The solar neutrino measurements

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The solar neutrino measurements
Yusuke Koshio Kamioka, ICRR, Univ.of Tokyo LNGS,
INFN

• Introduction
• Brief history of the solar neutrino experiments
• Recent results
• Multi-MeV energy region of solar neutrinos
• Super-Kamiokande, SNO, and so on.
• Future prospects
• Summary
• (including other neutrinos as an astro-particle)

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Solar neutrinos
How does the sun shine?
Nuclear fusion reactions occur deep inside the sun
4p ? 4He 2 e 2 ne 26.7MeV
convective zone
thermal energy
corona

• Flux 66 billon neutrinos / sec /cm2
• Go through the sun immediately (2sec) ?
  Measurements of solar neutrinos can see the
  current status in the center of the sun.

radiative zone
chromospher
Core
Neutrino-measured luminosity
Actually, this reaction is realized via pp-chain
and CNO cycle
Standard Solar Model (SSM) e.g. J.N.Bahcall
Structure of the sun
Photon-measured luminosity
? 40000years radiated from the center to the
surface.
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ltpp-chaingt
pp
pep
p p ? 2He?e p e- p ? 2H ?e
2H p ? 3He ? 3He 3He ?a 2p 3He a ?
7Be ? 3He p ? 4He e ?e 7Be e- ? 7Li
?e 7Be p ? 8B ? 7Li p ? 2a
8B ? 8Be e ?e

8Be ?
2a
0.25
99.75
hep
86
14
0.15
99.85
8B
7Be
ltCNO cyclegt
g
e
13N
ne
13N
12C
13C
p
p
g
4He
p
p
15N
14N
4He
g
15O
e
g
ne
15O
17O
16O
p
p
17F
ne
g
17F
e
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Solar neutrino spectrum
Cl
Ga
Kam
BOREXINO
pp
7Be
Super-K, SNO
13N
Flux (cm-2 sec-1MeV-1)
15O
pep
8B
17F
7Be
hep
Neutrino energy (MeV)
http//www.sns.ias.edu/jnb/
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Requirement for astro neutrinos detection
n
Target

• Large amount of target
• No signal from neutrino itself
• Rare interaction probability (stot10-44(cm2))
• Deep underground
• Remove particles from cosmic rays (mainly cosmic
  ray muons)

Observable particles
nucleon, electron, etc
Cosmic ray (p,He,...)
p, K
L1020 km
m
nm
e
ne
nm
detector
L up to13000 km
ne
nm
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Underground laboratoryfor solar neutrino
experiment
Sudbury
Homestake
Baksan
Kamioka
Gran Sasso
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Early stage (19701995)
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The first solar neutrino measurement
Homestake experiment by R.Davis, at Homestake
gold mine, South Dakota, 1500m underground,
since 1970.
ne 37Cl ? e 37Ar (CC) (Eth0.814MeV)
Raymond Davis jr.
t1/235days
0.31 ? 0.03
Observed solar neutrino flux is significantly
less than prediction by SSM
Solar Neutrino Problem
Neutrino Astrophysics J.N.Bahcall
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Kamiokande (19831996)
Kamioka mine, Japan, 3000 ton water Cherenkov
detector 1000 of 20 PMTs Energy threshold 7.5MeV
e
qsun
n
0.48 ? 0.07
Masatoshi Koshiba
Flux deficit was observed
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Another result in Kamiokande (1987)
First observation of neutrinos from SuperNova
Large Magellanic Cloud 49kpc (160,000 ly)

• Date 23 Feb. 1987
• Time 073535(UT)
• 11 events within 13 sec.

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Gallium experiment

• SAGE
• BAKSAN in Russia, 1800m underground, since 1990.
• GALLEX/GNO
• GranSasso in Italy, 1300m underground, since
  1991.

ne 71Ga ? e 71Ge (CC) (Eth0.233MeV)
t1/211days
Measurable pp neutrinos
0.53 ? 0.04 (SAGE) 0.55 ? 0.04 (GALLEXGNO) 0.54
? 0.03 (combined)
Flux deficit was observed
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Summary of this stage

• Several solar neutrino experiments (Homestake,
  Kamiokande, Gallex, SAGE) were operated since
  1970.
• In all of the experiments, observed neutrino flux
  is significantly smaller than expected flux by
  the standard solar model. (Solar Neutrino
  Problem)
• More precise measurements are needed in order to
  solve the problem.
• Neutrino oscillation?
• Problem in the solar model?
• Others? (experimental systematics, etc.)

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Recent results (19962008)
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Super Kamiokande
50kt Water for total volume (22.5kt fiducial
volume) Operated since 1996 20PMT
photocathode (inner) coverage
SK 11,146 40
41.4m
1000m
SK
39.3m
Placed inside the Kamioka mine 1000m underground
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Results in Super Kamiokande (1998)
Discovery of neutrino mass in atmospheric
neutrinos
(Elt1.33 GeV)
(Elt1.33 GeV)
w/o n oscillation
with n oscillation
nm nt
1.5x10-3ltDm2lt3.4x10-3eV2 sin22q gt 0.92 at 90C.L.
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Neutrino oscillation
A flavor of neutrinos (ne ,/ nm / nt) is changed
while traveling
(In the case of two neutrinos)
A flavor eigenstate (na , nb ) is a mixture of
mass eigenstate (n1 , n2 )
P(nx) survival probability of nx flavor state q
mixing angle Dm2 m22-m12 L distance from
source to detector (for a time t) E Neutrino
energy n Electron density
Mass eigenstate oscillates while traveling y(t)
e-iEt
This effect is required for neutrinos to have
mass.
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Neutrino oscillation by atmospheric neutrinos
(with accelerator experiments)
ne
nm
nt
Best Fit Results Dm2 2.43 x 10-3 eV2
sin2(2q) 1.0
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Solar neutrino measurement in Super Kamiokande
nsolar
nsolar e n e (ES)

• Strong directionality
• Find solar direction
• Large statistics
• Precise flux measurement (3 level)
• Realtime measurement
• Day/Night flux differences
• Seasonal variation
• Energy spectrum
• Less than 1 precision of energy determination

50,000 ton of water
Scientific American
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How can solar neutrinos be seen in SK
Correlation to the direction of the sun
Track of the sun on the galactic coordinate
Galactic Latitude
Galactic Longitude
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Solar neutrino flux in SK
May 31, 1996 July 13, 2001
Best fit
e
Background
q
Data
n
?
55200 events predicted by theory (SSM)
22404 solar n events (15.0 events/day)
0.4060.003(stat.)0.014(sys.)
Significant flux deficit can be seen
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Time variation of solar neutrino flux
Flux (x106/cm2/s)
Consistent with expected variations due to
eccentricity of Earths orbit.
No correlation with solar cycle minima or maximum
seen.
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SNO
Sudbury, Ontario, in Canada, since Nov. 1999 Eth
5MeV
http//www.sno.phy.queensu.ca/
2092m underground
1000t D2O
Each flux from CC, NC, ES can be separately
observed.

• Charged Current (CC)
• ne d ? p p e
• Only ne ne
• Neutral Current (NC)
• n d ? n p n
• All n types nenmnt
• Elastic Scattering (ES)
• n e ? n e
• All n types ne0.154(nmnt)

12m diameter Acrylic vessel
17.8m diameter 9456PMTs
Water
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SNO
Sudbury, Ontario, in Canada, since Nov. 1999 Eth
5MeV
http//www.sno.phy.queensu.ca/
2092m underground
1000t D2O
Each flux from CC, NC, ES can be separately
observed.
Neutrino oscillation effect
ne
nm
nm
ne
ne
ne
Generated in the sun
NC CC ES

• Verify neutrino oscillation w/o uncertainty of
  solar model
• NC ? total 8B n flux from the Sun even if
  neutrino oscillation happens

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SK vs SNO (2001)
This difference comes from the neutrino
oscillation effect. (ne?nm)
nm
ne
ne
SK/SNO combined allowed parameter region (ne?nm)
CC ES (SNO) (SK)
Evidence of neutrino oscillation in solar
neutrinos
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Results in all SNO (2002)
e
q
n
8B flux NC CC ES by SSM
8B solar neutrino flux is consistent with the
model expectation
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KamLAND
http//www.awa.tohoku.ac.jp/KamLAND/index.html
In the Kamiokande cavern since Jan. 2001

• Reactor neutrinos (L160km from the main
  reactor)
• Geo neutrinos
• Solar neutrinos

1000t liquid scintillator
ne p ? e n
200msec
1879 PMTs
n p? d g
H2O Cherenkov veto counter
n energy measurement Eth 1.8MeV Realtime
measurement
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Results in KamLAND ()
Energy spectrum distortion was found
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Neutrino oscillation parameter region
(solarreactor)
ne
nm
nt
Best Fit Results Dm2 7.2 x 10-5 eV2 sin2(q)
0.28
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Summary of this stage

• Precise measurements in several Solar and Reactor
  neutrino experiments (Super-Kamiokande, SNO,
  KamLAND) have been carried out, and they are very
  successful.
• Combining the results of these experiments, a
  neutrino oscillation scenario has been built up
  as a solution of the solar neutrino problem.
• Total 8B solar neutrino flux is consistent with
  the expectation by solar model.

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Future prospects
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Whats next?

• The astrophysics of the solar interior and the
  physics of neutrino propagation both deserve to
  be explored independently.

J.N.Bahcall
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Solar neutrino spectrum
Neutrino property
pp
7Be

• Search for definite sign of neutrino oscillation
  in solar neutrino data
• Spectrum upturn
• ne ne comparison
• Solar n vs Reactor n
• Other possibility
• n magnetic moment, etc
• How much fraction of CNO cycle? ? For investigate
  the heavy abundance in the sun.
• Important to measure the fully solar neutrino
  spectrum, especially pp neutrinos

13N
Flux (cm-2 sec-1)
pep
15O
8B
17F
hep
7Be
Astrophysics of the Sun
ne survival probability
P(ne ? ne)
Expectation by neutrino oscillation
Neutrino energy (MeV)
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BOREXINO
Scintillator 270 t PCPPO (1.5 g/l) in a 150 ?m
thick inner nylon vessel (R 4.25 m)
Stainless Steel Sphere R 6.75 m 2212 PMTs
1350 m3
Buffer region PCDMP quencher (5 g/l) 4.25 m lt R
lt 6.75 m
Water Tank ? and n shield ? water C detector 208
PMTs in water 2100 m3
Outer nylon vessel R 5.50 m (222Rn barrier)
Carbon steel plates
20 steel legs
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Summary

• Solar neutrinos produced by nuclear fusion
  reaction in the Sun have been measured for the
  last few decades.
• The deficit of solar neutrino flux was observed.
  It comes from neutrino oscillation by recent
  several observations.
• The absolute 8B solar neutrino flux, which is
  higher energy region, is directly measured. It is
  consistent with calculation by solar model.
• Several challenging experiments are going and
  being proposed. The final goal is measurement of
  a fully resolved solar neutrino spectrum.

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• Arigato gozaimasu