Antineutrino Detectors for a High-Precision Measurement of the Neutrino Mixing Angle θ13 at Daya Bay

Transcription

1 Antineutrino Detectors for a High-Precision Measurement of the Neutrino Mixing Angle θ13 at Daya Bay Karsten M. Heeger University of Wisconsin On behalf of the Daya Bay Collaboration 1

2 Precision Measurement of θ 13 with Reactor Antineutrinos Search for θ 13 in new oscillation experiment with multiple detectors Δm 2 P ee 1 sin 2 2θ 13 sin 2 31 L Δm cos 4 θ 13 sin 2 2θ 12 sin E ν 4E ν 2 L Small-amplitude oscillation due to θ 13 integrated over E 1.1 Large-amplitude oscillation due to θ θ 13 ~1-1.8 km > 0.1 km νe N osc /N no_osc Δm 2 13 Δm 2 23 detector 1 detector Baseline (km) 2

3 Concept of Reactor θ13 Experiments Measure ratio of interaction rates in multiple detectors νe near distance L ~ 1.5 km far 3

4 Concept of Reactor θ13 Experiments Measure ratio of interaction rates in multiple detectors νe near distance L ~ 1.5 km far Measured Ratio of Rates Detector Mass Ratio, H/C Detector Efficiency Ratio sin 2 2θ 13 3

5 Daya Bay, China Powerful ν e Source: multiple reactor cores, 11.6 GW th now,17.4 GW th in 2011 Shielding from Cosmic Rays: up to 1000 mwe

6 Daya Bay, China 5

7 Daya Bay, China experimental hall PMTs RPCs water pool muon veto system 5

8 Daya Bay, China experimental hall PMTs RPCs water pool muon veto system 5

9 Daya Bay, China experimental hall PMTs RPCs water pool muon veto system antineutrino detectors 5

10 Measuring θ13 at Daya Bay Far (80 t) LA (40 t) DYB (40 t) sin 2 2θ13 < 90% CL in 3 years of data taking 6

11 Measuring θ13 at Daya Bay Far (80 t) LA (40 t) DYB (40 t) sin 2 2θ13 < 90% CL in 3 years of data taking sensitivity: use rate and spectral shape detectors: identical detectors are near and far site relative error: near/far detector systematic error is 0.38% side-by-side comparison: compare event rates and spectra in two detectors detector swapping: detectors are movable, can be swapped but not necessary to reach design sensitivity, can cross-check and reduce systematics with moving control of systematics is key to the experimental sensitivity 6

12 Antineutrino Detector Design Requirements Design criteria from physics considerations Item Requirement Justification Target mass at far site 80 T Achieve sensitivity goal in three years over allowed m 2 31 range Precision on target mass 0.3% Meet detector systematic uncertainty baseline per module Energy resolution 15%/ E Assure accurate calibration to achieve required uncertainty in energy-threshold cuts (dominated by energy threshold cut) Detector efficiency error <0.2% Should be small compared to target mass uncertainty Positron energy threshold 1 MeV Fully efficient for positrons of all energies Radioactivity singles rate Hz Hz Limit accidental background to less than other backgrounds and keep data rate manageable key feature of experiment: identical detectors at near and far sites 7

13 Daya Bay Antineutrino Detectors Eight identical, 3-zone detectors calibration system liquid scintillator mineral oil ν e + p e + + n Gd-doped liquid scintillator reflectors steel tank acrylic tanks photomultipliers target mass: 20t per detector detector mass: ~ 110t photosensors: 192 PMTs energy resolution: 12%/ E 8

14 Antineutrino Detection Signal and Event Rates ν e + p e + + n 0.3 b + p D + γ (2.2 MeV) (delayed) Daya Bay near site 840 Ling Ao near site 760 Far site 90 events/day per 20 ton module 49,000 b + Gd Gd* Gd + γʼs (8 MeV) (delayed) Prompt Energy Signal Delayed Energy Signal 1 MeV 8 MeV 6 MeV 10 MeV

15 Daya Bay Antineutrino Detectors 3-Zone Design no position reconstruction, no fiducial cut oil buffer (MO) thickness > 15cm buffer between PMT and OAV MO Gd-LS (20 tons) LS gamma catcher (LS) thickness Efficiency (%) thickness = 42.5 cm det. efficiency > 91.5% = 5m (tunnel limitations) Gamma catcher thickness (cm)

16 Antineutrino Detector Performance Detection Efficiencies Geant4-based simulations Prompt e + Signal 1 MeV cut for prompt positrons: >99%, uncertainty negligible Delayed n Signal 6 MeV cut for delayed neutrons: 91.5%, uncertainty 0.22% assuming 1% energy uncertainty 6 MeV 10 MeV 11

17 Antineutrino Detector Event Distributions Geant4-based simulations Gd-LS R 2 distribution of neutron production point LS spill out 12% / E 1/2 reconstructed energy resolution R 2 distribution of neutron capture position 12

18 Antineutrino Detector Response z Detector Uniformity Geant4-based simulations R along radial R direction along vertical symmetry axis (z-direction) Gd-LS boundary Gd-LS boundary reflectors help with detector uniformity 13

19 Daya Bay Systematic Uncertainties Detector-Related Uncertainties Absolute measurement Relative measurement O( %) precision for relative measurement between detectors at near and far sites Ref: Daya Bay TDR 14

20 Daya Bay Systematic Uncertainties Detector-Related Uncertainties Absolute measurement Relative measurement O( %) precision for relative measurement between detectors at near and far sites Ref: Daya Bay TDR 14

21 Antineutrino Detector Overview overflow tanks, gas and electrical distribution boxes calibration pipes calibration boxes top/bottom reflector PMTs inner 3-m acrylic vessel outer 4-m acrylic vessel 15

22 Antineutrino Detector Construction An International Collaborative Effort Across Continents US - orange - 4m acrylic vessel with removable lid - acrylic overflow tanks for Gd-LS and LS - calibration pipes + bellows - overflow tank instrumentation - PMT mounts and ladders - PMTs, bases, and testing - PMT cables and feedthroughs - Gd-LS and LS China - grey - stainless steel vessel (SSV) - SSV lid - reflector - mineral oil (MO) overflow tank - overflow tank instrumentation - Gd-LS, LS, and MO Taiwan - blue - 3m acrylic vessel with bonded lid 16

23 Detector Steel Tank 17

24 Detector Steel Tank Delivery of first detector steel tank to Daya Bay Assembly Building March 13,

25 Detector Acrylic Vessel System Pair of nested acrylic vessels 3.1-m and 4-m diameter, fabricated from UVT acrylic 3 calibration pipe connections 4m vessel Reynolds, Colorado hold-down mechanism 3m vessel wall thickness: 15mm IAV 18mm OAV 4m vessel 3m vessel Nakano, Taiwan 19

26 Assembly of 4m Acrylic Vessel Prototype 20

27 Detector Reflective Panels specular reflector consists of ESR high reflectivity film on acrylic panel lifting structure tests total pe reflector flattens detector response 21 z (cm) z (cm)

28 PMT Ladders with Radial Light Shield 3 mm thick P-95 acrylic (black matte) as radial shield individual conical magnetic shields from 16 μm-thick Finemet foil eight PMT ladders with PMTs (R5912) magnetic shield reduces charge variation due to the local magnetic field from 25% to 5%. 22

29 Liquid Scintillator Detector Target 0.1% Gadolinium-Liquid Scintillator Proton-rich target Easily identifiable n-capture signal above radioactive backgrounds Short capture time (τ~28 µs) Good light yield ν e + p e + + n 0.3 b 49,000 b Isotopic Abundance Gd(152) Gd(154) 2.18 Gd(155) Gd(156) Gd(157) Gd(158) Gd(160) p D + γ (2.2 MeV) (delayed) + Gd Gd* Gd + γʼs (8 MeV) (delayed) 155Gd Σ E γ=7.93 MeV 157Gd Σ E γ=8.53 MeV fraction by weight C H N O Gd Gd capture 86.7% H capture 13.2% C capture 0.08% other Gd isotopes with high abundance have very small neutron capture cross TIPP09, sections March 14,

30 Gd-Liquid Scintillator Production System Daya Bay experiment uses 200 ton 0.1% gadolinium-loaded liquid scintillator (Gd-LS). Gd-TMHA + LAB + 3g/L PPO + 15mg/L bis-msb 5000-L Acrylic Vessel 500-L Acrylic Vessel 4-ton test batch production in March Two 1000-L Acrylic Vessels All Gd-LS will be produced as one batch on-site, to ensure identical detectors. 24

31 AD Filling and Target Mass Measurement LS Gd-LS MO AD is filled with liquids from three reservoirs: GD-LS, LS, and MO 3-zones of detector have to be filled simultaneously to avoid stresses on the acrylic vessels We assemble and fill pairs of detectors. Filling within ~2 weeks from each other. overflow tanks Gd-LS overflow tank LS overflow tank 25

32 AD Filling and Target Mass Measurement ISO Gd-LS weighing tank filling platform with clean room pump stations load cell accuracy < 0.02% load cell stands and calibration weights detector Coriolis mass flowmeters < 0.1% 26

33 Monitoring the Detectorʼs Effective Target Mass calibr. hardware 600 calibr. hardware 800 ~60mm ID gate valve 100 LITER LS OVERFLOW 300 stainless tank lid GDLS OVERFLOW 100 LITER overflow tank OIL OIL calibration pipe precise liquid level sensing in overflow tanks total mass ~ 20 tons REFLECTOR mass in calibration pipes ~ few kg mass in overflow tanks ~ O(100 kg) outer acrylic lid inner acrylic lid LS GD LS target mass (# protons) = total mass delivered to AD (measured) - mass in calibration pipe (calculated) - mass in overflow tank (calculated + monitored) LS target 27

34 Instrumentation for Target Mass Monitoring LS level monitor: visual CCD LS level monitor: pressure, ultrasound MO level monitor: capacitance, ultrasound Gd-LS level monitor: capacitance, ultrasound Gd-LS level monitor: visual CCDs ultrasonic gauge capacitance CCD camera to monitor fill level 28

35 Daya Bay Antineutrino Detector Construction 29

36 Daya Bay Antineutrino Detector Construction 29

37 Daya Bay Antineutrino Detector Construction detector tank 29

38 Daya Bay Antineutrino Detector Construction detector tank photomultipliers 29

39 Daya Bay Antineutrino Detector Construction detector tank calibration system photomultipliers 29

40 Daya Bay Antineutrino Detector Construction detector tank calibration system photomultipliers acrylic target vessels 29

41 Antineutrino Detector Assembly at Daya Bay surface assembly building detector assembly on surface entrance portal construction tunnel complete, empty detectors are moved underground 30

42 Antineutrino Detector Assembly at Daya Bay surface assembly building detector assembly on surface entrance portal construction tunnel March 2009: Assembly building occupancy Summer 2009: Near Hall occupancy Summer 2010: Near Hall ready for data Summer 2011: Far Hall ready for data 31

43 Deployment of Antineutrino Detectors < 0.5% 1. Moving detectors underground on < 10% grade when empty (20t) 2. Filling detectors underground with liquids < 10% < 0.5% LS Hall 3. Moving on < 0.5% tunnel grade when full (~110 t) 4. Lifting full detector (~110t) into water pool 5. Swapping detectors optional Automatic Guide Vehicle for detector transport 120 t overhead crane 32

44 Summary and Conclusions Daya Bay experiment is designed to measure sin 2 2θ13 < 0.01 at 90% CL in 3 years of data taking. Daya Bay is the most sensitive reactor θ13 experiment. Day Bay is funded. Civil and detector construction are progressing. Data taking at near site will begin in Daya Bay will use eight identical antineutrino detectors Relative detector systematic error < 0.38%. 3-zone detector design allows observation of antineutrino signal without fiducial cuts. Detectors are movable. Swapping is an option but not required to reach baseline sensitivity. 33

45 Daya Bay Collaboration Europe (3) (9) JINR, Dubna, Russia Kurchatov Institute, Russia Charles University, Czech Republic North America (14)(73) BNL, Caltech, George Mason Univ., LBNL, Iowa state Univ. Illinois Inst. Tech., Princeton, RPI, UC-Berkeley, UCLA, Univ. of Houston, Univ. of Wisconsin, Virginia Tech., Univ. of Illinois-Urbana-Champaign ~ 210 collaborators Asia (18) (125) IHEP, Beijing Normal Univ., Chengdu Univ. of Sci. and Tech., CGNPG, CIAE, Dongguan Polytech. Univ., Nanjing Univ.,Nankai Univ., Shandong Univ., Shenzhen Univ., Tsinghua Univ., USTC, Zhongshan Univ., Hong Kong Univ., Chinese Hong Kong Univ., National Taiwan Univ., National Chiao Tung Univ., National United Univ.

46 35

47 36 Phase-I, started in 2006, ended in Jan. 2007

48 37 IHEP Prototype filled with 0.1% Gd-LS Gd-TMHA complex synthesis Phase-II, filled with half-ton 0.1% Gd-LS, started in Jan and keep running until now. The prototype is also used for the FEE and Trigger boards testing.