The Borexino experiment is designed to measure the Be-7 neutrino flux from the Sun in real-time. The signal is generated by neutrino-electron scattering in a scintillator. Since the Be-7 neutrino is mono-energetic, the signature in our resulting spectra will be a 'Compton-like' edge, with few other distinguishing characteristics. The detector has the ability to separate alpha- from beta-events, however, and there is also the potential to observe a solar 'signature' due to the annual variation of the neutrino rate arising from the changing Earth-Sun distance. Thus, energy, particle ID, and fiducial volume calibration are all of paramount importance.
Measuring the Be-7 neutrino flux (to ~5%) is critical to establishing that the MSW mechanism is indeed the operating physics behind the solution of the 'solar neutrino problem' as implied by measurements at higher neutrino energies (such as SNO and SuperK).
This grant will enable the calibration of the Borexino detector using internal (and external) radioactive sources which can be accurately located within the detector. It will also allow for an analysis effort at Virginia Tech to help extract meaningful results from a background dominated experiment (the purities in the scintillator required are extraordinary: in the range of 10^-17 to 10^-15 g(U/Th)/g(scint).
While the principle goal is to measure the Be-7 solar neutrino flux, if the purity is sufficient, there may be opportunity to detect the pep neutrinos as well. This would be equivalent to measuring the pp-neutrino flux from the Sun (and thus the Solar 'neutrino' luminosity). This would provide an excellent overall check of our neutrino and SSM knowledge.
The group working under this grant is also pursuing other means of measuring the pp flux, and the expertise/techniques being developed to calibrate Borexino may eventually prove useful in this endeavor as well.
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R. Bruce Vogelaar www.phys.vt.edu/~vogelaar Physics Department (0435) mailto:vogelaar@vt.edu Virginia Tech Blacksburg, VA 24061 (540) 231-8735 office (540) 231-7511 fax (540) 239-5963 cell (540) 951-4875 home
