by Virginia Greco. Published: 11 June 2018

The first Chair of the ALICE Collaboration Board, Emanuele Quercigh played an important role during the first years of the experiment’s history. We talked with him about his brilliant career and about heavy-ion physics at CERN.

Emanuele Quercigh at the celebration for the 25 years anniversary of the ALICE experiment.

 

After the ALICE Collaboration was established, in 1994 Emanuele Quercigh was elected Chair of the Collaboration Board (CB). Already fully involved in heavy-ion physics at the Super-Proton-Synchrotron (SPS), he accepted this assignment and the challenge of guiding (together with the spokesperson) the community gathered around this project through the first steps of such an endeavour.

On the occasion of the 25 years anniversary of the ALICE experiment, we talked with him about his professional trajectory and the origin of heavy-ion physics as an independent research field. 

 

Emanuele Quercigh was born in Naples, but he moved to Friuli (in the North-East of Italy) with his mother and his younger brotherwhen he was still a child, after the early death of his father.

Once he concluded high school, being very interested in science, he went to study physics at the University of Milan in Italy. There, in 1959, he initiated his scientific activity as an assistant of Giuseppe Occhialini, a brilliant physicist who had contributed to the discovery of pions and was playing an important role in cosmic ray physics, thanks to his experiments with photographic emulsions. During that period, Quercigh worked in particle and cosmic ray physics, as well as on their associated technologies, and found an unconventional way of generating high magnetic fields (around 340 KG) by using an exploding liquid mercury coil. ‘Once, while I was conducting my tests, a small explosion occurred in the laboratory,’ Quercigh recalls laughing slightly. ‘Nobody was hurt, but I certainly attracted the attention of the researchers working in the neighbouring laboratories.’ In those years, he also developed a capacitive read-out system for spark chambers.

In 1964 he became a fellow at CERN, where later he obtained an indefinite appointment as staff physicist. Here, he first took part in various experiments using the CERN 2 m Bubble Chamber and then he proposed and led, together with David Lord, the ERASME Project. ‘This was a system for digitizing bubble chamber pictures,’ Quercigh explains. Indeed, photographic film was still used to record subnuclear interactions and with big bubble chambers the event patterns had become very complex. The ERASME project consisted in using a light ray to precisely scan the films on which physics events were recorded. ‘That system was used until 1987 for the analysis of several bubble and streamer chamber experiments.

In 1974, Quercigh was appointed Spokesperson of the high statistics 8.25 GeV/c Kp bubble chamber experiment, which discovered the φ(1850) particle – the first Regge recurrence of the φmeson – and performed a detailed study of the lifetime of the Ωbaryon, as well as a first evaluation of its spin.

In 1979, he moved to the Omega Spectrometer, of which he had been one of the proponents, and became involved in several experiments at the CERN SPS designed to study hadron spectroscopy, particle production mechanisms, soft photon production and quantum chromodynamics (QCD) processes.

My involvement in heavy-ion physics started in the early eighties,’ Quercigh recalls, ‘when this branch of research was taking its first steps at the SPS. I remember that the physicists who attended the Workshop on Future Relativistic Heavy-Ion Experiments, held at GSI (Darmstadt) in October 1980, were very enthusiastic, since they considered head-on collisions of heavy nuclei as the way to create in the laboratory the Quark-Gluon Plasma (QGP), a phase of matter that was believed to have existed for a short time in the early Universe. Johann Rafelski and Berndt Müller had predicted that an enhancement of strange particle abundances (increasing with the strangeness content of the particles) would have been observed as a signature of the formation of QGP during the interaction.

My colleagues and I,’ he continues, ‘had been thinking about how to measure these predicted strangeness enhancements, in particular those of the strange baryons. But since CERN’s priority at that time was to build the LEP, we could not use CERN budget to buy new equipment. As a consequence, we had to adapt existing detectors and magnets. We immediately thought of employing the Omega spectrometer, located in the CERN West Experimental Area, which we had been using for hadron spectroscopy.

Hence, in the following years, Quercigh led a research group which studied the production in heavy-ion collisions of baryons and anti-baryons carrying one or more strange quarks, using the Omega spectrometer. In particular, he took part in the WA85 and WA94 experiments, which used a beam of sulphur ions at 200 GeV/nucleon impinging on a lead fixed target, and later in the WA97 and NA57 experiments, in which a 160 GeV/nucleon lead ion beam was employed.

The hardware of the experiments became more and more sophisticated in order to deal with new needs and challenges’, explains Quercigh. ‘For example, in order to identify the numerous tracks produced by particles generated in lead beam collisions, an array of silicon pixel detectors was used as the main tracking system. WA97 was the first high-energy physics experiment using this new technology (developed by Erik Heijne and his RD19 collaborators). The experience gained led then to a large employment of silicon pixels in LHC inner tracking detectors. Indeed, we can state that the ALICE silicon pixel micro-detectors are direct descendants of those used in WA97 and NA57.

The research in the new-born field of heavy-ion physics started producing interesting results, making the physics case for the development of a dedicated experiment at the future LHC. While serving as a Consultant in the Programme Advisory Committee of the Brookhaven National Laboratory (BNL), during the approval phase of the first experiments to be built around the Relativistic Heavy Ion Collider (RHIC), Quercigh decided to support the proposal of a heavy-ion programme at the new CERN accelerator. So, he took part in the LHC Aachen workshop, held in October 1990, where he presented some “remarks on hyperon detection at LHC energies”, and started working on this project. In particular, together with several of his close collaborators – F. Antinori, D. Di Bari, A. Jacholkowski, F. Meddi, E. Nappi, F. Navach, K. Safarik and O. Villalobos-Baillie among them –  Quercigh collaborated with Jürgen Schukraft and Hans Gutbrod to lay down the foundations of the ALICE experiment. He was then elected Chairman of the Collaboration Board for the period from 1994 to 1998. ‘Those were crucial years,’ he comments, ‘in which the CB had to trace the roadmap of the experiment’s development, as well as to facilitate the creation of a solid and effective collaboration. “Consensus” and “balance” were the key words.’

Quercigh in 2000 [Font: CERN Courier]

In the meanwhile, the SPS experiments were harvesting important results, which eventually led to CERN announcing the observation of the QGP in February 2000.

Events in which particles containing up to three strange quarks had been produced were, in fact, detected by various experiments. ‘Our hopes were confirmed,’ recalls Quercigh. ‘We found, as expected, an enhanced production of multi-strange baryons and anti-baryons in heavy-ion collisions with respect to proton-proton ones. In addition, we observed that this enhancement increased with the strangeness content of the produced particle, i.e. the number of strange quarks included in the baryon or anti-baryon. We saw, for example, that the rare Omega particle, which contains three units of strangeness, was produced twenty times more frequently in central Pb-Pb events (i.e. lead-lead collisions in which the two ions bump head-on into each other) than in the pp counterparts!’ Quercigh himself presented these results in the announcement seminar in 2000, even though he was officially retired since December of the previous year. 

As it is common among researchers, he did not interrupt his activities after retiring. In fact, he continued to work in ALICE as an Honorary Member and contributed to the first rounds of ALICE publications. ‘The first LHC scientific paper published after the new accelerator started to run has been ALICE’s. Of course, it preceded only by a few days the papers of the other experiments, but still I like mentioning it.’ 

He was also Guest Professor at the University of Padua between 2001 and 2003, gave several invited talks and wrote various papers and some book sections (in ‘Melting Hadrons and Boiling Quarks’, edited by J.Rafelski, and in ‘Technology Meets Research: 60 Years of CERN Technology’, edited by H.Wenninger and C.Fabjan).

For me, physics has always been a hobby besides a job, so it has accompanied me in the retirement as well,’ he concludes, ‘but I am also fond of travelling and of history. Indeed, now I have time to read lots of history books.

Emanuele Quercigh giving his talk at the jubilee event for the 25 years anniversary of the ALICE experiment.