Harnessing the CERN model

3 May 2021

Experimental physicist Paul Lecoq’s half-century-long career illustrates the power of CERN in fostering international collaboration, writes Craig Edwards.

Paul Lecoq in China in 1982

CERN’s international relationships are central to its work, and a perfect example of nations coming together for the purpose of peaceful research, regardless of external politics. Through working in China during the 1980s and the Soviet Union/Russia in the early 1990s, physicist Paul Lecoq’s long career is testament to CERN’s influence and standing.

Originally interested in astrophysics, Lecoq completed a PhD in nuclear physics in Montreal in 1972. After finishing his military service, during which he taught nuclear physics at the French Navy School, he came across an advertisement for a fellowship position at CERN. It was the start of a 47-year-long journey with the organisation. “I thought, why not?” Lecoq recalls. “CERN was not my initial target, but I thought it would be a very good place to go. Also, I liked skiing and mountains.”

Royal treatment

During his third year as a fellow, a staff position opened for the upcoming European Hybrid Spectrometer (EHS), which would test CERN’s potential for collaboration beyond its core member states. “The idea was to make a complex multi-detector system, which would be a multi-institute collaboration, with each institute having the responsibility to build one detector,” says Lecoq. One of these institutes was based in Japan, allowing the exchange of personnel. Lecoq was one of the first to benefit from this agreement and, thanks to CERN’s already substantial image, he was very well-received. “At the time, people were travelling much less than now, and Japan was more isolated. I was welcomed by the president of the university and had a very nice reception almost every day.” It was an early sign of things to come for Lecoq.

During the lifetime of the EHS, a “supergroup” of CERN staff was formed whose main role was to support partners across the world while also building part of the experiment. By the time the Large Electron–Positron Collider (LEP) came to fruition it was clear that it would also benefit from this successful approach. At that time, Sam Ting had been asked to propose an experiment for LEP by then Director-General Herwig Schopper, which would become the L3 experiment, and with the EHS coming to an end, says Lecoq, it was natural that the EHS supergroup was transferred to Ting. Through friends working in material science, Lecoq caught wind of the new scintillator crystal (BGO) that was being proposed for L3 – an idea that would see him link up with Ting and spend much of the next few years in China. 

BGO crystals had not yet been used in particle physics, and had only existed in a few small samples, but L3 needed more than 1 m3 of coverage. After sampling and testing the first crystal samples, Lecoq presented his findings at an L3 collaboration meeting. “At the end of the meeting, Ting pointed his finger in my direction and asked if I was free on Saturday. I responded, ‘yes sir’. Then he turned to his secretary and said, ‘book a flight ticket to Shanghai – this guy is coming with me!’”

This is something unique about CERN, where you can meet fantastic people that can completely change your life

Unknown to Lecoq upon his arrival in China, Ting had already prepared the possibility to develop the technology for the mass production of BGO crystals there, and wanted Lecoq to oversee this production. BGO was soon recognised as a crystal that could be produced in large quantities in a reliable and cost-effective way, and it has since been used in a generation of PET scanners. Lecoq was impressed by the authority Ting held in China. “The second day we were in China, we, well Ting, had been invited by the mayor of Shanghai for a dinner to discuss the opportunity for the experiment.” The mayor was Jiang Zemin, who only a few years later became China’s president. “I have been very lucky to have several opportunities like this in my career. This is something unique about CERN, where you can meet fantastic people that can completely change your life. It was also an interesting period when China was slowly opening up to the world – on my first trip everyone was in Mao suits, and in the next three to five years I could see a tremendous change that was so impressive.”

Lecoq’s journeyman career did not stop there. With LEP finishing towards the turn of the millennium and LHC preparations in full swing, his expertise was needed for the production of lead tungstate (PWO) crystals for CMS’s electromagnetic calorimeter. This time, however, Russia was the base of operations, and the 1.2 m3 of BGO crystal for L3 became more than 10 m3 of PWO for CMS. As with his spell in China, Lecoq was in Russia during a politically uncertain time, with his arrival shortly following the fall of the Berlin Wall. “There was no system anymore. But there was still very strong intellectual activity, with scientists at an incredible level, and there was still a lot of production infrastructure for military interest.”

It was interesting not only at the scientific level, but on a human level too

At the time, lithium niobate, a crystal very similar to PWO, was being exploited for radar communication and missile guidance, says Lecoq, and the country had a valuable (but unknown to the public) production-infrastructure in place. With the disarray at the end of the Cold War, the European Commission set up a system, along with Canada, Japan and the US, called the International Science and Technology Center (ISTC), whose role was to transfer the Soviet Union’s military industry into civil application. Lecoq was able to meet with ISTC and gain €7 million in funding to support PWO crystal production for CMS. Again, he stresses, this only happened due to the stature of CERN. “I could not have done that if I had been working only as a French scientist. CERN has the diplomatic contact with the European Commission and different governments, and that made it a lot easier.” Lecoq was responsible for choosing where the crystal production would take place. “These top-level scientists working in the military areas felt isolated, especially in a country that was in a period of collapse, so they were more than happy not only to have an opportunity to do their job under better conditions, but also to have the contacts. It was interesting not only at the scientific level, but on a human level too.”

Crystal clear

Back at CERN, Lecoq realised that introducing a new scintillating crystal, optimising its performance to the harsh operating conditions of the LHC, and developing mass-production technologies to produce large amounts of crystal in a reliable and cost-effective way, was a formidable challenge that could not be dealt with only by particle physicists. Therefore, in 1991, he decided to establish the Crystal Clear multidisciplinary collaboration, gathering experts in material science, crystal-growth, luminescence, solid-state physics and beyond. Here again, he says, the attractiveness of CERN as an internationally recognised research centre was a great help to convince institutes all over the world, some not connected to particle physics at all, to join the collaboration. Crystal Clear is still running today, and celebrating its 30th anniversary. 

Through developing international connections in unexpected places, Lecoq’s career has helped build sustained connections for CERN in some of the world’s largest and fruitfully scientific places. Now retired, he is a distinguished professor at the Polytechnic University in Valencia, where he has set up a public–private partnership laboratory for metamaterial-based scintillators and photodetectors, to aid a new generation of ionisation radiation detectors for medical imaging and other applications. Even now, he is able to flex the muscles of the CERN model by keeping in close contact with the organisation.

“My career at CERN has been extremely rich. I have changed so much in the countries I’ve worked with and the scientific aspect, too. It could only have been possible at CERN.”

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