Neutrino Physics: Borexino & LENS

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The Borexino experiment is designed to measure the Be-7neutrino flux from the Sun in real-time. The signal is generatedby neutrino-electron scattering in a scintillator. Since the Be-7neutrino is mono-energetic, the signature in our resulting spectra will bea 'Compton-like' edge, with few other distinguishing characteristics.The detector has the ability to separate alpha- from beta-events, however, andthere is also the potential to observe a solar 'signature' due to theannual variation of the neutrino rate arising from the changingEarth-Sun distance. Thus, energy, particle ID, and fiducial volumecalibration are all of paramount importance. Measuring the Be-7 neutrino flux (to ~5%) is critical toestablishing that the MSW mechanism is indeed the operating physicsbehind the solution of the 'solar neutrino problem' as implied bymeasurements at higher neutrino energies (such as SNO and SuperK). This grant will enable the calibration of the Borexinodetector using internal (and external) radioactive sources which can beaccurately located within the detector. It will also allow foran analysis effort at Virginia Tech to help extract meaningfulresults from a background dominated experiment (the purities inthe scintillator required are extraordinary: in the range of10^-17 to 10^-15 g(U/Th)/g(scint). While the principle goal is to measure the Be-7 solarneutrino flux, if the purity is sufficient, there may beopportunity to detect the pep neutrinos as well. This wouldbe equivalent to measuring the pp-neutrino flux from the Sun(and thus the Solar 'neutrino' luminosity). This would providean excellent overall check of our neutrino and SSM knowledge. The group working under this grant is also pursuing othermeans of measuring the pp flux, and the expertise/techniquesbeing developed to calibrate Borexino may eventually proveuseful in this endeavor as well.-- R. Bruce Vogelaar http://www.phys.vt.edu/~vogelaarPhysics Department (0435) mailto:vogelaar@vt.eduVirginia TechBlacksburg, VA 24061(540) 231-8735 office(540) 231-7511 fax(540) 239-5963 cell(540) 951-4875 home