Latest SNO Results from Salt-Phase Data and Current NCD-Phase Status

Melin Huang

● Introduction● Results of Salt Phase (Phase II)● Status of NCD Phase (Phase III)

University of Texas at Austinon behalf of the SNO Collaboration

After Six Solar Experiments• 3 Gallium (Radiochemical): SAGE/GALLEX/GNO -- 0.58• 1 Chlorine (Radiochemical): Homestake -- 0.33• Kamiokande + Super-Kamiokande (Water Cerenkov) -- 0.46

Direct observation of solar neutrinoflavor change via inclusive appearance

Main goal:

Sudbury Neutrino Observatory

1700 tonnes InnerSield light water

5300 tonnes OuterShield light water

Supportstructure for9500 PMTsconcentrators

12m diameteracrylic vessel Norite rock

Urylon liner andRadon Seal

Vectran supportropes

Control room

1000 tonnesheavy water

2090 m to surface10^5 m to upperatmosphere

10^11 m to Sun

10^20 m to Galactic center

The SNO Detector

e + d p + p + eCC

• Q = -1.445 MeV• good measurement of e energy spectrum• some directional info (1 – 1/3 cos)• e only

Neutrino Reactions in SNO

x + d x + p + nNCNC

• Q = -2.22 MeV • measures total 8B flux from the Sun• all types

x + e x + eES

• low cross section ( few events)

mainly sensitive to e , some

and

strong directional sensitivity

Charged Current

Neutral Current

Elastic Scattering

CC/NC = 1 & CC/ES = 1 means No Neutrino OscillationCC/NC < 1 & CC/ES < 1 means electron neutrino --> Other neutrino types

Implication:

Recall:

Testing Neutrino Oscillation – Inclusive Appearance

Note: This technique is Independent of solar model !!!

Advantage: Cross section uncertainties canceled for CC/NC

Neutron Detection Methods:

Phase I (Nov 1999 – Apr 2001) : Neutron capture on deuterium in pure D2O: Lower neutron sensitivity, Poor discrimination between neutrons & electrons

Phase II (Jun 2001 – Oct 2003) : Neutron capture on Cl

using NaCl in D2O: very good neutron sensitivity, Better neutron-electron separation

Phase III (Nov 2003 – Dec 2006) : Neutron capture in He proportional counters in D2O: Good neutron sensitivity, Great neutron-electron separation

Three Phases of SNO

SNO Phase II (Salt Phase) Advantages of NaCl: Capture Efficiency

2 tons of NaCl added June 1, 2001

The volume-weighted neutron detection efficiency:40.7% in Salt Phase and 14.4% in Phase

SNO Salt Phase Advantages of NaCl: Event Isotropy

multiplicity means PMT hit pattern for neutron events moreisotropic than for single Cerenkov electrons

Pl: legendre polynominal of order l

: angle between PMTs i and j

N : total # of triggered PMTs in the event

SNO Phases I & II (MC pdfs for signal extraction)

Phase I

Phase II

Phase I

Phase II

Phase I

Phase II

Phase II

SNO Phases I & II (MC pdfs for signal extraction)

MC pdfs are modeled based on several different calibration sources

Data Processing (Phase II – Salt Phase)

4772 candidates (~ 7 x 10^-6 triggered events)

(1 hit PMT ~ 0.12 MeV)

Background Measurement (Phase II – Salt Phase)

The distributions of high-level cut parameters

Instrumental events

Primarily U and Th chains+24Na in Salt Phase

Cherenkov eventsinside signal box

Low Energy Radioactivity (in-situ/ex-situ)Misreconstruction

neutrino events

Other Backgrounds:● Cosmic-ray muon● Atmospgeric neutrino● (alpha, n) process● natural fission● anti-neutrino

Signal Extraction Fit to Data

Phase II (Salt Phase) Results Flux Measurements (units 106 cm-2 s-1)

Using 8B spectral information in fit

Compare to D2O measurements:

Constraints on Mixing Parameters

All solar neutrino experiments only

All solar neutrino experimentsand KamLAND 766 ton-year data(assuming CPT invariance)

SNO I & II

Maximal mixng ruled out at ~5.3

SNO Phase III (NCD Phase) 3He Proportional Counters

Array of 3He counters

40 strings on 1-m grid 400 m total active length

• Neutrino enters D2O

• Interacts with deuterium to produce neutron

• Neutron wanders (ms)

• Neutron captures on NCD (or D2O)

Production data taking began Dec 2004

SNO Phase III (NCD Phase) Physics Motivation---Energy Spectrum

• CC and NC separation in pure D2O had big covariances (>90% correlations)

• Salt phase broke covariance with isotropy, but additional neutrons dilute CC signal

• Third phase has best of both worlds

• 3He (`NCD’) counters remove neutrons from CC -- Independently calibrate remainder• Event-by-event separation – measure CC & NC in separate data streams• Different systematic uncertainties than neutron captures in Phase I & II

small

SNO Phase III (NCD Phase)NCD Event Pulse Shapes

neutron with p-t track wire

1.5

1.0

0.5

0.0

-0.586420

De-l

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ed

cu

rrent

Time (microseconds)

neutron with p-t track || wire14

12

10

8

6

4

2

0

86420

De-l

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ed

cu

rrent

Time (microseconds)

track wire

20

15

10

5

0

5 4 3 2 10

De-l

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Time (microseconds)

Current preamplifiers allow pulse shapes to be digitized for particle identification.

alphas come from Th & U decay chains

SNO Phase III (NCD Phase)NCD Pulse Energy & Electronic Parameter Calibrations

● Goal: Separation of background alpha events from physics neutron events ● Calibrations: -- pulse energy from shaper ADC information -- time constants of all effective low pass filters and high pass filters -- time constants used for describing dispersion of a pulse -- characteristic logarithmic amplifier (logamp) parameters

Delay line

NCD SimplifiedElectronic System

NCD Pulse Energy & Electronic Calibrations (Preliminary Results)SNO Phase III (NCD Phase)

AD

C S

hap

er B

in

Pulse Amplitude

neutron peak (764 KeV) ~149 ADC bin

proton edge (191 KeV) ~48 ADC bin

energy vs ADC bin

Blue: simulatedBlack: data

Energy Calibration Logamp Parameter Calibration

Time Constant Extraction (No Logamp)Time Constant Exatrction (in Multiplexer/Logamp)

Pink: dataBlack: simulated

SNO Phase III (NCD Phase)SNO Phase III (NCD Phase)NCD Neutron Pulse Fits (Preliminary Results)

● Neutron energy close to neutron energy peak● Alpha pulses still on going

SNO Phase III (NCD Phase)NCD Neutron Calibration (Preliminary Results)

Calibration Sources:● Americium-Beryllium (AmBe) :● Californium (252Cf): Generate 3 to 4 neutrons per fission

Conclusions

• Salt allowed enhanced NC capture and better separation between neutrons and electrons • Phase II first measurement of total flux without assumptions about shape of survival probability -- Results are consistent with neutrino oscillation with Large-Mixing Angle parameters -- New precision has ruled out maximal mixing at high level• Phase III analysis is on-going