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Welcome to SNOLABAnd to the Neutrino Geoscience
Conference
Art McDonaldQueen’s University, Kingston
Director, SNO Institute
(+)
The Enigmatic Neutrino
I have done a terrible thing. I have done a terrible thing.
I have postulated a particle that cannot be detectedI have postulated a particle that cannot be detected..
W. Pauli 1930
• Neutrinos, along with electrons and quarks are the basic particles of nature that we do not know how to sub-divide further. Neutrinos come in three types (electron, mu, tau) as described in The Standard Model of Elementary Particles, the accepted basic theory of particle physics. They have a mass, but it is more than 5 million times smaller than an electron.
• Neutrinos are made in very large numbers in the nuclear reactions that power the Sun. Neutrinos only stop if they hit the nucleus of any atom or an electron head-on. They can pass through a light-year of lead without stopping. Therefore they are very difficult to detect and far less is known about them than the other basic particles.
• Anti-neutrinos are created in the beta decays such as U and Th and in nuclear reactors. Geo-neutrinos are electron anti-neutrinos.
What are Neutrinos?
A short summary of Neutrino History
1914 Continuous Beta Spectra Observed: Chadwick
1930 Pauli invents the neutrino to save Energy Conservation
1933 Fermi baptizes the “neutrino”: The Little Neutral one.
1948 Pontecorvo (Chalk River Report): Detection of Neutrinos from Reactors and the Sun
1950 Pontecorvo, Hanna: Neutrino mass limit from Tritium beta decay.
1956 Reines & Cowan observe electron anti-neutrinos from a reactor
1957 Pontecorvo: Postulates Neutrino Oscillations
1962 Lederman, Schwartz, Steinberger observe muon neutrinos
1968 Solar Neutrino flux is too low: Davis measurements with Chlorine, Bahcall calculations
1968 Solar Neutrino Oscillations?: Pontecorvo
1974 Discovery of Electroweak neutral currents via neutrino beams
1987 Neutrinos from Supernova 1987a: IMB, Kamiokande
1989 Low Solar Neutrino 8B flux: Kamiokande with water
1992 Low solar neutrino pp flux: Gallex, SAGE with Gallium
1991 LEP experiments show that there are only three light neutrinos
1998 Atmospheric muon neutrino disappearance: Super-Kamiokande
First Tennis Champion at Chalk River – 1948Bruno Pontecorvo
relic supernova neutrinos
hep solar neutrinos
Neutrino fluxes at the Earth
Bahcall et al.
, SNO
Solving “The Solar Neutrino Problem”Solar Model Flux Calculations
CNO
SNO was designed to observe separately e and all neutrino types to determine if low e fluxes come from flavor change or solar models
Previous Experiments Sensitive to Electron Neutrinos
+ 0.014Flux/SSM = 0.465 +- 0.005 - 0.012
Kamiokande (1000 tons), followed by
SuperKamiokande (50,000 tons)
Unique Signatures in SNO (D2O)
Charged-Current (CC)e+d e-+p+pEthresh = 1.4 MeV
ee onlyonly
Elastic Scattering (ES) (D2O & H2O)x+e- x+e-
x, but enhanced for e
Neutral-Current (NC) x+d x+n+p Ethresh = 2.2 MeV
Equally sensitive to Equally sensitive to e e
3 ways todetect neutrons
nepe
Anti-neutrino detection in a material with hydrogen
The neutron subsequently is thermalized and captured by a proton producing a 2.2 MeV gamma, so there is a few msec time coincidence with the positron.
Phase II (salt)July 01 - Sep. 03
Phase III (3He)Nov. 04-Dec. 06
Phase I (D2O)Nov. 99 - May 01
SNO: 3 neutron (NC) detectionmethods (systematically different)
n captures on2H(n, )3H
Effc. ~14.4% NC and CC separation by energy, radial, and
directional distributions
40 proportional counters
3He(n, p)3HEffc. ~ 30% capture
Measure NC rate with entirely different
detection system.
2 t NaCl. n captures on35Cl(n, )36ClEffc. ~40%
NC and CC separation by event isotropy
36Cl
35Cl+n 8.6 MeV
3H
2H+n 6.25 MeV
n + 3He p + 3H
p3H
5 cm
n
3He
Acrylic vessel (AV) 12 m diameter
1700 tonnes H2O inner shielding
1000 tonnes D2O($300 million)
5300 tonnes H2O outer shielding
~9500 PMT’s
Creighton mineSudbury, CA
The Sudbury Neutrino Observatory: SNO6800 feet (~2km) underground
The heavy water has recently been returned and development work is in progress on SNO+ with liquid scintillator and 150Nd additive.
- Entire detectorBuilt as a Class 2000
Clean room- Low RadioactivityDetector materials
Cerenkov Light
= v/c
Cerenkov Light is emitted whenever a charged particle exceeds the phase velocity of light in a medium. Example electrons in water:
The light is emitted in a cone, whoseopening angle is defined by the velocityof the particle.
However, it is the total light emitted thatprovides the accurate measure of particleenergy in SNO and SuperK.
SNO: One million pieces transported down in the 9 ft x 12 ft x 9 ft mine cage and re-assembled under ultra-clean conditions. Every worker takes a showerand wears clean, lint-free clothing.
Over 70,000Showersto date andcounting
’s from 8Li ’s from 16N and t(p,)4He
252Cf neutrons
6.13 MeV
19.8 MeV
Energy calibrated to ~1.5 %
Throughout detector volume
Optical calibration at 5 wavelengths with the “Laserball”
SNO Energy Calibrations: 25% of running time
+ AmBe, 24Na
Measuring U/Th Content Ex-situ Ion exchange (224Ra, 226Ra) Membrane Degassing (222Rn) Count daughter product decays
In-situ Low energy data analysis Separate 208Tl & 214Bi
Using Event isotropy
NeutronEvents
D2O H2O/AV
+8-944 +8
-827
SNO Phase 2 neutrino data: 391 live days with salt
Total Spectrum
hep-ex/0502021 March 2005
(NC)
“Blind” analysis of data
ISOTROPY: NC, CC separation
DIRECTION FROM SUN
EVENTS VS VOLUME: Bkg < 10%
ENERGY SPECTRUM FROM CC REACTION
NOOBSERVABLEDISTORTION
Heavy water
SNO Phase 2 with salt
)syst.()stat.( 35.2
)syst.()stat.( 94.4
)syst.()stat.( 68.1
15.015.0
22.022.0
38.034.0
21.021.0
08.009.0
06.006.0
ES
NC
CC
)scm10 of units(In 126
029.0031.0)stat.(023.034.0
NC
CC
Electron neutrinos
The Total Flux of Active
Neutrinos is measured
independently (NC) and agrees
well with solar model
Calculations:
5.82 +- 1.3 (Bahcall et al),
5.31 +- 0.6 (Turck-Chieze et al)
CC, NC FLUXESMEASURED
INDEPENDENTLY
Flavor change determined by > 7
Electron neutrinos areOnly about 1/3 of total!
Final Phase: SNO Phase III
• Search for spectral distortion in CC
• Improve solar neutrino flux by breaking the CC and NC correlation:
CC: Cherenkov Signal PMT Array NC: n+3He NCD Array
Neutral-Current Detectors (NCD): An array of 3He proportional counters
40 strings on 1-m grid~440 m total active length
Phase III production data taking Dec 2004 to Dec 2006. D2O now removed.
Very low Background. About one count per 2 hours in region of interest. To be reduced in future analyses by pulse shape discrimination.
Blind Data: Include hidden fraction of neutrons that follow muons and omit an unknown fraction of candidate events until all analysis parameters fixed
stat stat + systSNO Fluxes: 3 Phases
p-value for consistency of NC/CC/ES in the salt & NCD phases + D2O NC(unconstr) is 32.8%
• Direct observation (7 ) of neutrino flavor change via an appearance measurement: Neutrino Physics Beyond the Standard Model for Elementary Particles.
• Direct measurement (10 % accuracy) of total flux of active solar neutrinos: Strong confirmation of Solar Models.
• With Kamland: Strong confirmation of neutrino oscillation due to finite mass (MNSP mechanism) as the primary physics explanation for appearance and disappearance measurements.
• With other solar measurements: Strong evidence for Matter Enhancement of oscillations in the Sun.
Summary of SNO results
ijijijij
τττ
μμμ
eee
li
sandcwhere
cs
sc
iδecs
sccs
sc
UUU
UUU
UUU
U
sin,cos
0
010
0
00
010
001
0
0
001
100
0
0
1313
1313
2323
23231212
1212
321
321
321
ilil U If neutrinos have mass:
)E
LΔm.(θ)νP(ν eμ
222 271sin2sin
Solar,Reactor Atmospheric
The most favored explanation for the data to date is:Neutrino Oscillations of 3 active massive neutrino types
For two neutrino oscillation in a vacuum: (valid approximation in many cases)
CP Violating Phase Reactor, Accel.
Range defined for m12, m23
Maki-Nakagawa-Sakata-Pontecorvo matrix
??
Solar + KamLAND fit results
m2 7.94 0.260.42 10 5 eV2
degrees4.13.112 8.33
)05(88 873.0 OPBSBBB
Impact on models for neutino properties
(Smirnov summary at Neutrino 2008)
Tri-Bi-Maximal Mixing: 35.2 deg
Quark-Lepton Complementarity: 32.2 deg(12 + Cabbibo = 45 deg)
SNO Physics Program Solar Neutrinos (6 papers to date)
Electron Neutrino Flux Total Neutrino Flux Electron Neutrino Energy Spectrum Distortion Day/Night effects hep neutrinos hep-ex 0607010 Periodic variations: [Variations < 8% (1 dy to 10 yrs)] hep-ex/0507079
Atmospheric Neutrinos & Muons Downward going cosmic muon flux Atmospheric neutrinos: wide angular dependence [Look above horizon]
Supernova Watch (SNEWS) Limit for Solar Electron Antineutrinos
hep-ex/0407029
Nucleon decay (“Invisible” Modes: N ) Phys.Rev.Lett. 92 (2004) [Improves limit by 1000]
Supernova Relic Electron Neutrinos hep-ex 0607010
For an event at the
Center of the Galaxy
SNO would observe
~1000 events evenly
Distributed among
Electron, mu, tau
Neutrinos,
SuperK about 5000
events, mostly anti-e
Supernova Early WarningSystem: SNEWSA central computer wheresignals are sent byexperiments to look fora coincidence and alertthe astronomicalcommunity.
X