Detection Methods at Reactor Neutrino Experiments

Jun Cao Institute of High Energy Physics (Beijing)

Feb. 11-15, 2013

2

A better title: Liquid Scintillator Detector for High Precision (Reactor) Neutrino Studies.

Reactor neutrino experiments Towards a high precision measurement Highlighted technologies Future reactor neutrino detector Summary

Outline

3

Daya Bay, Double Chooz, RENO DYBII

Reactor Neutrino Experiments

Reactor anti-neutrino experiments have played a critical role in the 60-year-long history of neutrinos.

The first neutrino observation in 1956 by Reines and Cowan.

Determination of the upper limit of mixing angle 13 in 90's (Chooz, Palo Verde)

The first observation of reactor anti-neutrino disappearance at KamLAND in 2002.

Measurement of the smallest mixing angle 13 at Daya Bay and other experiments in 2012.

4

Reactor Neutrinos Most commercial reactors are PWR or BWR.

235U, 239Pu, 241Pu beta spectra measured at ILL, 238U theoretically. In LS: Energy 1-10 MeV, Rate : ~ 1 event/day/ton/GW @ 1km

Power fluctuation <1%, rate and shape precision 2-3% Rate and spectra were verified by Bugey, Bugey3, Bugey4 Reactor anomaly

Peak at 4 MeV

5

Non-proliferation Monitoring

Bowden, LLNL, 2008

Non-proliferation monitoring studies supported by IAEA (France, US, Russia, Japan, Brazil, Italy)

Ton-level detector, very close to core. Water-based liquid scintillator for safety?

6

The Cowan-Reines Reaction

The first observation of neutrinos in 1956 by Reines & Cowan. Inverse beta decay in CdCl3 water solution coincidence of prompt

and delayed signal Liquid scintillator + PMTs Underground

Modern experiments are still quite similar, except Loading Gd into liquid scintillator Larger, better detector Deeper underground, better shielding

e nep 2e e

Capture on H, or Gd, Cd, etc.Delayed signal

Prompt signal

7

keV Scattering Experiments Neutrino magnetic moments exp.

Texono, GEMMA (HPGe) MUNU (TPC)

8

CHOOZ

Baseline 1.05 km 1997-1998, France 8.5 GWth300 mwe5 ton 0.1% Gd-LSBad Gd-LS

Parameter Relative error

Reaction cross section 1.9 %

Number of protons 0.8 %

Detection efficiency 1.5 %

Reactor power 0.7 %

Energy released per fission 0.6 %

Combined 2.7 %

R=1.012.8%(stat) 2.7%(syst), sin2213<0.17

Eur. Phys. J. C27, 331 (2003)

9

Palo Verde

1998-1999, US11.6 GWthSegmented detector12 ton 0.1% Gd-LSShallow overburden32 mwe

Baseline 890m & 750m

R=1.012.4%(stat) 5.3%(syst)

Palo Verde Gd-LSChooz Gd-LS 1st year 12%, 2nd year 3%

60%/year

Phys.Rev.D64, 112001(2001)

10

KamLAND

2002-, Japan53 reactors, 80 GWth1000 ton LS2700 mweRadioactivity fiducial cut,

Energy threshold

Baseline 180 km

11

Measuring 13

1 13 13

13 13

23 23

23 23

2 12

12 12

1 0 00 00

0 00 c s0 s c 0

c s 0s c 00 0 1

c 0 s0 0s 0 c 1

i

iiU eee

23 ~ 45Atmospheric Accelerator

12 ~ 34SolarReactor

013 = ?Reactor

Accelerator

Fogli et al., hep-ph/0506307

sin2213~0.04

Precision Measurement at reactors

12

Precision Measurement at Reactors

Parameter Error Near-farReactor ν flux 1.9 % 0

Energy released per fission 0.6 % 0Reactor power 0.7 % ~0.1%

Number of protons 0.8 % < 0.3%Detection efficiency 1.5 % 0.2~0.6%CHOOZ Combined 2.7 % < 0.6%

Major sources of uncertainties:

Reactor related ~2% Detector related ~2% Background 1~3%

Lessons from past experience: CHOOZ: Good Gd-LS Palo Verde: Better shielding KamLAND: No fiducial cut

Near-far relative measurementMikaelyan and Sinev, hep-ex/9908047

13

The Daya Bay Experiment• 6 reactor cores, 17.4 GWth • Relative measurement

– 2 near sites, 1 far site• Multiple detector modules• Good cosmic shielding

– 250 m.w.e @ near sites– 860 m.w.e @ far site

• Redundancy

3km tunnel

14

Daya Bay Results

2011-8-15

2011-11-5

2011-12-24

Mar.8, 2012, with 55 day datasin2213=0.0920.016(stat)0.005(sys

t)5.2 σ for non-zero θ13

Jun.4, 2012, with 139 day datasin2213=0.0890.010(stat)0.005(sys

t)7.7 σ for non-zero θ13

15

Double ChoozDaya Bay

Double Chooz

16

Double Chooz Results

Far detector starts data taking at the beginning of 2011 First results in Nov. 2011 based on 85.6 days of data

Updated results on Jun.4, 2012, based on 228 days of data sin2213=0.0860.041(Stat)0.030(Syst), 1.7σ for non-zero θ13

sin2213=0.1090.030(Stat)0.025(Syst), 2.9σ for non-zero θ13

17

RENO6 cores16.5 GW

16t, 450 MWE

16t, 120 MWE

Daya BayRENO

Double Chooz

18

RENO

Data taking started on Aug. 11, 2011 First physics results based on 228 days data taking (up to

Mar. 25, 2012) released on April 3, 2012, revised on April 8, 2012:

sin2213=0.1130.013(Stat)0.019(Syst), 4. 9σ for non-zero θ13

19

Rate and Spectrum

R = 0.944 ± 0.007 (stat) ± 0.003 (syst)

sin22θ13=0.089±0.010(stat)±0.005(syst)

Chinese Physics C, Vol. 37, No. 1 (2013) 011001

EH1 140 000 events EH2 66 000 eventsEH3 30 000 events

Still dominated by statistics

20

Global Picture of 13 MeasurementsTi

me

line

21

Detecting Reactor Antineutrino

e nep 2e e

Delayed signal, Capture on H (2.2 MeV) or Gd (8 MeV), ~30s

Prompt signal Peak at ~4 MeV

Capture on H

Capture on Gd

Inverse beta decay

Energy selection, time correlationMajor backgrounds: Cosmogenic neutron/isotopes

8He/9Li fast neutron

Ambient radioactivity accidental coincidence

0.1% Gd by weight

22

Detector Design Water Shield radioactivity and

cosmogenic neutron Cherekov detector for muon

RPC or Plastic scintillatormuon veto

Three-zone neutrino detectorTarget: Gd-loaded LS

8-20 t for neutrino-catcher: normal LS

20-30 t for energy containmentBuffer shielding: oil

40-90 t for shielding

( ton ) DYB DC RENOTarget 20 8.3 16

-catcher

20 18 28

Buffer 37 88 65Total 77 114 110

23

Detector Design Water Shield radioactivity and

cosmogenic neutron Cherekov detector for muon

RPC or Plastic scintillatormuon veto

Three-zone neutrino detectorTarget: Gd-loaded LS

8-20 t for neutrino-catcher: normal LS

20-30 t for energy containmentBuffer shielding: oil

40-90 t for shielding

Daya Bay Reflective panelsReduce PMT numbers to 1/2

24

Gadolinium-doped Liquid Scintillator

nH, 2.2 MeV nGd, 8.05 MeV

Coincidence pair in (1-200) s

e nep 2e e

Delayed signal, Capture on H (2.2 MeV) or Gd (8 MeV), ~30s

Prompt signal

Significantly Lower the low-background requirement

Well-defined target mass(no fiducial volume cut)

KamLAND didn't dope; DYB-II will not dope.

w/o doping, DYB 20 t detector 5m, 110 t --> 6.5m, 210 t; lower eff. due to muon veto; larger uncer.

Singles Spectrum

Natural Radioactivity

25

Inner Gd-LS: precise target mass, E higher than radioact. Middle layer: -catcher to contain gamma energy

attenuation length of 1 MeV ~ 20 cm neutron selection eff increase from 0.2% to 0.4% for 2-layer Energy resolution is NOT sensitive (7% 12%)

Outer layer: shield radioactivity, uniform response. Uncertainty from accidental backgrounds (DYB) ~0.05%

Why 3-layer

w/ -catcher w/o -catcher

26

Idea of "identical detectors" throughout the procedures of

design / fabrication / assembly / filling. For example: Inner Acrylic Vessel, designed D=31205 mm

Variation of D by geometry survey=1.7mm, Var. of volume: 0.17% Target mass var. by load cell measurement during filling: 0.19%

Functional Identical Detectors

Diameter IAV1 IAV2 IAV3 IAV4 IAV5 IAV6Surveyed(mm

)3123.12 3121.71 3121.77 3119.65 3125.11 3121.56

Variation (mm)

1.3 2.0 2.3 1.8 1.5 2.3 "Same batch" of liquid scintillator

5x40 t Gd-LS, circulated

200 t LS, circulated4-m AV in pairs Assembly in pairs

20 t filling tank

27

Side-by-side Comparison (1) Relative uncertainties: difference between detectors

nGd 8 MeV peak

Energy scale of 6 ADs

Two ADs in EH1

within 0.5%

n capture time AD spectra

28

Designed detector uncertainties (relative)

Daya Bay 0.15-0.38%, Double Chooz 0.5%, RENO 0.5% Comparing to 2.7% of CHOOZ

Achieved 0.2% in short term

The State-of-the-art Neutrino Detector

Can be improved w/ det. by det. correction

Can be further constrained w/ more data

29

Side-by-side Comparison (2)

Expected ratio of neutrino events: R(AD1/AD2) = 0.982 The ratio is not 1 because of target mass, baseline, etc.

Measured ratio: 0.987 0.004(stat.) 0.003(syst.)

This check shows that syst. are under control, and will eventually "measure" the total syst. error

Neutrino Enery spectraData set: 2011.9 to 2012.5

30

Doping metal into organic LS is not easy.

Previous Gd-LS

Palo Verde Gd-LSGdCl3+EHA (carboxylic acid)

Chooz Gd-LSGd(NO3)3 + hexanol

3%/y60%/y

Solvent: Xylene, Pseudocumene, ... attack acylic (+MO) New solvents of high flash point, low toxicity ...

LAB, PXE, DIN, PCH

31

Systematic studies on Gd-LS after the failure of CHOOZ.

β-diketones: Acac, DBM, BTFA, HPMBP, THD Carboxylic acid: 2-MVA(6C), n-heptanoic(7C), EHA(8C),

TMHA(9C) Organophosphorous: TOPO, D2EHP, TEP, DBBP

Stability, solubility, transparency and purification, large-scale production ...

Gd-LS

Exp. Solvent Gd Agent Quantity (t)

CHOOZ IPB Hexanol 5Palo Verde PC+MO EHA 12

Double Chooz

PXE+dodecane

-dikotonate

s

8

Daya Bay LAB TMHA 185fluor: PPO, second wavelenth shifter: bis-MSB

32

Gd-LS Production in DYB

Clear Gd(TMHA) in LAB~ 0.5% concentration

Fluor-LAB

4 ton MixingN2 bubbling

filtrationTo 40ton Tank

GdCl3 purification

Gd(TMHA)3

synthesis and dissolution

5x40t Gd-LS tanks

Wet solidPH tuned TMHA

GdCl3

33

Radiopurification of GdCl3

Co-precipitation to remove U/Th: increase the PH of GdCl3 water solution (~5% precipitate), filter, and tune back.

Complexing to remove Ra• 232Th228Ra228Th224Ra212Bi212Po(164s)

• 238U234Th234U230Th226Ra214Bi214Po(0.3s)210Pb210Po

• 235U231Pa227Ac219Rn215Po(1.78ms)

(1s, 3s)

(10s, 160s)

(1ms, 2ms)

Total

232Th

238U

227Ac

227Ac

Delayed energy (MeV)

Prom

pt e

nerg

y (M

eV)

232Th: 10 mBq/ton (2.5e-3 ppb) 238U: 0.5 mBq/ton (4e-5 ppb)227Ac: 10 mBq/ton

Chin. Phys. C37, 011001 (2013)

Natural abundance 238U/235U ~ 22In DYB Gd-LS: 238U/235U ~ 0.05

Purification of at least 400 times (some are during refining of Gd)

34

Daya Bay: weekly calibration

ACU (enable >99.7% μ eff.): LED, Ge, Co, 241Am-13C (0.5 Hz) Special ACU: Cs, Mn, Am-Be Manual (4π): Co, 238Pu-13C (4% 6 MeV gamma)

Double Chooz: laser, Cs, Ge, Co, Cf RENO: LED, Cs, Ge, Co, Cf Relative energy scale uncertainty within 0.5%

Calibration

ACU-A ACU-CACU-B

35

ESR film: Specular reflection for better understanding of detector Sandwich structure, keep intact surface with vacuum pressure Electrostatic adherence to ensure a perfect specular surface.

Reflective Panels4.5 m in diameter

2 cm thick

1cm Acrylic sheet

1cm Acrylic sheet

65 m ESREpoxy sealingbulk polymerization

PMT Coverage

pe yield(pe/MeV

)

pe yield

/Coverage

Daya Bay 192 8"

~6% 163 1.77

RENO 354 10"

~15%

230 1

Double Chooz

390 10"

~16%

200 0.81

36

Reflective Panel in Detector

37

Next Step: Daya Bay-II Experiment

Daya Bay Daya Bay II 20 kton LS detector 3%/E̅ resolution Rich physics

Mass hierarchy Precision measurement

of 4 oscillation parameters to <1%

Supernovae neutrino Geoneutrino Sterile neutrino Atmospheric neutrinos Exotic searches

Talk by Y.F. Wang at ICFA seminar 2008...NuFact 2012; by J. Cao at Nutel 2009...NPB 2012 (ShenZhen); Paper by L. Zhan, Y.F. Wang, J. Cao, L.J. Wen, PRD78:111103,2008; PRD79:073007,2009

DYB-II has been approved in China in Feb. 2013 Equivalent to CD1 of US DOE

38

The reactors and possible sites Daya Bay Huizhou Lufeng Yangjiang Taishan

Status Operational Planned Planned Under construction Under constructionPower 17.4 GW 17.4 GW 17.4 GW 17.4 GW 18.4 GW

Daya BayHuizhou Lufeng

Yangjiang

Taishan

Hong Kong

Kaipin, Jiangmeng, Guang Dong

39

Detector ConceptMuon tracking

Liquid Scintillator20 kt

Acrylic sphere ： φ34.5m

SS sphere ： φ 37 .5m

Water Seal

~15000 20” PMTsoptical coverage: 70-80%

Stainless Steel Tank

Oil buffer 6kt

Water Buffer 10kt

VETO PMTs

1) Traditional Design (figure)• Alternate: acrylic -> ballon• Alternate: acrylic -> PET sphere

2) No SST (like SNO)3) Only SST, no inner vessel4) Modulized oil box in SST

40

DYB-II Energy Resolution

, or (2.6/

DYB-II MC, based on DYB MC (p.e. tuned to data), except DYBII Geometry and 80% photocathode coverage SBA PMT: maxQE from 25% -> 35% Lower detector temperature to 4 degree (+13% light) LS attenuation length (1 m-tube measurement@430 nm)

from 15 m = absoption 24 m + Raylay scattering 40 m to 20 m = absorption 40 m + Raylay scattering 40 m

Uniformly Distributed Events

After vertex-dep. correction

R3

41

Discovery Power

If m232 at 1% precision，mass

hierarchy could be determined to ~5 in 6 years. (core distribution and energy non-linearity may degrade it a little bit.

Taking into account m232 from

T2K and Nova in the future：

Contribution from absolute m2

32 measurement

Current DYB II m2

12 3% 0.6%

m223 5% 0.6%

sin212 6% 0.7%

sin223 20% N/A

sin213 14% 4% ~ 15%

Will be more precise than CKM matrix elements !

Probing the unitarity of UPMNS to ~1% level

42

15000 20-in PMTs with maxQE 35% MCP-based PMT, led by IHEP, since 2008. Hamamatsu dynode PMTs (or HPD-based) LAPPDs, Borosilicate capillary array for

MCP, U. Chicago, ANL, etc. Ultra-transparent liquid scintillator

Default recipe: LAB + PPO + bis-MSB (Daya Bay undoped LS)

High transparence LAB Purification of LS

Mechanics of the giant detector Energy calibration

Technical Challenges

43

DYBII: Brief schedule Civil preparation： 2013-2014 Civil construction： 2014-2017 Detector R&D： 2013-2016 Detector component production： 2016-2017 PMT production： 2016-2019 Detector assembly & installation： 2018-2019 Filling & data taking： 2020

Welcome collaborators

44

S.B. Kim, talk at Neutrino 2012

• Mass Hierachy• Solar neutrino• Geoneutrino• Supernovae• T2K beam• exotic

45

Summary Reactor Neutrino experiments were prosperous. Liquid scintillator + PMTs Detector uncertainties reduced from ~3% to 0.2% in

recent 13 measurements. As the most powerful man-made neutrino source,

reactor neutrinos will continue to contribute in Mass hierarchy Precision measurement of mixing parameters to < 1%

unitarity test of the mixing matrix Sterile neutrinos, Neutrino magnetic moments, ...

Challenges: Liquid scintillator, PMTs, Gaint detector

Happy New Year !

In 2013:Feb. 3 Kitchen God FestivalFeb. 10 Chinese New YearFeb. 24 The Lantern Festival