New Results from the Salt Phase of SNO

Kathryn Miknaitis Center for Experimental Nuclear Physics and Astrophysics, Univ. of Washington

For the

Sudbury Neutrino Observatory

In this talk:

•SNO overview•Salt phase overview

•New solar neutrino flux, spectrum, and day-night

asymmetry results from 391 days of salt data!

The Sudbury Neutrino Observatory

The SNO Detector

Acrylic vessel (AV), 12 m diam.

1700 tonnes H2O inner shielding

1000 tonnes D2O

6800 feet (~2km) underground

5300 tonnes H2O outer shielding

~9500 PMTs, 54% coverage

SNO’s Three Reactions

-eppd (CC) eCharged Current:

Neutral Current:

npd (NC) xx

Elastic Scattering:

-- ee (ES) xx

•Detect the e-

• energy spectrum

• Weak directional sensitivity

e

•Detect the n through secondary capture

• No directional or neutrino energy info

•Detect the e-

•Mainly sensitive to

•Highly directional

e

-- ee (ES) xx

npd (NC) x x

-eppd (CC) e

NCx

CCESCCx

)154.0/1()(

Solar Neutrino Physics with SNO (I)

Measurement of the 8B Solar Neutrino Flux:

Flavor change:

)(154.0

e

e

ES

CC

e

e

NC

CC

Solar Neutrino Physics with SNO (II)

Spectrum

6 MeV 13 MeV

No.

of

CC

eve

nts

Increasing Δm2

Day

Night

ee

eee DN

DNA

)(2

Day-Night Asymmetry:

MSW Signatures MSW Parameter Constraints

hep-

ph/0

4063

28 J

uly

21 2

004

Ban

dyop

adhy

ay,

Cho

ubey

, Gos

wam

i, P

etco

v, a

nd R

oy

Global analysis of solar neutrino and KamLAND data from 2004

SNO measurements of CC/NC, spectrum, and day-night

asymmetry contribute to MSW constraints

“LMA region”

Pure D2O

Salt 3He

Nov. 99 - May 01 July 01 - Sep. 03 Nov 04 - Dec. 06

γγ

γ

35Cl 36Cl

36Cl*

nγ

2H 3H

3H*

n

n captures on deuterium

σ = 0.0005b

6.25 MeV γ

n captures on chlorine

σ = 44b

8.6 MeV multiple γs

n captures on 3He in discrete prop.

counter array

σ = 5330b

0.764 MeV

n + 3He p + 3H

p3H

5 cm

n

3HePRL 87, 071301, 2001PRL 89, 011301, 2002PRL 89, 011302, 2002

PRL 92, 181301, 2004(for first 254 days) nucl-ex/0502021391-DAY RESULTS!

npd (NC) xx Three ways to catch that neutron!

1. Higher capture cross-section means more neutrons detected

2. Boosts energy of NC events further above analysis threshold

…

3H 36Cl

2H+n

35Cl+n

6.25 MeV

= 0.0005 b = 44 b

8.6 MeVAdvantages of Salty D2O (I)

Define an “isotropy parameter” based on Legendre polynomials in θij

3. Multiple gammas for NC means light is more isotropic than for CC, ES

ij

4114 4

)(cos

jiijll P

Advantages of Salty D2O (II)

Statistical separation of CC, NC events with no constraint on the CC spectrum shape

20

Energy Isotropy

Direction Radius

Extracted Events:

391- day salt results!

4722 events, r<550cm, Teff>5.5MeV

(Patience! Energy spectrum coming up soon!)

CC: 2176 ± 78

NC: 2010 ± 85

ES: 279 ± 26

External neutrons: 128 ± 42

Backgrounds fixed in fit: 128

)syst.()stat.( 35.2

)syst.()stat.( 94.4

)syst.()stat.( 68.1

15.015.0

22.022.0

38.034.0

21.021.0

08.009.0

06.006.0

ES

NC

CC

391- day salt results!

)scm10

of units(In 126

029.0031.0)stat.(023.0340.0

NC

CC

Systematics

Dominant systematic uncertainties for the shape-unconstrained analysis:

Energy scale -0.9% +1.0%

-3.3% +3.8%

-1.6% +1.9%

β14 mean -4.0% +3.7%

-3.6% +4.5%

-1.2% +1.3%

Radial scale -2.6% +2.5%

-3.0% +3.3%

-2.6% +3.0%

Angular Res. -0.4% +0.4%

-0.2% +0.2%

-5.1% +5.1%

CC NC ES

For spectrum analysis:

Systematic uncertainties evaluated

in each extracted CC energy bin

CC Spectrum

Extracted CC spectrum with statistical and systematic

uncertainties

Extracted CC spectrum with statistical uncertainties,

compared to model predictions:

CC spectrum consistent with LMA, undistorted 8B

Systematics for the Day-Night Analysis

DN Correlated Uncertainties: overall energy scale uncertainty… “cancel” in asymmetry ratio

Differential Uncertainties: time variations (diurnal and long term) evaluate with in-situ techniques geometric uncertainties evaluate with calibration data

Classes of Events Used to Limit Diurnal Variations:

“Muon Followers” – neutrons induced by cosmic ray muons“Hot Spot” - radioactive spot on the acrylic vessel (AV)D2O radioactivity - uranium and thorium in the D2OH2O radioactivity - uranium and thorium in the H2OAV radioactivity - radioactive decays in the acrylicPMT beta - gammas from decays in the PMTs

ACC= -0.056 ± 0.074 (stat.) ± 0.051 (syst.)

ANC= 0.042 ± 0.086(stat.) ± 0.067 (syst.)

AES= 0.146 ± 0.198(stat.) ± 0.032 (syst.)

(CC, ES spectrum shapes unconstrained in this analysis)

DN

DNA

)(2Day-Night Asymmetries (I)

ACC and ANC are correlated (ρ = -0.532)

In standard neutrino oscillations, ANC should

be zero…

Day-Night Asymmetries (II)

ACC= -0.037 ± 0.063(stat.) ±0.032(syst.)

AES= 0.153 ± 0.198(stat.) ±0.030(syst.)

Constraining ANC to be zero:

In the pure-D2O phase,

(shape constrained, ANC constrained)

013.0012.0e 049.0070.0A

DN

DNA

)(2

Combine with analogous ACC from the salt phase:

Convert Super-Kamiokande AES to Ae, and combine with SNO:

040.0037.0A OD salt 2

027.0035.0A SK SNO

MSW Constraints

Previous global analysis of solar neutrino data

Global Solar, with

new salt results

Global Solar + KamLAND 766

ton-year data

09.007.0

2256.04.0

2

09.008.0

2254.43.2

2

45.0tan ,eV100.8 b)

45.0tan ,eV105.6 a)

m

m

Detection Principle

2H + x p + n + x - 2.22 MeV (NC)

3He + n p + 3H + 0.76 MeV

x

n

40 Strings on 1-m grid

440 m total active length

NCD

PMT

SNO Phase III (NCD Phase)

3He Proportional Counters (“NC Detectors”) now installed Production data taking underway

Physics Motivation

Event-by-event separation. Measure NC and CC in separate data streams.

Different systematic uncertainties than neutron capture on NaCl.

Conclusions

• Results from full 391-day salt phase available nucl-ex/0502021

• Solar neutrino flux results confirm and improve previous results

• CC spectrum presented, consistent with LMA prediction (also consistent with no distortion)

• Day-Night asymmetries consistent with LMA prediction (also with no asymmetry)

•MSW mixing parameters:

09.007.0

2256.04.0

2 45.0tan ,eV100.8

m