Luc Pape 1939–2021

28 June 2021
Luc Pape

Our colleague and friend Luc Pape passed away on 9 April after a brief illness. Luc’s long and rich career covered all aspects of our field, from the early days of bubble-chamber physics in the 1960s and 1970s, to the analysis of CMS data at the LHC.

In the former, Luc contributed to the development of subtle methods of track reconstruction, measurement and event analysis. He participated in important breakthroughs, such as the first evidence for scaling violation in 1978 in neutrino interactions in BEBC and early studies of the structure of the weak neutral current. Luc developed software to allow the identification of produced muons by linking the extrapolated bubble-chamber tracks to the signals of the external BEBC muon identifier.

Luc’s very strong mathematical background was instrumental in these developments. He acquired a deep expertise in software and stayed at the cutting edge of this field. He also exploited clever techniques and rigorous methods that he adapted in further works. At the end of the bubble-chamber era, Luc was among the experts studying the computing environment of future experiments. He was also one of the people involved in the origin of the Physics  Analysis Workstation (PAW) tool.

After this, Luc joined the DELPHI collaboration. Analysing the computing needs of the LEP experiments, he was among the first to realise the necessity of moving from shared central computing to distributed farms for large experiments. He thus conceived, pushed and, with motivated collaborators, built and exploited the DELPHI farm (DELFARM), allowing physicists to rapidly analyse DELPHI data and produce data-summary (DST) files for the whole collaboration. Using his strong expertise in most available software tools, Luc progressively improved track analysis, quality checking and event viewing. DELPHI users will remember TANAGRA (track analysis and graphics package), the backbone of the DELANA (DELPHI analysis) program, and DELGRA for event visualisation.

Luc’s passion for physics never faded. Open minded, but with a predilection for supersymmetry (SUSY), the subtle phenomenology of which he mastered brightly, he became the very active leader of the DELPHI, and then of the full LEP SUSY groups.

After retiring from CERN in 2004, he enjoyed the hospitality of the ETH Zurich group in CMS, to which he brought his expertise on SUSY. Collaborating closely with many young physicists, he introduced into CMS the “stransverse mass” method for SUSY searches, and pioneered several leptonic and hadronic SUSY analyses. He first convened the CMS SUSY/BSM group (2003–2006), then the SUSY physics analysis group (2007–2008), preparing various topological searches to be performed with the first LHC collisions. Responsible for SUSY in the Particle Data Group from 2000–2012, he helped define SUSY benchmark scenarios within reach of hadron colliders, present and future. Comforted by the discovery of a light scalar boson in 2012 (a necessary feature of but not proof of SUSY), he continued exploring novel analysis methods and strategies to interpret any potential evidence for SUSY particles.

We will remember Luc for the exceptional combination of a genuine enthusiasm for physics, an outstanding competence and rigour in analysis, incorporating quite technical matters, and a deep concern about young colleagues with whom he interacted beautifully. Luc had a strong interest in other domains, including cosmology, African ethnicities and arts, and Mesopotamian civilisations. With his wife, he also undertook some quite demanding Himalayan treks.

We have lost a most remarkable and complete physicist, a man of great integrity, devoid of personal ambition, a rich personality, interested by many aspects of life, and a very dear friend.

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