UMass Amherst Scientist Among Winners of Prestigious Physics Prize for Work on Sun’s Energy

Team, including physicist Andrea Pocar, recognized for pioneering work in understanding how the sun works
andrea pocar
UMass Amherst physicist Andrea Pocar

AMHERST, Mass. – University of Massachusetts Amherst physicist Andrea Pocar is among the international team of scientists recently awarded the European Physical Society’s Giuseppe and Vanna Cocconi Prize. The team, known as the Borexino Collaboration, has spent more than a decade unlocking the secrets of how the sun produces its energy. The Cocconi prize goes to researchers who have made “an outstanding contribution to particle astrophysics and cosmology in the last fifteen years, in an experimental, theoretical or technological area.”

The Borexino Collaboration was awarded the Cocconi prize “for their ground-breaking observation of solar neutrinos from the proton-proton and carbon-nitrogen-oxygen chains that provided unique and comprehensive tests of the sun as a nuclear fusion engine.” These measurements were made possible by an instrument called the Borexino detector, which is buried half a mile beneath the Apennine Mountains in Italy. The detector features a giant nylon balloon, almost 30 feet across, filled with 300 tons of an ultra-pure aromatic hydrocarbon. The balloon is itself housed in a 45-foot diameter, spherical vessel filled with a similar hydrocarbon and surrounded by ultra-pure water.

The Borexino detector is capable of sensing low-energy neutrinos emitted by stars. Neutrinos are subatomic particles that are difficult to measure, but important because, says Pocar, they are the only direct probe scientists have for examining the core of stars. Though 400 billion of them hit every square inch of the Earth every second of the day, most neutrinos pass entirely through the planet without interacting with anything.

The Borexino Detector. Photo courtesy: Andrea Pocar

The Borexino detector is one of the few instruments both large enough and sensitive enough to detect such particles, which show up as brief flashes of light once they hit the detector.

Borexino has run since 2007 and measures the entire composition of the solar neutrino spectrum in great detail. The project began in the early 90s. One of the team’s milestones was the first snapshot of the complete spectrum of neutrinos emitted by the sun’s proton-proton, or pp chain. More recently, Borexino discovered that the carbon-nitrogen-oxygen cycle, or CNO cycle, is also at work in our sun. This was the first time that the CNO cycle had been directly observed.

Pocar has been with the Borexino Collaboration for more than twenty years, since his graduate student days, and was a member of the team that designed and constructed the detector’s nylon balloon and the fluid-handling system. “It’s very exciting to receive this recognition from the EPS and to join such highly regarded scientists who have been awarded the Cocconi prize for particle astrophysics,” he says. “The Borexino experiment is truly an incredible scientific adventure, which has set a new standard in ultra-low background, rare event physics. My UMass students and I have contributed to some of the key analyses that have allowed us to extract the feeblest and lowest energy solar neutrino signals.”

Borexino is an international collaboration and is supported by the National Science Foundation in the US, as well as the Italian National Institute for Nuclear Physics (INFN), and funding agencies in Germany, Russia and Poland.