Michael J. Longo, professor emeritus at the University of Michigan, passed away peacefully in Ann Arbor, Michigan, on 14 September 2023. A fellow of the American Physical Society, Mike had an extensive career in experimental elementary particle physics research and later in astrophysics.
Born in Philadelphia on 7 April 1935, Mike graduated from LaSalle College with a BA in physics. He subsequently earned a MA and PhD from the University of California, Berkeley, where he performed pioneering measurements of the π+ total cross section in collaboration with his thesis adviser, Burt Moyer. He also was able to study π− cross sections using the same apparatus, piggybacking on an experiment by Larry Jones and Martin Perl from the University of Michigan. The acquaintance with Jones and Perl led to an offer of an assistant professorship at Michigan after he had finished an NSF fellowship at Saclay. He joined the University of Michigan physics department in 1962 and remained there until his retirement in 2008.
At Michigan he initiated a series of novel experiments, including an experiment to measure the polarization in proton–proton elastic scattering at the 3 GeV Brookhaven Cosmotron, an experiment at the Bevatron to test for time-reversal violation in the decay K0 → π− µ+, and an experiment at the Berkeley 184" cyclotron to test for time-reversal violation in the reaction n + p → γ + d.
Early on, Mike had the idea of using high-energy neutron beams to study neutron scattering. This led to a series of neutron elastic scattering experiments at most of the accelerators in the US, including the first measurement of the neutron–proton elastic scattering measurement at GeV energies.
His primary research activities were conducted at Fermilab. Around 1972 he proposed a measurement of the neutron total cross section as one of the first experiments at the new National Accelerator Laboratory (now Fermilab) 200 GeV “Main Ring.” This was probably the first published cross section result from the new laboratory. Later he collaborated on E871 (HyperCP). He was also part of the MACRO collaboration, a large underground detector under the Gran Sasso in Italy. His team built most of the liquid scintillation counters that covered the vertical faces of the detector. He published extensively throughout his life and was pleased that all of his experiments were successful.
Mike will be remembered as a highly respected member of the University of Michigan community. He mentored many PhD students, including Homer A. Neal, who went on a distinguished career that included serving as president of APS. Mike had a dry sense of humor and a love of world travel and the Michigan Wolverines. He touched the lives of countless family members, friends, and students and will be missed greatly.
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