The French theoretical physicist, Henri Cornille, passed away on 23 February, aged 83.
Henri was a typical product of the French education system before 1968, i.e. an elitist system in which someone of modest origin could climb the ladder provided that he was good and courageous. Henri followed thetroisième cycle organized by Maurice Lévy at the Ecole Normale but it was Roger Nataf (who, like Lévy, was from North Africa) at the Institut de Physique Nucléaire, Orsay, who realized that he had real talents. Nataf sent Henri to work with me at CERN, where we had a fruitful collaboration in the fields of potential scattering and high-energy scattering. Our best result, I believe, was the proof that the ratio of the widths of the diffraction peaks for particle–particle scattering and for particle–antiparticle scattering was approaching unity asymptotically. He was also the inventor of the "Cornille plot", which gives the allowed domain for total and elastic cross-sections when they behave like powers of log s for large energies.
Henri never recoiled in the face of difficulty. This is well illustrated by his work with Jean-Michel Drouffe on phase-shift analysis for scattering amplitudes with maximum angular momentum L= 4. In this context, one problem that is well posed but not yet completely solved is that given a differential cross-section at an energy such that only elastic collisions can take place, what are the corresponding scattering amplitudes or, equivalently, the phase shifts corresponding to the various partial waves? Are there several solutions except for changing the sign of all phase shifts? J H Crichton has shown that there are cases where there is a two-fold ambiguity. Many theoreticians have worked on this problem and obtained some results, in which more than two solutions have never appeared. In my opinion, the work of Cornille and Drouffe is the most convincing indication that there are never more than two solutions.
After officially retiring, Henri was given the status of emeritus – something rare in France – and continued to work at Saclay. In all of his work, he showed intellectual integrity, perseverance, and imagination. We shall miss him.
• André Martin, CERN.