Status of Solar Neutrino Oscillations With many thanks to Dave Wark - RAL/ University of Sussex and Stephen Brice - Fermilab
The Solar Neutrino Problem Next three plots adapted from http://www.sns.ias.edu/~jnb/
The Solar Neutrino Problem
The Solar Neutrino Problem
The Solar Neutrino Problem
Neutrino Oscillations u Let us assume that neutrinos have (different) masses - m 2 u Let us assume that the mass eigenstates are not identical to the weak eigenstates u If we consider 2 flavours the mixing is characterized by a single angle θ analogous to the Cabibbo angle in case of quarks
Neutrino Oscillations u Recall that: i ieit ( t) = ( 0) e i u Consider θ = 45 ν µ ν e ν µ
Vacuum Oscillations P( ν u In general this leads to the disappearance of the original neutrino flavour e ν e ) = 1 sin 2 θ 2 sin m L (1.27 ) E u With the corresponding appearance of the wrong neutrino flavour 2 2
The MSW effect u ν e have an extra diagram for scattering from electrons. u gives ν e an effective mass in matter. u can lead to resonant enhancement of oscillations the MSW effect
MSW effects on survival probabilities Taken from the US KamLAND proposal Taken from Micheal Smy s talk, Moriond 2001
Global fit, 8 B Flux a free parameter u Includes: Rates:» Homestake» SAGE» GALLEX/GNO» Super-K Super-K spectra» day» night From Bahcall, Krastev, and Smirnov; hep-ph/0103179
Sterile ν solutions u Includes: Rates:» Homestake» SAGE» GALLEX/GNO» Super-K Super-K spectra» day» night From Bahcall, Krastev, and Smirnov; hep-ph/0103179
Smoking guns? u ν oscillations are consistent with the data, but are they the right explanation? u Other models have been proposed - FCNC, extra dimensions, violations of the EP, neutrino decay, neutrino magnetic moments, etc. u What would be proof for oscillations?
The Super-Kamiokande Detector
Super-K Elastic Scattering Directly towards the Sun Directly away from the Sun
Smoking guns from solar ν? Pre-SNO u The appearance of the wrong-flavor neutrinos in the beam - not seen yet for solar neutrinos u A variation of the rate with L/E Spectral distortions Seasonal variations u Regeneration of neutrinos passing through the Earth.
Day/Night variation in Super-K Taken from Micheal Smy s talk, Moriond 2001
SNO
The SNO Detector Surface: 2 km 1000 tons D 2 O Acrylic Vessel 10 4 8 PMTs Phototube Support Structure (PSUP) 6500 tons H 2 O
ν Reactions in SNO CC ν e + d p + p + - e -Good measurement of ν e energy spectrum -Weak directional sensitivity 1-1/3cos(θ) ν e only NC ν + d p + n +ν x -Measure total 8 B ν flux from the sun. x Equal cross section for all ν types + - + e ES - _ x e _ x -Low Statistics -Strong directional sensitivity All ν types but enhanced sensitivity to ν e
SNO run sequence u u The Three Ph ases Pure D 2 O Good CC sensitivity Added Salt in D 2 O Enhanced NC sensitivity Neutron Detection Method Capture on D n + d t + γ e (E γ = 6.3 MeV) Capture on Cl Capture on 3 He n + 35 Cl 36 Cl + Σγ e (E Σγ = 8.6 MeV) u Neutral Current Detectors 3 He proportional counters in the D 2 O Event by event separation of CC and NC events n + 3 He p + t
The enemy.. βs and γs from decays in these chains interfere with our signals at low energies And worse, γs over 2.2 MeV cause d + γ n + p Design called for: D 2 O < 10-15 gm/gm U/Th H 2 O < 10-14 gm/gm U/Th Acrylic < 10-12 gm/gm U/Th
Signals in SNO NC Salt (BP98)
Acrylic Vessel Assay u u u Every piece sampled and tested Sample bonds tested Direct Assay by Cherenkov light AV well below (~1/10) the target level of 2 ppt U/Th Berkeley Blob 9 +20 m 3 µg Th -5
Instrumental Background Cuts
Solar Neutrino Spectrum
SNO cos(θ) sun distribution Electron Angle with respect to the direction from the Sun
Smoking Guns in SNO - 1 ES Charged-current spectrum is more sensitive to shape distortions! CC
Smoking Guns in SNO - 2 Charged-Current to Neutral Current ratio is a direct signature for oscillations CC NC = ν e ν e + ν µ + ν τ Bahcall etal., Phys. Rev. D 54, 5147 (1996)
Smoking Guns in SNO - 3 CC/ES Could also show significant effects! CC ES = ν e + ν e 0.14( ν µ + ν τ )
Borexino ES in 300t superclean scintillator target Under Construction, data taking end 2001
Signals and Backgrounds Background suppression is challenging! Signal suppression is promising!
Oscillation Sensitivity Reactor ν disappearance
Conclusions u Neutrino Oscillations very strongly indicated. u A real Solar ν smoking gun from SNO collaboration. u We live in interesting times...