The eminent theoretical physicist James Stirling died on 9 November at his home in Durham, UK, after a short illness. He will be greatly missed, not only by his family but by his many friends and colleagues throughout the particle physics community. His wide-ranging contributions to the development and application of quantum chromodynamics (QCD) were central in verifying QCD as the correct theory of strong interactions and in computing precise predictions for all types of processes at hadron colliders such as the LHC.
James was born in Belfast, Northern Ireland, and educated at Peterhouse, Cambridge University, where he obtained his PhD in 1979. After post-doc positions at the University of Washington in Seattle and at Cambridge, he came to CERN, first as a fellow and then as a staff member, leaving in 1986 for a faculty position at Durham University, where he remained until 2008. He was elected a Fellow of the Royal Society in 1999. At Durham, he played a major role in the foundation of the University’s Institute of Particle Physics Phenomenology in 2000, and served as its first Director. In 2005 he was appointed Pro-Vice Chancellor for Research. He moved to Cambridge in 2008 to take up the Jacksonian Professorship of Natural Philosophy in the Cavendish Laboratory, becoming Head of the Department of Physics in 2011. Then, in 2013, he was appointed to the newly created position of Provost, the chief academic officer, at Imperial College, London, from which he retired last August, moving back to Durham, where his retirement was tragically curtailed by illness.
James was a prolific and meticulous researcher, publishing more than 300 papers, including some of the most highly cited of all time in particle physics. His research, always full of insight, focused on the confrontation of theoretical predictions with experimental results. Over the years, he performed frontier research on a vast range of phenomenological topics. Already during his graduate studies at Cambridge, in the early days of QCD, he clarified in detail the connection between deep inelastic lepton–hadron scattering and hadron–hadron processes such as lepton pair production, which led on to his later work on parton distributions at Durham. An example of his pioneering research is the first computation of the resummed transverse momentum distribution of W and Z bosons in hadron collisions at next-to-leading logarithmic order, performed with Christine Davies in 1984. Another is the development of the powerful helicity amplitude method, completed with Ronald Kleiss while they were at CERN. This enabled them to show that the “monojet” events at the CERN proton–antiproton collider, which had been thought to be a possible signal of new physics, could be explained by vector boson plus jet production. The method has since facilitated the calculation of many other important Standard Model processes.
After moving to Durham in 1986, James formed a long-standing and successful research collaboration with Alan Martin, Dick Roberts and, later, Robert Thorne. Among other projects, they set the standard for determining the quark and gluon distributions in the proton, which led to the widely used MRS, MRST and MSTW parton distribution functions. Later, when James returned to Cambridge, he became interested in processes in which more than one parton from each colliding hadron participates (double parton scattering), bringing a new level of rigour to the analysis of such processes.
James had the gift of being able to explain complicated concepts and ideas simply. He was highly sought after as a plenary or summary speaker at the major international particle physics conferences. His textbook QCD and Collider Physics, written with Keith Ellis and Bryan Webber, has been a standard reference for more than 20 years.
James was a humble and modest person but his intellectual brilliance, coupled with a very strong work ethic and exceptional organisational skills, meant that his advisory and administrative services were always in great demand. In 2006 he received the national honour of Commander of the Most Excellent Order of the British Empire (CBE) from the Queen for his services to science.
In addition to the great respect in which he was held as a scientist, James was much loved as a friend, colleague and mentor. He treated everyone with the same respect, courtesy and attention, whatever their status. His warmth, kindness and fundamental humanity made a deep impression on all who came into contact with him.
Alan Martin and Bryan Webber