USA/Belgium

Francis Halzen

2015 Balzan Prize for Astroparticle Physics Including Neutrino and Gamma-ray Observation

For his unparalleled accomplishments which have led to the construction of the large IceCube Neutrino Observatory in the south polar ice, a facility that has opened up a new window into the Universe through the study of cosmological high-energy neutrinos.

Francis Halzen, born in Belgium in 1944, got his PhD at the University of Leuven and is currently Professor at the University of Wisconsin-Madison. He is a US citizen. He has served on several advisory committees for various leading research institutions and major international large-scale experiments, and on research-prioritization panels.

Francis Halzen has been a leading scientist in the development of cosmic ray physics and astroparticle physics for several decades. In addition to particle physics he published many early papers on cosmic ray anomalies and quark matter, and on relations between particle physics and cosmic rays, on particles from supernovae and on muon production in atmospheric gamma-ray showers. From early in his career in the 1970s, he discussed the possibility of detecting high-energy neutrinos from cosmic sources, such as supernovae and other objects.

In the 1990s he initiated the building of a large neutrino detector, AMANDA, in the south polar ice. Although the first findings suggested that air-bubbles in the ice would scatter the Cherenkov light and thus prevent a clear signal, he was able to resolve this issue by expanding the detector to greater depths, where the ice was found to be much more transparent. As Principal Investigator he played a key role in all parts of the project, and was responsible for its successful completion. He next argued vigorously for its successor, the much larger IceCube project, which takes data from a 1 km³ volume of ice. He again served as a Principal Investigator for this project and succeeded in attracting a number of excellent scientists (including 15 different European groups), and also to secure sufficient financing from American and European sources.

The most important result from the IceCube was the clear break-through observation of high-energy neutrinos (about 100 times more energetic than the particles accelerated today in the world’s most powerful machine, the LHC at CERN) in 2013, from as yet not identified sources outside the Galaxy. This discovery has stimulated the planning and development of even larger neutrino telescopes, both at the South Pole and deep under the ocean. Another important result was that limits could be put on high-energy neutrinos from gamma- ray bursts (strong pulses of gamma radiation from very distant objects, perhaps merging pairs of neutron stars). These limits place strong constraints on the nature of these enigmatic objects.

Francis Halzen is an inspiring example of a scientist who, though coming from a different research discipline, had the foresight to see where the next breakthrough in our understanding on the universe is likely be found, and who has the energy and leadership to realize this vision.