results and prospects for sno low energy threshold analysis (leta) motivations analysis details...
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Results and Prospects for SNO
• Low Energy Threshold Analysis (LETA)• Motivations• Analysis Details• Results
• Status of `three-phase’ Analysis• Summary and Other Recent Results
Josh Klein, for the SNO CollaborationUniversity of Pennsylvania
15 June 2010
Sudbury Neutrino Observatoryneutrino reactions on deuterons
Neutrino-Electron Scattering (ES)
Neutral Current (NC)
Charged Current (CC)
Signal rates determined by statistical fit
National Geographic
Phase I: Just D2O • Simple detector configuration, clean measurement• Low neutron sensitivity• Poor discrimination between neutrons and electrons
Phase II: D2O + NaCl• Very good neutron sensitivity• Better neutron electron separation
Phase III: D2O + 3He Proportional Counters• Good neutron sensitivity• Great neutron/electron separation
Three Phases of SNO
Low Energy Threshold Analysis
En=6 MeV En=6 MeV
Motivations: ne Statistics
CC ES
Night
Day
Low Energy Threshold Analysis Motivations: NC Precision
Phase I (D2O) NC
+74%
+68%
Phase II (D2O+NaCl)
NC
nx (NC) Statistics
“Beam On”
“Beam Off”
Breaking NC/CC Covariance
I
Low n capture eff.
High n capture eff.
II
Low Energy Threshold Analysis Overview
1. Joint-Phase (I+II) fit for all signals and remaining bkds2. Reduction of Backgrounds3. Reduction of Systematic Uncertainties4. `Float’ Dominant Uncertainties in Fit
Key components:
Results: 8B flux measured by NC rates Bin-by-bin electron energy spectrum using CC & ES Parameterized Psurv(En) (New) Two-flavor and three-flavor extraction of mixing params.
Needed to rework SNO’s entire analysis chain and simulation, from measurement of charge pedestals to final fit methods.
Low Energy Threshold AnalysisSignal Extraction Fit (Signal PDFs)
Not used
1-D projections of 3-D and 4-D PDFS
Teff (MeV) cosqsu
n
(R/RAV)3 Isotropy =
Monte Carlo
(unconstrained in fit)
Low Energy Threshold AnalysisCosmic rays < 3/hour Low Energy Backgrounds
D2OAcrylic VesselH2O
}×{+
PMT 208Tl
++
Acrylic Vessel Surface Neutrons [(α,n) reactions]
214Bi (U, Rn)208Tl (Th)
24Na (neutron activation of salt)
= 12 external bkds + 5 internal bkds
Teff>3.5 MeV
All events ( but only ~5000 ns)
For each phase
(most backgrounds constrained by ex-situ radioassays)
3 neutrino signals+ 17 backgrounds
Kinetic Energy Spectrum
Low Energy Threshold Analysis
New Threshold = 3.5 MeV
MCPMT -b gs
internal (D2O)
external (AV + H2O)
NC+CC+ES (Phase II)
Old
thre
shold
Low Energy Backgrounds
Low Energy Threshold AnalysisSignal Extraction Fit (3 out of 17(x2) Background PDFs)
Teff (MeV) cosqsu
n
(R/RAV)3 Isotropy =
1-D projections of 3-D and 4-D PDFS
Monte Carlo
Low Energy Threshold Analysis Background Reduction: Energy Resolution
`Prompt’ (direct) light easy to model: we know the path traveled
Using all hits increased hit statistics by ~12%->6% reduction in resolution~60% reduction internal bkds
Time Residual (ns)
Prompt Timing Cut
Late Timing Cut
Rayleigh Scatter
t t0 t pmt d
c
(used in prior analyses)
Low Energy Threshold Analysis
Only information is PMT charges, times, and hit patterns
• 4 KS tests of PMT pattern against single Cherenkov e-
• 1 KS test of PMT times against Cherenkov e-
• 3 cuts on various isotropy parameters• 2 cuts on energy reconstruction uncertainty• In-time ratio vs. Nhit to remove misreconstructed events
Background Reduction: New Cuts
Low Energy Threshold Analysis
Fiducial Volume
βγβ
High charge early in time
• `Early’ Charge to cut PMT b-gs
Note: This would have been impossible if we hadn’t fixed `little’ things like charge pedestals
Background Reduction: New Cuts
Low Energy Threshold Analysis
PassFail
FailPass
FailFail
PassPass
NPF = e1(1-e2)Nb
NFP = (1-e1)e2Nb
NFF = (1-e1)(1-e2)Nb
NPP = e1e2Nb + Ns
NPMT= NPP – Ns = NFP * NPF /
NFF
Special Case: PMT b-g PDFs
Not enough CPUs to simulate sample of events Use data instead
In-time ratio In-time ratio
Earl
y c
harg
e p
rob
abili
ty
Earl
y c
harg
e p
rob
abili
ty`Bifurcated’ analysis
Low Energy Threshold AnalysisSystematic Uncertainties: Brief Summary
b14
(isotropy)
0% 1% 3% 4%2%
n capture
Teff scale
Fiducial volume
I
II
LETA I
LETA II
N/A
I=D2OII=D2O+Salt
Low Energy Threshold AnalysisSystematic Uncertainties
Comparison of 208Tl calibration source data to MC
Run near the AV(to model AV 208Tl events)
Tests of PDF shapes
Low Energy Threshold Analysis
Tests of PDF shapes Distributed Rn Spike
Low Energy Threshold Analysis
Fit to spike energy spectrum allowing Teff scale to float: shift is 0±0.6%
1. Maximum likelihood with binned pdfs: Manual scan of likelihood space
• Data helps constrain systematics• `human intensive’
2. Kernel estimation---ML with unbinned pdfs:
Low Energy Threshold AnalysisSignal Extraction Fit
(3 signals+17 backgrounds)x2, and pdfs are multidimensional:ES, CC
NC, backgrounds
Two distinct methods:
• Allows full `floating’ of systematics, incl. resolutions
• CPU intensive---use graphics card!
Low Energy Threshold AnalysisFit Results: Binned fit, 1D Projections
LETA A LETA B
Low Energy Threshold Analysis8B Flux Results with `unconstrained’ CC spectrum
Low Energy Threshold Analysis `Unconstrained’ CC Electron Spectrum
Flat:2 = 21.52/15 d.o.f.
Low Energy Threshold Analysis `Unconstrained’ CC Electron Spectrum
PeeDAY(E) = c0 + c1 (E - 10 MeV)
+ c2 (E - 10 MeV)2
PeeASYM(E) = a0 + a1 (E - 10 MeV)
PeeNIGHT(E) = Pee
DAY(E) x [1 + (1/2)*PeeASYM(E)]
[1 – (1/2)*PeeASYM(E)]
Parameterize distortion to ne spectrum with quadraticPsurv is independent of any flux model:
CC and ES rates constrained to be less than NC
Note: Fit is now in En, not Teff
Low Energy Threshold Analysis Direct fit to data for Psurv(En)
This helps separate signals and backgrounds: PDFs are now 4D
Direct Fit for Energy-Dependent Survival
Probability
No distortion, no D/N:2 = 1.94 / 4 d.o.f.LMA-prediction:2 = 3.90 / 4 d.o.f.
Previous global best-fit LMA point: tan212 = 0.468, m2 = 7.59x10-5 eV2
DAY
NIGHT ASYM
8B = 5.046 +3.8 -
3.9 %
Borexino
SNO Day
Night
Comparisons of 8B SpectraJ.L. Raaf, Boston University
arXiv:0808.2868v2
Oscillation Analyses: SNO Only
Best-fit point:
tan212=0.437±0.058
m2=1.15x10-7 +0.438-0.18
eV2
LETA paper 2009:LETA joint-phase fit+ Phase III (3He)
(LOW)
SNO Collaboration, Phys. Rev C81, 55504
Solar + KamLAND 2-flavor Overlay
KamLAND Collab, Phys.Rev.Lett.90:021802,2003.
Brief History
Solar + KamLAND 2-flavor Overlay
KamLAND collaboration
Brief History
Solar + KamLAND 2-flavor OverlayBrief History
S. Abe et al. (KamLAND Collaboration), PRL 100, 221803 (2008)
Solar + KamLAND 2-flavor OverlayBrief History
LETA paper 2009:LETA joint-phase fit+ Phase III+ all solar expts+ KamLAND
LETA paper 2009:LETA joint-phase fit+ Phase III+ all solar expts+ KamLAND
2-flavor overlay
2 model
Solar + KamLAND 2-flavor Overlay
Oscillation Analyses: Solar + KamLANDLETA paper 2009:LETA joint-phase fit+ Phase III+ all solar expts+ KamLAND
Best-fit LMA point:
tan212 = 0.457 +0.040-0.029
(q12=34.06+1.16-0.84 deg)
sin2q12-1/3=-0.02+0.016-
0.018
m2 = 7.59x10-5 eV2 (+0.20 -0.21)8B uncert = +2.38
-2.95 %
2 model
LETA paper 2009:LETA joint-phase fit+ Phase III+ all solar expts+ KamLAND
3-flavor fit/overlay->Pointed out by many authors
3 model
Solar + KamLAND 3-flavor Overlay
Best-fit:
sin213=2.00 +2.09-1.63 x10-2
sin213 < 0.057 (95%
C.L.)
• Combine LETA+Phase III (3He) in single fit
• Pulse Shape Analysis to separate 3He signal from background
• Constrain 3-phase fit using 3He neutron count• Output is 8B flux using NC + Psurv(En)
``Three-Phase’’ Analysis
+
``Three-Phase’’ AnalysisPulse Shape Analysis
Hypoth
esi
s Te
st 1
Hypothesis Test 2
Two 2-D Cuts:
Fit to counter pulse energy spectrum used to constrain number of neutrons in full fit
See poster by R. Martin, N. Oblath, N. Tolich
``Three-Phase’’ AnalysisPulse Shape Analysis
All phases combined with Psurv(En) fit
See poster by P-L. Drouin, C. Howard, N. Barros
Also: expect to bring limits on hep down by x2
Expected Dm2 improvement
Other SNO Results
High frequency periodicity search
See poster by A. Anthony,ApJ. 710:540-548
Low-multiplicity burst search
Expected Sensitivity
Neutrons and spallation products
See poster by J. Loach
• LETA analysis improved precision on NC by more than factor of 2.
• Lowest analysis threshold yet achieved by water Cherenkov technique
• Low E spectrum (still) consistent with no distortion
• First model-independent fit for solar ne survival probability
• 3-flavor analysis shows non-zero q13 but consistent with q13=0:
• Expect further improvement with 3-phase analysis
• Just a few other things left to do…
Summary
sin213=2.00 +2.09-1.63 x10-2sin213 < 0.057 (95% C.L.)
Central runs remove source positioning offsets,
MC upgrades reduce shifts
Fiducial volume uncertainties (> factor of 3 improvement: Old: Phase I ~ ±3% Phase II ~ ±3% New: Phase I ~ ±1% Phase II ~ ±0.6%
Systematic UncertaintiesPosition
Tested with: neutron captures, 8Li, outside-signal-box ns
Old New
Systematic UncertaintiesIsotropy (b14)
MC simulation upgrades provide biggest source of improvementTests with muon `followers’, Am-Be source, Rn spike
b14 Scale uncertainties (factor of 2 improvement): Old: Phase I --- , Phase II = ±0.85% electrons, ±0.48% neutrons New: Phase I ±0.42%, Phase II =±0.24% electrons,+0.38%
-0.22% neutrons
8B Flux Result
NC = 5.140 +4.0 -3.8 %
J. N. Bahcall, A. M. Serenelli, and S. Basu, AstroPhys. J. 621, L85 (2005)
Calibrations
Parameters for simulation measured and tested with sources
• Laser source (optics/timing)• 16N 6.13 MeV ’s• Radon `spikes’• Neutrons 6.25 MeV ’s• pT 19.8 MeV ’s• 8Li ’s, E<14 MeV• Encapsulated U and Th
sources
Monte Carlo Upgrades
Volume-weighted uncertainties: Old: Phase I = ±1.2% Phase II = ±1.1% New: Phase I = ±0.6% Phase II = ±0.5% (about half Phase-correlated)
Systematic UncertaintiesEnergy Scale
No correction With correction
16N calibration source6.13 MeV gs
Tested with: Independent 16N data, n capture events, Rn `spike’ events…
New Cuts Summary
~80% reduction in external bkds
Direct Fit for Energy-Dependent Survival Probability
Previous global best-fit LMA point: tan212 = 0.468, m2 = 7.59x10-5 eV2
DAYNIGHT
Survival Probability
DAY
NIGHT
Survival Probability
DAY
NIGHT
Survival Probability
DAY
NIGHT
Survival Probability
DAY
NIGHT
Oscillation Analyses: Global SolarLETA paper 2009:LETA joint-phase fit+ Phase III+ all solar expts
Best-fit LMA point:
tan212 = 0.457 (+0.038 -0.041)
m2 = 5.89x10-5 eV2 (+2.13 -2.16)
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