Changgen Yang

Institute of High Energy Physics, Beijingfor the Daya Bay Collaboration

Daya Bay Neutrino Experiment

International UHE Tau Neutrino Workshop, April 24-26, 2006

13The Last Unknown

Neutrino Mixing Angle UMNSP Matrix

U Ue1 Ue2 Ue3

U1 U2 U 3

U1 U 2 U 3

1 0 0

0 cos23 sin23

0 sin23 cos23

cos13 0 e iCP sin13

0 1 0

e iCP sin13 0 cos13

cos12 sin12 0

sin12 cos12 0

0 0 1

1 0 0

0 e i / 2 0

0 0 e i / 2i

?

atmospheric, K2K reactor and accelerator 0SNO, solar SK, KamLAND

12 ~ 32° 23 = ~ 45° 13 = ?

Large and maximal mixing!

?

• What ise fraction of 3?• Ue3 is a gateway to CP violation in neutrino sector: P( e) - P( e) sin(212)sin(223)cos2(13)sin(213)sin

13 from Reactor and Accelerator Experiments

Pee 1 sin2 213 sin2 m312L

4E

cos4 13 sin2 212 sin2 m21

2L

4E

- Clean measurement of 13

- No matter effects

CP violation

mass hierarchy

matter

reactor

accelerator

- sin2213 is missing key parameter for any measurement of CP

Current Knowledge of 13

Direct search

At m231 = 2.5 103 eV2,

sin22 < 0.15

allowed region

Fogli etal., hep-ph/0506083

Sin2(213) < 0.09

Sin2213 < 0.18

Best fit value of m232 = 2.4103

eV2

Global fit

Limitations of Past and CurrentReactor Neutrino Experiments

Palo Verde, CHOOZTypical precision is 3-6%

due to• limited statistics• reactor-related systematic

errors:

- energy spectrum of e

(~2%)

- time variation of fuel

composition (~1%)• detector-related systematic

error (1-2%)• background-related error

(1-2%)

Daya Bay: Goals And Approach• Utilize the Daya Bay nuclear power facilities to:

- determine sin2213 with a sensitivity of 1%- measure m2

31

• Adopt horizontal-access-tunnel scheme:

- mature and relatively inexpensive technology- flexible in choosing overburden and changing baseline- relatively easy and cheap to add experimental halls- easy access to underground experimental facilities - easy to move detectors between different

locations with good environmental control.

• Employ three-zone antineutrino detectors.

How To Reach A Precision of 0.01 ?

• Powerful nuclear plant • Larger detectors

• “Identical” detectors

• Near and far detectors to minimize reactor-related errors

• Optimize baseline for best sensitivity and smaller residual reactor-related errors

• Interchange near and far detectors – cancel many detector systematic errors

• Sufficient overburden/shielding to reduce background

• Comprehensive calibration/monitoring of detectors

Ling Ao II NPP:2 2.9 GWth

Ready by 2010-2011

Ling Ao NPP:2 2.9 GWth

Daya Bay NPP:2 2.9 GWth

1 GWth generates 2 × 1020 e per sec

55 k

m

45 km

The Daya Bay Nuclear Power Facilities

• 12th most powerful in the world (11.6 GW)• Top five most powerful by 2011 (17.4 GW)• Adjacent to mountain, easy to construct tunnels to reach underground labs with sufficient overburden to suppress cosmic rays

Where To Place The Detectors ?

P(e e ) 1 sin2 213 sin2 m312 L

4E

cos4 13 sin2 212 sin2 m21

2 L

4E

• Place near detector(s) close to reactor(s) to measure raw flux and spectrum of e, reducing reactor-related systematic

• Position a far detector near the first oscillation maximum to get the highest sensitivity, and also be less affected by 12

• Since reactor e are low-energy, it is a disappearance experiment:

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

0.1 1 10 100

Nos

c/Nn

o_os

c

Baseline (km)

Large-amplitudeoscillation due to

12

Small-amplitudeoscillation due to 13

neardetector

fardetector

Baseline optimization and site

selection

• Neutrino spectrum and their error

• Neutrino statistical error

• Reactor residual error

• Estimated detector systematical error:

total, bin-to-bin

• Cosmic-rays induced background

(rate and shape) taking into mountain

shape: fast neutrons, 9Li, …

• Backgrounds from rocks and PMT glass

2

22 2

1 1,3

2 2 22 2 2

2 2 2 2 2 21 1,3

(1 )

min

rAA A A A Aii i D c d i r iANbin

r iA A As

i A i i b i

A ANbinc i dD r

r i AD c r shape d B

TM T c b B

T

T T B

c b

Daya BayNPP

Ling AoNPP

Ling Ao-ll NPP(under const.)

Entrance portal

Empty detectors: moved to underground halls through access tunnel.Filled detectors: swapped between underground halls via horizontal tunnels.

Total length: ~2700 m

230 m(15% slope)290 m

(8% slope) 73

0 m

570 m

910 m

Daya Bay Near360 m from Daya BayOverburden: 97 m

Ling Ao Near500 m from Ling AoOverburden: 98 m

Far site1600 m from Ling Ao2000 m from DayaOverburden: 350 m

Mid site~1000 m from DayaOverburden: 208 m

A Versatile Site• Rapid deployment:

- Daya Bay near site + mid site - 0.7% reactor systematic error

• Full operation: (A) Two near sites + Far site (B) Mid site + Far site (C) Two near sites + Mid site + Far site Internal checks, each with different systematic

Geophysical profile (Daya–mid--far)

Bore Samples Zk4 (depth: 133 m)

Zk2 (depth: ~180 m)

Zk3 (depth: ~64 m) Zk1 (depth: 210 m)

At tunneldepth

Findings of Geotechnical Survey

• No active or large fault• Earthquake is infrequent• Rock structure: massive and blocky

granite• Rock mass: most is slightly

weathered or fresh• Groundwater: low flow at the depth of

the tunnel• Quality of rock mass: stable and hard

Good geotechnical conditions for tunnel construction

Detecting Low-energy e

e p e+ + n (prompt)

+ p D + (2.2 MeV) (delayed)

+ Gd Gd* Gd + ’s(8 MeV) (delayed)

• Time- and energy-tagged signal is a good tool to suppress background events.

• Energy of e is given by:

E Te+ + Tn + (mn - mp) + m e+ Te+ + 1.8 MeV 10-40 keV

• The reaction is the inverse -decay in 0.1% Gd-doped liquid scintillator:

Arb

itra

ry

Flux Cross

Sectio

n

Observable Spectrum

From Bemporad, Gratta and Vogel

0.3b

50,000b

What Target Mass Should Be?

Systematic errorBlack : 0.6%

DYB: B/S = 0.5% LA: B/S = 0.4% Far: B/S = 0.1%

m231 = 2 10-3 eV2

tonnes

(3 year run)

Red : 0.25% (baseline goal)Blue : 0.12%

Design of Antineutrino Detectors• Three-zone structure:

I. Target: 0.1% Gd-loaded liquid scintillatorII. Gamma catcher: liquid scintillator, 45cmIII. Buffer shielding: mineral oil, ~45cm

• Possibly with diffuse reflection at ends. ~200 PMT’s around the barrel:

Isotopes(from PMT)

Purity

(ppb)

20cm

(Hz)

25cm (Hz)

30cm

(Hz)

40cm

(Hz)

238U(>1MeV) 50 2.7 2.0 1.4 0.8

232Th(>1MeV) 50 1.2 0.9 0.7 0.4

40K(>1MeV) 10 1.8 1.3 0.9 0.5

Total 5.7 4.2 3.0 1.7

Oil buffer thickness

buffer

20 tonne

s

Gd-LS

gamma catchervertex

14%~ , 14cm

(MeV)

E E

Why three zones ?

3-ZONE 2-ZONE

n capture on Gd yields 8 MeV with 3-4 ’s

Chooz

background

• 3 zones provides increased confidence in systematic error associated with detection efficiency and fiducial volume

• 2 zones implies simpler design/construction, some cost reduction but with increased risk to systematic error

Gd-loaded Liquid Scintillator For Daya BayA

bso

rban

ce a

t 43

0 n

m

Calendar Date

507 days (1.2% Gd in PC)

455 days (0.2% Gd in PC)367 days (0.2% Gd in 20% PC + 80% C12H26)130 days (0.2% Gd in LAB)

• Require stable Gd-loaded liquid scintillator with - high light yield- long attenuation length

• BNL/IHEP/JINR nuclear chemists study on metal-loaded liquid scintillator (~1% Gd diluted to ~0.1% Gd) for Daya Bay:

- technology of 1% Gd in pseudocumene (PC) is mature- need R&D for 1% Gd in mixture of PC and dodecane, and with linear alkyl benzene (LAB)

Attenuation lengths > 15 m

BNL samples

Design of Shield-Muon Veto

• Detector modules enclosed by 2m of water to shield neutrons and

gamma-rays from surrounding rock• Water shield also serves as a Cherenkov veto• Augmented with a muon tracker: scintillator or RPCs• Combined efficiency of Cherenkov and tracker > 99.5%

2 m ofwater

Neutron background vs thickness of water

Fast

neutr

ons

per

day

water thickness (m)

0.05

0.10

0.15

0.20

0.25

0.30

0. 1. 2.

50-ton crane

Electronic Hut Electronic Hut

Cart for moving detector module

pure water

ports for calibration

frame also serves as cable trays

Conceptual design of a underground water pool-based experimental hall

tunnel

Active Water Shield and Muon Tracker

• Specifications– High efficiency muon tracker; less than 0.3% inefficiency when

combined with the muon water Cherenkov – Good (ns) timing resolution to reduce accidentals due to ambient

radioactivity background– Muon tracker can be deployed in water pool – Robust, good long-term stability

PMT's for water Cherenkov

Moving Detectorsin Horizontal

Tunnels

Aircraft Pushback Tractors are Ideal

• Zero emission vehicles available

• Low-speed towing

• Forward and reverse towing

• Vehicle ballasted

• OK for incline (<8%)

Prototype setup at IHEP

LED

Cables

Flange to put Source Purposes: Test reflection, energy resolution, LS performance …

• Inner acrylic vessel: 1m in diameter and 1m tall, filled with normal liquid scintillator(70% mineral oil + 30% mesitylene).

• Outer stainless steel vessel: 2m in diameter and 2m tall, filled with mineral oil. PMTs mounted and immerged in oil.

• 45 MACRO PMT, 15 PMT/Ring

Attenuation Length and Light Yield

Lattn = 8.5+/-0.3m

PMTXP2020

PMTGlassTube

SourceCs137 orSr90

Liquid Scint.Or AnCrystal

61% relative to Anthracene

Very PreliminaryResolution: 15.5%@0.662MeV

Backgrounds

~350 m

~97 m

~98 m~210 m

Cosmic-ray Muon• Apply modified Gaisser parametrization for cosmic-ray flux at surface• Use MUSIC and mountain profile to estimate muon flux & energy

DYB LA Mid Far

Elevation (m) 97 98 208 347

Flux (Hz/m2) 1.2 0.73 0.17 0.045

Mean Energy (G

eV)

55 60 97 136

Summary of Background

Near Site Far Site

Radioactivity (Hz) <50 <50

Accidental B/S <0.05% <0.05%

Fast neutron background B/S 0.15% 0.1%8He/9Li B/S 0.41% ± 0.18% 0.02% ± 0.08%

• Use a modified Palo Verde-Geant3-based MC to model

response of detector:

(neutrino signal rate 560/day 80/day)

Further rejection of background may be possible by cuttingshowering muons.

Detector-related Uncertainties

Baseline: currently achievable relative uncertainty without R&D Goal: expected relative uncertainty after R&D

Absolutemeasurement

Relativemeasurement

→ 0→ 0.006

→ 0.06%

w/Swapping

→ 0

Swapping: can reduce relative uncertainty further

Summary of Systematic Errors• Reactor-related systematic errors are:

0.09% (4 cores)0.13% (6 cores)

• Relative detector systematic errors are:

0.36% (baseline)0.12% (goal)0.06% (with swapping)

• These are input to sensitivity calculations

90% confidence level90% confidence level

2 n

ear +

far (3

years)

near (4

0t) +

mid

(40 t)

1 year

Near-mid

Use rate and spectral shapeUse rate and spectral shape

Sensitivity of Daya Bay in sin2213

Daya Baynear hall

(40 t)

Tunnel entrance

Ling Aonear hall

(40 t)

Far hall(80 t)

Synergy Between Reactor and Accelerator Experiments

Before 2011: Daya Bay provides basis for early decision on future program beyond NOA for CP and mass hierarchy

After 2011: Daya Bay will complement NOA and T2K for resolving 23, mass hierarchy, and CP phase

Overall Project Schedule

Summary• The Daya Bay nuclear power facility in China and the mount

ainous topology in the vicinity offer an excellent opportunity for carrying out a reactor neutrino program using horizontal tunnels.

• The Daya Bay experiment has excellent potential to reach a sensitivity of 0.01 for sin2213.

• The Daya Bay Collaboration continues to grow.

• Will complete detailed design of detectors, tunnels and underground facilities in 2006.

• Plan to commission the Fast Deployment scheme in 2009, and Full Operation in 2010.

The Daya Bay Collaboration: China-Russia-U.S.

X. Guo, N. Wang, R. WangBeijing Normal University, Beijing

L. Hou, B. Xing, Z. ZhouChina Institute of Atomic Energy, Beijing

M.C. Chu, W.K. NgaiChinese University of Hong Kong, Hong Kong

J. Cao, H. Chen, J. Fu, J. Li, X. Li, Y. Lu, Y. Ma, X. Meng, R. Wang, Y. Wang, Z. Wang, Z. Xing, C. Yang, Z. Yao, J. Zhang, Z. Zhang, H. Zhuang, M. Guan, J. Liu, H. Lu, Y. Sun, Z. Wang, L. Wen, L. Zhan, W. ZhongInstitute of High Energy Physics, Beijing

X. Li, Y. Xu, S. JiangNankai University, Tianjin

Y. Chen, H. Niu, L. NiuShenzhen University, Shenzhen

S. Chen, G. Gong, B. Shao, M. Zhong, H. Gong, L. Liang, T. XueTsinghua University, Beijing

K.S. Cheng, J.K.C. Leung, C.S.J. Pun, T. Kwok, R.H.M. Tsang, H.H.C. WongUniversity of Hong Kong, Hong Kong

Z. Li, C. ZhouZhongshan University, Guangzhoz

Yu. Gornushkin, R. Leitner, I. Nemchenok, A. Olchevski

Joint Institute of Nuclear Research, Dubna, Russia

V.N. Vyrodov

Kurchatov Institute, Moscow, Russia

B.Y. Hsiung

National Taiwan University, Taipei

M. Bishai, M. Diwan, D. Jaffe, J. Frank, R.L. Hahn, S. Kettell, L. Littenberg, K. Li, B. Viren, M. Yeh

Brookhaven National Laboratory, Upton, New York, U.S.

R.D. McKeown, C. Mauger, C. Jillings

California Institute of Technology, Pasadena, California, U.S.

K. Whisnant, B.L. Young

Iowa State University, Ames, Iowa, U.S.

W.R. Edwards, K. Heeger, K.B. Luk

University of California and Lawrence Berkeley National Laboratory, Berkeley, California, U.S.

V. Ghazikhanian, H.Z. Huang, S. Trentalange, C. Whitten Jr.

University of California, Los Angeles, California, U.S.

M. Ispiryan, K. Lau, B.W. Mayes, L. Pinsky, G. Xu,

L. Lebanowski

University of Houston, Houston, Texas, U.S.

J.C. PengUniversity of Illinois, Urbana-Champaign, Illinois, U.S.

20 institutions, 89 collaborators