SNO

1
SNO Solar Neutrino Results
José Maneira (LIP-Lisboa, Portugal) (on behalf
of the SNO collaboration, with thanks to Y.
Takeuchi from SuperK)

• Neutrino Oscillation Workshop - NOW2006
• Otranto, September 11, 2006

2
Outline

• Introduction
• The SuperK and SNO detectors
• Solar Neutrino Results from SNO Super-K
• 8B fluxes
• Spectral measurements
• Time variations (Day-Night, Periodicities)
• Hep solar neutrino limits
• Prospects for SNO
• Low energy threshold analysis and Phase III

See this afternoon's talks by G. Ranucci and
M.Smy on Prospects for Borexino and Phase III of
SuperK
3
the SuperK and SNO detectors
4
SuperKamiokande
?? e- ? ? e-
Electronics hut
LINAC
Water and air purification system
(for solar neutrinos)

• Sensitive to ?e??????????
• ???????e-??0.15???ee-?

Control room
Atotsu entrance
41.4m

• Timing
• Vertex position
• Ring pattern
• direction
• Number of hit PMTs
• Energy
• (calibration with LINAC and 16N)

Ikeno-yama Kamioka-cho, Gifu
1km (2700mwe)
2km
3km
SK
Mozumi
Atotsu
39.3m
Inner Detector
Outer Detector 1885 of 8 inch PMTs (SK-III)
50 kton water fid. vol. 22.5 kton
5
SuperK data taking phases
Feb-1996
Apr-2006
Aug-2002

• SK-III (2006-)
• Photo coverage 40

• SK-II (2002-2005)
• Photo coverage 19

• SK-I (1996-2001)
• Photo coverage 40

6
Sudbury Neutrino Observatory

• Creighton mine in
• Sudbury, Canada
• 2039 m depth
• 6000 mwe

Heavy Water 1000 ton
Support structure for 9500 PMT
Acrylic Vessel 12 m diameter
Internal H2O shielding 1700 ton
External H2O shielding 5300 ton
Urylon liner Radon sealing
7
Neutrino Reactions in SNO
CC
?e d ? p p e-

• ?e only
• Energy spectrum sensitivity
• Weak directional sensitivity ? 1-1/3cos(?)

NC
?x d ? ?x p n

• Same cross section for all 3 flavors
• Total flux measurement of 8B solar neutrinos

ES
?x e- ? ?x e-

• Higher cross section (6x) for ?e,than for ??and
  ??
• Low statistics
• Strong directional sensitivity

8
SNO observables
PMT Measurements

• position
• time
• charge

Reconstructed event

• vertex
• direction
• energy
• isotropy

9
8B solar neutrinos
10
8B flux from SK-II

• Full SK-II run period
• (Dec. 2002 Oct. 2005)
• first 159 days
• 8.0-20MeV
• last 631 days
• 7.0-20MeV
• Total 791 days
• Systematic errors are under study.
• Consistent with SK-I

New
Flux x 106 cm-2 s-1
SK-I result 2.35 /-0.02(stat.) /-0.08(syst.)
11
Signal Extraction in SNO Salt Phase

• maximum likelihood fit of model PDFs to data
• event variables R (radial position) ?14(isotropy)
  cos?sun and E(energy)

ES separation
CC-NC separation
?14
cos?sun
CC
NC
ES
dont use E -gtenergy-unconstrained -gt fit out
CC spectrum!
12
SNO flux results (salt)
SNO Collaboration, PRC 72, 055502 (2005) 391 Days
of Dissolved Salt Data
ES
CC
SSM
x 106 cm-2 s-1

• Evidence for flavor change
• Confirmation of solar model prediction
• Consistent with Phase I results

NC
13
Energy spectra

• SNO CC spectrum from salt phase unconstrained fit

• No evidence for deviations from standard 8B shape

14
Day-Night asymmetry
Preliminary for SK-II
(Day-Night)
ADN
(systematic errors are under study)
(DayNight)/2
ADN (SK-II) -0.064 0.043 (stat.) ADN (SK-I)
-0.021 0.020
SNO Combined III
0.013
- 0.012
15
Global oscillation analysis of solar and
reactor data

• 2-flavor analyis
• Cl Ga SK-I day-night spectra SNO-I SNO-II
• LMA-I only allowed region
• Maximal mixing excluded

?
?
Solar KamLAND
16
time modulations
17
SuperK Periodicity analysis
Following claims of
periodicity in their data,
SuperK published (see
hep-ex/0307070) its own
periodicity analysis, using
a Lomb periodogram. The event arrival
times are fit to ??????(t) N1A cos
(?t?) For the combined data sets, the biggest
peak occurs at a period of 13.76 days, with a
Lomb power7.51 Monte Carlo shows that 19 of
simulated data sets give a peak at least this
large, so no statistical fluctuations are
consistent. See also Ranucci, Phys. Rev.
D73103003, 2006
18
SNO Periodicity Analysis

• SNO has published (see PRD 72 2005, 052010) its
  own periodicity analysis of the D2O and salt data
  sets, using both a Lomb-Scargle periodogram and
  an unbinned maximum likelihood fit.
• The event arrival times are fit to
• ??????(t) N1A cos (?t?)
• For the combined data sets, the biggest peak
  occurs at a period of 2.4 days, with a
  significance statistic of S8.8
• Monte Carlo shows that 35 of simulated data sets
  give a peak at least this large.

No evidence for modulation in any of SNO's data.
See also Ranucci Rovere (hep-ph/0605212)
19
Observed Time Variations

• Only evidence for time modulation in SNO and
  SuperK is due to the Earth orbit eccentricity
• SNO

• SuperK-I II

Best-fit eccentricity ? 0.0143
0.0086 Actual eccentricity ? 0.0167
20
hep solar neutrinos
21
hep searches

• Possible hep signal lies between 8B solar
  neutrinos and atmospheric neutrinos

Standard Solar Model (7.97 1.24) x 103 cm2 s-1
18.77 MeV
22
Hep limit from SK-I

• Expected hep signal in 18-21MeV 1.06
• (Expected 8B bkg in 18-21MeV 1.72 )
• 4.9 2.7 observed
• Assuming all signals are hep , then flux limit
  (90CL) 7.9 x SSMBP2001 7.3 x 104/cm2/s
• Assuming oscillations, total flux limit
  1.5 x 105/cm2/s

MC
MC

• hep-ex/0508053

23
Hep search in SNO-I
6.13 MeV Gamma Rays 16N


D2O Data


8B Electrons
neutrons
atmospheric neutrinos
DSNB Electrons
DSNB Electrons
19.8 MeV Gamma Rays pT
Michel Electrons
hep Electrons
24
Hep limits from SNO-I

• We define an optimal signal box based on MC
  simulations while hiding the energy interval
  12ltTelt35 MeV
• Expect
• 3.1 0.6 bkg events
• 0.99 0.09 signal events
• We observe 2 events
• Total flux limit
• ?heplt 2.3 x104 cm-2 s-1 (90 C.L.)
• lt 2.9 Solar Models
• Improves Previous Limits x 6.5

• hep-ex/0607010

25
Limits on Diffuse SupernovaNeutrino Background

• Neutrinos from extragalactic supernovae since the
  beginning of star formation in the Universe
• Model predictions of DSNB ne flux in range 22.9 lt
  En lt 36.9 MeV
• 0.19 to 1.49 cm-2s-1
• Best direct limit 6.8x103 cm-2s-1 in 25 lt En lt 50
  (Mont Blanc)

• SNO analysis
• In 21 lt Ee lt 35 MeV
• 0.18 background expected
• No events observed
• Limit
• 70 cm-2s-1 in 22.9lt En lt 36.9 MeV
• 2 orders of magnitude better than previous

See F. Fleurot's talks for online burst SN
analysis
26
Prospects for SNO
27
Precision MSW measurements

• Push sensitivity for spectral distortions,
  improve CC/NC
• In LMA region, tightness of sin2?12 contour is
  driven mainly by SNO CC/NC ratio
• But ?13 also depends on CC/NC

28
Solar neutrino sensitivity to ?13
Maltoni et al., hep-ph/0309130
90, 95, 99 CL
Chooz
?m232 from SK atmospheric
29
Low energy threshold analysis

• New combined analysis of Phase I and II data
• Better energy estimation, better resolution
• Several other improvements to MC and cuts
• Reduction of background tails
• Low threshold 4 MeV looks good
• Lower systematics

Simulated data Preliminary!!
30
Improving resolution by accounting
channel-by-channel variations
31
New energy estimators
Comparison between 16N calibration source data
and MC
New Total Light Energy Estimator
Improved Prompt Light Energy Estimator
RMS Spread in Previous Analyses ? 0.7
32
SNO Phase III
33
3 neutron detection methods
Phase II (salt) July 01 - Sep. 03
Phase III(3He) Summer 04-Dec. 06
Phase I (D2O) Nov. 99 - May 01
40 proportional counters 3He(n, p)3H ? 5330
b independent readout Event by Event NC
2 t NaCl. n captures on 35Cl(n, ?)36Cl ? 44
b Observe multiple ?s PMT array readout Enhanced
NC
n captures on 2H(n, ?)3H ? 0.0005 b Observe
6.25 MeV ? PMT array readout Good CC
35Cln
2Hn
5 cm
8.6 MeV
n
6.25 MeV
3H
p
3H
3He
36Cl
n 3He ? p 3H
Initial Results
Recent Results
Now Running
34
Neutral Current Detectors
3He n ? p 3H 0.764 MeV

• The Neutral Current Detectors (NCDs) are 3He
  proportional counters, that detect the p and/or
  3H from neutron capture
• 5 cm wide and 10 m long, attached to the bottom
  of the acrylic vessel
• 40 are installed, 4 of which have 4He instead of
  3He, for background control
• Measure NC with different systematics
• Break NC,CC correlations

35
4He
3He
36
Working around the NCDs in the Optical Calibration

• PMT occupancy map with Laser source in the center
  of the detector

NCD shadows
37
Preliminary Blind Analysis of NCD energy spectrum
Next Adding Pulse Shape Discrimination
38
Backgrounds

• More calibrations in phase III
• All the optics, 16N, point neutron and background
  sources from previous phases, plus
• Distributed neutron and background sources (Rn,
  24Na)
• Alpha beam tests

Signal
Surface alpha
Neutron perpendicular to anode
Embedded alpha
Neutron parallel to anode
HV Discharge
39
Summary

• Update results on fluxes, energy spectra, D/N
  asymmetries
• From SNO pure D2O and salt phases, SK-I and new
  results from SK-II
• Time variations and Periodicity analyses
• SuperK and SNO analyses indicate no evidence for
  periodicities beyond the expected due to Earth
  orbit eccentricity
• New search for hep solar neutrinos
• ?hep lt 2.9 SSM, 6.5x lower than previous limits
• Future Prospects
• SuperK-III now taking data -gt see M.Smy's talk
• SNO phase III with Neutral Current Detectors
• Low Energy Threshold Analysis of existing data

As well as Borexino and KamLAND for 7Be
neutrinos
40
(No Transcript)
41
The New SNOLAB
New Excavation To Date
SNO
42
Cosmic ray muons vs. depth
43
SNO

• After heavy water is removed from SNO in 2007
• SNO plus liquid scintillator physics program
• pep and CNO low energy solar neutrinos (11C 20 x
  lt Gran Sasso)
• SSM pep flux uncertainty 1.5 ? allows
  precision test.
• Comparison with the photon luminosity.
• Tests the neutrino-matter interaction, sensitive
  to new physics.
• non-standard interactions, mass-varying
  neutrinos, CPT violation,large ?13, sterile
  neutrino admixture.
• geo-neutrinos
• 240 km baseline reactor oscillation confirmation
• supernova neutrinos
• double beta decay (150Nd) ?

44
Survival Probability Rise
stat syst SSM errors estimated
SSM pep flux uncertainty 1.5 known source
? precision test

• ?m2 8.0 10-5 eV2
• tan2? 0.45

Improves precision on ?12

• Sensitive to new physics
• non-standard interactions
• solar density perturbations
• mass-varying neutrinos
• CPT violation
• large ?13
• sterile neutrino admixture

SNO CC/NC
Studying the rise confirms MSW or perhaps shows
us new physics
pep ?
45
Event Rates (oscillated)
resolution with 450 photoelectrons/MeV
7Be solar neutrinos
3600 pep/year/kton gt0.8 MeV
using BS05(OP) and best-fit LMA
2300 CNO/year/kton gt0.8 MeV
46
Cosmogenic 11C background
11
these plots from the KamLAND proposal
muon rate in KamLAND 26,000 d-1 compared with
SNO 70 d-1
47
Geo-Neutrino signal

• terrestrial antineutrino event rates
• Borexino 10 events per year (280 tons of C9H12)
  / 29 events reactor
• KamLAND 29 events per year (1000 tons CH2) /
  480 events reactor
• SNO 64 events per year (1000 tons CH2) / 87
  events reactor

based on Rothschild, Chen, Calaprice Geophys.
Res. Lett. 25, 1083 (1998)
KamLAND
geo-? in SNO
KamLAND geo-neutrino detectionJuly 28, 2005 in
Nature
SNO geo-neutrinos and reactor background
48
SNO (Nd Double Beta Decay)

• 0? 1057 events per
• year with 1 natural
• Nd-loaded liquid
• scintillator in SNO.
• Simulation
• assuming light
• output similar to
• Kamland.

Very preliminary simulation one year of
data m?? 0.15 eV