Transcript The Importance of Low-Energy Solar Neutrino Experiments

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)
70  5.7

71 5.9

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
• 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
If neutrinos have mass leptons can mix:
  
U
ne  

e1
 

n   U
  
1
n  
U
   
  1


U
U n 
e2
e3  1 
U
U n 
2
3 2 
U
U n 
2
 3  3
Flavor eigenstates are a mixture of mass eigenstates
n e  Ue1n 1  Ue 2n 2 Ue3n 3
States evolve with time or distance
ne  Ue1e
E 1t
n1  Ue2e
 E2 t
n2  Ue3e
E 3 t
n3
The ne survival probability for two flavor mixing is:
2

1
.
27

m
L
2
2
12

Pe e  1  sin 212 sin 

E


Nuclear Physics
Reactor Neutrino Experiment
Terrestrial Neutrinos
KamLAND
is aEXP
1 kton
(NOBS - NBG)/N
=
liquid scintillator detector
that
0.611observes
± 0.085 (stat)
from a
number
of reactors
± 0.041
(syst) in
Japan at an average
distance of 180 km
Photomultipliers
KamLAND observes a
significant deficit of
neutrinos and confirms
solar neutrino LMA
neutrino oscillation solution
Nuclear Physics
Neutrino Properties
• What We Know
–
–
–
–
There are 3 types of neutrinos : ne , n, n
Neutrinos have mass and oscillate
Oscillation parameters (m2 and tan2) 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 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 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, 7Be, CNO)
Measurement
Uncertainties
of CNO neutrinos
in/ dimension
the solar
provides
neutrino
an
fluxes
important
test:
• Determine
unitarity
of
n
mixing
matrix
7Beis from
8B cycle
• 1.5% of the Sun’s
p-penergy
CNO
the CNO
Goal
to measure
the35%
flavor
composition
8 yr convective
Present
• CNOisburning
is15%
crucial
in
first100%
10
6%
stage
of the p-p solar n’s to 1% precision in
With
present test of 12%
initial metallicity
8%
100%
of the4%
Sun
a• Provides
model-independent
manner
generation
dets CC and ES/NC measurement
Requires
Future expts (assuming
1-3%
2-5%
10-20% 2-4%
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 Future
Solar Neutrino Experiments (II)
• Use p-p neutrinos as “standard candle”
Precision test for CPT violation comparing
n e and n e
Model-dependent
cross-check
sterile
neutrinos
Measurement of the p-p
rate to 1%for
provides
knowledge
of 12
to allow
a search
for CPT(90%
violation
at a scale of 10-20 GeV
with
≈ 2%
sensitivity
CL)
Compared
to the present
CPTthe
test
fromcomponent
the upper limit
on
Various
scenarios
imply
that
sterile
of
solar
-19 GeV
the
mass
difference
in
the
kaon
system
of
4.4
x
10
• Provide
improved
precision
of
mixing
angle
neutrino fluxes may be energy dependent
Future p-p solar neutrino experiments offer the best prospect

solar
neutrino expts
must be part of any
forLow-energy
improvingfull
our
knowledge
of

12
study
of sterile
neutrinos
• Search for n magnetic
moment
with
improved
Qsolar required to determine mn in 0n-bb decay
sensitivity (contribution  1/Te)
 Expect sensitivity of 10-11 B
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
p-p
7Be
CNO
pep
8B
To match
To match
current expts: projected expts:
15%
12%
35%
8%
100%
100%
100%
100%
6%
4%
To match
LMA prediction:
2%
5%
100%
2%
6%
Mixing parameters:
To match current limits on tan2:
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 12
• 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:
LENS, MOON
Goal: Measure ne component of p-p (7Be)
with 1-3% (2-5%) accuracy
Elastic Scattering Experiments:
CLEAN, HERON, TPC, XMASS
Goal: Measure ne / n, n 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
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 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
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
Ga  SNO  KamLAND  BOREXINO  BP00
Ga
Ga
CNO
Exp’t X-Sect. SSM



+0.05
fpp = 1.05 (1 ± 0.11
SNO KamLAND BOREXINO
CC
Exp’t
Exp’t
Sterile




+0.01
+0.00
± 0.007
- 0.08
- 0.02
± 0.05
± 0.04
)
- 0.02
= 1.05 (1 ± 0.15)

Flux Predictions for a pp
Elastic Scattering Experiment
Dedicated pp Experiments
required to make Improvements.
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
SAGE: 1990-2003
Progress in determining
the flux of
low-energy solar ne can only be achieved
in the next decade by improved Ga measurements
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