The Importance of Low-Energy Solar Neutrino Experiments Thomas Bowles Los Alamos National Laboratory Markov Symposium Institute for Nuclear Research 5/13/05 Nuclear Physics

Standard Solar Model Nuclear Physics

Comparison of measured rates and Standard Solar Model (After 30+ years of effort) Nuclear Physics

Flavor Content of the Solar 8 B Neutrino Flux Nuclear Physics CC Interaction ES Interaction NC Interaction Sensitive to electron neutrinos only Sensitive to all flavors, but most sensitive to electron neutrinos Equally sensitive to all flavours Detecting Neutrinos in SNO

What We Know Flux of 8 B ’s has a large non- e component Survival probability P ee for E > 5 MeV is essentially independent of E P ee for ’s of lower energy (p-p) is larger There is no significant (> 2  ) D/N asymmetry All observations are consistent with the following hypotheses : Mass-induced flavor oscillations (with LMA as the favored solution) Nuclear Physics

Neutrino Oscillations Nuclear Physics States evolve with time or distance Flavor eigenstates are a mixture of mass eigenstates If neutrinos have mass leptons can mix: The e survival probability for two flavor mixing is:

Reactor Neutrino Experiment Nuclear Physics Terrestrial Neutrinos KamLAND is a 1 kton liquid scintillator detector that observes from a number of reactors in Japan at an average distance of 180 km Photomultipliers (N OBS - N BG )/N EXP = ± (stat) ± (syst) KamLAND observes a significant deficit of neutrinos and confirms solar neutrino LMA neutrino oscillation solution

Neutrino Properties Nuclear Physics What We Know – There are 3 types of neutrinos : e, ,  – Neutrinos have mass and oscillate – Oscillation parameters (  m 2 and tan 2  ) known to ~ 30% – Neutrino masses are small 50 meV < m < 2.8 eV (90% CL) – Lower limit from atmospheric neutrino results – Upper limit from tritium beta decay results Neutrinos account for at least as much mass in the Universe as the visible stars

Neutrino Properties Nuclear Physics What We Don’t Know - Neutrino Properties – Are neutrinos their own antiparticles? (Majorana ) – What is the absolute scale for neutrino mass? – Is the mass scale normal ordered or inverted hierarchy? – Are there sterile neutrinos? – What are the elements of the MNS mixing matrix? – Is CP / CPT violated in the neutrino sector? What We Don’t Know - Neutrino Astrophysics – Is the Standard Solar Model correct? – What is the flux of solar neutrinos below 5 MeV? What is the flux of CNO neutrinos? – What is the radial temperature distribution of the Sun? – How do neutrino properties affect supernovae?

Physics Program for Future Solar Neutrino Experiments (I) Directly observe the 99.99% of solar neutrinos that are below 5 MeV Direct test of solar models (p-p, 7 Be, CNO) Goal is to measure the flavor composition of the p-p solar ’s to 1% precision in a model-independent manner Requires CC and ES/NC measurement (assuming active oscillations) Model-indep test for sterile ’s using measured oscillation parameters (p-p + KamLAND) Uncertainties in the solar neutrino fluxes p-p 7 BeCNO 8 B Present15%35%100%6% With present12% 8%100%4% generation dets Future expts1-3%2-5% 10-20% 2-4% Determine unitarity / dimension of mixing matrix  Can achieve ≈ 13% sensitivity (90% CL) Nuclear Physics Measurement of CNO neutrinos provides an important test: 1.5% of the Sun’s energy is from the CNO cycle CNO burning is crucial in first 10 8 yr convective stage Provides test of initial metallicity of the Sun

Use p-p neutrinos as “standard candle” Precision test for CPT violation comparing and Physics Program for Future Solar Neutrino Experiments (II) Model-dependent cross-check for sterile neutrinos with ≈ 2% sensitivity (90% CL) Provide improved precision of mixing angle Search for magnetic moment with improved sensitivity (contribution  1/T e ) Measurement of the p-p rate to 1% provides knowledge of  12 to allow a search for CPT violation at a scale of GeV Compared to the present CPT test from the upper limit on the mass difference in the kaon system of 4.4 x GeV Various scenarios imply that the sterile component of solar neutrino fluxes may be energy dependent  Low-energy solar neutrino expts must be part of any full study of sterile neutrinos  Expect sensitivity of  B Future p-p solar neutrino experiments offer the best prospect for improving our knowledge of  12  solar required to determine m in 0 -  decay Nuclear Physics

p-p Solar Neutrino Experiments: Physics Goals Nuclear Physics Search with sterile neutrino components with an order of magnitude improved sensitivity Present limits Future Sensitivity  Total =  Active +  Sterile

Next-Generation Solar Neutrino Experiments Nuclear Physics What is required of future experiments: Mixing parameters: To match current limits on tan 2  : 3% p-p accuracy To match projected SNO, KamLAND limits: 2% p-p accuracy Measurement of e fluxes: SourceTo matchTo matchTo match current expts:projected expts:LMA prediction: p-p 15% 12% 2% 7 Be 35% 8% 5% CNO100%100%100% pep100%100% 2% 8 B 6% 4% 6%

Looks at solar 7 Be line (862 keV) Precision measurement of  12 Will provide test of SSM for 7 Be flux Possible future extension to p-p neutrinos Future Experiments - Borexino Nuclear Physics

p-p Solar Neutrino Experiments Nuclear Physics Charged-Current Experiments: LENS, MOON Goal: Measure e component of p-p ( 7 Be) with 1-3% (2-5%) accuracy Elastic Scattering Experiments: CLEAN, HERON, TPC, XMASS Goal: Measure e / ,  component of p-p ( 7 Be) with 1-3% (2-5%) accuracy

Nuclear Physics Spokesman: Raju Raghavan CC p-p Experiments: LENS 40 tons In target in 400 tons scintillator Modular design with In cells surrounded by non-In cells (2000 tons scintillator) Fundamental problem: 115 In beta decay

Nuclear Physics CC p-p Experiments: LENS

Nuclear Physics LENS Count Rates Design Parameters (assumed) 40 tons In  480 tons InLS, 4 kton non-InLS 4 years of running (5 calendar years) Detection efficiency ~ 22% for p-p, 57% for 7 Be, CNO 300 MeV/pe scintillator, 3 m attenuation length No backgrounds Calibrated by 8 MCi 51 Cr source SourceStatistical Accuracy p-p2.3% 7 Be 2.8% CNO 5.8% pep 11.8% Issue: estimated cost ~ $140M

Nuclear Physics CC p-p Experiments: MOON

Nuclear Physics CC p-p Experiments: MOON Issue: Double beta decay background!

Nuclear Physics ~ 5,000 events/yr (10 ton fid. Vol.) BP00 SSM Spokesman: Bob Lanou ES p-p Experiments: HERON

Low Energy Solar Neutrino Fluxes Ga  SNO  KamLAND  BOREXINO  BP00 Ga Ga CNO SNO KamLAND BOREXINO Exp’t X-Sect. SSM CC Exp’t Exp’t Sterile        f pp = 1.05 (1 ± 0.11 ± ± 0.05 ± 0.04 ) = 1.05 (1 ± 0.15) Bahcall, Gonzalez-Garcia, Pena-Garay, hep-ph/  Dedicated pp Experiments required to make Improvements. Nuclear Physics Flux Predictions for a pp Elastic Scattering Experiment ± (100 keV) ± ( 50 keV)

Low Energy Solar Neutrino Fluxes Nuclear Physics SAGE Results: /-4.3 (stat) +3.7/-3.2 (syst) SNU GALLEX + GNO: 70.8  4.5 (stat)  3.8 (syst) SNU SAGE: Progress in determining the flux of low-energy solar e can only be achieved in the next decade by improved Ga measurements The Gallium experiments should continue to operate until they are systematics limited

The Russian-American Gallium Experiment Nuclear Physics It has been my experience that SAGE has proved to be a perfect example of the value of international scientific collaborations The SAGE collaboration has provided the means for achieving a significant scientific result It has been my privilege and honor to play a role in SAGE I am extremely grateful to the many people who have made SAGE a success - Without all of their support the success and recognition that we have received in the world scientific community would not have been possible.