Transcript Document 7168079

Results and Future
Challenges of the
Sudbury Neutrino
Observatory
Neil McCauley
University of Pennsylvania
WIN 2005 : Delphi, Greece.
7th June 2005
Overview
The Sudbury Neutrino Observatory.
 Results from the Salt Phase.
 Future Challenges:

Phase 3: 3He Counters.
 Reducing the energy threshold in
SNO.


Conclusions.
The SNO Collaboration
C.W. Nally, S.M. Oser, T. Tsui, C.E. Waltham, J.Wendland
University of British Columbia
J. Boger, R.L. Hahn, R. Lange, M. Yeh
Brookhaven National Laboratory
A.Bellerive, X. Dai, F. Dalnoki-Veress, R.S. Dosanjh,
D.R. Grant, C.K. Hargrove, L. Heelan, R.J. Hemingway,
I. Levine, C. Mifflin, E. Rollin, O. Simard, D. Sinclair,
N. Starinsky, G. Tesic, D. Waller
Carleton University
M. Bergevin,P. Jagam, H. Labranche, J. Law, I.T. Lawson,
B.G. Nickel, R.W. Ollerhead, J.J. Simpson
University of Guelph
B. Aharmim J. Farine, F. Fleurot, E.D. Hallman, A. Krüger,
S. Luoma, M.H. Schwendener, R. Tafirout, C.J. Virtue
Laurentian University
Y.D. Chan, X. Chen, C. Currat, K.M. Heeger, K.T. Lesko,
A.D. Marino, E.B. Norman, C.E. Okada, A.W.P. Poon,
S.S.E. Rosendahl, R.G. Stokstad
Lawrence Berkeley National Laboratory
M.G. Boulay, S.R. Elliott, J. Heise, A. Hime,
R.G. Van de Water, J.M. Wouters
Los Alamos National Laboratory
T. Kutter
Louisiana State University
S.D. Biller, M.G. Bowler, B.T. Cleveland, G. Doucas, J.A. Dunmore, H. Fergani,
K. Frame, N.A. Jelley, J.C. Loach, S. Majerus, G. McGregor, S.J.M. Peeters,
C.J. Sims, M. Thorman, H. Wan Chan Tseung, N. West, J.R. Wilson, K. Zuber
Oxford University
E.W. Beier, H. Deng, M. Dunford, W. Frati, W.J. Heintzelman, C.C.M. Kyba,
N. McCauley, M.S Neubauer, V.L. Rusu, R. Van Berg, P. Wittich
University of Pennsylvania
S.N. Ahmed, M. Chen, F.A. Duncan, E.D. Earle, H.C. Evans,
G.T. Ewan, B. G Fulsom, K. Graham, A.L. Hallin, W.B. Handler,
P.J. Harvey, C. Howard, L.L Kormos, M.S. Kos, C. Kraus, C.B. Krauss,
A.V. Krumins, J.R. Leslie, R. MacLellan, H.B. Mak, J. Maneira,
A.B. McDonald, B.A. Moffat, A.J. Noble, C. Ouellet, B.C. Robertson,
P. Skensved, M. Thomson, Y. Takeuchi, A. Wright
Queen’s University
D.L. Wark
Rutherford Appleton Laboratory
R.L. Helmer
TRIUMF
A.E. Anthony, J.C. Hall, M. Huang, J.R. Klein, S. Seibert
University of Texas at Austin
T.V. Bullard, G.A. Cox, P.J. Doe, C.A. Duba, J.A. Formaggio, N. Gagnon,
R. Hazama, M.A. Howe, S. McGee, K.K.S. Miknaitis, N.S. Oblath,
J.L. Orrell, K. Rielage, R.G.H. Robertson, M.W.E. Smith,
L.C. Stonehill, B.L. Wall, J.F. Wilkerson
University of Washington
The Sudbury Neutrino
Observatory
6800 ft level
INCO’s Creighton Mine
Sudbury, Ontario
1000 tonnes of D2O
12m diameter acrylic vessel
17m diameter PMT support
structure with ~9500 PMTs
7000 tonnes of H2O
Urylon liner and radon seal
Norite rock
2039m to
surface
Sensitivity to Neutrino Flavour:
Signals in SNO

Charged Current
 D+nep+p+e•

Neutral Current
 D+nxp+n+nx
•
•

Electron energy closely corresponds
to neutrino energy.
Equally sensitive to all active
neutrino flavors.
Threshold 2.2MeV.
Elastic Scattering
 e-+nxe-+nx
•
•
Good directional sensitivity.
Enhanced ne sensitivity.
FCC=Fe
FNC=Fe + Fmt
FES=Fe + 0.154Fmt
Neutron Detection:
The 3 Phases of SNO.

Phase 1: Pure D2O.


Nov 1999 – May 2001 : 306 days.
Neutrons Capture on D
• Detect 6.25MeV g-ray.

Phase 2: D2O+NaCl


Jul 2001-Sep 2003 : 391 days.
Neutrons Capture on 35Cl
• Detect multiple g-rays. SE=8.6MeV

Phase 3: 3He Proportional Counters (NCD)


Nov 2004-Dec 2006
Neutrons capture on 3He
• Captures are detected in the counters.
Increase in Capture Cross
Section.


Increase in visible
Cerenkov energy.



0.5mb→44b
More neutrons above
threshold.
Detection efficiency: 14.4%
→ 40.7%
Multiple g-rays in the final
state.


r/cm
Events/Day

Detection Eff /%
Why add
salt?
Events are more isotropic.
Can statistically separate
neutrons from electrons.
E/MeV
Measuring Isotropy

Use the angle between PMT
hits from the fit event vertex.

Decompose distribution in
spherical harmonics.
N
N
2
 bl 
Pl (cos ij )


N ( N  1) i 1 j i 1


Use b14 = b1 + 4b4

Note that b14 depends on
energy.
Contribution of b14
uncertainty is relatively large.

4% of CC,NC flux.
Low energy isotropy fit.
Radioactive
Backgrounds

Three low energy decay of
concern.
 208Tl



(Th chain)
214Bi (U chain / Rn)
24Na (Na activation)


Neutrons (Eg>2.2MeV)
Cherenkov Tail. Teff>5.5MeV
• New Calibration using Rn
spikes.

b14
Two sources of background.
Two monitoring techniques


Ex-situ: Radio Assays.
In-situ: Cherenkov light.
• Fit to isotropy distribution at
low energy.
Rn spike.
n/dayData:MC
comparison
238
0.04
U  0.28-0.07
232
Th  0.29  0.18 n/day
24
Na  0.064  0.016 n/day
1.0
D 2 O Tail  3.6 -0.9
events
H 2 O Tail  18.5 events (68%
CL)
Teff/MeV
Extraction of Neutrino Signals.
CC

Carry out a maximum
Likelihood fit of the data to
signal PDFs.

Energy.
Radius.
Direction.
Isotropy (salt only).
In salt isotropy allows us to
drop CC and ES energy
PDFs.


NC
E/MeV
4 Dimensional fit.
•
•
•
•

ES
Model Independent Flux
Extraction.
Extract the Spectrum.
(r/600cm)3
cos()
Isotropy
Fit Results



Isotropy
Full Salt Data Set: 391
Days.
Fit for CC,NC,ES and
External Neutrons.
nucl-ex/0502021
Radius
Direction
Neutrino Fluxes
0.08
6
2 1
F CC  1.6800..06
06 ( stat.) 0.09 ( sys.) 10 cm s

Fit Using:



Teff>5.5MeV
rfit<550cm
Dominant systematics





b14 Mean Value
Energy Scale
Radial Bias
Neutron Capture (NC)
Angular Resolution (ES)
22
15
F ES  2.3500..22
( stat.) 00..15
( sys.) 106 cm 2 s 1
0.38
6
2 1
F NC  4.9400..21
21 ( stat.) 0.34 ( sys.) 10 cm s
F BP04  5.82  1.34 106 cm 2 s 1
Flavour content of solar flux.
Electron Energy
Spectra

CC Spectrum and LMA
Fit to data was done without
CC/ES energy constraints.


Spectra Extracted from Fit.
Beware Correlations.
• Systematic CCiCCj
• Statistical CCiNCCCj
CC events
ES events
Can carry out many analyses.




Statistics Dominated Results.

ACC = -0.037±0.071
• ANC  0
• CC,ES Spectrum
Unconstrained

Teff/MeV
ANC 0
Extract asymmetry spectrum.


ANC floating
ANC floating
ANC  0
Include/Remove CC,ES spectral
constraints.
ACC

ACC
2 (F N  F D )
A
Day-Night Asymmetry
FN  FD
Best fit LMA shown.
Combine with D2O result.

Ae,combined= 0.037±0.040
• ANC  0
• CC/ES Spectrum Constrained
Teff/MeV
Interpretation of Results.

With SNO results



All Solar
Data
Add other solar data.


Large mixing angle
regions are selected.
Maximal mixing is
rejected.
LMA region is selected.
Add KamLAND data.
m122  6.542..43 105 eV 2
09
tan 2 12  0.4500..08
Solar +
KamLAND
Phase 3 : 3He Counters.

Timeline to phase 3

Salt Removal.
• Sept 2003.

PMT Electronics
Upgrade.
• Oct/Nov 2003.

Counter Deployment.
• Nov2003-May2004.

Commissioning.
• May – Nov 2004.

40 Strings on 1 m grid.
Total Active length 398m.
Phase 3 Production Data.
Taking Commences.
• Nov 2004.
3He
 n+3He

p+T
Background Free Region.
Measure Current vs Time
in the proportional
counters.
Expect capture efficiency:



Baseline Analysis:
~25% on 3He
~20% on D
Unique identification of
neutrons.



Substantially reduce
CCNC correlation.
Reduce uncertainty in
CC/NC
Reduce uncertainty in 12
Pulse Width / ms

Counters.
E/KeV
To carry out neutron
analysis, we need to
remove instrumental
backgrounds.

We are developing a suite
of cuts.
A neutron
Time/ns
Time/ns
A fork cut
Current /Arb Units

Current /Arb Units
Instrumental Backgrounds.
A fork event
Time/ns
PMT Data in Phase 3.

Presence of
proportional counters
blocks lights.

Adds effective
attenuation.
• Fewer hits per MeV
Compensate by:
Lower Trigger Threshold.
Lower Channel Thresholds.
Increased PMT High Voltage.

Breaks Spherical
Symmetry
More Complex Signal Extraction.

New Background
Sources.
More Complicated insitu
Background Analysis
• U/Th on the
counters.
New variables: Distance to
Nearest Counter.
Enhanced
Spectral Analysis

The current LMA paradigm
suggests that the ne
survival probability
increases sharply between
1-5MeV

Our current threshold is
Te>5.5MeV


Q value for CC reaction is
1.4MeV
SNO CC Effective
Threshold.
En/MeV
Lower our threshold to
look for the turn up.


Positively identify LMA.
Look for new physics.
• Non standard
interactions.
Miranda, Tortola, Valle: hep-ph/0406280
Enhanced Spectral Analysis



To lower the threshold
and improve spectral
determination we must
fight backgrounds.

Reduce Cherenkov tail:
• Select data with lower
background levels.
• Lower background levels in the
water.

Neutrons
• Background Neutrons
• NC events.
Reduce background in the signal
box
• Reduce energy resolution.
• Reduce energy systematics.
• Improve reconstruction.
Cherenkov Tail Events
• 208Tl,214Bi,24Na
• D2O and H2O tails.

Reduce total background.

Reduce covariance between
neutrons and electrons.




Isotropy.
3He Counters.
Multi-Phase fits.
Fit the background and signal
simultaneously.
Improved Energy Estimation
Model Local Variations.
Reduce Energy
Uncertainties.
16N
Use “Late” Light.
Increase Hit Statistics
(R/RAV)3
Reduce Energy Resolution.
Other Physics Topics

Solar Neutrino Topics



hep Neutrinos.
Periodicity
Muons

Atmospheric Neutrino Oscillations via Through-Going
Muons.
• Measure flux normalzation above the Horizion.


Muon Spallation.
Exotic Physics



Proton Decay
Neutron – AntiNeutron Oscillations.
Supernovae
Conclusions
SNO results show that neutrinos change
flavour.
 Along with other data the LMA neutrino
oscillation solution is selected.
 Phase 3 is underway.



Further reductions in the size of the LMA
region are expected.
SNO plans an enhanced spectral analysis
to look for positive signatures of LMA.