Emilio Picasso’s contagious enthusiasm for physics

27 January 2015

A tribute to his many contributions to physics, especially at CERN.

Never has such an illustrious career at CERN hung from so slender a thread of improbability. He was in Genoa, I was in Geneva. Were we destined to meet? In Bristol? As a result of some tiny chance? His final day of a one-year sabbatical. My first day of a visit. All alone on his last evening, Emilio wanted to say goodbye to Bristol and went to a bar. Out of hundreds of options, I ended up in the same bar…and got a warm welcome. I described the new g-2 experiment, which was just starting to roll: the first ever muon storage ring at 1.2 GeV to dilate the muon lifetime to 27 μs and see more precession cycles. Simon van der Meer was on board but no one else. Emilio loved fundamental physics, and there and then he offered to join the project, visiting CERN from Genoa and later becoming a full-time member of staff. Little did I know that I would be making speeches and writing articles in his honour: Chevalier of Legion of Honour of France and Knight Grand Cross of the Order of Merit of the Republic of Italy.
Francis J M Farley

Emilio read physics at the University of Genoa, where he stayed after receiving his doctorate in July 1956. Within a small team, he worked mainly on technical aspects of visual particle detectors, first with gas bubble chambers – based on using a supersaturated solution of gas in a liquid at room temperature – and diffusion chambers. By the early 1960s, he had moved on with some of his collaborators to study proton and meson interactions in nuclear emulsions, and participated in the International Co-operative Emulsion Flights, which took two large stacks of emulsion plates high into the atmosphere to detect the interactions of energetic cosmic rays. This international collaborative effort included the Bristol group of Cecil Powell, recipient of the 1950 Nobel Prize in Physics for his work on emulsions and their use in the discovery of the particle now known as the pion in cosmic rays.

So it was not surprising that Emilio arrived in Bristol as a NATO postdoctoral fellow in 1962/1963. There, his chance meeting with Farley in Bristol in 1963 set him on course to CERN. When he offered to join the g-2 experiment, Farley accepted with pleasure, and soon Emilio started travelling to Geneva from Genoa, becoming a research associate at CERN in 1964. From the beginning he insisted on understanding everything in depth. He wrote Fortran programs, checked the calculations and found some mistakes, which luckily for the future of the experiment were not lethal.

Emilio’s enthusiasm was contagious, and he and Farley gradually assembled a small team. Farley recalls: “There were many difficulties, but eventually it worked and we measured the anomalous moment of the muon to 270 ppm. The result disagreed with theory by 1.7σ but we were sure of our number (confirmed by the next experiment) and we published anyway. (The fashionable shibboleth is that you need 5σ for an effect; true if you are looking for a bump in a wiggly graph, which might be anywhere. But for one number 2–3σ is important and anything over 3σ is huge). The discrepancy was enough to worry the theorists, who set to work and discovered a new correction. Then they agreed with us. This was a triumph for the experiment.”

In 1967 Farley moved to a job in England and Emilio became group leader, having joined the CERN staff in November 1966. Together with John Bailey they discovered the magic energy, 3.1 GeV, at which electric fields do not affect the spin precession. This led to a new muon storage ring with a uniform magnetic field and vertical focusing using an electric quadrupole field. Emilio masterminded this much larger project, creating a warm happy atmosphere and encouraging new ideas. The muon precession could now be followed out to 500 μs and g-2 was measured to 7 ppm. The team had the right number again (confirmed by the later measurement at Brookhaven National Laboratory) and this time it agreed with the theory.

While the g-2 saga was coming to an end, Emilio and Luigi Radicati, who was then a visiting scientist at CERN, became interested in the possibility of detecting gravitational waves by exploiting suitably coupled superconducting RF cavities. The idea was to detect the change of the cavity Q-value induced by gravitational waves. They were joined by Francesco Pegoraro and CERN’s Philippe Bernard, and published papers analysing the principle in 1978/1979. It was an unconventional idea, which Emilio continued to consider and improve on and off with various collaborators for the next quarter of a century. However, at the end of the 1970s a much larger project lay on CERN’s horizon.

In November 1978, John Adams – then CERN’s executive director-general – decided to push R&D on superconducting RF with a view to increasing the energy reach of the proposed Large Electron–Positron (LEP) collider. He asked Philippe Bernard and Herbert Lengeler to put together a research programme, and they in turn proposed that Emilio should co-ordinate collaboration with outside laboratories because of his “vivid interest in RF superconductivity” and his “excellent contacts” in the field. The result was that in spring 1979, Emilio became team leader of the development programme at CERN, and responsible for co-ordination with other laboratories – in Genoa, Karlsruhe, Orsay and Wuppertal.

The development work at CERN led to superconducting cavities that could achieve the necessary high electric-field gradients, and the team went on to design and build, in collaboration with European industries, the system of superconducting RF that was eventually deployed in LEP during the 1990s. In 1986, Emilio and others proposed the installation of a maximum of 384 superconducting cavities to reach an energy of at least 220 GeV in the centre-of-mass. In the end 288 such cavities were installed, and LEP eventually reached a total energy of 208 GeV. Emilio would later express sadness that the collider’s energy was never brought to its fullest potential with the maximum number of cavities.

Leader of LEP
However, he was to take on a still more significant role in 1980, when at the suggestion of the new director-general, Herwig Schopper, CERN Council designated him LEP project leader. With Schopper’s agreement, Emilio began by setting up the LEP Management Board, consisting of the best experts at CERN, in all of the various aspects, from magnets, RF and vacuum to civil engineering and experimental halls. The board met one day a week throughout the period of LEP’s construction, discussing all of the decisions that needed to be taken, including the technical specifications for contracts with industry. Schopper would regularly join in, mainly to observe and participate in the decision-making process, which took place in a warm and enthusiastic atmosphere.

The main aspect of the project in which Emilio had no experience was civil engineering, but one of the early major issues concerned the exact siting of the tunnel, which in the initial plans was to pass for 12 km beneath some 1000 m of water-bearing limestone in the Jura mountains. While this would avoid the larger communities in France and Switzerland, it presented formidable tunnelling challenges. Rather than downsize, Emilio decided to look into locating the ring further from the mountains. This needed crucial support from the local people, and he was instrumental in setting up regular meetings with the communes around CERN. The result was that in the final design, the LEP tunnel passed for only 3.3 km under the Jura, beneath 200 m of limestone at most.

This final design was approved in December 1981 and construction of the tunnel started in 1983. It was not without incident: when water burst into the part of the tunnel underneath the Jura, it formed a river that took six months to eliminate, and the smooth planning for construction and installation became a complex juggling act. Nevertheless by July 1988, the first sector was installed completely. A test with beam proved that the machine was indeed well designed, and just over a year later, the first collisions were observed on 13 August 1989.

Following the completion of the construction phase of LEP, and the end of his successful mandate as leader of the LEP project, Emilio began to focus again on the detection of gravitational waves, an interest that had continued even while he was a director at CERN, when he supported the installation of the EXPLORER gravitational-wave detector at the laboratory in 1984. He was nominated director of the Scuola Normale Superiore in Pisa in 1991, where he had been named professor a decade earlier, and served as such for the following four years, retiring from CERN in 1992. At Pisa, he played a key role in supporting approval of Virgo – the laser-based gravitational-wave detector adopted by INFN and CNRS, which is currently running near Cascina, Pisa.

Emilio’s love for physics problems lasted throughout his life in science – a life during which warmth and welcome radiated. He knew how to switch people on. Now, sadly, this bright light is dimmed, but the afterglow remains and will be with us for many years.

Emilio Picasso 1927–2014

After a long illness, Emilio Picasso passed away on 12 October. One of the earliest and most outstanding staff members of CERN, he made remarkable contributions to the prodigious success of the organization for more than 50 years.

Born in Genoa on 9 July 1927, Emilio first studied mathematics, followed by two years of physics. After his doctorate he became assistant professor for experimental physics at the University of Genoa, and began research in atomic physics before changing to particle physics.

Short stays with the betatron at Torino and with the electron synchrotron at Frascati provided him with his first experiences with particle accelerators. He then went to Bristol in the years 1962/1963, where he joined the group of Cecil Powell, who had received the Nobel prize in 1950 for investigating cosmic radiation using photographic emulsions and discovering the π meson. There Emilio met Francis Farley who told him that he intended to measure at CERN the anomalous magnetic moment of muons circulating in a storage ring. After some drinks they became friends, and Emilio decided to join Farley on the CERN experiment.

The measurement of the anomalous magnetic moment – or more precisely the deviation of its value from the Bohr magneton, expressed as “g-2” – yields an extremely important quantity for testing quantum electrodynamics (QED). Emilio was attracted by this experiment because it matched two different aspects of his thinking. He was fascinated by fundamental questions, and at the same time the experiment required new technologies for magnets.

From 1963, Emilio commuted between Genoa and CERN, becoming a research associate in 1964 to work on the g-2 experiment and a CERN staff member in 1966. In addition to Farley, John Bailey and Simon van der Meer joined the group, which Emilio was later to lead. The measurements went on for 15 years at two successive storage rings (the second with Guido Petrucci and Frank Krienen), and achieved an incredible accuracy of 7 ppm, so becoming one of the most famous precision tests of QED.

In 1978, Luigi Radicati convinced Emilio to participate in an experiment to look for gravitational waves produced by particles circulating in a storage ring. Superconducting RF cavities were to be used as detectors. The attempt was unsuccessful, but it gave Emilio the opportunity to get to know the technology of superconducting cavities – knowledge that was to serve him extremely well later at the Large Electron–Positron collider (LEP).

In 1981, the LEP project was approved by CERN Council, alas under very difficult conditions, i.e. with a reduced and constant budget. In addition, the requisite personnel had to be found among the staff of the newly unified CERN I and CERN II laboratories. Under such conditions it was not easy to find the right person to lead the LEP project. Several outstanding accelerator experts were available at CERN, and it would have been an obvious step to appoint one of them as project leader. However, because it became necessary to reassign about a third of the CERN staff to new tasks – implying that personal relations established across many years had to be broken – I considered the human problems as dominant. Hence I appointed Emilio as project leader for LEP, a decision that was greeted by many with amazement. I considered his human qualities for this task to be more important than some explicit technical know-how. Emilio was respected by the scientists as well as by the engineers. He was prepared to listen to people, and his moderating temper, his honesty and reliability, and last but not least his Mediterranean warmth, were indispensable for the successful construction and operation of what was by far the largest accelerator of its time. His name will always remain linked with this unique project, LEP – a true testament to Emilio’s skills as a scientist and as a project leader.

After his retirement I visited Emilio often in a small office in the theory division, where he had settled to study fundamental physics questions again. But he also took up other charges. One of the most important tasks was the directorship of the Scuola Normale Superiore at Pisa from 1991 to 1995, where he had been nominated professor in 1981 – a commitment that he could not fulfil at the time because of his CERN engagements.

Emilio received many distinctions, among them the title of Cavaliere di Gran Croce dell’Ordine al Merito della Repubblica, one of the highest orders of the Italian state.

Despite the heavy demands of his job he always cared about his family, and in return his wife Mariella gave him loving support in difficult times.

We all regret that sadly Emilio was not well enough to enjoy the enormous recent success of CERN. Science has lost a great physicist and many of us a dear friend.

Herwig Schopper, CERN director-general, 1981–1988.


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