External Backgrounds (γs) in partial-fill and the RopeAnalysis
Pouya Khaghani
August 13, 2021
Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 1 / 17
PhD candidate,Laurentian University/SNO+
Weekend line cook,Motley Kitchen.
Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 2 / 17
The SNO+ Experiment
2km Underground at SNOLABin Vale’s Creighton Mine (∼70cosmic muons/day)
Acrylic vessel (AV): 6m radius,5cm thickness
9400 Photo Multiplier Tubes(PMTs), ∼8m radius PSUP
905 tonnes of ultra-pure water/780 tonnes of liquid scintillatorbased cocktail
7000 tonnes external watershielding.
Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 2 / 17
What is SNO+ searching for?
Physics GoalsWater Phase: 8B SolarNeutrinos and Invisible nucleondecay1.
Pure Scintillator Phase: Solarneutrinos, Geo/Reactoranti-neutrinos, and studyinternal backgrounds.
Tellurium-loaded Scintillator:Neutrino-less double betadecay with 130Te
All phases:
Supernova NeutrinosReactor- and Geo-antineutrinos
1see Physical Review D 99 (1), 012012 & Physical Review D 99 (3), 032008).Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 3 / 17
Current Status
Water phase data taking 2017-2019 - In addition to Physics andcalibration, SNO+ made a measurement of external backgrounds(γ)s.Partial-fill 2020 APR-NOV: Filling process stopped due toCOVID-19 for 7 months while the detector was half-full.SNO+ used the partial-fill data to study internal/externalbackgrounds in scintillator.Detector is full and SNO+ is about to start the scintillator phase.
1The figures were taken on April 28th
Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 4 / 17
External γs from 208Tl and 214Bi and 40K
External Backgrounds: High energy γs from Tl208, Bi214 and K40which are generated outside of the scintillator volume (AV) but canpropagate and reconstructed inside.
They come from the AV. external water, HU/HD ropes, PMTs, ...
Tl208 generate γs up to 2.6 MeV which can be background for 0νββand solar signals.
0 0.5 1 1.5 2 2.5 3 3.5 4True MC Energy (MeV)
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dep_energy True energy of the gammas from Tl208_AV (MC simulation)
gammas from Bi214_AV (MC simulation)
Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 5 / 17
Identification of the 2.6 MeV γs from external 208Tl inpartial-fill
The major background for this signal are the 214Bi and 212Bi β decaysinside the detector.
Bi-Po events are tagged using the delayed coincidence taggingtechnique.
A set of MC was generated including the external signals as well as214Bi-Po in partial fill with the interface at 0.8 m and 0.5 g/L PPO.
400 500 600 700 800 900 1000Nhits
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BiPo214MC_bipo214_MC_partial
BiPo214 evts
External Tl208 gammas
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sum external
Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 6 / 17
214BiPo rejection efficiency and the external sacrifice
99% of the externals are being reconstructed beyond R > 5.2maccording to MC.
ROI: 5.2m< R & 2m< ρ (to avoid PFA tubing) & 1.5 < z < 5.3m
For rope studies the same cuts were used plus 1.5 < z < 3m
1000 2000 3000 4000 5000 6000R [mm]
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310even
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Pos R[mm]
gammas from Tl208_AV (MC) 0.5g/L PPO
BiPo214 in scintillator (MC)
gammas from Bi214_AV (MC)
Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 7 / 17
Tagging and rejecting 214BiPo events for 4.2m < R between 20200401 and
20200808 ( 70 days, most of June/July data are not included!)
nhits_PoEntries 41000Mean 239.8Std Dev 21.7
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nhits_PoEntries 41000Mean 239.8Std Dev 21.7
1500 2000 2500 3000 3500 4000 4500 5000rho [mm]
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m]
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0 100 200 300 400 500 600 700 800 900 1000delta R [mm]
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Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 8 / 17
Removing BiPo214/212 events
nhits_NoBiPosEntries 5379441
Mean 223.2
Std Dev 28.72
200 300 400 500 600 700 800 900 1000Nhits
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nhits_NoBiPosEntries 5379441
Mean 223.2
Std Dev 28.72
nhits (removed BiPos)
Tl208K40
Bi214/(gammas)
Bi210
Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 9 / 17
Removing BiPo214/212 events and identifying 208Tl signal
The fit values: µ = 762 ± 86 consistent with the calibration lightcurve.
Light yield has a significant radial dependency.
nhits_Tl208Entries 26293
Mean 728.2Std Dev 85.54
600 650 700 750 800 850 900 950 10000
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nhits_Tl208Entries 26293
Mean 728.2Std Dev 85.54
ExTl208_like_nhits
No upper R cut R<6m R<5.95m R<5.90m R<5.85m R<5.8m
Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 10 / 17
Reconstructed position and angular distribution
Total events with a validfitter:
6000− 4000− 2000− 0 2000 4000 6000x [mm]
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after tagging and rejectingBiPo214/212s:
6000− 4000− 2000− 0 2000 4000 6000pos x [mm]
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Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 11 / 17
Azimuthal analysis of the ropes through stacking method
Rope Analysis cuts: 1.5 < Z < 3m & 5.2m < R & energy > 2.6MeV.
Stacking method done is used to measure the level of backgroundfrom the HD ropes. (see SNO+-doc-5169-v1).
Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 12 / 17
Month by month Azimuthal analysis of data(20200401-20200920)
Stack_Theta_Tl208_750
Entries 2091Mean 8.951Std Dev 4.782
0 2 4 6 8 10 12 14 16 18Phi
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Stack_Theta_Tl208_750
Entries 2091Mean 8.951Std Dev 4.782
events vs. azimuthal angle (E>2.6 MeV)
April livetime = 713hrs
Stack_Theta_Tl208_750
Entries 1715Mean 9.098Std Dev 4.799
0 2 4 6 8 10 12 14 16 18Phi
120
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Stack_Theta_Tl208_750
Entries 1715Mean 9.098Std Dev 4.799
events vs. azimuthal angle (E>2.6 MeV)
July 705 hrs
Stack_Theta_Tl208_750
Entries 662Mean 9.218Std Dev 4.809
0 2 4 6 8 10 12 14 16 18Phi
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90
Stack_Theta_Tl208_750
Entries 662Mean 9.218Std Dev 4.809
events vs. azimuthal angle (E>2.6 MeV)
May 370.3 hrs
Stack_Theta_Tl208_750
Entries 1154Mean 9.151Std Dev 4.782
0 2 4 6 8 10 12 14 16 18Phi
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Stack_Theta_Tl208_750
Entries 1154Mean 9.151Std Dev 4.782
events vs. azimuthal angle (E>2.6 MeV)
August 662 hrs
Stack_Theta_Tl208_750
Entries 664Mean 8.782Std Dev 4.579
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Stack_Theta_Tl208_750
Entries 664Mean 8.782Std Dev 4.579
events vs. azimuthal angle (E>2.6 MeV)
June 470.4 hrs
Stack_Theta_Tl208_750
Entries 623Mean 9.101Std Dev 4.628
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Entries 623Mean 9.101Std Dev 4.628
events vs. azimuthal angle (E>2.6 MeV)
September448.4 hrs
Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 13 / 17
Conclusions and the next steps
The 2.6 MeV γs is identified in partialfill, and used for calibrationpurposes.
The γs from the ropes is estimated in partialfill and (data/MC) isconsistent with previous measurements. data/MC ∼0.31 ±0.04(doc-6580-v1).
In order to reject the externals several classifiers are developed andoptimized based on timing and geometry of the events.
Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 14 / 17
MC production for partial-fill and expected rate of externalbackgrounds.
RAT-6.18.7
source Tl208 AV Tl208 HD K40 AV K40 HD K40 water Bi214 AV Bi214 HDPMT gammasTl208
Expectednumber ofevts/year
1.5e+06(2.32/1.55)e+6
(full/shell)7.32e+7 1.89e+8 3.92e+06 2.67e+6
(4.06/2.72)e+6
(full/shell)—-
Simulatedevts.
614248 580637 3044471 5442269 – 1130866 542112 500458
Scale factor(roughly 70 days)
0.5856 0.64021 — 0.2046 2.7923
No. of evtswith valid fit
165100
No, eventsRope cuts**with E>2.6 MeVNhit>600 (MC)
2057
Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 15 / 17
Backup; BiPo214 tagging
Pouya Khaghani (LU) External Backgrounds (γs) in partial-fill and the Rope AnalysisAugust 13, 2021 16 / 17