The Daya Bay Calibration System Kimberly Boddy on behalf of the Daya Bay Collaboration Caltech DBD 2009: Session II 12 October 2009 Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 1 / 18
Outline Systematic Uncertainties 1 Automated Calibration Units 2 Simulations of Calibration Sources 3 Concluding Remarks 4 Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 2 / 18
Systematic Uncertainties Requirements on Systematic Uncertainties � 2 � ǫ f � N p , f P sur ( E , L f ; sin 2 2 θ 13 ) � � L n � R f = P sur ( E , L n ; sin 2 2 θ 13 ) R n N p , n L f ǫ n ���� � �� � � �� � Measured Proton Detector Ratio of Number Efficiency Rates Ratio Ratio Sensitivity goal: sin 2 2 θ 13 < 0 . 01 N p relative uncertainty: 0.3% Attained using load cells and Coriolis mass 40 Ton and volume flow meters Mixing Tank ǫ relative uncertainty: 0.2% Near Far Key requirement of calibration program Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 3 / 18
Systematic Uncertainties IBD Detection Detect ¯ ν s via inverse beta-decay in 20 tons of 0.1% Gd-doped LS: IBD threshold: E thr = 1 . 806 MeV ν ¯ ν e + p → e + + n ¯ Prompt Signal: e + + e − → 2 γ Delayed Signal: n + Gd → Gd + γ ( ∼ 8 MeV) [ ∼ 50,000 barns] n + p → d + γ (2.2 MeV) [0.3 barns] Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 4 / 18
Systematic Uncertainties Detector Efficiency Calibration Positron detection : Energy cuts at 1 and 8 MeV Neutron detection : Energy cuts at 6 and 10 MeV Delayed timing cuts [0.3 µ s, 200 µ s] Gd/H ratio To achieve 0.2% on detector efficiency, need to know e + relative threshold to 2% (easy) and relative n threshold to 1% (more difficult). Calibration program : ⋄ Routine (weekly) deployment of calibration sources ⋄ Radioactive sources → fixed energy LED light source → fixed time ⋄ Tagged cosmogenic background Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 5 / 18
Automated Calibration Units Outline Systematic Uncertainties 1 Automated Calibration Units 2 Simulations of Calibration Sources 3 Concluding Remarks 4 Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 6 / 18
Automated Calibration Units Automated Calibration Units (ACU) 3 ACUs: LS and on-/off-axis GdLS Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 7 / 18
Automated Calibration Units Automated Calibration Units Source deployment (speed × 5): Loading... Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 8 / 18
Automated Calibration Units Calibration Sources Positron source: LED source (deployed): β + 68 Ge EC → 68 Ga → 68 Zn 430 nm LED in 3/4” nylon − − − − diffuser ball Rate: 100 Bq (T 1 / 2 =270 days) ⇒ PMT timing, gain ⇒ Positron threshold ⇒ Optical properties ⇒ Relative PMT quantum efficiencies Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 9 / 18
Automated Calibration Units Calibration Sources Fixed LEDs in mineral oil to monitor reflectors and attenuation length. 2” PMT ( × 6) Fixed LEDs Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 10 / 18
Automated Calibration Units Calibration Sources Neutron source: Gamma source: 241 Am ( α ) + 13 C → n + 16 O 60 Co → 1.173 + 1.333 MeV Rate: 0.5 Hz Rate: 150 Bq Attenuate α to < 4 . 5 MeV with ⇒ Energy calibration Au foil to suppress excited 16 O ⇒ Monitor light (6.13 MeV) yield/attenuation ⇒ Neutron energy scale ⇒ e + threshold Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 11 / 18
Automated Calibration Units Spallation from Cosmogenic Muons Use spallation neutrons to determine stability of detectors. Near Far Neutrons 13500/day/AD 1100/day/AD 12 B 300/day/AD 28/day/AD σ E / E = 0 . 5% 1 day/AD 10 days/AD per pixel Spallation products 18 m uniformly distributed Z (cm) 150 0.97 0.98 0.99 1.01 1.04 100 pixels/detector 0.98 0.99 1.01 1.03 100 1.03 Energy stability (relevant 1.00 1.00 1.02 1.04 50 1.02 to neutron capture ǫ ): 1.00 1.01 1.02 1.04 1.01 0 σ E / E ∼ 0 . 5% 1.00 1.01 1.02 1.05 1 -50 0.99 1.00 1.02 1.04 12 B β -decay: 0.99 -100 0.98 0.99 1.01 1.03 T 1 / 2 = 20 . 2 ms and 0.98 0.97 0.98 1.00 1.01 -150 Q = 13 . 4 MeV 0 20 40 60 80 100 120 140 160 R (cm) Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 12 / 18
Automated Calibration Units Additional Calibration Systems Manual calibration: CIAE MO clarity: CUHK and HKU Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 13 / 18
Simulations of Calibration Sources Outline Systematic Uncertainties 1 Automated Calibration Units 2 Simulations of Calibration Sources 3 Concluding Remarks 4 Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 14 / 18
Simulations of Calibration Sources Deployed Neutron Source Energy spectrum of AmC + 60 Co source at center of AD with backgrounds from stainless steel tank and PMTs: reconEnergy reconEnergy AmC + Co Source Entries Entries 799991 799991 Events / sec 10 ± ± Constant Constant 0.01002 0.01002 0.01747 0.01747 60 Co 2.5 MeV ± ± Mean Mean 8.034 8.034 0.593 0.593 1 ± ± Sigma Sigma 0.4174 0.4174 0.4173 0.4173 -1 10 Gd n -capture ∼ 8 MeV -2 10 -3 10 -4 10 0 2 4 6 8 10 Reconstructed Energy [MeV] Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 15 / 18
Simulations of Calibration Sources Deployed Positron Source Energy spectrum of 68 Ge source at center of AD with backgrounds subtracted: reconEnergy reconEnergy Ge Source Constant Constant ± ± 0.9727 0.9727 0.0238 0.0238 1 1 Events / sec 1.6 ± ± Mean Mean 0.9215 0.9215 0.0019 0.0019 1 1 Sigma Sigma ± ± 0.08849 0.08849 0.00221 0.00221 1.4 1 1 Constant Constant ± ± 0.7209 0.7209 0.0184 0.0184 2 2 1.2 Mean Mean ± ± 0.74 0.74 0.01 0.01 2 2 Sigma Sigma ± ± 0.2179 0.2179 0.0030 0.0030 1 2 2 0.8 positron annihilation 1.022 MeV 0.6 0.4 0.2 0 -0.2 0 0.5 1 1.5 2 2.5 3 Reconstructed Energy [MeV] Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 16 / 18
Concluding Remarks Outline Systematic Uncertainties 1 Automated Calibration Units 2 Simulations of Calibration Sources 3 Concluding Remarks 4 Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 17 / 18
Concluding Remarks Status Report Fabrication of first 2 ACUs complete - delivered in August Longevity tests performed (4 years worth of deployment) Software complete and undergoing testing Test during AD dry run Ge source: Ready Co source: Ready AmC source: Prototyped, developing protocol for assembly and shipment Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 18 / 18
Backup Slides
Background from Neutron Source in ACU Limit neutron source to 0.5 Hz ∼ 1-2% of neutrons from AmC source in ACU create signal in AD Accidental bkg rate (event/day/AD) 1.20 (DB) Acc/IBD event rate (%) 0.19 (LA) Acc/IBD event rate (%) 0.18 (Far) Acc/IBD event rate (%) 1.33 Investigating correlated background rate
IBD Detection Efficiency Positron Detection Efficiency Low-energy cut: 68 Ge source (two 511 keV γ s) High-energy cut: n Gd capture (8 MeV) Neutron Detection Efficiency ǫ n = P Gd ǫ E ǫ t P Gd = 1 / (1 + Γ H / Γ Gd ) Measure τ = 1 / Γ to 0.5% ⇒ provide relative value of P Gd to 0.1% uncertainty ǫ E energy cut efficiency: 1% energy scale uncertainty leads to 0.2% uncertainty in ǫ E Negligible uncertainty due to high-energy cut ǫ t time cut efficiency: Event window [0.3 µ s,200 µ s] can be determined to ∼ 10 ns precision by using common master clock for all electronics
Reducing Systematic Uncertainties Source of uncertainty Chooz Daya Bay ( relative ) ( absolute ) Baseline Goal # protons 0.8 0.3 0.1 Detector Energy cuts 0.8 0.2 0.1 Efficiency Position cuts 0.32 0.0 0.0 Time cuts 0.4 0.1 0.03 H/Gd ratio 1.0 0.1 0.1 n multiplicity 0.5 0.05 0.05 Trigger 0 0.01 0.01 Live time 0 < 0.01 < 0.01 Total detector-related uncertainty 1.7% 0.38% 0.18% All numbers are in percent. Chooz has a one-detector absolute uncertainty. Daya Bay will have a two-detector relative uncertainty.
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