latest sno results from salt-phase data and current ncd-phase status melin huang ● introduction...
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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
ogg
ed
cu
rrent
Time (microseconds)
neutron with p-t track || wire14
12
10
8
6
4
2
0
86420
De-l
ogg
ed
cu
rrent
Time (microseconds)
track wire
20
15
10
5
0
5 4 3 2 10
De-l
ogg
ed
cu
rrent
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