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Culture, history and society

2020 Joseph Thomson Medal and Prize

Professor Michael Charlton for scientific leadership in antimatter science, particularly within the ATHENA and ALPHA collaborations, and the formation and study of antihydrogen, including precision two-photon spectroscopy of the 1S – 2S transition.

Professor Michael Charlton 2020 Joseph Thomson Medal and Prize winner

Professor Michael Charlton has been a leader in atomic physics for over 30 years.

His early work focused on atomic collisions with positrons and antiprotons, including first identification of the excited state of the positronium atom.

His focus since then has been on the creation, trapping, and study of antihydrogen.

Three decades ago he led an effort to calculate antihydrogen formation cross sections via charge conjugation and time reversal of the reaction of positrons with ordinary hydrogen.

He later showed that anti-atom formation could be greatly enhanced using excited-state Ps atoms, a route to antihydrogen formation that is actively pursued today.

The programme to conduct antihydrogen experiments began in earnest in the late 1990s with the formation of the ATHENA collaboration at CERN of which Charlton was a founding member and intellectual leader. He built a buffer-gas positron trapping system, an approach copied by the five CERN antihydrogen efforts.

This and other novel developments led to the first creation of low-energy antihydrogen in 2002.

Charlton then became a founding (and the senior) member of the ALPHA collaboration, whose first challenge was to trap anti-atoms. They developed a minimum-magnetic-field atom trap and succeeded in capturing anti-atoms in 2010 and then storing and accumulating them.

An immense amount of new science followed: the first measurement of hyperfine transitions in the ground state; the first determination of the frequency of the 1S-2S transition and precision measurement of the line shape and line centre to a relative precision of a few parts in 1012.

Recently they made the first observation of the 1S-2P (Lyman alpha) transition, which will enable laser cooling to further the precision of the measurements.

In service to the scientific community, following his move from University College London to Swansea University in 1999, Charlton has built an outstanding AMO and quantum group and played a leadership role in strengthening the department in other ways, serving as chair twice for a total of 10 years.