Lepton-Photon 2003 Plenary Talk

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Solar Neutrino Experiments
Alain Bellerive Canada Research Chair Carleton
University
Thanks toE. Bellotti, M. Boulay, J. Formaggio,
V. Gavrin, K. Graham, K. Heeger, R. Hemingway,
A. Ianni, A. Marino, M. Nakahata, A. Poon, Y.
Takeuchi, J. Wilkerson
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Outline

• Introduction
• First Generation of Solar Neutrino Experiments
• Standard Solar Model (SSM)
• Solar Neutrino Problem
• Neutrino Oscillation and Matter Effects
• Second Generation of Solar Neutrino Experiments
• Constraints on Oscillation Parameters
• Future Prospects
• Summary and Conclusion

• Chlorine Gallium Kamiokande

• SuperK SNO

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Evidence for Neutrino Oscillations
First evidence of neutrino oscillation
Atmospheric Neutrinos high energies
Solar Neutrinos low energies
Todays talk !!!
Todays talk !!!
Neutrino Beams and Reactors
Tunable energies and distances!
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Macroscopic Properties of the Sun
Mean Distance from the Earth 1.5 x 1011m Mass 2
x 1030 kg Radius 6.96 x 108 m Luminosity 3.8 x
1026 W Neutrino flux 6.5 x 1010 cm-2 s-1
SNU Product of solar neutrino fluxes (measured
or calculated) and calculated
cross-sections 1 SNU ? 1 capture per s per
1036 target atoms
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Neutrino Production in the Sun
Neutrino Production Radius

Light Element Fusion Reactions
p p ?2H e ?e
99.75
p e- p ? 2H ?e
0.25
10-5
3He p ?4He e ?e
7Be e- ?7Li ?e
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8B ? 8Be e ?e
0.02
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Chlorine Measurements Homestake

• 1960s 37Cl ne ? 37Ar e-
• Construction of the Chlorine detector by Ray
  Davis
• Depth 4850 ft
• Detector fluid 3.8 x 105 l of C2Cl4
• Energy Thresold 0.814 MeV
• 1970 1995
• Measurements of solar n flux
• Sensitive to 8B 7Be ns
• Observed rate (SNU)
• 2.56 0.16(stat) 0.16(syst)
• Expected rate (SNU)
• 7.6 1? from BP2000

Cleveland et al.,Ap. J. 496, 505(1998)
1.3
1.1
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Gallium Experiments
71Ga ne ? 71Ge e- Radiochemical
Target

• Energy Threshold 0.233 MeV
• Sensitive to pp, 7Be, 8B, CNO, and pep ns

• Small proportional counters are used to count the
  Germanium

Typical energy distribution from Auger
electrons and X-rays emitted during the 71Ge
electron capture decays ? 16.5 days

• SAGE Russian-American
• Gallium solar neutrino
• Experiment (INR RAS)
• A liquid metal target which contains 50 tons of
  gallium.

• GALLEX/GNOGallium Neutrino
• Observatory in
• Gran Sasso
• 30 tons of natural gallium in an
• aqueous acid solution.

• K peak

• L peak

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Gallium Measurements SAGE (LowNu03)

Expected rate 1? from BP2000 129 SNU
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7
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Gallium Measurements GALLEX GNO

GNO
GALLEX
Expected rate BP2000 129 SNU

Neutrino 2002
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Water Measurements Kamiokande
January 87 February 95 ?
Real-time Cerenkov Detector 2140 tons of
water 948 PMTs Energy Thresold 7 MeV Sensitive
to 8B neutrinos

• ? mainly ne

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Water Detector Super-Kamiokande

• 8B neutrino measurement by
• nx e- ? nx e-
• Sensitive to ne, nm, nt
• ?(??,? e- ) ? 0.15 x ?(?e e-)
• High statistics 15ev./day
• Real time measurement allow studies on time
  variations
• Studies energy spectrum
• 50 ktons of pure water with 11,146 PMTs (fiducial
  volume
• of 22.5 ktons for analysis)

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Water Measurements Super-Kamiokande
0.08
? 2.32 0.03 (stat) (syst) x 106 cm-2 s-1
-0.07
0.013
(?night - ?day)/ ?average 0.033 0.022 (stat)
(syst)
-0.012

• Kamiokande SuperK provided the first evidence
  of neutrino production in the core of the Sun
  with directional information
• Energy threshold
• 6.5 MeV (1996)
• 5.5 MeV (1997-2000)

1258 days May 96 Oct. 00

• No spectral distortion
• hep (90 C.L. UL) 40x103 cm-2 s-1
• i.e. 4.3 the expected rate (BP2000)

Phys.Rev.Lett.865651-5655,2001
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Astrophysical Solutions?

Hata and Langacker Pre SNO
?8B/ ?8BSSM
?7Be/ ?7BeSSM
The data are incompatible with the Standard Solar
Model !!!
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Solar n Flux Measurement Results
Chlorine Gallium Water experiments have
different energy threshold
!!! The data suggest an energy dependence !!!
??? What could explain such a variation ???
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Solar Neutrino Problem

• Historically the first culprit was assumed to be
  the method of determining the solar ? flux.
• In fact, the last 30 years showed that the SSM
  provides and accurate description of the
  macroscopic properties of our Sun.
• The mass, radius, shape, luminosity, age,
  chemical composition, and photon spectrum of the
  Sun are precisely determined and used as input
  parameters.
• Equation of state relates pressure and density
  while the radiative opacity dictates photon
  transport.
• Experimental fusion cross sections used to
  determined the nuclear reaction rates.

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Test of Standard Solar Model
SSM determines the present distribution of
physical variables inside the Sun (like the core
temperature and density), photon spectrum, the
speed of sound, , and the neutrino fluxes.
(Model-Sun)/Sun
Fractional differences between the calculated
sound speeds for the SSM and the accurate sound
speeds measured by helioseismology,



R/Rsun



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Neutrino Mixing Pontecorvo

• As in the quark sector, it is possible to define
  a neutrino mixing matrix which relates the mass
  and weak eigenstates

Mixing Matrix
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Solar Neutrino Oscillations

• Pee sin2(2q) sin2(1.27Dm2 L / E)
• Physics
• Dm2 sin(2q)
• Experiment
• Distance (L) Energy (E)

3 Parameters !
The state evolves with time or distance
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Sensitivity to n oscillations

• Vacuum Oscillations
• Different types of experiments sensitive to
  different aspects of oscillation space

Dm2 (eV2 )
Accelerator GeV
Reactor MeV
Atmospheric GeV
Solar MeV
L/E (km/GeV)
MSW Mikheyev Smirnov - Wolfenstein
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Matter-Enhanced Neutrino Oscillations
Pee

• Neutrinos produced in weak state ?e
• High density of electrons in the Sun
• Superposition of mass states ?1, 2, 3 changes
  through the MSW resonance effect
• Solar neutrino flux detected on Earth consists
  of ?e ?m,t

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Neutrino Oscillations
in matter
Time Evolution
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Mixing Parameters
SMA

• Combination of the
• Chlorine, Gallium,
• SK, and CHOOZ
• restricted the mixing
• parameters
• Pre SNO

LMA
LOW
?m2 (eV2)
VAC
JustSo2
Allowed Regions
tan2?

Phys.Rev. D64 (2001) 093007
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SK and SNO

• SuperK
• Time variation and spectral distortion
• Search for anti-?e
• SNO
• Measurement of ?e and ?total
• Day/Night fluxes

OVERAL PICTURE
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Solar neutrino data in SK (period I)
May 31, 1996 July 13, 2001 (1496 days )
22400?230 solar n events
Ee 5.0 - 20 MeV
8B flux 2.35 ? 0.02 ? 0.08 x 106 /cm2/sec
Data
0.016
?0.005
0.465
0.015
SSM(BP2001)
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Time variation of the solar neutrino flux
Expected time variation by eccentricity (1/r2)
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Daily Variation of SK Rate
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SK Constraint on mixing parameters
zenith spectrum shape alone
using SSM 8B ? flux prediction


Allowed Regions
Excluded Regions
Phys. Lett. B (2002) 179
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SK Search for solar ?e
If neutrinos have magnetic moment, ne ? ne
(Dirac n) ne ? nm,nt ? osc. ? ne
(Majorana n)


Combine 8-20 MeV, ne flux lt 0.8 of SSM U.L. _at_
90 C.L.
Solar ne
selected
Reaction ne p ? n e
cos ?sun
Spallation background
Phys.Rev.Lett.90(2003)
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Sudbury Neutrino Observatory
2092 m to Surface (6010 m w.e.)
PMT Support Structure, 17.8 m 9456 20 cm
PMTs 55 coverage within 7 m
Acrylic Vessel, 12 m diameter
1000 tonnes D2O
1700 tonnes H2O, Inner Shield
5300 tonnes H2O, Outer Shield
Urylon Liner and Radon Seal Energy Threshold
5.511 MeV
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Underground laboratory in Sudbury
SNOLAB
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Neutrino Reactions in SNO
Produces Cherenkov Light Cone in D2O


?

n
CC
e-
p
p
d
e

• Q 1.445 MeV
• good measurement of ne energy spectrum
• some directional info ? (1 1/3 cosq)
• ne only

n captures on deuteron 2H(n, g)3H Observe 6.25
MeV g

• Q 2.22 MeV
• measures total 8B n flux from the Sun
• equal cross section for all n types

Produces Cherenkov Light Cone in D2O


?

e-
n
e-
n
ES
x
x

• low statistics
• mainly sensitive to ne, some n? and n?
• strong directional sensitivity

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Shape Constrained Signal Extraction Results



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Shape Constrained Neutrino Fluxes

• Signal Extraction in FCC, FNC, FES with

E gt 5.511 MeV
Signal Extraction in Fe, Fmt
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SNO NC in D2O (April 2002)
2/3 of initial solar ne are observed at SNO to
be nm,t
Flavor change at 5.3 s level.
Sum of all the fluxes agrees with SSM.
Phys. Rev. Lett. 89 (2002)
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The Solar Neutrino Problem
Experiment Exp/SSM

• SAGEGALLEX/GNO 0.55
• Homestake 0.34
• KamiokandeSuperK 0.47
• SNO CC (June 2001) 0.35

SNO NC (April 2002) 1.01
SNO CC vs NC implies flavor change, which can
then explain other experimental results.
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Day/Night Asymmetries
Signal Extraction for ?CC, ?NC, ?ES ? ?e and
?TOT

Allowing Atot ? 0
2.4 - 2.5
ATOT -24.2 16.1
Night - Day

With constraint Atot 0
1.3 - 1.2
Ae 7.0 4.9
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SNO Constraint on mixing parameters
Day/Night and Energy Spectra SNO Alone

Allowed Regions
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Progress in 2002 on the Solar Neutrino Problem
March 2002
April 2002 with SNO
Dec 2002 with KamLAND
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Status and Future Prospect
SuperK SNO
Borexino KamLAND

RD
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Super-Kamiokande restart (SK-II)
LowNu 03
Pure water filling Oct-Dec, 2002 Tank was full
on Dec10, 2002 Only 13 months after the incident
Typical cosmic ray muon in SK-II
Total number of PMTs in SK-II 5200 PMTs
(47 of SK-I)
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SNO Salt Phase (in progress)

• Added 2 tons of salt (0.2) in
• June 2001
• Higher n-capture efficiency
• Higher NC event light output
• Light pattern differs from e-
• Results SOON (CC/NC, ?e, hep)!

n ? 35Cl ? 36Cl ? ?g ? e? (E?g 8.6 MeV)
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SNO Statistical Significance
CC Single electron Cerenkov signal less
isotropic
NC Multiple gs from n capture on 35Cl Cerenkov
signal more isotropic
Variables CC Stat. Error NC Stat. Error ES Stat. Error
E,R,?sun 3.4 8.6 10
R, ?sun 9.5 24 11
E,R,?sun 4.2 6.3 10
E,R,?sun, Iso. 3.3 4.6 10
R,?sun,Iso. 3.8 5.3 10
Light Pattern
Simulation
Phys. Rev. Lett. 89 (2002)
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SNO Future Plans
Neutral Current Detectors
n ? 3He ? p ? t

• Event by event separation
• Break the correlation between
• NC CC events
• Measure in separate data
• streams NC CC events
• Different systematic errors
• than neutron capture on NaCl
• Deployment in September 03

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What SNO might tell us in the future
LMA Allowed
Day Night Contours ()
CC/NC Contours
hep-ph/0212270 hep-ph/0204253
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BOREXINO Sensitivity to 7Be ?s

• Liquid Scintillator Spill Consequences (LOWNu03)
• Dedication of BX to seal the detector and resume
  activities within 2003
• Possibility that legal procedure will take longer
  should be seriously considered implying no BX
  operations

Work on installation continues Needs to resolve
political situation
Challenge Control of Low Energy Background nx
e- ? nx e- Energy window 0.25,0.8 MeV
18m
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KamLAND Sensitivity to 7Be ?s

• 1000 ton liquid scintillator
• 13 m thin transparent balloon
• 1325 inner looking PMTs

Shift from a coincidence experiment to a ES low
energy experiment nx e- ? nx
e- Backgrounds will be the main
concern, especially radioactive krypton
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Upcoming Experiments and RD Efforts

• Ongoing Gallium experiments important
• More about the 8B from SuperK and SNO
• Borexino KamLAND real-time look at the 7Be ?s
• Real-time low energy ?s are the ultimate probe
  of the Sun and test of the Standard Solar Model

pp ?s projects ES CC 7Be ?s projects ES CC
XMASS LENS BOREXINO LENS
CLEAN MOON KamLAND MOON
HERON SIREN TPC SIREN
TPC MUNU
MUNU LITHIUM
GENIUS
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Conclusion

• Solar neutrino oscillation was established by
  Chlorine, Gallium, SuperK and SNO experiments
• SNO provided direct evidence of flavor conversion
  of solar ?es
• Real-time data do not show large energy
  distortion nor time-like asymmetry
• Matter Effect explains the energy dependence of
  solar oscillation
• Large mixing angle (LMA) solutions are favored
• Solar Neutrino Problem is now an industry for
  precise measurements of neutrino oscillation
  parameters

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Implications and Outlook

• Solar neutrinos demonstrate that neutrinos have
  mass and the minimum SM is incomplete
• Unlike the quark sector where the CKM mixing
  angles are small, the lepton sector exhibits
  large mixing
• The ? masses and mixing may play significant
  roles in determining structure formation in the
  early universe as well as supernovae dynamics and
  the creation of matter
• The coming decade will be exciting for neutrino
  physics helping delineate the New Standard Model
  that will include neutrino masses and mixing
• Precision measurements of the leptonic mixing
  matrix
• Determination of neutrino masses
• Investigation of lepton sector CP and CPT
  properties

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