# Presentation: 582280

## The Sudbury Neutrino Observatory Determination of Solar Neutrino Mixing Parameters with (very slightly) Salty Water

- The Sudbury Neutrino Observatory Determination of Solar Neutrino Mixing Parameters with (very slightly) Salty Water

- Kevin Lesko
- Institute for Nuclear & Particle Astrophysics
- Berkeley Lab
- Sacramento State, 22 April 2004

## Sudbury Neutrino Observatory

- Neutrinos, the Solar Neutrino Problem & SNO
- Why add Salt?
- First Experimental Results with Salt *(from discovery to precision measurements)*
- Global Analyses & Neutrinos
- Where do we go from here?

## Why go into neutrino physics?

- Experiments are easy
- Results are quick and analyses straightforward
- Clean and modern labs
- Great working hours
- Work close to home

## What we know about neutrinos...

- 1899  Rutherford classified radiation into 3 types: , , and . The Curie’s show that s are electrons.
- 1914  J. Chadwick shows that the s emitted in radioactive decays do not have a fixed energy.  This seems to contradict energy conservation.
- 1930  Pauli first proposes the existence of light (<0.01mp), neutral, spin-1/2, fermions to explain missing energy.  Calls them “neutrons”.
- 1932  Chadwick discovers the neutron, but it is much too heavy to explain the missing energy in beta-decay.
- 1933-34 Fermi develops theory of -decay & coins the name “neutrino”.
- 1956  Lee and Yang develop theory of parity violation to explain tau-theta puzzle.  They introduce a two-component theory where neutrinos have only one handedness.  This theory requires that they are **massless** and travel at the speed of light.

## What we know about neutrinos...

- 1956 Neutrinos are finally observed by Reines and Cowan. (Cowan *et al*. Science, 1956, **124**, 103-104, Reines and Cowan, Phys. Rev., **113**, No. 1., 1959)
-  “Detection of the **Free**** ****Neutrino**:
-      A Confirmation”
- 1957  Experiment performed by C.S. Wu observes maximal parity violation in
- 1957 Goldhaber group determined that neutrinos are left-handed. (Goldhaber,Grodzins, and Sunyar, Phys. Rev., 109, No. 5, 1957)
- 1962   is *observed* in pion decay

## What we know about neutrinos...

- 1989 At LEP and SLD, the Z boson decay suggests there are 3 flavors of light neutrinos coupling to the Z.
- 1995 Reines Nobel Prize Detection of the Neutrino
- 2000 *Observation* of  in DONUT experiment at Fermilab.
- 2001 SNO/Super-K CC/ES result
- 2002 SNO NC Results

- 2002 Davis & Koshiba Nobel Prize
- for pioneering contributions to astrophysics, for the detection of cosmic s
- 2003 Davis and Bahcall Enrico Fermi Award (DOE) & A. Suzuki Nishina Prize for neutrino studies
- 2003 SNO Salt Results, KamLAND’s 1st Reactor Results

## The Solar Neutrino Problem -  source

- “...to see into the interior of a star and thus verify directly the hypothesis of nuclear energy generation in stars.”
- 	Phys. Rev. Lett. 12, 300 (1964) Phys. Rev. Lett. 12, 303 (1964)
*	**Bahcall and Davis*

- 4p      4He + 2e + 2e+ + ~25 MeV

## Solar Neutrino Experiments (pre-SNO)

**Homestake**
- (S Dakota, USA)

**Super-Kamiokande**
- (Japan)

**SAGE** (Baksan, Russia)

**GALLEX** (Gran Sasso, Italy)

- Only e directly observed

## The Solar Neutrino Problem

- Subsequent 35 years have seen 5 experiments,  all measure a deficiency of solar neutrinos

- Either
- Solar Models are Incomplete or Incorrect
- Or
- Neutrinos Undergo Flavor Changing Oscillations => New Physics!

## Two-Flavor Neutrino Oscillations

- Probability of being in flavor state is governed by two parameters,  and  m2

## Matter Enhanced Oscillations

- If neutrinos travel through matter, the MSW effect can also contribute to oscillations. The probability of oscillation for electron neutrinos only is enhanced in matter by an additional phase.
- Effect arises due to the fact that only electron neutrinos can interact with electrons in matter through charged-current.
- Effect is similar to coherent regeneration of K-mesons in matter and to birefringent crystals, where index of refraction is different for the different linear polarizations.
- Does not introduce any additional free parameters

## Standard Model

- And Neutrinos

- The quark mass eigenstates are a mix of current (flavor) eigenstates

- The Measured CKM Matrix

- Standard Model Neutrinos are not mixed

- Start with the Standard
- Model - Quarks and Leptons

- No R! thus no massive neutrinos

## The Sudbury Neutrino Observatory

**Large**
**Deep**
**Clean**
**Sensitive**

## Slide 14

## How does SNO work?

- Electromagnetic Shock Wave:
- Cherenkov - radiation

## A Candidate Neutrino Event

- e-

- 42o cone

## Neutrino Interactions in SNO

**Charged Current (CC):**
-     e+dp+p+e-
- Electron neutrinos only
**Elastic Scattering (ES):**
-     x+ e-  x +e-
- Direction strongly correlated to neutrino direction
- 0.154(e)=()=()
**Neutral Current (NC):**
-     x+dp+n+x
- Same for all neutrino flavors

## Detecting NC Interactions

- If NC > CC, then neutrinos are *oscillating*
**First Phase (Pure D****2****O)**** **- Ended May 2001
- Neutrons walk ~1-2 meters before capturing on 2H, producing a single 6.25 MeV Gamma
- If they reach edge of D2O and capture on 1H, a 2.2 MeV gamma is produced
**Second Phase (D****2****O+NaCl)**** **- Ended Sept 2003
- 2 tonnes NaCl added into heavy water
- Neutrons typically capture on 35Cl, producing cascade of ~2-3 gammas with an energy of 8.6 MeV
- Boosts capture cross section and energy
**Third Phase (****3****He Proportional Counters, NCDs)**
- Installation underway November 2003 (just completed 21 April!)
- ~ 2 calendar years of data, at least

- 3H

- 2H+n

- 6.3 MeV

-  = 0.5 mb

- 36Cl

- 35Cl+n

- 8.6 MeV

-  = 44 b

## Results from Pure D2O Phase

-  Fluxes measured **assuming the ****8****B energy spectral shape**, in units of 106 neutrinos cm-2 sec-1.
-  Direct evidence for neutrino flavor transformation at 5-

- Energy Constrained

- Energy Unconstrained

## Neutrino Signals in D2O

- Neutrino Signals in D2O

- CC

- NC

- ES

- Fiducial
- Volume

- Acrylic
- Vessel
- (“AV”)

## Neutrino Signals in D2O+NaCl

- Neutrino Signals in D2O+NaCl

- CC

- NC

- ES

- Fiducial
- Volume

## Using Light Isotropy

- With salt added, can’t rely on radial profiles to distinguish CC / NC
- CC & ES signals yield an electron, producing a single cone of Cherenkov light
- In D2O phase NC signal yields a single  ray, while in salt phase there are multiple  rays
- We can use isotropy to help distinguish CC and NC signals

## Measure of Isotropy

**Legendre Polynomial Parameter**
- Take spatial pattern of PMT hits, based on event position, and decompose it into spherical harmonics
- These can be combined to form a set of rotationally invariant parameters, I
- A particular combination of these parameters (1+4 4) was found to be effective in separating CC / NC

- Reconstructed
- event position

- ith PMT

- jth PMT

- ij

## The Dataset

** ****254.2 live days** of data, taken from July 26, 2001 to October 10, 2002
- To perform a **blind analysis**,
- NC cross section was spoiled in MC
- Unknown fraction of data set was set aside (<30%)
- Some of the neutrons following muons were initially left in
- The data was reduced via series of cuts designed to removed instrumental backgrounds, similar to the cuts used in the pure D2O dataset.
- A fiducial volume cut of **r < 550cm** and a kinetic energy cut of **K.E. > 5.5 MeV** were also applied, leaving 3055 events in the dataset

## Data Reduction

| Total Event Triggers | 435,721,068 |
| --- | --- |
| Neutrino data Triggers | 196,417,438 |
| Nhits > 20 | 55,446,430 |
| Instrumental Background Cuts | 50,912,120 |
| Muon Follower Cuts | 50,030,008 |
| High Level Cuts | 38,113,660 |
| R< 550 cm | 1,184,211 |
| K.E. > 5.5 MeV | 3055 |
| Total Events in Final Dataset | 3055 |

## Analysis Overview

- To analyze the neutrino signals we need:
- Event position and direction reconstruction (similar to pure D2O)
- Event isotropy information
- Energy response
- Removal of instrumental backgrounds
- Measurements of other physics backgrounds
- Neutron efficiency
- Then we can perform a signal extraction and measure the neutrino fluxes

## Energy Calibration

- Energy scale determined by the use of a 16N source, which provides a 6.13 MeV tagged gamma
- 252Cf neutron source and 8Li  source are used to check consistency
- Positional and temporal behavior is well modeled by Monte Carlo

- Energy response is Gaussian
- Energy scale uncertainty is 1.1%, dominated  by source position uncertainties

## Neutron Capture Efficiency

- Determined using a 252Cf fission source at various positions
- Integrated capture efficiency inside 550 cm and above 5.5 MeV is 0.3990.012, ~3x efficiency in pure D2O due to fiducial volume and energy threshold effects

## Backgrounds to Neutrino Signals

- Instrumental backgrounds: electrical discharges, flashing phototubes, etc.
- Low Energy backgrounds: Progenies of U and Th in D2O, H2O, acrylic, PMTs can photodisintegrate D, yielding background neutrons and Cherenkov light signals
- Muons and related backgrounds: spallation neutrons and other radioactive nuclei
- Neutron backgrounds: fission, alpha reactions, rock walls
- Atmospheric neutrinos:

## Muon-Induced Backgrounds

- Muon rate in SNO is ~70/day, ~33/day enter D2O
- Muons produce free neutrons & radionuclides by spallation
- After cut, the largest expected muon background is 16O(n,p)16N, with 10 sec lifetime
- Cut all events <20 sec after a muon

- Study was performed to study time distribution of events following a muon.  No significant signal was seen beyond 1 second after a muon

## Low Energy Backgrounds

- In-Situ: Examines a low-energy window of PMT data in H2O and D2O.  Uses isotropy information decomposes the observed signal into U and Th backgrounds
- Ex-Situ: Uses MnOx and hydrous Titanium oxide (HTiO) materials to chemically extract Ra from the water and performs a direct counting.  Also an extraction of radon is performed by degassing the water and then alpha counting the extracted gas for radon

## Low Energy Backgrounds

## Low Energy Backgrounds

- The results are in agreement.  With the U and Th concentrations understood, photodisintegration neutron backgrounds can be measured
- At or below target levels

| Results | In-Situ  | Ex-Situ |
| --- | --- | --- |
| D2O U x10-15g/g  | 8.67 +2.6-2.2 | <16.4 |
| D2O Th x10-15g/g | 1.20 ±1.1 | 2.82 +1.0-1.6 |
| H2O U x10-14g/g | 18.4 +9.1-4.9 | 16.0 ± 4.0 |
| H2O Th x10-14g/g | 5.9 +4.8-2.1 | 5.67 +1.76-1.70 |

## Neutron Background Summary

| Deuteron Photodisintegration from D2O U & Th | 73.1+24.0-23.5 |
| --- | --- |
| Fission and Atmospheric Neutrinos | 23.0±7.2 |
| Terrestrial and reactor anti-neutrinos | 2.3 ± 0.8 |
| 2H()p n | 2.8 ± 0.7 |
| 17,18O(n) | 1.4 ± 0.9 |
| Neutrons from Rock | <1 |
| 24Na activation | 8.4 ± 2.3 |
| n from CNO | 0.3 ± 0.3 |
| Total Internal Neutron Background | 111.3 +25.3 -24.9 |

| Total External Neutron Background  | 84.5 +34.5 -33.6 |
| --- | --- |

-  Internal neutrons look like NC signal.  Background is calculated and subtracted from fit results
-  External neutron background is obtained from a fit to the radial distribution of data

## Non-neutron Background Summary

| Cerenkov backgrounds from - backgrounds | <14.7 events |
| --- | --- |
| s  from fission and atmospheric s  | 5.2 ± 1.3 events  |
| 16N decays from O(n,p)  | <2.5 events |
| “AV events” | <5.4 events |

## Counting Neutrinos

- After fixing all of the analysis cuts and procedures, the analysis was performed on the full dataset for R<550 cm and K.E.>5.5 MeV.
- The extraction involves performing a statistical separation of the events into CC, NC, ES and External Neutrons using a maximum likelihood fit.
- The fits were performed using **isotropy**, event **radius** and the cosine of the event **direction relative to the Sun’s** position.  (No energy!)

## Data Radial Distribution

- Statistical Errors Only

## Data Isotropy Distribution

- Statistical Errors Only

- Isotropy

## Data cos(sun) Distribution

- Statistical Errors Only

- cos(sun)

## Extracted Results (Energy unconstrained fit)

- Event types:
- CC =                     events
- ES =                    events
- NC =                     events
- External Neutrons =                  events
- Fluxes (in units of 106 cm-2s-1):
- CC =
- ES =
- NC =
- Predicted Flux:              Bahcall et al., Astrophys. J,** 555** 990 (2001)

- A paper plus a “companion” guide can be found at
- sno.phy.queensu.ca
- Submitted to PRL;
- nucl-ex/0309004.

## Comparison of Extractions

## Systematic Uncertainties (%)

- Cross Section Uncertainties: NC 1.1%, CC 1.2 %, ES 0.5%

- Energy scale

- Resolution

- Radial accuracy

- Angular res.

- Isotropy mean

- Isotropy width

- Radial E bias

- Cherenkov bkds

- “AV” events

- Neutron capture

- Total

- Internal Neutrons

## Kinetic Energy

- Energy

- Neutrons

- Total Data

- Neutron shape is determined by capture on Cl and is well understood by calibration. The total number of neutrons has already been determined by fit. So, we know how many neutrons there are per bin.

- Single
- Bin

- Isotropy

- Angle to Sun

- With neutrons fixed, we can extract CC and ES in each bin using angle to sun and isotropy info

## Kinetic Energy - with salt

- Here the data points for CC and ES are extracted in each energy bin using isotropy and angular information

- Stat errors only!!!

## Oscillation Parameters - SNO Only

- Two flavor neutrino mixing

- Pure D2O

## Global Oscillation Parameters

## Conclusions

- Neutrinos change flavor
- CC / NC = 0.3060.026 0.024, >7- from 1
- NC Flux results are in agreement with SSM predictions (but experimental error bars are now smaller than model uncertainties)
-  Neutrino Oscillation Parameters:
- No LMA2 (KamLAND should see shape distortion)
- Excludes maximal mixing at 5.4 
- MSW matter effects are now *required*, >5-
- Fogli et al., hep_ph/0309100

## What’s Next for SNO

- Neutral Current Detectors will be installed in November
- Array of 3He proportional counters
- 3He+n->p+3H+764 keV
- Allows for event by event separation for NC events
- Other papers
- Nucleon decay (*submitted*)
- Day/Night in salt
- CC energy spectrum
- Anti-neutrinos
- Long D2O paper

## Slide 49

## What does this mean?

- Neutrinos are massive, solved SNP
- Confirmed Solar Model
- Neutrinos mix
- But differently from quarks
- Strong evidence for MSW effects
- Moving to phase of Precision Measurements
- Identified some of the dark matter
- As much mass as all luminous matter
- New physics
- Neutrinos are a new physics frontier
- SNO + KamLAND are a beachheads

## Are we done? 

- Absolute mass, what is the mass of a neutrino?
- How many neutrinos are there? 3 or more?
- Sterile neutrinos? (miniBOONE, solar neutrinos)
- Are neutrinos their own anti-particle or not?
- Neutrinoless double beta decay? (Majorana, Cuore, EXO,...)
- Understanding the full mixing of neutrinos?
- Precision Measurements of parameters (MINOS, solar, reactor)
-  13 of particular interest (reactor?, JPARC, LBL, off-axis)
- CP violation in Leptons?
- Extend the Standard Model
- Hints for new symmetries and origins of mass?

## Karsten Heeger

- Yuen-dat Chan

- Kevin Lesko

- Alysia Marino

- Bob Stokstad

*Not pictured: Rick Norman*

- Alan Poon

- websites
- neutrino.lbl.gov
- kamland.lbl.gov

- SNO Salt: nucl-ex/0309004
- KamLAND: Phys.Rev.Lett. 90 (2003) 021802
- SNO NC paper: Phys.Rev.Lett. 89 (2002) 011301
- SNO D/N paper:Phys.Rev.Lett. 89 (2002) 011302
- SNO CC/ES paper:Phys.Rev.Lett. 87 (2001) 071301

## The SNO Collaboration

**University of British Columbia, **Vancouver, BC, Canada
- S. Gil, J. Heise, R. Helmer, R.J. Komar, T.Kutter, C.W. Nally, H.S. Ng,
- Y.I. Tserkovnyak, C.E. Waltham
**Brookhaven National Laboratory, **Upton, NY, USA
- J. Boger,R.L. Hahn, J.K. Rowley, M. Yeh
**University of California at Irvine,** Irvine, CA, USA
- R.C. Allen, G. Bühler, H. H. Chen†
**Carleton University,** Ottawa, ON, Canada
- I. Blevis, F. Dalnoki-Veress, D.R. Grant, C.K. Hargrove, I. Levine,
- K. McFarlane,C. Mifflin, A.J. Noble, V.M. Novikov, M. O’Neill, M. Shatkay,
-  D. Sinclair, N. Starinsky
**University of Guelph, ** Guelph, ON, Canada
- T.C. Anderson, P. Jagam, J. Law, I.T. Lawson, R.W. Ollerhead, J. J. Simpson,
-  N. Tagg, J.X. Wang
**Laurentian University, **Sudbury, ON, Canada
- 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
**Lawrence Berkeley National Laboratory, **Berkeley, CA, USA
- Y.D.  Chan, X. Chen, M.C.P. Isaac, K.T. Lesko, A.D. Marino, E.B Norman,
-  C.E. Okada, A.W. Poon, S.S.E. Rosendahl, A . Schülke, A. R. Smith,
- R. G. Stokstad
**Los Alamos National Laboratory,** Los Alamos, NM, USA
- 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. Wilhemy,
-  J.M. Wouters
**National Research Council of Canada, ** Ottawa, ON, Canada
- J.D. Anglin, M. Bercovitch, W. F. Davisdson, R.S. Storey†

**University of Oxford, **Oxford, UK
- 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, A.P. Ferarris,
- H. Fergani,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. Thornewell, P.T. Trent,  N. West, J.R. Wilson, D.L. Wark
**University of Pennsylvania, ** Philadelphia, PA
- E.W. Beier, D.F. Cowen, M. Dunford,E.D. Frank,W. Frati,
- W.J. Heinzelman, P.T. Keener, J.R.Klein, C.C.M. Kyba, N. McCauley,
-  D.S. McDonald, M.S. Newbauer, F.W. Newcomer, S.M. Oser, V.L. Rusu, R.Van Berg, P. Wittich
**Queen’s University, **Kingston, ON
- E. Bonvin, M. Chen, E.T.H. Clifford,Y. Dai, 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. Maniera, A.B. McDonald, B.A. Moffat, T.J. Radcliffe,
- B.C. Robertson, P. Skensved, B. Sur
**University of Washington, ** Seattle, WA, USA
- 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. Germani, A.A. Hamian,R. Hazama,
- K.M. Heeger, K. Kazkaz, J. Manor, R. Meijer Drees, J.L. Orell,
- R.G.H. Robertson, K.K. Schaffer, M.W.E. Smith, T. D. Steiger,
- L.C. Stonehill, J.F. Wilkerson
- † Deceased