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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 - PowerPoint PPT Presentation
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The Importance of Low-EnergySolar Neutrino Experiments
Thomas BowlesLos 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
⎛
⎝
⎜
⎜
⎜
⎜
⎜
⎞
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⎟
⎟
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⎟
=
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
⎛
⎝
⎜
⎜
⎜
⎜
⎜
⎜
⎞
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ν
1
ν
2
ν
3
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νe =Ue1e−E1tν1 +Ue2e
−E2tν2 +Ue3e−E3tν3
νe =Ue1ν1 +Ue2ν2 +Ue3ν3States evolve with time or distance
Flavor eigenstates are a mixture of mass eigenstates
If neutrinos have mass leptons can mix:
⎟⎟⎠⎞
⎜⎜⎝⎛ Δ
−=→ ELmP
ee
2122
122 27.1sin2sin1 θυυ
The νe survival probability for two flavor mixing is:
Reactor Neutrino Experiment
Nuclear Physics
Terrestrial NeutrinosKamLAND 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 12to 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 any
full 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.