Solar neutrino collisions with carbon at SNO+
"The result has now been published in Physical Review Letters"
Deep underground in Sudbury, Canada, the SNO+ experiment has captured the first evidence of solar neutrinos colliding with carbon nuclei in the detector target volume.
The SNO+ team searched for events where a carbon-13 nuclei is struck by a neutrino and transformed into radioactive nitrogen-13, which decays about ten minutes later. They used a 'delayed coincidence' method, which looks for two linked signals: an initial flash from a neutrino striking a carbon-13 nucleus, followed several minutes later by a second flash from the resulting radioactive decay.
This time signature was crucial to validate the result, explains Valentina Lozza, a researcher at LIP and analysis coordinator of the SNO+ collaboration. “Detecting two signals separated in time acts as a unique signature of this interaction, making it possible to distinguish solar neutrinos from the detector’s background noise,” she adds.
The analysis found 5.6 observed events over a 231-day period, statistically consistent with the 4.7 expected to be generated by neutrinos during this time. The low number of events observed is the combined result of the very low interaction probability of neutrinos, which allows them to come from the center of the Sun and travel 2 km of rock down to the detector, and of the low natural abundance of this isotope of Carbon.
The result, now published in Physical Review Letters, opens up new avenues for the study of neutrinos as they travel from the Sun and provides a new test of nuclear models describing their interactions with matter.
LIP has a very active team in SNO+, namely in analyses of neutrinos and antineutrinos from the Sun, the Earth and nuclear reactors, but also of radioactive backgrounds and detector calibrations. Valentina Lozza is SNO+'s analyses coordinator and was directly involved in the background estimates for this new result.
More information on SNO+ results: https://snoplus.phy.queensu.ca/
Image credit: SNOLAB
The 12-metre-diameter acrylic vessel surrounded by 9,000 photomultiplier tubes at the heart of the the Sudbury Neutrino Observatory and SNO+ experiments. The vessel currently holds about 800 tonnes of liquid scintillator for neutrino detection.