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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

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the importance of low energy solar neutrino experiments

The Importance of Low-EnergySolar Neutrino Experiments

Thomas Bowles

Los Alamos National Laboratory

Markov Symposium

Institute for Nuclear Research


Nuclear Physics

standard solar model
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 8B Neutrino Flux

Detecting Neutrinos in SNO

CC Interaction

Sensitive to electron neutrinos only

NC Interaction

Equally sensitive to all flavours

ES Interaction

Sensitive to all flavors,

but most sensitive to electron neutrinos

Nuclear Physics

what we know
What We Know
  • Flux of 8B n’s has a large non-ne component
  • Survival probability Pee for En > 5 MeV is

essentially independent of En

  • Pee for n’s of lower energy (p-p) is larger
  • There is no significant (> 2s) 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
Neutrino Oscillations

If neutrinos have mass leptons can mix:

Flavor eigenstates are a mixture of mass eigenstates

States evolve with time or distance

The ne survival probability for two flavor mixing is:

Nuclear Physics

reactor neutrino experiment
PhotomultipliersReactor Neutrino Experiment

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


0.611 ± 0.085 (stat)

± 0.041 (syst)

KamLAND observes a

significant deficit of

neutrinos and confirms

solar neutrino LMA

neutrino oscillation solution

Nuclear Physics

neutrino properties
Neutrino Properties
  • What We Know
    • There are 3 types of neutrinos : ne , nm , nt
    • Neutrinos have mass and oscillate
    • Oscillation parameters (Dm2 and tan2q) known to ~ 30%
    • Neutrino masses are small
      • 50 meV < mn < 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

Nuclear Physics

neutrino properties1
Neutrino Properties
  • What We Don’t Know - Neutrino Properties
    • Are neutrinos their own antiparticles? (Majorana n)
  • 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?

Nuclear Physics

Physics Program for FutureSolar Neutrino Experiments (I)
  • Directly observe the 99.99% of solar neutrinos
  • that are below 5 MeV

Direct test of solar models (p-p, 7Be, CNO)

Uncertainties in the solar neutrino fluxes

p-p 7Be CNO 8B

Present 15% 35% 100% 6%

With present 12% 8% 100% 4%

generation dets

Future expts 1-3% 2-5% 10-20% 2-4%

  • 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 108 yr convective stage
    • Provides test of initial metallicity of the Sun
  • Determine unitarity / dimension of n mixing matrix
  • Goal is to measure the flavor composition
  • of the p-p solar n’s to 1% precision in
  • a model-independent manner
  • Requires CC and ES/NC measurement
  • (assuming active oscillations)
  • Model-indep test for sterile n’s using measured
  • oscillation parameters (p-p + KamLAND)

 Can achieve ≈ 13% sensitivity (90% CL)

Nuclear Physics

Physics Program for FutureSolar Neutrino Experiments (II)
  • Use p-p neutrinos as “standard candle”

Precision test for CPT violation comparing


  • Model-dependent cross-check for sterile neutrinos
  • with ≈ 2% sensitivity (90% CL)

Measurement of the p-p rate to 1% provides knowledge of q12

to allow a search for CPT violation at a scale of 10-20 GeV

Compared to the present CPT test from the upper limit on

the mass difference in the kaon system of 4.4 x 10-19 GeV

Various scenarios imply that the sterile component of solar

neutrino fluxes may be energy dependent

  • Provide improved precision of mixing angle
  • Future p-p solar neutrino experiments offer the best prospect
  • for improving our knowledge of q12

 Low-energy solar neutrino expts must be part of any

full study of sterile neutrinos

  • Search for n magnetic moment with improved
  • sensitivity (contribution  1/Te)

Qsolar required to determine mn in 0n-bb decay

 Expect sensitivity of 10-11mB

Nuclear Physics

p-p Solar Neutrino Experiments:Physics Goals

fTotal= fActive + fSterile

Search with sterile neutrino components with

an order of magnitude improved sensitivity

Future Sensitivity

Present limits

Nuclear Physics

Next-Generation Solar Neutrino Experiments

What is required of future experiments:

Measurement of ne fluxes:

Source To match To match To match

current expts: projected expts: LMA prediction:

p-p 15% 12% 2%

7Be 35% 8% 5%

CNO 100% 100% 100%

pep 100% 100% 2%

8B 6% 4% 6%

Mixing parameters:

To match current limits on tan2q: 3% p-p accuracy

To match projected SNO, KamLAND limits: 2% p-p accuracy

Nuclear Physics

Future Experiments - Borexino
  • Looks at solar 7Be line (862 keV)
  • Precision measurement of q12
  • Will provide test of SSM for 7Be flux
  • Possible future extension to p-p neutrinos

Nuclear Physics

p-p Solar Neutrino Experiments

Charged-Current Experiments:


Goal: Measure ne component of p-p (7Be)

with 1-3% (2-5%) accuracy

Elastic Scattering Experiments:


Goal: Measure ne / nm, nt component of p-p (7Be)

with 1-3% (2-5%) accuracy

Nuclear Physics

CC p-p Experiments: LENS

Spokesman: Raju Raghavan

40 tons In target in 400 tons scintillator

Modular design with In cells surrounded

by non-In cells (2000 tons scintillator)

Fundamental problem: 115In beta decay

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 7Be, CNO
  • 300 MeV/pe scintillator, 3 m attenuation length
  • No backgrounds
  • Calibrated by 8 MCi 51Cr source

Source Statistical Accuracy

p-p 2.3%

7Be 2.8%

CNO 5.8%

pep 11.8%

Issue: estimated cost ~ $140M

Nuclear Physics

CC p-p Experiments: MOON

Issue: Double beta decay background!

Nuclear Physics

ES p-p Experiments: HERON

Spokesman: Bob Lanou

~ 5,000 events/yr (10 ton fid. Vol.) BP00 SSM

Nuclear Physics

Low Energy Solar Neutrino Fluxes

Bahcall, Gonzalez-Garcia, Pena-Garay, hep-ph/0204194



Exp’t X-Sect. SSM CC Exp’t Exp’t Sterile

      

+0.05 +0.01 +0.00

fpp = 1.05 (1 ± 0.11 ± 0.007 ± 0.05 ± 0.04 )

- 0.08 - 0.02 - 0.02

= 1.05 (1 ± 0.15)

Dedicated pp Experiments

required to make Improvements.

Flux Predictions for a pp

Elastic Scattering Experiment

0.697 ± 0.023 (100 keV)

0.693 ± 0.024 ( 50 keV)

Nuclear Physics

Low Energy Solar Neutrino Fluxes

SAGE Results: 69.6 +4.4/-4.3 (stat) +3.7/-3.2 (syst) SNU

GALLEX + GNO: 70.8  4.5 (stat)  3.8 (syst) SNU

Progress in determining the flux of

low-energy solar ne can only be achieved

in the next decade by improved Ga measurements

SAGE: 1990-2003

The Gallium experiments should continue to operate

until they are systematics limited

Nuclear Physics

The Russian-American Gallium Experiment

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.

Nuclear Physics