Ugo Camerini, a professor emeritus of physics at the University of Wisconsin–Madison who had a long career in particle physics and astrophysics, died on 22 November 2014 at his home in Madison.

Camerini was born in Milan, Italy, on 27 March 1925. When the Italian Fascist regime promulgated anti-Semitic laws in 1939, he and his family, who were Jewish, emigrated to Brazil. After graduating from the University of São Paulo in 1946 with bachelor’s degrees in physics and mathematics, he continued his studies in physics at the University of Bristol, UK, in the laboratory of Cecil Powell.

The Powell group had developed the use of nuclear emulsions for studies of cosmic rays at high altitudes. Shortly after Camerini arrived, the group discovered charged π mesons, an event widely regarded as the birth of particle physics as a distinct subdiscipline. He and the group also discovered several decay modes of the charged K mesons, particularly their decays into three π mesons.

That decay mode would have been the topic for Camerini’s doctoral dissertation, but in 1951 he cut short his graduate studies to take a UNESCO-funded position at the Brazilian Center for Research in Physics in Rio de Janeiro. The center was founded by César Lattes, a codiscoverer of the pion. Camerini never wrote his dissertation, and in later years he often boasted that he was the only full professor in the natural sciences at Wisconsin with no degree beyond a bachelor’s.

At the high-altitude laboratory at Mount Chacaltaya in the Bolivian Andes, Camerini continued to study cosmic rays with nuclear emulsions, but he found the intellectual and political atmosphere in South America less than conducive to serious research. So in 1957 he moved to the University of Wisconsin–Madison, where he joined Jack Fry in a collaboration that lasted for the rest of his career. Two years later Camerini was appointed to a faculty position.

The focus of the Fry–Camerini group was initially on studies of hyperfragments, light nuclei that incorporate a strange baryon in place of one of the nucleons. The group soon moved into tests of symmetries and other properties of the weak interactions and transitioned from emulsions to bubble chambers. Through those studies, the team developed long-lasting collaborations with Wilson Powell’s group at Lawrence Berkeley Laboratory and with Milla Baldo Ceolin’s group at the University of Padua in Italy. In the early 1960s, Camerini helped design a 30-inch hydrogen bubble chamber for the Zero Gradient Synchrotron at Argonne National Laboratory.

From 1959 to 1966, Camerini and coworkers made a series of measurements of the K2–K1 mass difference that received widespread attention. They followed them up with studies of rare K+ decay modes and the first test of time-reversal invariance in the so-called Kµ3 mode. In 1974 Camerini was part of the CERN Gargamelle bubble-chamber group that discovered weak neutral currents, which researchers had been searching for since 1964. Throughout that period Camerini maintained an active program of studies of neutrino interactions in bubble chambers at Fermilab and CERN.

In the late 1970s, Camerini joined the effort to build a muon detector, the “iron ball,” for the Positron–Electron Project (PEP) e+e collider at SLAC. The detector was designed to search for asymmetries in the annihilation of e+e to create µ+µ. The asymmetry proved too small to detect at PEP energies, but the experiment did manage to observe muonic decay modes of the newly discovered tau lepton.

From his experience at PEP, Camerini concluded that serious research at colliders would require elaborate detectors that could only be built by huge collaborations, a style of work he wanted no part of. He switched to particle astrophysics in 1979, which in effect returned him to studies of the cosmic rays that were the basis of his early career. But he did not entirely abandon particle studies at accelerators; he and Fry continued bubble-chamber searches for the decays of “charmed” particles at Fermilab.

Camerini’s particle-astrophysics research included constructing a high-energy cosmic gamma-ray detector on Haleakala in Hawaii; searching for proton decay with a large water Cherenkov detector in a mine near Park City, Utah; and participating in the DUMAND project, an effort to put a Cherenkov detector on the ocean bottom near the island of Hawaii. DUMAND was terminated in 1998 due to technical difficulties. Two years later Camerini retired to an active emeritus status.

Over his 42-year career at Wisconsin, Camerini supervised the doctoral research of 20 students. For his undergraduate teaching, he preferred introductory-level courses for nonscience majors and enjoyed a reputation as a lucid and entertaining lecturer. He also created a popular laboratory course in sound and light, targeted to musicians and artists.

Camerini began his career in an emerging field and always tried to work near its cutting edge, frequently in high-risk projects. If not all of them bore fruit, he still had the satisfaction that comes with being a pioneer. He always encouraged his students and colleagues to be equally daring, because “safe” physics was boring. He will be missed by those who had the pleasure of working with him.