Giuseppe Cocconi 1914–2008

Giuseppe Cocconi, a central figure in particle physics and cosmic rays, passed away at the beginning of November aged 94.

Born and raised in Como, it was there that Giuseppe developed his passion for astronomy. Following the advice of a friend and fellow astronomer, he went to study physics at Milan University. Shortly after completing his studies, he was invited by Edoardo Amaldi to go to Rome in February 1938 and spend six months at the Institute of Physics where work on cosmic rays was starting. There, Giuseppe met Enrico Fermi, Gilberto Bernardini, and others. With Fermi in particular, he worked on the construction of a cloud chamber to study meson decay.

In August 1938, back in Milan, Giuseppe laid the foundations there for research into cosmic rays. He worked mainly with Geiger counters at sea level and at Plateau Rosà and Passo Sella, in the Alps, until 1942, when he was called for military service to do infrared research work in Rome for the Italian Air Force. While in Milan, he met Vanna Tongiorgi, who was his student. They co-authored a first paper in 1939 on the nature of secondary radiation in cosmic rays and married in 1945. In 1942, Giuseppe was appointed professor at Catania University, a post that he took up only at the end of 1944, owing to the fighting during the Second World War.

Giuseppe’s decade of cosmic-ray work in Italy concluded with the publication of five articles and a letter in the December 1946 issue of Physical Review. Shortly after, in 1947, he received an offer from Hans Bethe of a post at Cornell University where work on cosmic rays was being reorganized after Bruno Rossi had moved to MIT. Giuseppe remained at Cornell as a full professor until 1963. Together with Vanna he performed cosmic-ray experiments at the university and at Echo Lake in the Rocky Mountains. After Cornell’s electron synchrotron and Brookhaven’s Cosmotron became operational, Giuseppe, a good friend of Albert Silverman and Bob Wilson, alternated his work between cosmic rays and accelerators.

Giuseppe’s cosmic-ray work in Italy and the US appears in about a hundred papers, most of them written either alone or with Vanna and/or Kenneth Greisen. The range of subjects is very wide, from extensive air-showers and penetrating showers – including very high-energy showers hinting at galactic or even extragalactic origin – to the interaction of very high-energy cosmic-ray particles with matter and considerations on the origin of cosmic rays. Also noteworthy are the observation of neutrons as a component of cosmic radiation (with the accompanying phenomenon now known as spallation) and Giuseppe’s "fireball" model for ultrarelativistic nucleon–nucleon collisions.

During sabbatical leave at CERN in 1959–61, Giuseppe, with his experience at the Cosmotron and with cosmic rays, contributed to setting up the experimental programme for the PS – which came into operation in November 1959. He performed a series of measurements on proton–proton elastic and inelastic scattering and proton–nuclei total cross-sections. Back in the US he continued this programme at the Brookhaven accelerator to measure large-angle scattering for two more years.

Giuseppe wrote his most widely known paper with Philip Morrison at a time both were visiting CERN. In this paper, published by Nature in September 1959, they showed that the best frequency to search for signals from intelligent extraterrestrials is 1420 MHz, corresponding to the 21 cm line of neutral hydrogen. The Search for Extra-Terrestrial Intelligence (SETI) based on the Cocconi-Morrison paper continues today.

In 1963 Giuseppe and Vanna joined CERN and he, Alan Wetherell, Bert Diddens and others formed a group working at the PS on proton–proton scattering. They found that the slope of the diffraction peak shrinks with energy, a phenomenon that was soon interpreted as a manifestation of the exchange of Regge-poles – the so-called Pomeron.

Giuseppe was Director of Research at CERN from 1967 to 1969. He was enthusiastic about the perspective promised by the Intersecting Storage Rings, and his group joined forces with Ugo Amaldi, Giorgio Matthiae and their team from Rome that had proposed to study small-angle proton–proton scattering with the technology now known as "Roman pots". This led to the discovery that the proton–proton cross-section rises with energy, showing that the proton expands with energy, and the correlated discovery that the nuclear–Coulomb interference becomes positive at high energy (as predicted by dispersion relations).

Later Giuseppe and the CERN–Rome collaboration moved to neutrino physics and, together with the group led by Klaus Winter, formed the CERN–Hamburg–Amsterdam–Rome collaboration. Giuseppe was especially interested in the delicate measurement of the elastic scattering of neutrinos on electrons.

After retirement in 1979, he maintained an active interest in experimental work at CERN and in the progress of the new accelerators. At same time he followed progress in the field of cosmic rays and astrophysics.

Giuseppe enjoyed the respect of many great physicists. As a man of culture and vision, he was curious and attentive to what was going on in the world, not only in the field of physics. He was also kind and ready to listen, straightforward but humble in his relations with his colleagues, always ready to admire other people’s success, and happy to share his knowledge with juniors. His refusal to associate with academies, and his lack of interest in prizes and honours, as well as his wish after his retirement not to talk publicly of his scientific life, are well known. He was a great physicist.

His colleagues and friends.