The Daya Bay Calibration System Kimberly Boddy on behalf of the - - PowerPoint PPT Presentation

The Daya Bay Calibration System

Kimberly Boddy

• n 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

1

Systematic Uncertainties

2

Automated Calibration Units

3

Simulations of Calibration Sources

4

Concluding Remarks

Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 2 / 18

Systematic Uncertainties

Requirements on Systematic Uncertainties

Rf Rn

• Measured

Ratio of Rates

= Np,f Np,n

• Proton

Number Ratio

Ln Lf 2 ǫf ǫn

• Detector

Efficiency Ratio

Psur(E, Lf; sin2 2θ13) Psur(E, Ln; sin2 2θ13) Sensitivity goal: sin2 2θ13 < 0.01 Np relative uncertainty: 0.3% Attained using load cells and Coriolis mass and volume flow meters ǫ relative uncertainty: 0.2% Key requirement of calibration program

40 Ton Mixing Tank Far Near Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 3 / 18

Systematic Uncertainties

IBD Detection

Detect ¯ νs via inverse beta-decay in 20 tons of 0.1% Gd-doped LS: IBD threshold: E thr

¯ ν

= 1.806 MeV ¯ νe + p → e+ + n Prompt Signal: e+ + e− → 2γ 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 µs, 200 µs] 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

1

Systematic Uncertainties

2

Automated Calibration Units

3

Simulations of Calibration Sources

4

Concluding Remarks

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:

68Ge EC

− − → 68Ga

β+

− − → 68Zn Rate: 100 Bq (T1/2=270 days) ⇒ Positron threshold ⇒ Relative PMT quantum efficiencies LED source (deployed): 430 nm LED in 3/4” nylon diffuser ball ⇒ PMT timing, gain ⇒ Optical properties

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:

241Am (α) + 13C → n + 16O

Rate: 0.5 Hz Attenuate α to < 4.5 MeV with Au foil to suppress excited 16O (6.13 MeV) ⇒ Neutron energy scale ⇒ e+ threshold Gamma source:

60Co → 1.173 + 1.333 MeV

Rate: 150 Bq ⇒ Energy calibration ⇒ Monitor light yield/attenuation

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

12B

300/day/AD 28/day/AD σE /E = 0.5% 1 day/AD 10 days/AD per pixel

0.97 0.98 1.00 1.01 0.98 0.99 1.01 1.03 0.99 1.00 1.02 1.04 1.00 1.01 1.02 1.05 1.00 1.01 1.02 1.04 1.00 1.00 1.02 1.04 0.98 0.99 1.01 1.03 0.97 0.98 0.99 1.01 R (cm) 20 40 60 80 100 120 140 160 Z (cm)

• 150
• 100
• 50

50 100 150 0.98 0.99 1 1.01 1.02 1.03 1.04

18 m

Spallation products uniformly distributed 100 pixels/detector Energy stability (relevant to neutron capture ǫ): σE/E ∼ 0.5%

12B β-decay:

T1/2 = 20.2 ms and Q = 13.4 MeV

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

1

Systematic Uncertainties

2

Automated Calibration Units

3

Simulations of Calibration Sources

4

Concluding Remarks

Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 14 / 18

Simulations of Calibration Sources

Deployed Neutron Source

Energy spectrum of AmC + 60Co source at center of AD with backgrounds from stainless steel tank and PMTs:

reconEnergy

Entries 799991 Constant 0.01747 ± 0.01002 Mean 0.593 ± 8.034 Sigma 0.4173 ± 0.4174 Reconstructed Energy [MeV] 2 4 6 8 10 Events / sec

• 4

10

• 3

10

• 2

10

• 1

10 1 10

reconEnergy

Entries 799991 Constant 0.01747 ± 0.01002 Mean 0.593 ± 8.034 Sigma 0.4173 ± 0.4174

AmC + Co Source

60Co 2.5 MeV

Gd n-capture ∼8 MeV

Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 15 / 18

Simulations of Calibration Sources

Deployed Positron Source

Energy spectrum of 68Ge source at center of AD with backgrounds subtracted:

reconEnergy

1

Constant 0.0238 ± 0.9727

1

Mean 0.0019 ± 0.9215

1

Sigma 0.00221 ± 0.08849

2

Constant 0.0184 ± 0.7209

2

Mean 0.01 ± 0.74

2

Sigma 0.0030 ± 0.2179 Reconstructed Energy [MeV] 0.5 1 1.5 2 2.5 3 Events / sec

• 0.2

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

reconEnergy

1

Constant 0.0238 ± 0.9727

1

Mean 0.0019 ± 0.9215

1

Sigma 0.00221 ± 0.08849

2

Constant 0.0184 ± 0.7209

2

Mean 0.01 ± 0.74

2

Sigma 0.0030 ± 0.2179

Ge Source

positron annihilation 1.022 MeV

Kimberly Boddy (Caltech) The Daya Bay Calibration System DBD 2009 16 / 18

Concluding Remarks

Outline

1

Systematic Uncertainties

2

Automated Calibration Units

3

Simulations of Calibration Sources

4

Concluding Remarks

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: 68Ge source (two 511 keV γs) High-energy cut: nGd capture (8 MeV) Neutron Detection Efficiency ǫn = PGdǫEǫt PGd = 1/(1 + ΓH/ΓGd) Measure τ = 1/Γ to 0.5% ⇒ provide relative value of PGd to 0.1% uncertainty ǫE energy cut efficiency:

1% energy scale uncertainty leads to 0.2% uncertainty in ǫE Negligible uncertainty due to high-energy cut

ǫt time cut efficiency: Event window [0.3 µs,200 µs] 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 0.01 0.01 Live time <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.

LabVIEW Software

LabVIEW Software