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.WendlandUniversity of British Columbia

J. Boger, R.L. Hahn, R. Lange, M. YehBrookhaven 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. StokstadLawrence Berkeley National Laboratory

M.G. Boulay, S.R. Elliott, J. Heise, A. Hime, R.G. Van de Water, J.M. WoutersLos Alamos National Laboratory

T. KutterLouisiana 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. ZuberOxford 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. WarkRutherford Appleton Laboratory

R.L. HelmerTRIUMF

A.E. Anthony, J.C. Hall, M. Huang, J.R. Klein, S. SeibertUniversity 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

2039m to surface

1000 tonnes of D2O

7000 tonnes of H2O

Norite rock

6800 ft level

INCO’s Creighton Mine

Sudbury, Ontario

12m diameter acrylic vessel

17m diameter PMT support structure with ~9500 PMTs

Urylon liner and radon seal

Sensitivity to Neutrino Flavour:Signals in SNO

Charged Current D+ep+p+e-

• Electron energy closely corresponds

to neutrino energy.

CC=e

Neutral Current D+xp+n+x

• Equally sensitive to all active

neutrino flavors.

• Threshold 2.2MeV.

NC=e +

Elastic Scattering e-+xe-+x

• Good directional sensitivity.

• Enhanced e sensitivity.

ES=e + 0.154

Neutron Detection: The 3 Phases of SNO.

Phase 1: Pure D2O. Nov 1999 – May 2001 : 306 days. Neutrons Capture on D

• Detect 6.25MeV -ray.

Phase 2: D2O+NaCl Jul 2001-Sep 2003 : 391 days. Neutrons Capture on 35Cl

• Detect multiple -rays. E=8.6MeV

Phase 3: 3He Proportional Counters (NCD) Nov 2004-Dec 2006 Neutrons capture on 3He

• Captures are detected in the counters.

Why add salt?

Increase in Capture Cross Section. 0.5mb→44b

Increase in visible Cerenkov energy. More neutrons above

threshold. Detection efficiency: 14.4%

→ 40.7% Multiple g-rays in the final

state. Events are more isotropic. Can statistically separate

neutrons from electrons.

E/MeV

Events

/Day

Dete

ctio

n E

ff /

%

r/cm

Measuring Isotropy

Use the angle between PMT hits from the fit event vertex. Decompose distribution in

spherical harmonics.

Use 14 = 1 + 44

Note that 14 depends on energy.

Contribution of 14 uncertainty is relatively large. 4% of CC,NC flux.

)(cos)1(

2

1 1ij

N

i

N

ijll P

NN

Radioactive Backgrounds

Three low energy decay of concern. 208Tl (Th chain) 214Bi (U chain / Rn) 24Na (Na activation)

Two sources of background. Neutrons (E>2.2MeV) Cherenkov Tail. Teff>5.5MeV

• New Calibration using Rn spikes.

Two monitoring techniques Ex-situ: Radio Assays. In-situ: Cherenkov light.

• Fit to isotropy distribution at low energy.

Low energy isotropy fit.

14

Teff/MeV

Rn spike. Data:MC comparison

CL) (68% events 18.5 Tail OH

events 3.6 Tail OD

n/day 0.0160.064 Na

n/day 0.180.29 Th

n/day 0.28 U

2

1.00.9-2

24

232

04.00.07-

238

Extraction of Neutrino Signals.

ES NCCC

E/MeV

(r/600cm)3

cos()

Isotropy

Carry out a maximum Likelihood fit of the data to signal PDFs. 4 Dimensional fit.

• Energy. • Radius.• Direction.• Isotropy (salt only).

In salt isotropy allows us to drop CC and ES energy PDFs. Model Independent Flux

Extraction. Extract the Spectrum.

Fit Results

Full Salt Data Set: 391 Days.

Fit for CC,NC,ES and External Neutrons.

nucl-ex/0502021

Isotropy

Radius Direction

Neutrino Fluxes

Fit Using: Teff>5.5MeV

rfit<550cm

Dominant systematics 14 Mean Value Energy Scale Radial Bias Neutron Capture (NC) Angular Resolution (ES)

Flavour content of solar flux.

12604

12638.034.0

21.021.0

1034.182.5

10.)(.)(94.4

scm

scmsysstat

BP

NC

12615.015.0

22.022.0

12608.009.0

06.006.0

10.)(.)(35.2

10.)(.)(68.1

scmsysstat

scmsysstat

ES

CC

ES events

Electron Energy Spectra

Fit to data was done without CC/ES energy constraints. Spectra Extracted from Fit. Beware Correlations.

• Systematic CCiCCj

• Statistical CCiNCCCj

CC events

CC Spectrum and LMA

Day-Night AsymmetryDN

DNA

)( 2

ANC floating

ANC 0

Teff/MeV

Teff/MeV

AC

CA

CC

Can carry out many analyses. ANC floating ANC 0 Include/Remove CC,ES spectral

constraints. Statistics Dominated Results.

ACC = -0.037±0.071• ANC 0• CC,ES Spectrum

Unconstrained Extract asymmetry spectrum.

Best fit LMA shown. Combine with D2O result.

Ae,combined= 0.037±0.040 • ANC 0• CC/ES Spectrum Constrained

Interpretation of Results. With SNO results

Large mixing angle regions are selected.

Maximal mixing is rejected.

Add other solar data. LMA region is selected.

Add KamLAND data.

09.008.012

2

254.43.2

212

45.0tan

105.6

eVm

All Solar Data

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. Phase 3 Production Data.

Taking Commences. • Nov 2004.

40 Strings on 1 m grid.Total Active length 398m.

3He Counters.

n+3He p+T Measure Current vs Time

in the proportional counters.

Expect capture efficiency: ~25% on 3He ~20% on D

Unique identification of neutrons. Substantially reduce

CCNC correlation. Reduce uncertainty in

CC/NC Reduce uncertainty in 12

Baseline Analysis:

Background Free Region.

E/KeV

Pul

se W

idth

/

s

Instrumental Backgrounds.

A fork cut

To carry out neutron analysis, we need to remove instrumental backgrounds. We are developing a suite

of cuts. Time/ns

A fork event

Time/ns

Cur

rent

/A

rb U

nits

A neutronCur

rent

/A

rb U

nits

Time/ns

PMT Data in Phase 3.

Presence of proportional counters blocks lights. Adds effective

attenuation.• Fewer hits per MeV

Breaks Spherical Symmetry

New Background Sources.

• U/Th on the counters.

Compensate by:

Lower Trigger Threshold.

Lower Channel Thresholds.

Increased PMT High Voltage.

More Complex Signal Extraction.

More Complicated insitu Background Analysis

New variables: Distance to Nearest Counter.

Enhanced Spectral Analysis

The current LMA paradigm suggests that the e survival probability increases sharply between 1-5MeV

Our current threshold is Te>5.5MeV Q value for CC reaction is

1.4MeV

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

E/MeV

SNO CC Effective Threshold.

Enhanced Spectral Analysis To lower the threshold

and improve spectral determination we must fight backgrounds. Cherenkov Tail Events

• 208Tl,214Bi,24Na

• D2O and H2O tails.

Neutrons• Background Neutrons• NC events.

Reduce Cherenkov tail: Reduce total background.

• Select data with lower background levels.

• Lower background levels in the water.

Reduce background in the signal box

• Reduce energy resolution.• Reduce energy systematics.• Improve reconstruction.

Reduce covariance between neutrons and electrons. Isotropy. 3He Counters. Multi-Phase fits. Fit the background and signal

simultaneously.

Improved Energy Estimation

Use “Late” Light.

Increase Hit Statistics

Reduce Energy Resolution.

Model Local Variations.

Reduce Energy Uncertainties.

(R/RAV)3

16N

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.