Wu for Co58 and the second rumor was that an Illinois group had measured the electron-neutrino angular correlation from A35 (a dominantly Fermi transition) and was finding a V instead of an S interaction. It looked very much as if the ß interaction was a combination of V and T, after all, and that UFI would have to be abandoned. This combination of circumstances put a crimp in my desire to bring up the universal V–A theory at the Seventh Rochester conference and was probably the reason why Matthews never spoke up. I cannot explain why I did not, as a minimum, ask whether the He6 experiment had been repeated elsewhere, except to acknowledge that there was a halo surrounding the Columbia ß-decay program at the time and that I partly succumbed to the prevalence view of the correctness of this crucial experiment. I know that this is a lame excuse, George, but I must tell this friendly audience about two further mistakes on my part before e I ask forgiveness for my three ‘cardinal blunders’.

While I was reluctant to argue at the April 1957 Rochester conference for V–A as the UFI option, as long as a consistent picture did not emerge from the parity-violating experiments, I know that I would be presenting a. Paper on our V–A theory at the forthcoming Padua-Venice Conference in September, and I expected to clarify the V, T situation with Boehm shortly after my arrival at the Rand Corporation in California in mid-June (to take up a short-erm consultantship). I told Sudarshan about my plans and we agreed that he could continue on the Rochester graduate student payroll as long as he continued working on the V-A theory while in California. This arrangement permitted us to meet with Boehm and to complete both the abstract and paper promised Professor N. Dallaporta, chairman of the Padua-Venice Conference. Apart from the muddled priority question that arose later, I still believe that this arrangement was reasonable since it allowed time for certain key ß-decay experiments to pass from sumo to completion stage and thereby to consolidate the experimental underpinning of the V-A theory.

Be that as it may, a few days after I arrived in Santa Monica in mid-June of 1957—to take up my duties at the Rand Corporation—I ran into Gell-Mann who was also a part-time consultant. Instead of talking about classified Rand business, I told Gell-Mann bout the V-A theory and asked him, I he would be so kind, to set up an early luncheon meeting with his colleague, Boehm, so the Sudarshan and I could reive an update on with the V, T combination was a mirage insofar as the parity-violating ß-decay experiments were concerned. The luncheon meeting too place during the first week of July and was attend by Boehm, Sudarshan, Gell-Man, Behold Stech (who was then a postdoc at CalTech) and myself. At this meeting, Boehm informed us that his most recent measurement in Sc46, of the same asymmetry parameter he had measured in Co58 was consistent with a V-A ß interaction (with a left handed neutrino) or a S, T ß interaction (with a right-handed neutrino); this was sufficient reassurance for Sudarshan and myself, and our abstract for the V-A paper was sent to Dallaporta in Padua, and the paper completed, within a matter of days. …

After the 'summit' meeting, I discharge my duties at the Rand Corporation, gave a seminar on the V=A there at Stanford and returned to Rochester in September where I arranged for a belated preprint of our V–A paper to be sent out, as I have said, on 16 September (the date of George’s 26th birthday) prior to its presentation to the Padua-Venice Conference during the last week of September. I recall telling the Pauda audience the the V-A theory required the ‘murder’ of four experiments (including the He6 experiment) and overhearing—during the intermission—Jack Steinberger whisper to Leon Lederman that Marshak was ‘nuts’ (or something to hat effect) to question the sacrosanct He6 experiment performed by the Columbia group. Whatever the skepticism of Steinberger and others about the V–A theory in Padua, Sudarshan and I were pushing hard for the redoing of the four experiments because the stakes were so high. As you all know, the four experiments, whose demise was required by the V-A theory, were all redone during the next two years and the new results were in complete accord with the V-A theory. The most striking additional. Confirmation of the V-A theory came in 1958 with the direct measurement of the left-handed helicity fo the neutrino in the ingenious experiment on K capture in Eu152, performed by Maurice Goldhaber and collaborators at Brookhaven, for which Goldhaber just won the Wolf Prize....


Returning to the months after the Padua Venice Conference, a second chastening experience occurred in January 1958, at the time of the APS meeting, which impelled me to commit what I call my third ‘cardinal blunder’ in the matter of the V–A theory. Feynman had been invited to speak on his V–A theory with Gell-Mann and told a large APS audience in his typical bravado fashion how he had been inspired in Brazil to construct the V-S theory and that several experiments had to be ‘killed’ to validate his theory. I could not resist subject myself to the embarrassment of remarking during the discussion period—in the presence of my former professor, Hans Bethe, was was chairing the session—that I had regaled a smaller audience at the Padua-Venice Conference the previous September with equal enthusiasm about our V–A theory and had listed four experiments that had to the ‘murdered’ in order for the theory to stand. Dick Feynman’s reply was that he ws aware that Sudarshan and I had first proposed the V–A theory but did not know what Gell-Mann would say. ….