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Kevin Lesko Lecture

Kevin Lesko's talk on neutrino astrophysics began with our primary source of neutrinos, the sun. The sun produces energy through the nuclear fusion process called the proton–proton chain. Throughout this process neutrinos are produced (mostly through beta decay) with a wide range of energies. These neutrinos are weakly interacting particles, which we can measure with very sensitive detectors. There are 3 different types of neutrinos referred to as the electron neutrino, muon neutrino, and tau neutrino. However, there is a significant discrepancy between the amount of predicted neutrinos and amount observed. This is referred to as the Solar Neutrino Problem and is answered by the neutrino’s strange ability to oscillate quantum mechanically between these different types. The only other possible answer to this problem is that there are flaws with our solar current solar models, however this does not look likely from present observations. The motivation for the research done at the Sudbury Neutrino Observatory is to solve these types of problems and uncover the mysteries surrounding this unique particle.

Kevin detailed the magnitude of facility at Sudbury Neutrino Observatory. 6800 feet underground sits SNO’s experimental apparatus containing 1000 tons of heavy water and nearly 10,000 high sensitivity photo-detectors. When neutrinos pass through the apparatus they react with the heavy water creating bursts of Cherenkov radiation. It is from observations of these reactions that neutrino astrophysics can be done. Since SNO is located so deeply underground, layers of Norite rock naturally shield these experiments from other types of background radiation, which yields a very high signal to noise ratio for each experiment. The three major phases of research at SNO were explained with their data reduction methods and data distributions. These phases included adding and removing salt from the heavy water to alter its neutral current reaction. Large datasets were taken while the apparatus was in each of these phases.

Another neutrino detecting facility Kevin mentioned was the Kamioka Liquid Scintillator Antineutrino Detector. This facility, located in a deep mine in Japan, is designed to detect high-energy electron antineutrino’s formed from inverse beta decay in nearby nuclear power reactors. These antiparticles are created in the exact inverse reaction as their particle counterparts. The data collected from KamLAND provided more evidence that neutrinos can oscillate between different flavors. This evidence supported the findings at SNO and surfaced more questions and problems about the mechanisms behind the behavior of neutrinos.

These questions necessitate the construction of the new Deep Underground Science and Engineering Laboratory in Homestake, South Dakota. If approved, this facility will be a state of the art laboratory that improves upon both the KamLAND and SNO designs for neutrino physics. It will perform experiments not only in physics but in geoscience, biology, and engineering as well. Kevin encouraged future students to consider neutrino physics as an exciting step in what’s next in science.