Experimental particle physicist Jean-Charles (Charlie) Chollet passed away on 24 August 2021. He had spent his whole scientific career at CERN, working as a member of the Orsay Laboratoire de l’Accélérateur Linéaire. His work was always in the area of precision measurements involving subtle analyses.
Charlie started at the CERN Proton Synchrotron with his thesis, defended in 1969 under the supervision of Jean-Marc Gaillard, on the observation of the interference between KL and KS in the π0π0 decay mode. He then contributed to the WA2 experiment at the Super Proton Synchrotron (SPS) studying leptonic decays of hyperons, where he took care of one of the most difficult components of the detector, the DISC Cherenkov counter, which led to the impressive achievement of separating ~200 GeV/c Σ– and Ξ– hyperons thanks to a combination of subtle optics and of a complex system of photodetection. He then participated in the UA2 experiment at the SPS pp̅ collider, where he was in charge of the pre-shower detector calibration and performance.
Later he engaged himself in the preparation of the ATLAS experiment at the LHC, where he performed several studies, notably on the pileup background properties and their expected impact on the design of the liquid-argon calorimeter electronics. He also participated in test-beam analysis of early “accordion calorimeters”, prototypes of this same calorimeter. He ended his career at the NA48 experiment, which was measuring the direct CP violation parameter ε´/ε in neutral kaon decays and where he made an important contribution with the analysis of kaon scattering in the collimator. From small inconsistencies in the data, he managed to find and understand the source of this background, thereby allowing it to be precisely taken into account in the measurement.
He was a great sportsman, especially sailing, skiing and cycling. Those who worked with Jean-Charles Chollet will always remember the pleasure of his company, his dry sense of humour and the depth and refinement of his work, which was always presented with the utmost modesty.