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

The Importance of Low-EnergySolar Neutrino Experiments

Thomas Bowles

Los Alamos National Laboratory

Markov SymposiumInstitute 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

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70 ± 5.7

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71± 5.9

Flavor Content of the Solar 8B Neutrino Flux

Nuclear Physics

CC InteractionCC Interaction

ES InteractionES Interaction

NC InteractionNC Interaction

−++→+ eppe H2ν

−− +→+ exx νν e

npxx ++→+ νν H2

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 8B ν’s has a large non-νe component• Survival probability Pee for Eν > 5 MeV is

essentially independent of Eν

• Pee for ν’s of lower energy (p-p) is larger• There is no significant (> 2) D/N asymmetry

All observations are consistent withthe following hypotheses:

Mass-induced flavor oscillations(with LMA as the favored solution)

Nuclear Physics

Neutrino Oscillations

Nuclear Physics

ν

e

ν

μ

ν

τ

⎛

⎝

⎜

⎜

⎜

⎜

⎜

⎞

⎠

⎟

⎟

⎟

⎟

⎟

=

U

e 1

U

e 2

U

e 3

U

μ 1

U

μ 2

U

μ 3

U

τ 1

U

τ 2

U

τ 3

⎛

⎝

⎜

⎜

⎜

⎜

⎜

⎜

⎞

⎠

⎟

⎟

⎟

⎟

⎟

⎟

ν

1

ν

2

ν

3

⎛

⎝

⎜

⎜

⎜

⎜

⎜

⎜

⎞

⎠

⎟

⎟

⎟

⎟

⎟

⎟

νe =Ue1e−E1tν1 +Ue2e

−E2tν2 +Ue3e−E3tν3

νe =Ue1ν1 +Ue2ν2 +Ue3ν3

States evolve with time or distance

Flavor eigenstates are a mixture of mass eigenstates

If neutrinos have mass leptons can mix:

⎟⎟⎠

⎞⎜⎜⎝

⎛ Δ−=→ E

LmP

ee

2122

122 27.1

sin2sin1 θυυ

The νe survival probability for two flavor mixing is:

Reactor Neutrino Experiment

Nuclear Physics

Terrestrial Neutrinos

KamLAND is a 1 ktonliquid scintillator detectorthat observes from anumber of reactors inJapan at an averagedistance of 180 km

Photomultipliers

(NOBS - NBG)/NEXP =

0.611 ± 0.085 (stat) ± 0.041 (syst)

KamLAND observes asignificant deficit ofneutrinos and confirmssolar neutrino LMAneutrino oscillation solution

Neutrino Properties

Nuclear Physics

• What We Know– There are 3 types of neutrinos : νe , ν , ν– Neutrinos have mass and oscillate– Oscillation parameters (Δm2 and tan2) known to ~ 30% – Neutrino masses are small

• 50 meV < mν < 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 ν)– 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 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)

Goal is to measure the flavor compositionof the p-p solar ν’s to 1% precision ina model-independent manner

Requires CC and ES/NC measurement(assuming active oscillations)

Model-indep test for sterile ν’s using measured oscillation parameters (p-p + KamLAND)

Uncertainties in the solar neutrino fluxesp-p 7Be CNO 8B

Present 15% 35% 100% 6%With present 12% 8% 100% 4%generation detsFuture expts 1-3% 2-5% 10-20% 2-4%

• Determine unitarity / dimension of ν 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 108 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 FutureSolar Neutrino Experiments (II)

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νe

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νeModel-dependent cross-check for sterile neutrinos

with ≈ 2% sensitivity (90% CL)

• Provide improved precision of mixing angle

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

Measurement of the p-p rate to 1% provides knowledge of 12

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

Compared to the present CPT test from the upper limit onthe 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

Low-energy solar neutrino expts must be part of anyfull study of sterile neutrinos

Expect sensitivity of 10-11 B

Future p-p solar neutrino experiments offer the best prospectfor improving our knowledge of 12

solar required to determine mν in 0ν- decay

Nuclear Physics

p-p Solar Neutrino Experiments:Physics Goals

Nuclear Physics

Search with sterile neutrino components withan 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 tan2: 3% p-p accuracyTo match projected SNO, KamLAND limits: 2% p-p accuracy

Measurement of νe fluxes:

Source To match To match To matchcurrent 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%

• Looks at solar 7Be line (862 keV)• Precision measurement of 12

• Will provide test of SSM for 7Be 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 νe component of p-p (7Be)with 1-3% (2-5%) accuracy

Elastic Scattering Experiments:CLEAN, HERON, TPC, XMASS

Goal: Measure νe / ν, ν component of p-p (7Be)with 1-3% (2-5%) accuracy

Nuclear Physics

Spokesman: Raju Raghavan

CC p-p Experiments: LENS

40 tons In target in 400 tons scintillatorModular design with In cells surrounded by non-In cells (2000 tons scintillator)

Fundamental problem: 115In 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 7Be, CNO• 300 MeV/pe scintillator, 3 m attenuation length• No backgrounds• Calibrated by 8 MCi 51Cr source

Source Statistical Accuracyp-p 2.3%7Be 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

+0.05 +0.01 +0.00fpp = 1.05 (1 ± 0.11 ± 0.007 ± 0.05 ± 0.04 )

- 0.08 - 0.02 - 0.02

= 1.05 (1 ± 0.15)

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

Dedicated pp Experiments

required to make Improvements.

Nuclear Physics

Flux Predictions for a ppElastic Scattering Experiment

0.697 ± 0.023 (100 keV) 0.693 ± 0.024 ( 50 keV)

Low Energy Solar Neutrino Fluxes

Nuclear Physics

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

SAGE: 1990-2003Progress in determining the flux oflow-energy solar νe can only be achieved

in the next decade by improved Ga measurements

The Gallium experiments should continue to operateuntil they are systematics limited

The Russian-American Gallium Experiment

Nuclear Physics

It has been my experience that SAGE has proved to be a perfectexample of the value of international scientific collaborations

The SAGE collaboration has provided the meansfor 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 peoplewho have made SAGE a success -

Without all of their support the success and recognitionthat we have received in the world scientific community

would not have been possible.