Hugh Muirhead 1925–2007

Hugh Muirhead, who died at the age of 81 on 19 January, was the last surviving member of the Bristol group that made the historic discovery of the pion in 1947. Cecil Powell’s group, which also comprised Cesare Lattes and Giuseppe Occhialini, found two events in nuclear emulsions exposed at high altitude that showed unequivocally that the pion was the true Yukawa meson, and that it decayed into a muon and a neutrino. It was for this landmark discovery and for the development of the nuclear emulsion technique that Powell later received the Nobel Prize.

After obtaining his PhD from Bristol, Hugh moved first to the University of Glasgow and in 1957 to Liverpool University, where he stayed until his retirement. The move to Liverpool coincided with the discovery at Columbia University of parity violation in nuclear beta decay and in muon decay. Using muons from the 400 MeV cyclotron, Hugh and his team of young research students demonstrated that parity was also violated in muon capture. This completed the third leg of the Puppi triangle, the first step towards establishing the universality of weak interactions (CERN Courier June 2007 p33). It was at this time that Hugh wrote his book The Physics of Elementary Particles (Pergamon 1965), an outstanding pedagogical contribution to the phenomenology of particle physics, which astonished many theorists when they realized that its author was a "mere" experimentalist.

In the mid-1960s Hugh joined the Liverpool Film Analysis group. He became a world expert on the study of antiproton physics using the bubble-chamber technique and made a number of significant contributions in this field.

Hugh was no stranger to CERN. In the early 1980s, and nearing the end of his career, he joined the UA1 collaboration, led by Carlo Rubbia and Alan Astbury, to study high-energy proton–antiproton collisions in the SPS. This applied Simon van der Meer’s brilliant invention of stochastic cooling to collect antiprotons in sufficient numbers and under suitable conditions for the production of the long-predicted W± and Z0 bosons. Hugh’s professional life thus began and ended with key roles in two of the great discoveries of 20th-century physics, both of which resulted in Nobel prizes.

Hugh was always grateful that he had been able to spend his entire working life pursuing the passion for physics that was first awakened by his part in cosmic-ray experiments in mountain observatories, and he maintained a keen interest in developments in the field long after his retirement. He is survived by his wife Jean and their three children. With his passing, a chapter has closed in modern physics.

Colleagues, former students and friends, Owen Lock, Mike Houlden, Alan Kemp, John Eades and Alan Astbury.