Precision measurement of the solar neutrino flux - rencontres de blois

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Precision measurement of the solar neutrino flux - rencontres de blois

BorexinoPrinciples of graded shieldingnγα,βμ1400m of rock (μ)Cherenkov water detectorInner PMTs (Rn emanation)n,p, 11 CQuenched scintillatorActive scintillatorFiducial mass (γ)Fast neutrons


Radio-purityInteractionRequirementsScintillationνe - e -UV• ν-e scattering effect• Indistinguishable from β/γbackgrounds• No directional signalνCritical to achieve lowestbackground levelsContamination Required Achieved Technique14C/ 12 C


Solar neutrinosBorexino’s major goal: the 7 Be monochromatic lineTotal flux of ~ 6.5 x 10 10 /cm 2 /secp p2H eep ep2He37He4BeeHe77BeLi e78Bep8B 2 eB e3He p4He eePhase II also aims for measurement of the CNO lines


Solar neutrinosBeyond The Standard Model: neutrino oscillations• Resonancecos(2)V22GFn2meE• E ν = 1.86 MeV• Adiabatic effect:


Before BorexinoPotential for new physics in the low energy oscillation transition region• Low region only from radiochemistry• Real-time measurement above 5MeV• Matter enhanced,• and transition regions


CalibrationPosition and Energy Scale tuningImprovements in precision:SystematicsLivetime 0.1% 0.04%Scintillator ρ 0.2% 0.05%Event SelectionLossPositionReconstruction0.3% 0.1%6.0% +1.3%/-0.5%Energy Scale 6.0% 2.7%TOTAL 8.5% +3.6%/-3.4%


SpectrumSelection of eventsRaw photoelectron charge spectrumγ from external src.• Major cuts :1) Muons, andfastcosmogenics,Electronicsnoise


SpectrumSelection of eventsRaw photoelectron charge spectrum• Major cuts :210Poγ from external src.11C1) Muons, andfastcosmogenics,Electronicsnoise2) FoducialVolume1/3 active mass


SpectrumSelection of events14CRaw photoelectron charge spectrum210Po – α subtractedγ from external src.• Major cuts :1) Muons, andfastcosmogenics,Electronicsnoise7Beshoulder11C2) FoducialVolume1/3 active mass3) α- subtraction(Gattiparameter)Total of 15 fine cuts remove noise and background events.


7Be ResultsAnalyticalConsistentMonteCarlo and Analytical FitsMeasured Rate:7Be: 46.0 1.5 stat+1.6-1.5 sys cpd/100tMonteCarloSSM w/ no MSW-LMAoscillations, PredictionHMetallicity74 5 theor 47.2 3.4MSW-LMA scenario:Φ ( 7 Be) = (4.87 0.24) X 10 9 /cm 2 /secf Be =0.97 0.05 stat 0.07 syst


Day-Night AsymmetryNeutrinos on their way from the Sun can undergo additional flavorconversion when traversing Earth’s matter at night.Such daily asymmetry in count rateLOWis defined asLMA11% - 80% =AdnR 2RNNRRDD= < 0.1%A nd = 0.007 0.073 stat A nd = 0.001 0.012 stat 0.007 sys


Day-Night AsymmetryNeutrinos on their way from the Sun can undergo additional flavorconversion when traversing Earth’s matter at night.Such daily asymmetry in count rateLOWis defined asLMA11% - 80% =AdnR 2RNNRRDD= < 0.1%A nd = 0.007 0.073 stat A nd = 0.001 0.012 stat 0.007 sys


Impact of Recent ResultsLOW solution to the solar deficit rejected at 8.5σ c.l.Hypothesis of no oscillations for 7Be rejected at 4.9 σUnder MSW-LMA and High MetallicityP ee(7Be) 0.520.070.06From the Global Fit252m 5.310eV2tan 12 0.46


Future• Borexino is entering phase II; purification of the scintillator will hopefullyresult in lower concentrations of 85 Kr and 210 Bi and open new perspectivesfor the CNO and pep flux measurements• Further improvements in lowering the systematics will hopefullyallow us to reach the ultimate goal of 3% uncertainty• Measurement of 8 B flux with a threshold at 2.2MeV requires meticulousunderstanding of external backgrounds- current Monte-Carlo simulationsare very promising• Borexino has also a possibility of studying oscillations at shortdistances, which unfortunatley requires sources of highest activities(~MCi 51 Cr, 37 Ar, or 90 Y)• In the free time Borexino is also ready for Supernovae(with ~90% duty cycle)


The EndAstroparticle and Cosmology Laboratory – Paris, FranceINFN Laboratori Nazionali del Gran Sasso – Assergi, ItalyINFN e Dipartimento di Fisica dell’Università – Genova, ItalyINFN e Dipartimento di Fisica dell’Università– Milano, ItalyINFN e Dipartimento di Chimica dell’Università – Perugia, ItalyInstitute for Nuclear Research – Gatchina, RussiaInstitute of Physics, Jagellonian University – Cracow, PolandJoint Institute for Nuclear Research – Dubna, RussiaKurchatov Institute – Moscow, RussiaMax-Planck Institute fuer Kernphysik – Heidelberg, GermanyPrinceton University – Princeton, NJ, USATechnische Universität – Muenchen, GermanyUniversity of Massachusetts at Amherst, MA, USAUniversity of Moscow – Moscow, RussiaVirginia Tech – Blacksburg, VA, USA


References• G. Bellini et al. (Borexino Coll.) arXiv:1104.1816v1 [hepex]10 Apr 2011, submitted to PRL• G. Bellini et al. (Borexino Coll.), article in preparation with detailsabout 7Be data analysis, day-night search and solar neutrino oscillationsanalysis.• G. Bellini et al. (Borexino Collaboration), paper on calibrations(in preparation)• (1969); J.N. Bahcall and R. Davis, Science 191, 264

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