# Presentation: 869867

## SNO II:Salt Strikes Back

- SNO II:Salt Strikes Back

- Joseph A. Formaggio
- University of Washington
- NuFACT’03

- Update from the Sudbury Neutrino Observatory

## Beyond a Reasonable Doubt...

- Our understanding of neutrinos has changed in light of new evidence:
- Neutrinos no longer massless particles (though mass is very small)
- Experimental evidence from three different phenomena:
- Solar
- Atmospheric
- Accelerator
- Reactor
- Data supports the interpretation that neutrinos *oscillate*.

- Murayama

## Solar Neutrino Experiments

## The SNO Experiment

- The SNO Experiment

## Mapping the Sun with ’s

- Mapping the Sun with ’s

- Neutrinos from the sun allow a direct window into the nuclear solar processes.
- Each process has unique energy spectrum
- Only electron neutrinos are produced
- SNO sensitive to 8B neutrinos

## The SNO Collaboration

**The SNO Collaboration**

- G. Milton, B. Sur
**Atomic Energy of Canada Ltd., Chalk River Laboratories**
- S. Gil, J. Heise, R.J. Komar, T. Kutter, C.W. Nally, H.S. Ng,
- Y.I. Tserkovnyak, C.E. Waltham
**University of British Columbia**
- J. Boger, R.L Hahn, J.K. Rowley, M. Yeh
**Brookhaven National Laboratory**
- R.C. Allen, G. Bühler, H.H. Chen*
**University of California, Irvine**
- I. Blevis, F. Dalnoki-Veress, D.R. Grant, C.K. Hargrove,
- I. Levine, K. McFarlane, C. Mifflin, V.M. Novikov, M. O'Neill,
- M. Shatkay, D. Sinclair, N. Starinsky
**Carleton University**
- T.C. Andersen, P. Jagam, J. Law, I.T. Lawson, R.W. Ollerhead,
- J.J. Simpson, N. Tagg, J.-X. Wang
**University of Guelph**
- J. Bigu, J.H.M. Cowan, J. Farine, E.D. Hallman, R.U. Haq,
- J. Hewett, J.G. Hykawy, G. Jonkmans, S. Luoma, A. Roberge,
- E. Saettler, M.H. Schwendener, H. Seifert, R. Tafirout,
- C.J. Virtue
**Laurentian University**
- Y.D. Chan, X. Chen, M.C.P. Isaac, K.T. Lesko, A.D. Marino,
- E.B. Norman, C.E. Okada, A.W.P. Poon, S.S.E Rosendahl,
- A. Schülke, A.R. Smith, R.G. Stokstad
**Lawrence Berkeley National Laboratory**
- M.G. Boulay, T.J. Bowles, S.J. Brice, M.R. Dragowsky,
- M.M. Fowler, A.S. Hamer*, A. Hime, G.G. Miller,
- R.G. Van de Water, J.B. Wilhelmy, J.M. Wouters
**Los Alamos National Laboratory**

- J.D. Anglin, M. Bercovitch, W.F. Davidson, R.S. Storey*
**National Research Council of Canada**
- J.C. Barton, S. Biller, R.A. Black, R.J. Boardman, M.G. Bowler,
- J. Cameron, B.T. Cleveland, X. Dai, G. Doucas, J.A. Dunmore,
- H. Fergani, A.P. Ferrarris, K. Frame, N. Gagnon, H. Heron, N.A. Jelley, A.B. Knox, M. Lay, W. Locke, J. Lyon, S. Majerus, G. McGregor,
- M. Moorhead, M. Omori, C.J. Sims, N.W. Tanner, R.K. Taplin,
- M.Thorman, P.M. Thornewell, P.T. Trent, N. West, J.R. Wilson
**University of Oxford**
- E.W. Beier, D.F. Cowen, M. Dunford, E.D. Frank, W. Frati,
- W.J. Heintzelman, P.T. Keener, J.R. Klein, C.C.M. Kyba, N. McCauley, D.S. McDonald, M.S. Neubauer, F.M. Newcomer, S.M. Oser, V.L Rusu,
- S. Spreitzer, R. Van Berg, P. Wittich
**University of Pennsylvania**
- R. Kouzes
**Princeton University**
- E. Bonvin, M. Chen, E.T.H. Clifford, F.A. Duncan, E.D. Earle,
- H.C. Evans, G.T. Ewan, R.J. Ford, K. Graham, A.L. Hallin,
- W.B. Handler, P.J. Harvey, J.D. Hepburn, C. Jillings, H.W. Lee,
- J.R. Leslie, H.B. Mak, J. Maneira, A.B. McDonald, B.A. Moffat,
- T.J. Radcliffe, B.C. Robertson, P. Skensved
**Queen’s University**
- D.L. Wark
**Rutherford Appleton Laboratory, University of Sussex**
- R.L. Helmer, A.J. Noble
**TRIUMF**
- Q.R. Ahmad, M.C. Browne, T.V. Bullard, G.A. Cox, P.J. Doe,
- C.A. Duba, S.R. Elliott, J.A. Formaggio, J.V. Germani,
- A.A. Hamian, R. Hazama, K.M. Heeger, K. Kazkaz, J. Manor,
- R. Meijer Drees, J.L. Orrell, R.G.H. Robertson, K.K. Schaffer,
- M.W.E. Smith, T.D. Steiger, L.C. Stonehill, J.F. Wilkerson
**University of Washington**

## Somewhere in the Depths of Canada...

## 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

- 1000 Tonnes D2O

- Acrylic Vessel, 12 m diameter

- 1700 Tonnes  H2O, Inner Shield

- 5300 Tonnes H2O, Outer Shield

- Urylon Liner and Radon Seal

## Unique Signatures

**Charged-Current (CC)**
- e+d  e-+p+p
- Ethresh = 1.4 MeV
- e only

**Elastic Scattering (ES)**
- x+e-  x+e-
- x, but enhanced for e

**Neutral-Current (NC)**
- x+d  x+n+p
- Ethresh = 2.2 MeV
- x

## Results from Pure D2O

- Results from Pure D2O

- Measurement of 8B flux from the sun.
- Final flux numbers:

- NCSNO*= 5.09

- 8BSSM*= 5.05

- +1.01
- - 0.81

- +0.44 +0.46
- - 0.43 -0.43

- * in units of 106 cm-2 s-1

## SNO Phase II - Salt

**Enhanced NC sensitivity**
- n~55% above threshold
- n+35Cl  36Cl+ ∑
**Systematic check of energy scale**
- E ∑ = 8.6 MeV
- NC and CC separation by event isotropy

**NC sensitivity**
- n~14.2% above threshold
- n+2H  3H+ 
**Energy near threshold**
- E  = 6.25 MeV
- NC and CC separation by energy, radial, and directional distributions

**D****2****O**

**Salt**

## Advantages of Salt

- Neutrons capturing on 35Cl provide much higher neutron energy above threshold.
- Gamma cascade changes the angular profile.
- Higher capture efficiency

- Same Measurement, Different Systematics

***n***

***36******Cl**********

***35******Cl***

***36******Cl***

******

## Steps to a Signal

**	****Calibrations**
- Optics
- Energy
- Neutron Capture
**	****Backgrounds**
- Internal photo-disintegration
- PMT -
- External neutrons and other sources
**	****Signal Extraction**
- Charged current (CC)
- Neutral Current (NC)
- Elastic Scattering (ES)

## Sources of Calibration

- Use detailed Monte Carlo to simulate events
- Check simulation with large number of calibrations:

## Optical Calibration

- The PMT angular response and attenuation lengths of the media are measured directly using laser+diffuser *(“laserball”).*
- Attenuation for D2O and H2O, as well as PMT angular response, also measured in-situ using radial scans of the laserball.
- Exhibit a change as a function of time after salt was added to the detector.

## 16N Calibration Source

- Energy response of the detector determined from 16N decay.
- Mono-energetic  at 6.13 MeV, accompanied by tagged  decay.
- Provides check on the optical properties of the detector.
- Radial, temporal, and rate dependencies well modeled by Monte Carlo.

## Energy Response

- In addition to 16N, additional calibration sources are employed to understand energy response of the detector.
- Muon followers
- 252Cf
- 8Li
- 24Na
- Systematics dominated by source uncertainties, optical models, and radial/asymmetry distributions

- Energy Scale = _+_ 1.1%*

- Energy Resolution = _+_ 3.5%*

- *Preliminary

## Neutron Response

- Use neutron calibration sources (252Cf and AmBe) to determine capture profile for neutrons.
- 252Cf decays by  emission or spontaneous fission.
- Observe resulting   cascade from neutron capture on 35Cl.
- Monte Carlo agrees well with observed distributions.

- Neutrons/fission = 3.7676 _+_ 0.0047

## Neutron Efficiency

**Neutron Efficiency**

**Salt Preliminary**

- Capture efficiency increase by 4-fold in comparison to pure D2O phase.
- Systematics include:
- source position
- energy response
- source strength
- modeling
- Less than 3% total systematic uncertainty on capture.

## Backgrounds

**	****Calibrations**
- Optics
- Energy
- Neutron Capture
**	****Backgrounds**
- Internal photo-disintegration
- PMT -
- External backgrounds and other sources
**	****Signal Extraction**
- Charged current (CC)
- Neutral Current (NC)
- Elastic Scattering (ES)

## An Ultraclean Environment

- Highly sensitive to any  above neutral current (2.2 MeV) threshold.
- Sensitive to 238U and 232Th decay chains

*“**I will show you fear in a handful of dust.”*
*-- T.S. Eliot*

## U / Th and Other Backgrounds

- Other Backgrounds
- Fission from possible U and Cf contamination
- Atmospheric neutrinos
- 24Na from the vessel
- 13C(,n) 16O from acrylic
-   activation from radon embedded on the surface of the acrylic vessel.
- Measured from neutron radial profile and internal e+e- high-energy gamma conversion from 16O.
- Salt provides unique window of sensitivity to external neutrons.

- Uranium and Thorium
- Two methods:
**In-situ:**
**Low Energy Data**
**Separate ****208****Tl and ****214****Bi based on event isotropy**
**Ex-situ:**
**Ion exchange (****224****Ra, ****226****Ra)**
**Membrane degassing**
**Count daughter product decays**
- Preliminary salt measurements yield background levels at par with what was measured in D2O

## Steps to a Signal

**	****Calibrations**
- Optics
- Energy
- Neutron Capture
**	****Backgrounds**
- Internal photo-disintegration
- PMT -
- External Neutrons and other backgrounds
**	****Signal Extraction**
- Charged current (CC)
- Neutral Current (NC)
- Elastic Scattering (ES)

## Changes in Signal Extraction

- Based on data taken from May 27, 2001 to October 10, 2002.
- Total 254 live days of neutrino data.
- Previous analysis used energy, radial, and solar angle distribution to separate events.

- Introduction of salt moves neutron energy higher (but disrupts radial separation).
- New statistical separation using event isotropy, allowing both energy dependent and independent analyses.

## Fit Result Uncertainties (Monte-Carlo)

- D2O results

- Simulated
- Salt Phase
- Results

- Published D2O energy-unconstrained statistical error was 24%

- Simulations assume 1 yr of data with central values  and
- cuts from D2O phase results

## What’s Inside Pandora’s Box?

## Day – Night

- Contours (%)

- Probability
- Contours

**De Holanda,**
**Smirnov**
**hep-ph/0212270**

## Coming Soon...SNO III:Return of the Neutron

- Coming Soon...SNO III:Return of the Neutron

## SNO Phase IIIThe Neutral Current Detectors

**Physics Motivation**
**Event-by-event separation**. Measure NC and CC in separate data streams.
**Different systematic uncertainties**
- than neutron capture on NaCl.
**NCD array as a neutron absorber**.

**Array of ****3****He counters**
- 	40 Strings on 1-m grid
- 	398 m total active length

**NCD**

**PMT**

## Counters

- Ultraclean nickel counters of varying length, connected as “string”.
- Mixture of 3He (85%) and CF4 (15%).
- Anchored to the bottom of the acrylic vessel.
- Radioassayed and polished to reduce U and Th backgrounds.

## The Remotely Operated Vehicle

- A remote controlled submarine will be used to deploy the NCDs in the acrylic vessel.
- The bottom end of the NCD string will be pulled to the floor of the acrylic vessel directly below the neck with a pulley.
- The ROV will then move the bottom end of the string along the floor of the acrylic vessel to its anchor point and anchor it.

## Future Solar Physics

- Salt Phase:
- More precise measurements of CC/NC ratio, due to increased sensitivity to neutrons.
- Ability to extract solar flux with and without assumptions regarding the energy spectrum.
- Final systematics and backgrounds currently being evaluated.

- NCD Phase:
- Event-by-event separation of charged current and neutral current events.
- Model-independent extraction of charged current and neutral current flux.
- Begin deployment of counters in October.

## ROV Training

## Slide 34

## Using Angular Information

- Use semi energy-independent variable 14 to separate neutrons from electrons via angular distributions.
- Allows one to reconstruct the energy profile of NC and CC events w/o use of energy constraint.
- Powerful check on the spectral shape of 8B

- Monte Carlo

- Monte Carlo

## SNO during Construction

## Masses and Mixings

- Pee ~ 1-sin**2**(2) sin2(1.27m2 L / E)
- Physics:
- m2 & sin2(2)
- Experiment:
- Distance (L) & Energy (E)

- 

- 

- 

- e

- e

- e

- 

## Three Pieces

- For a full understanding of neutrino properties, it is necessary to determine:
- The mixing parameters and phases
- The neutrino masses
- The physics governing mass

## Signal Extraction

## Summary of Backgrounds

## Status

- All the NCDs are underground.
- The 156 NCDs that will be deployed have been identified.
- Pre-deployment welding is in progress.
- The DAQ is operational and has been taking data from complete unwelded strings of NCDs underground.
- All of the electronics are underground and operational.
- The current estimated deployment date is October 2003, subject to removal of salt.

**Notes:**
Here is a brief summary of the current status of the NCD deployment preparations.  
All the NCDs are underground in the SNO lab.
The 156 NCDs that will be deployed have been identified.  
Pre-deployment welding is in progress.
The DAQ is operational and has been taking data from complete strings of NCDs underground.
All of the electronics are underground and operational.
The current estimated deployment date is May 2003, subject to removal of salt.

## What is changing?  Why?

- Combination of both attenuation length and reflectors changing over time.
- Change in optics accounts for why there was a large drop in energy response.
- Attenuation length change correlated with change in water chemistry
- Reflectors consistent with both a sudden drop in response, as well as a gradual decay.
- Possible causes:  petal degradation, temperature change

## Radon Spike

- Further aim at understanding backgrounds to lower energy threshold.
- Required to understand the detector uniformity and low energy tails.
- Injection of 50 ml of solution at 25 grid points in vessel
-  2.2 million Rn atoms/liter

## 16N Calibration Source

- 16N Calibration Source

- Energy response of the detector determined from 16N decay.
- Mono-energetic  at 6.13 MeV, accompanied by tagged  decay.
- Provides check on the optical properties of the detector.
- Radial, temporal, and rate dependencies well modeled by Monte Carlo.