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2019 Nobel Prize in Physics for cosmic perspectives

James Peebles, Michel Mayor and Didier Queloz

The Nobel Prize in Physics for 2019 has recognised two independent bodies of work that have transformed our view of the universe and humanity’s place in it. One half of the SEK 9 million prize, announced on 8 October in Stockholm, was granted to James Peebles of Princeton University for theoretical discoveries in physical cosmology, while the other was shared between Michel Mayor of the University of Geneva and Didier Queloz of the universities of Geneva and Cambridge for the discovery of an exoplanet orbiting a Sun-like star.

Peebles was instrumental in turning cosmology into the precision science it is today, with its ever closer links to collider and particle physics in general. Following the unexpected discovery of the cosmic microwave background (CMB) in 1965, he and others at Princeton used it to support the idea that the universe began in a hot, dense state. While the idea of a “big bang” was already many years old, Peebles paired it with concrete physics processes such as nucleosynthesis and described the role of temperature and density in the formation of structure. With others, he arrived at a model accounting for the density fluctuations in the CMB showing a series of acoustic peaks, which would demonstrate that the universe is geometrically flat and that ordinary matter constitutes just 5% of its total matter and energy content. In the early 1980s, Peebles was the first to consider non-relativistic “cold” dark matter and its effect on structure formation, and he went on to reintroduce Einstein’s forsaken cosmological constant – work that underpins today’s Lambda Cold Dark Matter model of cosmology.

Mayor and Queloz’s discovery of an exoplanet orbiting a solar-type star in the Milky Way opened a new field of study. 51 Pegasi b lies 50 light years from Earth and takes just four days to complete its orbit. It was spotted by tracking how it and its star orbit around their common centre of gravity: a subtle wobbling seen from Earth whose speed can be measured from the starlight via the Doppler effect. The problem is that the radial velocities are extremely low. Mayor mounted his first spectrograph on a telescope at the Haute-Provence Observatory near Marseille in 1977, but it was only sensitive to velocities above 300 ms–1 – too high to see a planet pulling on its star. It took almost two decades of work by him and his group to strike success, with doctoral student Queloz tasked with developing new methods to increase the machine’s light sensitivity. Today, more than 4000 exoplanets with a vast variety of forms, sizes and orbits have been discovered in our galaxy using the radial-velocity method and the newer technique of transit photometry, challenging ideas about planetary formation.

KAGRA complete

KAGRA

The construction of Japan’s first gravitational-wave (GW) detector, KAGRA, was finished on 4 October. Following agreement with the LIGO and Virgo collaborations, KAGRA will now participate in their third joint observation run, which began in April. The detector, which was built by the University of Tokyo, the National Astronomical Observatory of Japan and KEK, is the world’s fourth major GW detector, alongside LIGO in Washington state and Louisiana and Virgo in Italy. One of a suite of detectors in the Kamioka Observatory in northern Japan, KAGRA is also the first GW detector to operate at cryogenic temperatures, improving sensitivity at frequencies around 100 Hz – an important feature for proposed third-generation detectors such as the Einstein Telescope in Europe and the Cosmic Explorer in the US.

Spiro awarded Lagarrigue Prize

Michel Spiro

The 2018 André Lagarrigue Prize has been awarded to Michel Spiro, research director emeritus at CEA, for the exemplary nature of his career, from both a scientific and managerial point of view. Spiro contributed, among other things, to the discovery of the W and Z bosons with the UA1 experiment, was the initiator and spokesperson of the EROS experiment, and played a major role in the GALLEX experiment. He has held several senior positions at CEA and CNRS and from 2010–2013 was president of the CERN Council.

APS announces 2020 prizes

Wesley Smith

Wesley Smith of the University of Wisconsin-Madison, and member of the CMS collaboration, has won the American Physical Society (APS) 2020 W K H Panofsky Prize “for the development of sophisticated trigger systems for particle-physics experiments, which enabled measuring the detailed partonic structure of the proton using the ZEUS experiment at HERA and led to the discovery of the Higgs boson and the completion of the Standard Model with the CMS experiment at the LHC”.

Pierre Sikivie

The 2020 J J Sakurai Prize for theoretical particle physics went to Pierre Sikivie of the University of Florida for seminal work recognising the potential visibility of the invisible axion, devising novel methods to detect it, and for theoretical investigations of its cosmological implications.

Bruce Carlsten

In the accelerator arena, the 2020 Robert R Wilson Prize was awarded to Bruce Carlsten of Los Alamos National Laboratory for the discovery and subsequent implementation of emittance compensation in photo-injectors “that has enabled the development of high-brightness, X-ray free electron lasers such as the Linac Coherent Light Source”.

Matt Pyle

Among several other prizes awarded in the particle, nuclear, astrophysics and related fields, the 2020 Henry Primakoff Award for Early-Career Particle Physics went to Matt Pyle of the University of California at Berkeley for his development of high-resolution ultra-low-threshold cryogenic detectors for dark-matter searches.

Nikhef reappoints Bentvelsen

Stan Bentvelsen

Stan Bentvelsen has been reappointed for a second five-year term as director of Nikhef in the Netherlands. Bentvelsen, an experimental physicist on ATLAS and an academic at the University of Amsterdam, first became director in 2014 and has overseen Nikhef’s involvement in international projects such as KM3NeT, XENON, Auger and a test facility of the proposed Einstein Telescope. He plans “to continue to open doors to new physics through diversification of experiments, both accelerator-based and other detectors, from physics to astroparticle physics.”

Gianotti elected for second term

Fabiola Gianotti

On 12 December, the CERN Council unanimously decided to appoint Fabiola Gianotti as Director-General (DG) of CERN for a second term of office of five years, with effect from 1 January 2021. “I am deeply grateful to the CERN Council for their renewed trust,” she said in a statement. “The following years will be crucial for laying the foundations of CERN’s future projects and I am honoured to have the opportunity to work with the CERN Member States, Associate Member States, other international partners and the worldwide particle-physics community.” Gianotti, who is CERN’s first female DG, has been a research physicist at CERN since 1994 and was ATLAS spokesperson from March 2009 to February 2013 during the discovery of the Higgs boson.

Max Planck Medal for Buras

Andrzej Buras

Andrzej Buras of the Technical University of Munich has been awarded the Max Planck Medal by the German Physical Society for his outstanding contributions to applied quantum field theory, especially in flavour physics and quantum chromodynamics.

Smith continues at SNOLAB

Nigel Smith

Astroparticle physicist Nigel Smith has been appointed to a three-year extension as executive director of SNOLAB in Canada. Smith, who has been in the role since 2009, agreed to remain in position until 31 December 2022, with a search for a successor being revisited during 2020.

Kirkby bags aerosol award

Jasper Kirkby

The 2019 Benjamin Y H Liu Award of the American Association for Aerosol Research, which recognises outstanding contributions to aerosol instrumentation and experimental techniques, has been awarded to CERN’s Jasper Kirkby for his investigations into atmospheric new-particle and cloud formation using the unique CLOUD experiment at CERN, which he originated. The award committee described CLOUD as “arguably the most effective experiment to study atmospheric nucleation and growth ever designed and constructed, really by a country mile”, and said of Kirkby: “His irrepressible will and determination have adapted the culture of ‘big science’ at CERN to a major atmospheric science problem. Along the way, Jasper has also become a world-class aerosol scientist.”

Luigi Radicati 1919–2019

Luigi Radicati

Luigi Radicati, one of the eminent Italian theoretical physicists of the past century, passed away on 23 August 2019 in his home in Pisa, about 50 days before his 100th birthday.

Born in Milan, Radicati received his laurea in physics from the University of Torino under the supervision of Enrico Persico in 1943, and became the assistant professor of Eligio Perucca at Torino Polytechnic in 1948. In between this, during the Second World War he was also a member of a partisan division fighting against German occupation.

The years 1951–1953, which Radicati spent as a research fellow at the University of Birmingham in the group of Rudolf Peierls, had a major impact on his training. Then, in 1953 Radicati became a professor of theoretical physics, first at the University of Naples and two years later at the University of Pisa. In 1962 Radicati was finally called to the Scuola Normale Superiore (SNS) in Pisa as one of two professors in the “Classe di scienze”, the other being the great mathematician Ennio De Giorgi. Radicati remained at SNS until 1996, acting as vice-director between 1962 and 1964, and director between 1987 and 1991.

Luigi Radicati can be remembered for two main reasons: the special role that he attributed to symmetries; and the broadness of his interests in physics, as in the relations between physics and other disciplines. His most important and well known physics results stem from the early 1960s. After working with Paolo Franzini to show evidence for SU(4) symmetry in the classification of nuclear states, introduced by Wigner in 1937, in 1964 Radicati proposed, together with Feza Gürsey, the enlargement of SU(4) to SU(6) as a useful symmetry of hadrons. Gell-Mann had introduced the SU(3) symmetry in 1962 and at the beginning of 1964 had proposed, simultaneously with George Zweig, the notion of quarks. The SU(6)-subgroup SU(3) × SU(2) puts together Gell-Mann’s SU(3) with the spin SU(2) symmetry, thus unifying in single multiplets the pseudo-scalar together with the vector mesons and the J = 1/2 together with the J = 3/2 baryons. At a deeper level, SU(6) gave momentum to view the quarks as real entities obeying peculiar statistics, preliminary to the introduction of colour.

In the latter part of the 1960s Radicati began turning his attention to astrophysics, gravity, plasma physics and statistical physics. Here it is worth mentioning the long-lasting collaboration with Emilio Picasso, which started in 1977 during a discussion in the CERN cafeteria: the use of a gravitational-wave detector consisting of a system of two radio-frequency cavities, coupled to create a two-level system with a tunable difference between their oscillation frequencies.

Radicati’s collaborations brought frequent visits of eminent physicists to Pisa, among them Freeman Dyson, Feza Gürsey, T D Lee, Louis Michel, Rudolf Peierls, David Speiser and John Wheeler. Most of all, Radicati played a prominent role in bringing from CERN to the SNS Gilberto Bernardini, who acted as SNS director from 1964 to 1977, and Emilio Picasso, who was SNS director from 1992 to 1996.

Radicati was a member of the Accademia Nazionale dei Lincei from 1966, named Chevalier de la Légion d’Honneur and Doctor Honoris Causa at the École Normale in Paris in 1994, and was awarded the honour of Cavaliere di Gran Croce of the Italian Republic in 2004. During his career, he also translated and introduced important physics books into Italy, including The Meaning of Relativity by Albert Einstein, A History of Science by William Dampier and Quantum Mechanics by Leonard Schiff.

Luigi Radicati is survived by his wife and four of his sons.

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