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Nobel Prize for , 1979

Abdus Sal am

Physics' most prestigious accolade forces is a significant milestone in goes this year to Sheldon Glashow, the constant quest to describe as and Steven Weinberg much as possible of the world for their work in elucidating the inter­ around us from a minimal set of actions of elementary particles, and initial ideas. in particular for the development of 'At first sight there may be little or the theory which unifies the electro­ no similarity between electromag­ magnetic and weak forces. netic effects and the phenomena This synthesis of two of the basic associated with weak interactions', forces of nature must be reckoned as wrote Sheldon Glashow in 1960. one of the crowning achievements 'Yet remarkable parallels emerge...' of a century which has already seen Both kinds of interactions affect the birth of both and hadrons; both appear to and relativity. be 'vector' interactions brought and the weak about by the exchange of particles force might appear to have little to carrying unit spin and negative pari­ do with each other. Electromagne­ ty; both have their own universal tism is our everyday world — it holds which governs the atoms together and produces light, strength of the interactions. while the weak force was for a long These vital clues led Glashow to time known only for the relatively propose an ambitious theory which obscure phenomenon of beta-decay attempted to unify the two forces. radioactivity. However there was one big difficul­ The successful unification of these ty, which Glashow admitted had to two apparently highly dissimilar be put to one side. While electro-

magnetic effects were due to the exchange of massless (electromagnetic radiation), the car­ rier of weak interactions had to be fairly heavy for everything to work out right. The initial version of the theory could find no neat way of giving the weak carrier enough mass. Then came the development of theories using 'spontaneous sym­ metry breaking', where degrees of freedom are removed. An example of such a symmetry breaking is the imposition of traffic rules (drive on the right, overtake on the left) to a road network where in principle anyone could go anywhere. Another

Harvard Professors Sheldon Glashow (left) and Steven Weinberg at a news conference at Harvard after it was announced that they share the 1979 Physics with Abdus Salam.

(Photo Photopress)

CERN Courier, December 1979 395 Abdus Salam with members of the collaboration which worked with the heavy liquid bubble chamber. It was this detector which first saw the interaction predicted by the electroweak theory.

(Photo 392.10.79) example is the formation of crystals in a freezing liquid. These symmetry-breaking theo­ ries at first introduced massless particles which were no use to anybody, but soon the so-called '' was discovered which gives the carrier particles some mass. This was the vital devel­ opment which enabled Weinberg and Salam, working independently, to formulate their unified 'electro- weak' theory. One problem was that nobody hadrons) as well as the leptons of the ments at SLAC and at DESY. Particle knew how to handle calculations in a original theory. physics had entered a new age, and consistent way. The way round this In this picture, the basic particles the discoveries made by Ting and obstacle was shown by Gerard (the quarks and the leptons) can in Richter were recognized in the 't Hooft in the early seventies. With general spin either right- or left- award of the Nobel Prize in 1976. this, the initial ideas matured into a handedly (the neutrino however However there was still a lot of fully-fledged theory. appears to have no right-handed work to be done. In particular, physi­ One by-product of the unification form). The left-handed particles can cists had to look at the detailed was a type of be grouped into fours, each four behaviour of the neutral current which would not change the electric being composed of a pair of quarks interaction to see if it followed the charges of the participating parti­ and a pair of leptons. rules set out by the simplest elec­ cles. For a long time all weak inter­ One set of four basic particles — troweak theory, or whether some actions were seen to shuffle electric the 'up' and the 'down' quarks more elaborate version would be charges around. together with the electron and its required. Then in 1973 came the discovery neutrino, provides all the source While inevitably odd transient in the Gargamelle bubble chamber material for our everyday world of things appeared in the ebb and flow at CERN of the 'neutral current' of atoms whose nuclei are made from of experimental statistics which did weak interactions, in which neutri­ protons and neutrons. But there not agree with the theory, it is nos interacted with target particles, were still more basic particles to use impressive how all the results which but remained as neutrinos. This was up — there was the strange quark, stood the test of time have been in the first vital piece of experimental the muon and its neutrino. To get a line with the simplest model of elec­ evidence in favour of the unified second set of four basic particles troweak phenomena, as originally electroweak theory. After this the required a new type of quark. formulated by Weinberg and remaining pieces of the puzzle soon This was the heavy 'charmed' Salam. fell together. quark, which could account for the Particular mention should be If there is a neutral current, it problem of the neutral decays. made of the remarkable experiment should be seen in other ways, for However charm was to exhibit itself at Stanford which measured right- example the decay of a neutral kaon much more vividly. In November left asymmetries ( violation) in into a pair of muons. B ut this is only a 1974 came the simultaneous dis­ electron-nucleon scattering. These very rare form of kaon decay. What covery by the teams of Sam Ting at tiny effects are the result of the inhibits the direct decay through the Brookhaven and at delicate interference between weak neutral current? SLAC of a remarkably stable heavy and electromagnetic interactions The exact answer had been pro­ meson, the J/psi. and provide an acid test of the theory vided by Glashow, who with J. Ilio- This was explained as a bound (see July/August 1978 issue, poulos and L Maiani, showed how state of a charmed quark and its page 245). The agreement between the electroweak ideas could be fruit­ corresponding antiquark, and the experiment and theory is excellent. fully extended to cover quarks (the spectroscopy of charmed particles In addition, results continue to components of strongly interacting was unravelled in further experi­ come in from neutrino experiments.

396 CERN Courier, December 1979 Abdus Salam, the oldest of the three laureates, was born in 1926 in J hang, now in Pa­ kistan. He received his docto­ rate from Cambridge Univer­ sity in 1952. In 1957, he be­ came Professor of Theoretical Physics at Imperial College, London, a position which he still holds. He was also one of the main movers behind the establishment of the Interna­ at both high and low energies, which taneous symmetry breaking me­ tional Centre for Theoretical display further the remarkable chanism. Here the theory is still in a Physics in Trieste, which he power of the theory. volatile state and no firm predictions directs. But probably the greatest predic­ are possible. But this mechanism is She/don Glashow was born in tion of all remains untested. Just as crucial to the theory, and something in 1932, obtained Maxwell's formulation of the elec­ has to turn up. his doctorate at Harvard in tromagnetic field had to await The great success of the electro­ 1959, and is now Professor confirmation through Hertz' discov­ weak unification has led many theo­ at the Lyman Laboratory, Har­ ery of electromagnetic radiation, so rists to become more ambitious and vard. the electroweak theory awaits the look for ways to bring in the strong Steven Weinberg was born in discovery of its own radiation. interactions, and possibly as New York in 1933, and at­ The theory makes very exact well, to achieve a 'grand unification' tended the same Bronx high predictions for the heavy particles of the forces of nature. school as Glashow. He ob­ which provide this radiation, but However it is sobering to remem­ tained his doctorate at Prince­ which today is out of reach of any ber that a hundred years had to pass ton in 1957, and now holds Laboratory. The proton-antiproton between Maxwell's synthesis of the post of Higgins Professor collider project now under construc­ electricity and magnetism and the at Harvard. tion at CERN and scheduled to begin new electroweak unification. If this As well as their formulation experiments in the early 1980s, will pattern is repeated, grand unification of the electroweak theory, the for the first time open up the energy would be for the 21 st century. three men have also made nu­ range where this radiation is ex­ (A detailed account of the devel­ merous other important contri­ pected to be seen. opment and application of these butions to the theory of ele­ Another vital ingredient of the ideas to electroweak mentary particles. theory which remains to be tested unification was published in our are the Higgs particles of the spon­ September 1977 issue, page 271.)

Second ICFA Workshop

From 4-10 October a second Work­ chaired by John Adams and has ton-antiproton colliders (Barry Bar- shop on 'Possibilities and Limita­ representatives from the various ish). Deep inelastic experiments with tions of Accelerators and Detectors' regions of the world involved in high beams of a few TeV (Guido was held at Les Diablerets in Swit­ energy physics. Barbiellini), Hadron and ex­ zerland with reviewtalksatCERN on The Les Diablerets Workshop was periments at fixed target machines the final day on the work of the organized by Ugo Amaldi and (Yuri Prokoshkin) and Possibilities different groups. It followed a Work­ divided its work into several topics — and limitations of detectors and data shop at Fermilab in 1978 (see Very high energy electron-positron handling (Dave Nygren). November 1978 issue, page 389) colliders (reported by A.N. Skrinsky), In working on higher energy elec­ and was promoted by the Interna­ Many TeV proton accelerators and tron-positron machines it became tional Committee for Future Acceler­ proton-antiproton colliders (Lee even clearer that in the future this ators in the context of its very long- Teng), Extraction and external physics would have to be done with term thinking about the future of beams from a many TeV accelerator colliding beams from linacs. The high energy physics. ICFA, which (Bas de Raad), Electron-proton inter­ largest storage ring system consi­ was set up under the auspices of the action regions and experiments (Gus dered at the Workshop had International Union of Pure and Weber), Extrapolation of experi­ 260 GeV per beam and such fright­ Applied Physics, is at present ments at electron-positron and pro­ ening parameters as 29 GeV

CERN Courier, December 1979 397