Solar neutrinos have played a crucial role in the experimental confirmation that neutrinos have mass and oscillate, which is evidence of physics beyond the Standard Model. Borexino is a large solar neutrino detector in operation at the Gran Sasso Laboratory (LNGS), Italy. With its proven sensitivity, high radiopurity and low energy threshold, Borexino has the potential to resolve the solar neutrino energy spectrum into its various components and to probe the transition between vacuum and matter-enhanced oscillations in the ~ MeV energy region.
Building on their previous experience, the UMass group will contribute to the scientific goals of Borexino in two areas: (1) data analysis: the PI currently coordinates the US Borexino data analysis effort, focused on a deeper understanding of systematic effects, to reduce the uncertainty on the measured rate of Be-7 neutrinos; and (2) detector stability: as members of the vessel working group, the PIs are experts on the stress patterns and vessel deformations and on the laser diffuser system used for calibration and studies of light propagation properties. These skills will be fundamental to monitor the stability of the detector.
The broader impact of the program will provide students with the opportunity to experience research at a unique international physics laboratory, and to have an impact on important scientific results. The PIs will continue to participate in an outreach program that brings high school students from a relatively poor region of Italy to Princeton for a summer program in physics. This program has recently been extended to a group of women and minority high school students from South Dakota.
" covered the activities of the UMass Borexino group. Borexino is a neutrino experiment at the Gran Sasso underground laboratory in Italy. It detects neutrino-electron scattering events in a large target of ultra-pure liquid scintillator by recording the induced flashes of scintillation light, proportional to the event energy. The Borexino scientific program centered on the measurement of solar "berillium-7" neutrinos. These were a clue with which to understand why neutrinos were missing between the Sun and Earth. We now know that neutrino oscillations explain the deficit; Borexino has confirmed oscillations and looked for subdominant neutrino oscillations. Measuring Be7 solar neutrinos, with boron-8 and pep neutrinos in a neutrino "snapshot" of the Sun, tells us about the inner workings of our star and the nuclear fusion reactions that provide its thermal energy. Borexino has set the best limit on the flux of solar CNO neutrinos, providing a small fraction of the Sun’s energy but copiously produced in larger stars. This award partially supported the core work to measure solar pp-neutrinos, the most abundant and the ones with the lowest energy. This measurement confirms Borexino as the leader in ultra-clean detectors for rare events and neutrinos, reaching unprecedented purity of its target of order 10^-19 for the radioactive elements U-238 and Th-232. Borexino has measured anti-neutrinos from Earth’s radioactivity and from far-away nuclear reactors, and has set limits on the existence of exotic processes (violation of Pauli’s exclusion principle, electron decay, the existence of axions). The UMass group included graduate student Keith Otis and numerous undergraduate students, some of which have had significant roles in producing scientific results (John Quirk ’12, Keith Fratus and Amanda Lund ’11). It has focused on: detector stability radioactive calibration source insertion pep and pp solar neutrinos cosmic muon flux The outcomes of this award are summarize by the following Borexino and Borexino-related papers: Borexino collaboration, G. Bellini et al., "Final results of Borexino phase-I on low energy solar neutrino spectroscopy", submitted to Phys. Rev. D (Preprint arXiv 1308.0443). Borexino collaboration, G. Bellini et al., "New limits on heavy sterile neutrino mixing in 8B-decay obtained with the Borexino detector", Phys. Rev. D 88, 072010 (2013). Borexino collaboration, G. Bellini et al., "SOX: Short distance neutrino Oscillations with boreXino", JHEP 8, 38 (2013). Borexino collaboration, G. Bellini et al., "Cosmogenic Backgrounds in Borexino at 3800 m water-equivalent depth", JCAP 8, 49 (2013). Borexino collaboration, G. Bellini et al., "Measurement of geo-neutrinos from 1353 days of Borexino", Phys. Lett. B 722, 295 (2013). Borexino collaboration, G. Bellini et al., "Lifetimes of 214Po and 212Po measured with Counting Test Facility at Gran Sasso National Laboratory", Eur. Phys. J. A 49, 92 (2013). Borexino collaboration, H.O. Back et al., "Borexino calibrations: hardware, methods, and results", JINST 7, P10018 (2012). Borexino collaboration, G. Bellini et al., "Measurement of CNGS muon neutrino speed with Borexino", Phys. Lett. B 716, 401 (2012). Borexino collaboration, G. Bellini et al., "Search for Solar Axions Produced in p(d,3He)A Reaction with Borexino Detector", Phys. Rev D 85, 092003 (2012). Borexino collaboration, G. Bellini et al., "Cosmic-muon flux and annual modulation in Borexino at 3800 m water-equivalent depth", JCAP 05, 015 (2012). Borexino collaboration, G. Bellini et al., "First evidence of pep solar neutrinos by direct detection in Borexino", Phys. Rev. Lett. 108, 051302 (2012). Borexino collaboration, G. Bellini et al., "Absence of day-night asymmetry of 862 keV 7Be solar neutrino rate in Borexino and MSW oscillation parameters", Phys. Lett. B 707, 22 (2012) (Preprint arXiv:1104.2150). Borexino collaboration, G. Bellini et al., "Precision measurement of the 0.862 MeV 7Be solar neutrino interaction rate in Borexino", Phys. Rev. Lett. 107, 141302 (2011). Borexino collaboration, G. Bellini et al., "Muon and cosmogenic neutron detection in Borexino", JINST 6, P05005 (2011). Borexino collaboration, G. Bellini et al., "Study of solar and other unknown anti-neutrino fluxes with Borexino at LNGS", Phys. Lett. B 696, 191 (2011). Borexino collaboration, G. Bellini et al., "Measurement of the solar 8B neutrino rate with a liquid scintillator target and 3 MeV energy threshold in the Borexino detector", Phys. Rev. D 82, 033004 (2010). Borexino collaboration, G. Bellini et al., "Observation of geo-neutrinos", Phys. Lett. B 687, 299 (2010). Borexino collaboration, G. Bellini et al., "New experimental limits on the Pauli-forbidden transitions in 12C nuclei obtained with 485 days of Borexino data", Phys. Rev. C 687, 034317 (2010). The activities of the UMass Borexino group has contributed in forming several young students in nuclear physics and technology, as well as rather sophisticated data analysis projects. These skills prepare the future generation with skills essential for physics, medicine, high-tech industry, finance and homeland security.
