This award provides funding for the Virginia Tech group to continue their participation in the Borexino experiment at the Gran Sasso underground lab in Italy. Experiments with solar neutrinos gave the first evidence for neutrino mass and mixing. The Borexino experiment has recently made the first real-time measurement of the flux of low energy solar neutrinos from 7Be. The result is consistent with predictions of Standard Solar Models and neutrino oscillations.
The group plans to address the full utilization of the calibration system, participation in data acquisition and analysis, and the implications of anticipated Borexino results. With better purity and calibration now achieved, the potential for measuring the CNO and pep solar neutrino fluxes in Borexino is now realistic.
The broader impact on science, technology and outreach that is expected from the program includes deployment and utilization of ultra-clean calibration techniques and creating the possibility that, for the first time, one might directly measure the Sun?s energy generation today, versus what is currently seen in the photosphere after a delay of about 50,000 years. The outreach is to astrophysicists, cosmologists, geophysicists and geochemists, chemists and chemical engineers, teachers and students in universities in Virginia and neighboring states and the international scientific community.
Normal 0 false false false EN-US X-NONE X-NONE Normal 0 false false false EN-US X-NONE X-NONE Stars derive most of their energy by ultimately converting four hydrogen atoms (one proton each) into a helium atom (two protons and two neutrons each) through various burning ‘chains’. Twice in each chain a proton becomes a neutron + neutrino + anti-electron. These neutrinos are exceedingly hard to detect: about 10 billion ‘solar neutrinos’ per second pass through each square centimeter on Earth, yet multi-ton detectors typically see only see a few events per day. Neutrinos are the second most common fundamental particles in the Universe (next to photons), and measuring the energy spectrum of solar neutrinos at Earth tells us about their intrinsic properties and how our Sun works. Borexino was designed to measure the beryllium-7 neutrino flux coming from the Sun. The experiment is located at the Laboratori Nazionali del Gran Sasso near the town of Assergi, Italy, and is supported by an international collaboration with researchers from Italy, the United States, Germany, France and Russia. Funding is from multiple sources, including the NSF. The detector is a high-purity liquid scintillator calorimeter. Its central volume has a radius of 4.25 meters, which is enclosed in multiple layers of shielding, much like an onion skin (the host laboratory itself is located deep under the Gran Sasso mountain). In 2010, geo-neutrinos from Earth's interior have been observed for the first time. These are anti-neutrinos produced in radioactive decays of uranium, thorium, potassium, and rubidium. In 2011, the experiment published a precision measurement of the beryllium-7 neutrino flux as well as the first evidence for the pep solar neutrinos. Publications and implications can be found at its formal webpage: http://borex.lngs.infn.it/ This grant allowed Virginia Tech to calibrate the Borexino detector. The purity requirements were unparalleled, needing to not introduce contamination at the 10^-18 g[U/Th]/g[scintillator] level, while inserting a source anywhere within an 8.5m diameter vessel to a precision of much better than 2 cm. This entailed a double-differential seal and glove-box operation with precision environmental controls. The sources were radio-isotopes dissolved in scintillator and/or water and loaded into small heat-sealed quartz spherical vials. The position of the source was determined using imaging cameras, an approach now being adopted by other experiments, such as SNO+ and potentially Hyper Kamiokande. The grant also allowed Virginia Tech to host the US data repository, and be heavily involved in the analysis. The success of this experiment is on-going, and we suspect the extraordinary purity achieved will ultimately allow us to constrain the CNO neutrinos from the Sun sufficiently to resolve the recent discrepancy between the solar metalicity and helio-seismology measurements.
