The Importance of Low-Energy Solar Neutrino Experiments Thomas Bowles Los Alamos National Laboratory...
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Transcript of The Importance of Low-Energy Solar Neutrino Experiments Thomas Bowles Los Alamos National Laboratory...
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.