Review of Solar Neutrinos Alan Poon Institute for Nuclear and Particle Astrophysics & Nuclear Science Division Lawrence Berkeley National Laboratory
Solar Neutrinos pp chain: 4p + 2e 4 He + 2ν e + 26.7 MeV Detailed computer model of solar evolution Standard Solar Model Only ν e are produced in the pp chain
Solar Neutrino Spectrum SuperKamiokande, SNO (CC) SNO (NC) Chlorine Borexino Gallium
Solar Neutrino Experiments
Radiochemical Experiments ( 71 Ga, 37 Cl) Sensitive to ν e only. Charged-Current interaction: ν e + A Z A Z+1 + e Extract the radioactive daughters AZ+1 (~ a few atoms) from tons of target material. Half life of the daughters cannot be too short. Count AZ+1 AZ decays to infer solar ν e flux. Not real-time measurements. Experiment Depth (m.w.e.) Target Reaction Threshold (MeV) Homestake 4900 615 tons of C 2 Cl 4 e+ 37 Cl 37 Ar+e 0.814 SAGE 4700 60 tons metallic Ga e+ 71 Ga 71 Ge+e 0.233 Gallex + GNO 3300 30.3 tons GaCl 3 -HCl e+ 71 Ga 71 Ge+e 0.233
First Detection of Solar Neutrinos
Kamiokande and SuperKamiokande Detected 8 B solar neutrinos by neutrino-electron elastic scattering: ν x + e ν x + e Can detect all three active neutrino flavors, but the sensitivity to ν µ and ν τ is 1/6 of ν e. 39.3 m
SuperKamiokande φ SSM = 5.69(1±0.16) x 10 6 cm -2 s -1 (BSB05-OP: Bahcall, Serenelli, Basu Ap. J. 621, L85, 2005). Raaf 2008
SuperKamiokande SK-I vs SK-III Raaf 2008
Solar Neutrino Problem (~2000)
How to Solve the Solar Neutrino Problem
Sudbury Neutrino Observatory (SNO) 2 km to surface 1 kt D 2 O 12m ϕ acrylic vessel 1.7 kt H 2 O (inner shield) ~9500 PMT 5.3 kt H 2 O (outer shield) Charged-Current (CC): ν e + d p + p + e Neutral-Current (NC): ν e,µ,τ + d n + p + ν e,µ,τ Elastic Scattering ν e,µ,τ + e (ES): ν e,µ,τ + e Phase I: n + d 3 H+γ +6.25 MeV Phase II: n + 35 Cl 36 Cl + γ +8.6 MeV Phase III: n + 3 He 3 H+p +0.76 MeV
Smoking gun for ν flavor transformation Does the total flux of solar neutrinos equal the pure ν e flux? Measure: CC NC = Alternatively ν e ν e + ν µ +ν τ CC ES = ν e ν e + 0.15(ν µ + ν τ ) Transformation to another active flavor if: φ CC (ν e ) < φ NC (ν x ) φ CC (ν e ) < φ ES (ν x ) Flavor transformation can be demonstrated without any assumption on the Standard Solar Model prediction of the total neutrino flux.
SNO Phase III - Neutral Current Detection Array NCD
Comparing to Phase II Phase II Phase III
Comparisons CC ES D 2 O con. (306 d) SuperK (1496 d) Salt (391 d) D 2 O con. (306 d) Salt (391 d) NCD (385 d) NCD (385 d) Flux (x 10 6 cm -2 s -1 ) Flux (x 10 6 cm -2 s -1 ) Statistical unc. Total unc.
Comparisons NC Corrected to Winter 8 B spectrum Agreement with past measurements (estimated p-value = 0.328) Agreement with standard solar models D 2 O (306 d) Salt (391 d) Φ µτ (x10 4 cm -2 s -2 ) NCD (385 d) Flux (x 10 6 cm -2 s -1 ) φ SSM = 569(1±0.16) x 10 4 cm -2 s -1 (BSB05-OP: Bahcall, Serenelli, Basu Ap. J. 621, L85, 2005). Φ e (x10 4 cm -2 s -2 ) arxiv:0806.0989 (2008)
MSW Contours 2-neutrino mixing model. Marginalized 1-σ uncertainties. Solar + 766 t-y KamLAND: SNO only degree Solar Solar + KamLAND Cl-Ar Super-K SAGE Gallex GNO SNO Borexino (first result)
Is it really neutrino oscillation? SNO showed that there are non-ν e solar neutrinos. This is a demonstration of flavor transformation. Neutrino oscillation is the favored explanation. But could it be other exotic mechanisms that give rise to the observation of non-ν e solar neutrinos? Can we test the vacuummatter transition? Vacuum Bahcall et al. ~1 MeV Matter
Other possible explanations? Galbiati 2008
Borexino Located at Gran Sasso, Italy Active Target: 278 tons of liquid scintillator in Nylon Vessel of 4.25 m radius Scintillation has higher light output than Cherenkov process Ultra-clean detector Detect 7 Be solar neutrinos by neutrino-electron elastic scattering: ν x + e ν x + e
Borexino Galbiati 2008
Borexino - 192-day Results Galbiati 2008
After Borexino Galbiati 2008
Future Solar Neutrino Program Goals Astrophysics: Precision test of Standard Solar Models (pp and CNO neutrinos) Test for consistency between photo- and ν-luminosities Subatomic Physics: Understanding matter-vacuum transition; direct MSW observation: D- N asymmetry and/or spectral distortion Precision measurement of θ 12 Ancillary topics: search for 0ν ββ, proton decays, dark matter, sterile ν, ν magnetic moment to < ~10-11 μ B Needs Exclusive measurements of pp, pep, CNO and 7 Be neutrino fluxes CC (ν e ) and ES (ν e/μ/τ ): mixing angle measurements Multi-purpose detectors (0ν ββ, DM, proton decays... search) SSM guardians
Checking the SSM (An Example) Helioseismology convinced us that SSM was correct (even before SNO s resolution of the Solar Neutrino Problem). Recent measurements showed lower solar surface metallicity, which made the helioseismological predictions incompatible with observations.
Checking the SSM (An Example) Helioseismology convinced us that SSM was correct (even before SNO s resolution of the Solar Neutrino Problem). Recent measurements showed lower solar surface metallicity, which made the helioseismological predictions incompatible with observations.
Checking the SSM (An Example) Helioseismology convinced us that SSM was correct (even before SNO s resolution of the Solar Neutrino Problem). Recent measurements showed lower solar surface metallicity, which made the helioseismological predictions incompatible with observations. CNO neutrinos can resolve this by probing the core metallicity.
Matter-Vacuum Transition pep
Global Fit of θ 13 Fogli et al. arxiv:0806.2649 Further improvements in θ13 are possible with higher precision in θ12. Particularly with SNO CC/NC ratio:
Imminent... SNO I+II: Further improvements in θ 12. Joint fit of SNO Phases I and II data Improved radioactive background rejection Lowered analysis threshold. Integral CC statistics: +30%; Integral NC statistics: +70% +30% G. Orebi Gann
Near Future... 7 Be Improvements in Borexino: KamLAND (solar) coming online Decowski 2008
Future: pp [Charged-Current] LENS - 125t 115 In MOON - 30t nat Mo ν e + 100 Mo e + 100 Tc delayed β
Future: pp [Charged-Current]
Future: pp/pep [Elastic Scattering] ν x + e ν x + e CLEAN (10t LNe) XMASS (10t LXe) SNO+ 1 kt LS MUNU/TPC (61t He/CH 4 @10 atm.) pp pep ~1 detected pp ν event/(day ton) ~10 detected pep ν event/(day kton)
Future: pp/pep [Elastic Scattering] CLEAN: pp SNO+: pep McKinsey & Coakley Astropart. Phys. 22 (2005) 355-368 M. Chen
Future low-energy solar ν [J. Klein, Neutrino 2008]
Summary After 40 years of solar neutrino research, we have: solved the Solar Neutrino Problem observed neutrino oscillations in solar neutrinos and placed constraints on neutrino mixing parameters tested Δm 2 and θ with reactor anti-neutrinos We are now entering a new phase of solar neutrino research: Detailed tests of Standard Solar Models (pp and CNO neutrinos, neutrino-photo-luminosity comparison) Improvements to neutrino mixing parameters Lots of new experimental ideas are being tested. Decade(s)-long programs if these ideas materialize.