John Ellis— 'adventurous (or foolhardy) souls are riding off into the sunset, looking for deeper theory'. resolution and electron/hadron dis graded to make further studies of crimination. Suitable arrangements single photon production. of the ionization sampling electrodes At the SPS 400 GeV proton syn provided the spatial resolution and chrotron, a liquid argon detector is enabled the shape of the developing incorporated in the apparatus used shower to be monitored, so that by a Bristol/Geneva/Heidelberg/ showers of electromagnetic and ha Lausanne/London/Rutherford colla dronic origin could be clearly distin boration studying the interactions of guished. Lithium foil transition radi charged hyperons. ation detectors provided additional Liquid argon detectors have also electron identification power. made significant contributions at In the single photon experiment electron-positron machines, with which began in 1978, the lithium foil Mark II at the SPEAR and PEP rings at detectors were removed and the li SLAC and with TASSO and CELLO at quid argon calorimeter was moved the PETRA ring at DESY. further from the interaction region to increase the photon separation in Technicolour; oasis closely spaced pairs and facilitate or mirage? the isolation of a signal due to ge nuine single photons. This is the intriguing title of the talk In 1980-81, this detector oper given by CERN theoretician John Ellis ated in tandem with the new Axial at the recent Topical Conference on Field Spectrometer of a Brookhaven Particle Physics at SLAC. / CERN / Copenhagen / Lund / Spurred by the promise of quan Pennsylvania / Rutherford / Tel-Aviv tum chromodynamics in describing collaboration (see April 1979 issue, quark interactions and the successes page 65). This apparatus measures of the unified electroweak theory, demand the existence of the Higgs the charged particles produced with new 'grand unified' theories have particles, as yet unobserved. Even if the single photons and is used to test been proposed which attempt to the weak bosons predicted by the the prediction that in proton-proton bring together the strong and the standard theory are discovered, all collisions, the jet recoiling against electroweak sectors. These will not be finally wrapped up until the single high transverse momen schemes carry implications of a phy the Higgs particles too appear. tum photon originates predominant sics 'desert' with no radically new However these ideas are also a ly from a quark. (In proton-antiproton phenomena waiting to be discovered prolific source of other possibilities, collisions in the ISR, the recoiling par at energies accessible in the labora which as Ellis explains could make ticles should come from gluon jets tory (see for example October issue, the desert of orthodox theory bloom rather than quark jets.) page 347). Meanwhile others, par with many kinds of exotic new phe To extend the study of single ticularly at Harvard and Stanford, nomena. photons, a new experiment (Athens have been proposing different me / Bonn / Brookhaven / CERN / chanisms, such as 'technicolour', 'By now the orthodox picture of Moscow) is being prepared to run which could soon provide a rich pat quantum chromodynamics (QCD) alongside the Axial Field Spectro tern of new physics. These adventu combined with the electroweak in meter, making use of the uranium rous theorists propose that the so- teraction is the generally accepted calorimeter. The new experiment will called Higgs particles are no longer theory of fundamental physics at pick up photons using an array of indivisible, but appear as compo energies up to about 100 GeV. The sodium iodide blocks mounted in sites, in much the same way that model seems to pose few remaining front of the uranium calorimeter, and hadrons are composites of the more problems of principle, and most using existing electronics from the elementary quarks. work on it now concentrates on tink old liquid argon detector. The The standard theory of electro ering with technicalities, such as CERN/Columbia/Rockefeller experi weak interactions rests solidly on confining quarks in QCD so that they ment at the ISR has also been up ideas of symmetry breaking which do not appear as free particles, and
454 CERN Courier, December 1981 the existence of intermediate weak by an embarrassing rash of new bos full grand unified symmetry was ex bosons. ons, quarks and leptons, and possi act— no degrees of freedom had It is not surprising that some ad bly some new flavour-changing neu yet had a chance to 'freeze' out and venturous (or foolhardy) souls are tral interactions. produce the physics we now know. already riding off into the sunrise, However these various possible Even at temperatures above a few looking for the deeper theory beyond oases may be judged on the grounds hundred GeV (verging on the Wein the standard model. There is no con of aesthetics or theoretical plausibili berg era), quarks would not have sensus about which direction to ride ty, one thing cannot be denied. In been confined. The universe was in, or even how far one must ride until contrast to prospects of a great de then a quarlvgluon plasma (a condi the next landmark is reached. sert, they do provide plenty of exper tion increasingly being sought in high Perhaps there is indeed a great imental tests to be performed at pre energy experiments). desert to be crossed first, as advo sent accelerator energies. Contem The excess of matter over anti cated by the ascetic minimalist devo porary experiments can prove these matter in a universe whose equa tees of grand unified theories of ideas right or wrong.' tions of motion are largely mat strong and electroweak interactions ter/antimatter symmetric has long who suggest that there is no new Before the first three puzzled cosmologists, amateur and interaction scale below 1015 GeV. minutes professional alike. However grand They extrapolate the behaviour of unified theories, with their concomi the known coupling constants until Steven Weinberg's book 'The First tant prediction of the unstable pro they converge in a grand unified the Three Minutes' has quickly estab ton (see May 1979 issue, page 116), ory at the 'Planck' energy of 1019 lished itself as a classic of modern together with the more familiar me GeV where quantum gravity effects physical theory. It uses 'Big Bang' chanism which violates the com are predicted to appear. cosmology and standard particle bined charge/parity symmetry (in In making this enormous extrapo physics ideas to chart the probable kaon decays for example), provide lation, they assume that there are no formation of the universe. However the ingredients for a possible answer intervening oases out in the great even these imaginative ideas are in to this hoary question. desert. In particular, they assume sufficient to get to grips with the con The idea is that the rapid expan that the elementary quantities of ditions immediately (less than one sion of the early exploding universe, existing theories — intermediate hundredth of a second) following the which initially contained matter and bosons, quarks, leptons and Higgs initial cataclysm. antimatter in equal amounts, forced particles — remain structureless and Since the book's publication in mechanisms out of thermal equili pointlike down to distances of 10~29 1977, theoreticians emboldened by brium, thus upsetting the parti- cm or smaller. the continued successes of the elec cle/antiparticle balance. Numerous However many physicists con troweak theory have embarked on detailed explanations have been pro sider this grand scenario either a dan ambitious 'grand unification' posed. gerous manifestation of hubris, tech schemes encompassing electro- Another remnant of this genesis nically unsound, or just boring. They magnetism and both the strong and could be free magnetic monopoles. prefer to replace it with a picture in the weak nuclear interactions. These electromagnetic oddities which the great desert is riddled with When injected into cosmology, were first proposed 50 years ago by oases caused by the onset of new these new ideas push back the time Dirac but have never been observed. types of strong interactions, wheth frontier which can be probed, and Interest has recently revived as mod er they be called techni-, extended can predict what happened as close ern theories, including grand unifica techni-, metahyper-, super- or heavy as 10~35 seconds after the Big Bang. tion, predict the existence of mas colour. These theories are certainly Describing these speculations in an sive (about 1016 GeV) monopoles. richer at low energies than the mini invited paper earlier this year at the These would have been plentiful in mal grand unified theories, and all Lisbon particle physics conference, the initially symmetric universe and share the general feature that some Qaisir Shafi upstaged Weinberg, could still be around. However gen or all of the particles now considered proposing the title 'Before The First eral arguments of the mass density elementary take on a structure on an Three Minutes'! of the universe deem that such su energy scale of 1 to 100 TeV. This The temperature of this primaeval perheavy particles should make up new compositeness is accompanied fireball exceeded 1015 GeV and the no more than 10~14 of the whole.
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