2023 Paul Dirac Medal Prize

Professor Gavin P Salam has made many profound, wide-ranging and impactful contributions to particle physics. His work combines deep theoretical understanding with exceptional skills in computational physics and a strong motivation to contribute to the optimal interpretation of experimental data.

His early work on hadronic structure at small momentum fractions (small x) essentially solved the problem of extending the quantum chromodynamic treatment of structure evolution into this region. He improved and systematised the study of event shapes in hadronic final states and extended it to deep inelastic lepton scattering, which resulted in a wealth of new experimental studies. He discovered an important class of non-global enhanced effects overlooked in previous studies, which initiated a new area of theoretical research. His 2016 paper made a breakthrough in understanding the photonic content of the proton, reducing the uncertainty on the photon momentum fraction distribution by almost two orders of magnitude.

Salam’s work on hadronic jets has led to important new insights and tools for experimental studies. He proved that many of the existing jet definitions were ill-defined and proposed new definitions that solve this problem. He invented the ‘anti-kt’ jet algorithm, a development of outstanding originality that has been adopted universally by experimenters at the Large Hadron Collider (LHC). He developed novel methods from computational geometry that allow this and other well-formulated jet definitions to be implemented very fast and efficiently. This has proved a huge benefit and played a key role in the discovery of the Higgs boson. His work on jets in very high multiplicity environments helped to open up a whole new area of jet studies in heavy ion collisions and facilitates the elimination of pileup from multiple collisions. His paper ‘Towards an understanding of jet substructure’ established a firm theoretical foundation for that field, which has become a mainstay of searches for new physics with a dedicated annual conference (the Boost series). He proposed an innovative analysis of jet substructure to observe the Higgs boson decaying into bottom quarks, which contributed to the discovery of this decay mode.

Salam remains highly active in a wide range of projects, always aiming to achieve a better understanding of high-energy phenomena. His current research, improving the simulation of particle collisions, is of immense importance for the optimal exploitation of the LHC, both in searching for new phenomena and for achieving the best possible precision in measuring the fundamental parameters of particle physics.

_{Photo by John Cairns}