Solar Neutrino Results from SNO

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Solar Neutrino Results from SNO

• Kevin Graham
• Carleton University

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Ray Davis and John Bahcall
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Solar Neutrino Measurements

• understanding how the sun works
• - solar neutrino problem
• - solar neutrino flux measurements
• - temporal/consistency evaluations
• neutrino physics
• - flavour change/oscillation
• - MNSP parameters
• - new physics?

2n oscillation probability (modified by MSW for
solar)
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Solar Neutrino Spectra
8B Standard Solar Model (5.69 0.91)x106 cm2 s-1
18.77 MeV
hep SSM (7.97 1.24)x103 cm2 s-1
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The SNO Detector
9438 Inward- Looking PMTs
2039 m to surface
91 Outward Looking PMTs (Veto)
12 m diameter Acrylic vessel
Norite Rock
PMT Support Structure (PSUP)
5300 tonnes light water
1000 tonnes heavy water
1700 tonnes light water
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What We Measure
Cherenkov Light cosq 1/(index of refraction)
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PMT Measurements

• position
• charge
• time

Reconstructed Event
-event vertex -event direction -energy -isotropy
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Neutrino Reactions in SNO


?

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

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

?

e-
n
e-
n
ES
x
x

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

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SNO Data Taking Phases
Phase II (salty D2O) 391 live days
Te gt 5.5 MeV R lt 550 cm 4722 events
n capture on Cl Multiple gs 8.6 MeV High
CC-NC corr. Te unconstrained
Phase III (3He n counters) n capture on
3He n 3He g p t Channels indep. gno
correlation Reduced NC systematics
Phase I (pure D2O) 306.4 live days Te gt 5
MeV R lt 550 cm 2928 events n capture on D Single
6.25 MeV g High CC-NC corr. Te constrained
counters in and collecting data
Initial Results
Recent Results
Now Running
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Signal Extraction

• maximum likelihood fit of model PDFs to data
• event variables R (radial position) b14(isotropy)
  cosqsun and E(energy)

ES separation
dont use E g energy-unconstrained g fit out CC
spectrum!
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Results from Complete Phase II
4722 candidate events 391 live days
a
Flux Results
CC Energy Spectrum
Neutrino Flavour Change!
no significant sterile or NSI effects
Day/Night Asymmetry
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Global analysis of solar and reactor data
LMA I only allowed region Maximal mixing
rejected at 5 s
Solar KamLAND
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SNO Periodicity Analysis
search for sinusoidal periodicity in Phase I and
Phase II data used both a Lomb-Scargle
periodogram and an unbinned maximum likelihood
fit. (see PRD 72 2005, 052010) event arrival
times are fit to ????(t) N 1 A
cos(2pftd) largest peak in combined data set
occurs at a period of 2.4 days, with a
significance statistic of S8.8 Monte Carlo
shows that 35 of simulated data sets give a peak
at least this large.
No evidence for modulation in any of SNO's data.
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Preliminary Phase I hep and Diffuse Supernova
Neutrino Background
Observed 2 events Expected 3.13 0.60
background 0.99 0.09 signal
look in high energy windows for hep and DSNB
signals


8B
atm
hep
DSNB
DSNB for 22.9 lt En/MeV lt 36.9 flux limit lt70
cm-2s-1 (90CL) predicted flux 0.2?1.5 cm-2s-1
?hep lt 2.3 x 104 cm-2 s-1 (90 C.L.)
lt2.9 SSM
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NCD Phase Data
3He n ? p 3H 0.76 MeV

• event-by-event separation (pulse shape)
• different systematic uncertainties
• precision NC measurement

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Next adding Pulse Shape Discrimination
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Summary

• So far
• 8B neutrino results from first two phases
• including fluxes, spectrum, D/N asymmetry
• search for periodicity in data
• hep and diffuse SN neutrino results
• What is next
• first results from NCD phase
• muon and atmospheric analysis
• combined phase I and II results with lower energy
  threshold
• supernova watch
• other results to come!

• flavour change
• MSW effect
• q12 and Dm2
• solar physics

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Solar Neutrinos

• 8B only tiny fraction of solar neutrinos
• chlorine and gallium experiments
• integrate over different chains
• no real low energy spectrum

• 7Be interesting but large
• model uncertainty
• pep has small uncertainty
• and at right energy
• can provide most physics

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Neutrino Mixing
for two neutrino mixing
flavour eigenstates different from mass
eigenstates (like quark CKM)
2n oscillation probability ltYnmYnegt
Experimental Parameters L distance to
experiment E neutrino energy Physics
Parameters Dm2m12-m22 sin22q
appearance/disappearance
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3 Neutrinos Matter Effect
3 neutrinos (at least) a4 model parameters
matter enhancement modifies oscillation amplitude
(MSW effect)
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Vacuum vs Matter Enhanced Survival Probability
start with ne in sun
transition region
matter enhanced oscillation
vacuum oscillation
ne
solar pp pep 8B
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What do 8B n Measurements Tell Us?
Fluxes - CC/NC ratio
Day/Night - asymmetry
CC Energy Spectrum -shape distortion
Increasing ?m2 Decreasing q
No. of CC events
hep-ph/0406328 July 21 2004 Bandyopadhyay,
Choubey, Goswami, Petcov, and Roy
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Flux Results from Complete Phase II
4722 candidate events 391 live days
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energy-unconstrained results
Unconstrained Fit Key Systematics
CC NC
Neutrino Flavour Change!
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Measured Total Flux and SSM Predictions
8B Flux
experimental uncertainty smaller than
theoretical for this sector of solar neutrinos
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Day-Night Asymmetries
ACC -0.056 0.074 (stat.) 0.051 (syst.) ANC
0.042 0.086(stat.) 0.067 (syst.) AES 0.146
0.198(stat.) 0.032 (syst.)
Constraining ANC to be zero
ACC -0.037 0.063(stat.) 0.032(sys.) AES
0.153 0.198(stat.) 0.030(sys.)
Combined Pure D2O and Salt
No evidence for asymmetries from matter effects
in the earth
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2-n oscillation region defined by SNO
Allowed regions
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Muon and atmospheric neutrino analysis