Stockholm revisited

Stockholm 1984 - Physics Nobel prizewinners Carlo Rubbia (left) and .

(Photo Dagens Nyheter)

Technology played an extract from a recording made in 1979 which vividly demonstrated just how un­ expected it was at the time that the predicted particles would be found so soon. Nagel paid tribute to the achievements of the CERN Collider. Seldom have theoretical predic­ tions and experimental discoveries followed each other so closely in the Nobel annals, and Weinberg, speaking first, thanked the Nobel Physics Prize Committee for 'the marvellous idea of inviting back the class of 1979 so that they could bask in the reflected glory of Rubbia and van der Meer'. 'By the mid-nineteen seventies we appeared to have a good un­ derstanding of the fundamentals of the particles which can be cre­ ated in the laboratory,' continued Weinberg. 'However this under­ standing, as usual in physics, was incomplete. There were, and still are, a large number of loose ends — undetermined parameters whose values have to be taken from ex­ periment — masses, scales, cou­ plings, mixings, etc. In addition there was an obvious lack of total unification between the different sectors — electroweak and strong interactions, still left out, quarks and leptons treated sepa­ rately. There has been a tremendous effort by theorists throughout the The Nobel Physics Prize for 1984 gant 'electroweak' gauge theory world which has proved almost was shared by Carlo Rubbia and which unified weak interactions entirely frustrating. While our ex­ Simon van der Meer of CERN for with the electromagnetic force and perimental colleagues were going their decisive contributions to the predicted just where the W and Z ahead and dazzling us with new project which led to the discovery particles could be found. discoveries, we theorists have of the W and Z field particles In December, the three theorists been exploring one new idea after which carry the . returned to Stockholm to partici­ another — ideas of remarkable Five years before, Sheldon Gla- pate with the 1984 laureates in a beauty and sublety — without the

show# and Steven specially arranged panel discussion slightest success to show for our Weinberg had made the same trip for Stockholm students. Introduc­ pains. to receive the prize for their crucial ing the proceedings, Bengt Nagel For instance there was the effort roles in piecing together the ele­ of Stockholm's Royal Institute of (in which my colleagues Sheldon

CERN Courier, March 1985 47 : 'a tremendous effort by theorists has proved almost entirely frustrating'.

(Photo CERN 356.12.79)

will be able to confirm any of these ideas. Unfortunately they do not lead to precise quantitative predic­ tions because long after its various initial phases, the Universe passed through a long period of statistical equilibrium in which all the interest­ ing phenomena of the earlier epochs got washed out. In the 'grand cooking' of the Universe, we are now left with the final cos­ mic 'stew' without any idea of the individual ingredients that went into it.' Simon van der Meer of CERN began by spelling out to the largely student audience some 'facts of life' about present-day particle accelerators. Larger and larger such machines are needed to probe smaller and smaller consti­ tuents of matter. 'Current thinking has concluded that it is no longer useful to use fixed target accelerators with most of the energy lost in hitting the Glashow and Abdus Salam parti­ in experiments using current tech­ stationary target particles. Instead cipated very actively) to make a nology, and there are even signs the fashion is now colliders, with grand unified theory to bring to­ of this happening. all the energy being effectively gether the strong and electroweak The theorists may have their used. With colliders, people prefer interactions along the same lines direction set for them by the exper­ to use electrons and positrons as the electroweak unification. imentalists. But it is also possible rather than . and These grand unified theories led that new theoretical ideas will be collisions are a mess, to a general expectation of an un­ so successful that they will be able as the particles are full of quarks stable proton with a lifetime just to explain all the missing numbers.' and . The collision energy barely accessible to experiment. In reply to a question by dis­ has to be shared between the con­ But so far, to our great sorrow, cussion co-moderator Celia Jarls- stituent particles, and is effectively this has not been seen. kog on the new drive to link basic reduced. Many alternative models have physics ideas with cosmology, On the other hand, protons are been proposed, but none so far Weinberg replied: 'Despite the easier to handle in a circular ma­ have crystallized as candidates for great success in formulating qual­ chine, as light particles like elec­ the 'true' theory. Despite all this itative solutions to cosmological trons lose energy by radiation as theoretical activity, we have vir­ problems, there has not been one they move in a circle. At CERN, tually nothing to show in the way quantitative prediction to rival, for we had the possibility of using of concrete predictions to compare example, the 1960s prediction of protons and in the with experiments. the helium abundance which gives existing SPS ring. Handling contra- Despite the fact that many of any confidence that these cosmo­ rotating beams in a single ring this these new ideas look forward to logical scenarios have any reality. way is relatively cheap — much a grand synthesis at extremely I think the work is fascinating cheaper than building a new ring. high energies, I think it is still pos­ (I participated in some of it myself) However when we think about sible that new things will turn up but I don't see any hope that we plans for higher energies in bigger

48 CERN Courier, March 1985 Simon van der Meer — 'our current dilemma'.

(Photo CERN 715.1.84) rings, are these antiproton meth­ ods still useful? We have done it, and it works. But only just, and the process is difficult and painful. We have to collect antiprotons all day long, and if the slightest thing happens, we lose them and have to start all over again. If we build a new ma­ chine, I would think it would be better to build two rings and han­ dle protons. It's easier and more reliable, and the price difference is not all that big. At CERN, we are now building the LEP machine, eventually to collide 100 GeV electrons with positrons. In the US, the new su­ perconducting ring at accelerates to 800 GeV, and 1000 GeV (1 TeV) is planned. A study is underway for a 20 TeV machine, and if the Americans build this, then we in Europe are in trouble. One plan currently being discussed is to use the LEP tunnel for a proton ring,.which because about a tenth of a GeV per metre. that in our technological society, of its limited size can at most pro­ On this basis we can propose ma­ the 'big sciences' are the big spen­ vide about half the energy of the chines of 104GeV, but remember ders and will take the place of nu­ new US proposal. However it will this figure of 1019GeV. Beat-wave clear armaments the day these be much cheaper, and if the US laser-plasma accelerators are on stop being made. If our technolog­ community doesn't get the money the horizon and could be a thou­ ical society wants to go forward, to build the new machine, we in sand times more powerful. Even we will be its benefactors. The Europe will be in a good position. so, 1019 GeV is still far away. But required level of funding is abso­ That's our current dilemma.' I am sure that by the year 2006 lutely nothing compared to the Abdus Salam began by acknow­ there will be newer ideas to ex­ current investment in nuclear sub­ ledging the contributions of the ploit.' marines, but at the same time the 1984 laureates and all the other Then Salam turned to the thorny support for science is being eroded people at CERN responsible for problem of funding. 'We have to in some countries. I shudder to creating the proton-antiproton Col­ put a price on our curiosity and think what this means for the fu­ lider. 'Van der Meer has talked of our search for basic knowledge. ture.' plans for the immediate future,' he The usual amount suggested is Finally Salam took up his long- continued, 'but I would like to look one-tenth of two per cent of the cherished dream of unifying all the further ahead, in fact to the year gross national product — two per forces of Nature. 'We do not seem 2006 — my eightieth birthday! cent is the usual overall level of to have been following the right Theorists look at an energy of expenditure on science and re­ path. The proton decay which was 1019 GeV — the so-called 'Planck search and development. As I supposed to show the unification energy' given by the Einstein equa­ come from a developing country of the does not tions. How are we to get at this (Pakistan), people ask me how I seem to be materializing. However energy? Present accelerators are can justify vast expenditures on there is the possibility of an incre­ limited by accelerating fields of accelerators. My answer is always dibly beautiful symmetry — the

CERN Courier, March 1985 49 Abdus Salam, seen here at CERN in 1979 with Leon Van Hove (standing, left) and John Adams (right), CERN's Directors General at the time. At Stockholm last year, Salam paid tribute to their roles in making the CERN proton-antiproton Collider possible.

(Photo CERN 361. 10.79)

MM

supersymmetry between back to van der Meer and Rubbia experiments — one looking for ancLfermions. There is no firm evi­ and the accelerators.' very small masses, neutrino mass dence for this yet, and if this sym­ This was underlined by Carlo or oscillations, and at the other metry really exists we will only Rubbia. 'It seems clear that present and of the scale the proton decay know when we theoreticians can day physics is back in the hands • experiments looking for effects of 'gauge' it, and that means the the­ of the experimentalists. We are all very big masses. The search for ory of supergravity. This means waiting for a big surprise, we do proton decay is still going on and that the interactions get mixed up, not know from where. there are great chances of finding they don't show themselves neatly As mentioned by Simon van der it, if it is there, in the next few and individually. Meer, colliding beams — hadrons years. Going further, to extended super- as well as electrons and positrons In the accelerator field, we do gravity, recent work suggested — are taking over from fixed tar­ not really know where new sur­ that the best dimension for the gets. This very important revolu­ prises are going to turn up. To me unification was eleven, and this tion changes the picture of accel­ it is not obvious that we have to eleven-dimensional theory was so erators very much from when it build new machines a hundred beautiful that Stephen Hawking was started fifty years ago by times more powerful than present called it the Theory of Everything Lawrence. colliders. New physics could be — TOE. But it didn't work and we In parallel, there is a big devel­ closer than we think. Already some had to backtrack. opment in non-accelerator science. glimpses of evidence at the CERN So we are in the sad situation Not that long ago, it seemed that Collider suggest new things which where we have many competing the only way to become famous are not completely understood theories, but little to show for it. was to have your own accelerator. (see May 1984 issue, page 139). The moral is that physics will al­ Now there are ways of becoming Remember the case of the J/psi. ways be an experimental science, famous without one. At the time the CERN Intersecting and we shall have to keep coming There are two classes of such Storage Rings were operating at

50 CERN Courier, March 1985 Carlo Rubbia: 'new physics could be closer than we think'.

(Photo CERN 63.8.83) about 60 GeV and the new particle had an energy of only 3 GeV. So it was not just a question of ma­ chine energy. It was discovered by looking more carefully at what had gone before. The discovery of the W and Z particles brings in new mass scales, just as the discovery of the pion did. But when the pion was discovered, nobody suspected the wealth of new resonance states that would turn up. Likewise, we have no idea what the Ws can do when they get close to each other. What is the interaction of Ws like? There are lots of theories with lots of answers, but as an experimen­ talist I would like to see what any new spectroscopy looks like. This is an open experimental question and the only way to solve such questions is by more careful and more experiments.' The final speaker, Sheldon Gla-

show, paid a tribute to the CERN Collider. 'Few of us believed that this machine would work so well and would find not just the W and Z but the top quark as well. It is a miracle.' 'There have been attempts to find surprises outside the high en­ ergy domain,' he continued. 'Free quarks, magnetic monopoles, neu­ trino masses and proton decay, and for a brief period I thought this was the direction to go. But it seems not to be the case. The surprises are coming from high energy physics and despite their modesty Carlo Rubbia and Simon van der Meer are sitting on a bomb.' Glashow then adopted a more philosophical viewpoint. There

Sheldon Glashow: upwards and downwards paths.

(Photo CERN 327.12.79)

CERN Courier, March 1985 51 L3 — experiment for LEP

are two very distinct approaches To conclude our series of articles two basic pillars, gauge invariance to the mysteries of elementary on the four big experiments for and the mechanism of spontaneous . I call them the the giant LEP electron-positron symmetry breaking. Gauge invar­ upwards path and the downwards now being built at CERN, we turn iance, which provides the field the­ path. Abdus Salam and Steven to the L3 study. (The other three ories to describe electromagne- Weinberg, for example, follow the experiments are DELPHI — see tism, the electroweak unification latter — starting from some brilliant July/August 1984 issue, page and inter-quark forces, is now well idea, like the Einstein approach, 227, ALEPH - see September understood. one attempts to go from a theory 1984 issue, page 269, and OPAL However spontaneous symmetry of everything to the mundane silly — see November 1984 issue, page breaking, which provides for exam­ little effects seen at accelerators. 375.) ple the mass scales of the elec­ This downwards path is a difficult While the other three experi­ troweak theory, is on less sure one which began with Einstein's ments have concocted fancy acro­ ground. Underlying this mechanism brilliant discovery of general rela­ nyms, the title L3 simply stems are new particles, yet to reveal tivity in 1917 and has continued from the fact it was the third letter themselves — the 'Higgs' bosons. downhill ever since! of intent to be received back in There are no clear-cut predictions The upwards path is a dirtier 1982 when ideas for LEP experi­ of where these objects will be business. We listen to our exper­ ments were first tabled. However found (unlike the very precise pre­ imental colleagues and try to glean the modest label is no reflection dictions for the W and Z gauge little bits and pieces that do not on the experiment's ambitions, particles). To uncover signs of fit into our standard and arrogant and L3 head Sam Ting is still these particles at LEP will require picture of the universe. looking for a suitable name'for his precise measurements of relatively As my theoretical colleagues experiment. rare processes. L3 has been de­ have already said, the downwards Our understanding of the funda­ signed with this firmly in mind. An path is not getting very far. But mental forces of Nature leans on additional aim is to carry out pre- the upwards path is not getting very far either! Simon van der Meer spoke about international competition in high energy physics. I don't think we should regard this as competition any more. It was when it was cheap, but today it has become very much more expensive. I hope that what has been an active com­ petition in the past will evolve into a fruitful collaboration. The success of CERN — a collaboration of 13 nations — will be usefully ex­ panded. Let me say today, to be rebroadcast in five years, that this , awarded to these dis­ tinguished and very deserving Eu­ ropeans, will mark the beginning of a high energy physics collabo­ ration with the other countries of the world.'

Overall layout of the L3 experiment for the LEP electron-positron collider now under construction at CERN.

52 CERN Courier, March 1985