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Accelerators and detectors

Accelerators and detectors

CERN, the US and the W

01 Sep 2004 Robert P Crease

US particle physicists had never felt any real competition until the W boson was discovered at CERN in 1983. The new rivalry changed relations with Europe forever, says Robert P Crease

“The discovery of the W was a turning point for CERN from the point of view of the self-confidence of its physicists, the confidence of its fund-raisers, and its reputation in the US,” says John Krige, a historian at the Georgia Institute of Technology. “And it shows why competition meant different things for the Europeans and the Americans.”

Competition can come in two different forms, as I outlined in a previous column (September 2000 p17). In political competition – the kind at election time – the aim is a particular prize. Gaining the prize requires vanquishing your opponents, and your strength is inversely proportional to theirs. The aim of performance competition, in contrast, is to achieve a superior level of performance: you boost your performance by sharing with others, and your strength increases with theirs. Science involves both, ideally only the latter.

But in a fascinating article about the discovery of the W boson – a feat that earned CERN its first Nobel prize – Krige argues that CERN’s history reveals complexities in that picture (2001 Isis 92 517). The rivalry between CERN and the US initially concerned performance. In 1953 – a year before it was officially founded – CERN sent a team of researchers who were planning the lab’s first synchrotron to study the 3 GeV Cosmotron at the Brookhaven National Laboratory. While brainstorming improvements for CERN, Brookhaven’s scientists found a radical innovation called “strong focusing”. Both CERN and Brookhaven embarked on projects to build strong-focusing accelerators of about the same energy – the Proton Synchrotron (PS) and the Alternating Gradient Accelerator (AGS) – with both sides sharing information, personnel and experience.

But although the two racehorses started at about the same time – CERN’s PS was even six months ahead – the AGS benefited from years of US experience in scientific organization and management. It was to make the lion’s share of discoveries.

Two decades later the situation was changed – but only slightly. Only one horse could race at a time, but the US was still reaping the major finds. CERN chose to build an innovative type of proton collider – the Intersecting Storage Rings – and in 1971 it came on easier than expected. This inspired Brookhaven to abandon its plans for a large fixed-target accelerator and build instead a 200 x 200 GeV – later a 400 x 400 GeV – proton-proton collider named ISABELLE.

One of ISABELLE’s most important targets was the W boson, which had been predicted by the electroweak theory of Sheldon Glashow, Abdus Salam and Steven Weinberg. Unfortunately for Brookhaven, problems with ISABELLE’s innovative superconducting magnets delayed construction. Although these were solved by 1983, the lab lost time and credibility. Meanwhile, Fermilab near Chicago was making strides in its collider programme. And CERN began working on a clever way of accumulating antiprotons and injecting them into the new Super Proton Synchrotron (SPS), where they would collide with a beam of protons travelling in the opposite direction. The lab embarked on this risky project in part, wrote CERN’s director-general for research Leon van Hove, to keep its physicists from “repeating at improved level the experiments already done or in progress at Fermilab”. Krige arrived at CERN in autumn 1982, which was to prove to be a turning point in the lab’s history. That October and November, the SPS ran at sufficient energy and intensity to produce and detect the W. And in January 1983, Krige was one of those sitting in CERN’s main auditorium to hear Carlo Rubbia announce the discovery of the W, for which he and Simon van der Meer won the 1984 Nobel prize (see “Carlo Rubbia and the discovery of the W and the Z”). Four months later the Z boson was also found at CERN. A headline in the New York Times summed the situation up: “Europe 3, U.S. Not Even Z-Zero”.

Here the complexities enter. Unused to such competition – their accelerators were supposed to have found the W boson – US physicists grew unsure of themselves. Some who had backed ISABELLE now wavered. George Trilling of Berkeley wrote that ISABELLE was “likely to condemn US high-energy physics to second-rate status”. Fermilab’s director Leon Lederman, saying that ISABELLE would hold the US programme “hostage”, promoted the idea of

a huge new machine – soon called the Superconducting Super Collider (SSC) – to allow America to seize back the lead. US physicists decided to cancel ISABELLE in favour of the SSC. Some 10 years later, suffering magnet, budget and political problems of its own, the SSC was terminated by the US Congress. A half-dug tunnel in the Texas desert is all that remains of the project.

The critical point

Ironies permeate this story. One is that the US physics community decided to put all its eggs in the SSC basket out of a fierce desire to avoid playing second fiddle, so to speak, to CERN – but ended up in that role anyway after the project was terminated. But this development, Krige pointed out, forced the US into serious collaboration with CERN. “The success of CERN’s competition with the US was a precondition for true collaboration,” he says.

Today there is no more political competition over accelerators. It is not simply that only one horse – at most – can run at the same time, but that it requires an international collaboration just to get it there in the first place. Political competition is even vanishing from the large experiments.

Still, Krige argues, we can learn from exploring the complexities of stories such as this. One lesson is that scientists will only collaborate seriously and over the long term with those whom they trust and respect as their peers: this will necessarily limit the “international” scope of any “world accelerator”. Another lesson is that, since they supply the funds, governments will have to see international collaboration in such projects as coherent with their foreign-policy aims. In the current, rather tense, state of US-European relations, therefore, a world accelerator may be just an idle dream – or an instrument to paper over cracks between traditional allies.

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