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Predicting quarks and getting credit for it February 20, 2007

Posted by dorigo in books, physics, science.

Despite the fact that scientific knowledge in theoretical physics is distributed mainly through the publication of papers in journals which should be accessible to anybody -with the consequence that credit for a discovery or the prediction of an effect that is later found in experiments should be unequivocal and easy to assign- the history of science shows that it is the opposite which usually happens.

Theoretical papers are at times neglected -often because of language barriers-, they are often not recognized for their importance, and if they do not get cited straight away after a confirmation of their predictions comes from experimental evidence, they may fail to yield the deserved amount of fame to their authors.

I have several examples in mind, but the ones discussed below – spurred by a comment by Tony Smith on the slides of a recent seminar I gave to high-school students – are interesting to me, since they refer to a pivotal discovery in particle physics: the existence of quarks, through the observation of the J/psi meson, in November 1974, and the discovery of a third quark family in 1977.

Quoting Tony Smith’s comment, who quotes Staley’s book in turn:

Here are some details about the development of the Kobayashi-Maskawa model and its reception in the USA physics community, in the form of quotes from Kent Staley’s book “The Evidence for the Top Quark: Objectivity and Bias in Collaborative Experimentation” (Cambridge 2004). 

“… One of the most important physicists in Japan in the 1950s and 1960s was Shoichi Sakata of Nagoya University. Sakata proposed, in 1956, … the “Sakata model” …[in which]… the proton, neutron, and lambda were “fundamental” baryons …[and]… represented the fundamental baryons as expressions of SU(3) … the Sakata model …[was]… supplanted by … the “Nagoya model” … in 1960 …[which]… present[ed] a model of hadrons and leptons simultaneously …
In 1962, experiments at Brookhaven National Laboratory began to yield evidence of a second neutrino. That same year, two papers extending the Nagoya model to incorporate two neutrino appeared, one by … physicists at the University of Kyoto (Katayama, Matumoto, et al. …). … discussing at length both three- and four-baryon models …
in 1964 … Maki and Ohnuki …. hypothesized what they called “urbaryons” …[and that}… the fourth urbaryon … had to be treated differently …
… in the urbaryon proposal of 1964, the Nagoya physicists had their own version of the idea that the known baryons were composite states of more fundamental particles …

when [in 1964] J. D. Bjorken and Sheldon Glashow published the proposal that there might be “charmed” hadrons … some proponents of the Nagoya model had already been working with quartet schemes for two years …
Pekka Tarjanne and Vigdor Teplitz of Berkeley’s Lawrence Radiation Laboratory published such a model in 1963, based on … SU(4) …
Four CERN physicists (Amati, Bacry, et al.) explored various SU(4) models in a 1964 paper … and Caltech’s Yasuo Hara proposed a four-baryon model early in 1964 …

In spite of all this, it is common for Bjorken and Glashow to be given sole credit for the charm proposal. 

The second example is the proposal of a third generation of quarks, well before the discovery of even the charm, in 1971. In this case, Kobayashi and Maskawa did get credit for their prediction in the end, but their work was largely ignored before the bottom quark discovery – which is another aspect of the imperfect mechanism of the distribution of knowledge:

Kobayashi and Maskawa’s central claim was that no “realistic” quartet model allows for CP-violating weak interactions … Kobayashi and Maskawa considered … possible representations of a quartet scheme ….[and]… possibilities in which new fields are introduced … Only after these (forgotten) proposals were described did Kobayashi and Maskawa take up the “6-plet” model …[in which]… the 2×2 Cabibbo matrix must be replaced by a 3×3 unitary matrix … In order to retain unitarity, this matrix … must contain elements with a complex phase … that allows processes violating CP invariance … They did not discuss the top quark specifically …[and]… did not even present their discussion in terms of the quark model … For their reserve in presenting a revolutionaly idea, they were rewarded with several years of neglect.

The earliest citations of KM …[were]… first … a paper titled “CP Violation in the Six-Quark Mode” (Pakvasa and Sugawara 1976) …[in which they]… noted that “A few years ago Kobayashi and Maskawa pointed out the CP violation can be incorporated into the standard V-A Weinberg-Salam model if we increase the number of quarks from four to six”

The second paper … was by Luciano Maiani … in Physics Letters in May 1976 …[in which he said]… “The possible evidence recently found at SPEAR of a new charged lepton suggests that new quarks exist …” …[and]… he mentioned, in a footnote, that Kobayashi and Maskawa had already devised a similar scheme for CP violation

In PRL [1976], Steven Weinberg, noting the two papers just mentioned, cited KM not to praise it but to bury it. … Weinberg noted that “[f]rom the standpoint of the present paper, it is hoped that there are NOT more than four quarks, in order to insure that CP violation arises only from Higgs exchange” … involving more Higgs fields than required in the usual standard model formulation

The most generous … citation of KM … appeard in Nuclear Physics (Ellis, Gaillard, and Nanopoulos 1976)

the first of the new “heavy” quarks, the bottom quark, was unearthed at Fermilab by people at least some of whom were completely unaware of this theoretical development … The announcement of the true upsilon was made at Femilab at the end of June 1977 … Although the discovery of the upsilon eventually came to be recognized as the discovery of the bottom quark, Kobayashi and Maskawa’s paper does not seem to have any direct influence on this experiment. In their PRL article announcing the discovery, the Columbia-Fermilab-Stony Brook (CFS) collaboration does not include a citation of the KM paper. John Yoh, in later recollections, wrote:
“… The Kobayashi-Maskawa paper speculating on six quarks, though published in 1973, was totally unknown in the U.S., having been published in the obscure Japanese journal Progress of Theoretical Physics. …” …”.

 I wonder if any readers of this blog have a different input with respect to the discoveries of the charm and bottom quarks. What was the feeling in the years between 1974 and 1977 ? Did everybody believe a fifth quark was about to be found ?

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