1 The Daya Bay Reactor Electron Anti-neutrino Oscillation Experiment Jianglai Liu (for the Daya Bay Collaboration) California Institute of Technology APS.

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The Daya Bay Reactor Electron Anti-neutrino Oscillation Experiment

Jianglai Liu (for the Daya Bay Collaboration) California Institute of Technology

APS DNP Conference, Newport News, Oct. 13, 2007

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Physics Motivation

Weak eigenstate mass eigenstate Pontecorvo-Maki-Nakagawa-Sakata Matrix

3

2

1

3

2

1

321

321

321

7.06.04.0

7.06.04.0

?5.08.0

UUU

UUU

UUU eeee

100

00

00

cossin0

sincos0

001

cos0sin

010

sin0cos

100

0cossin

0sincos2

1

2323

2323

1213

1313

1212

1212

i

i

i

i

e

e

e

e

Parametrize the PMNS matrix as:

Solar, reactor reactor and accelerator 0Atmospheric, accelerator

23 ~ 45° 12 = ~ 32° 13 = ?

13 is the gateway of CP violation in lepton sector!

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Measuring 13 Using Reactor Anti-neutrinos

E

Lm

E

LmPee 4

sin2sincos4

sin2sin12

21212

213

42

13213

2

Electron anti-neutrino survival probability

e disappearance at short baseline(~2 km): unambiguous measurement of 13

Large oscillation >50 km; negligible <2 km

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Increase statistics: Use powerful reactors & large target mass & optimized baselineSuppress background:

Go deeper underground

High performance veto detector to MEASURE the background

Reduce systematic uncertainties:Reactor-related: Utilize near and far detectors to minimize reactor-related errors

Detector-related:

Use “Identical” pairs of detectors to do relative measurement

Comprehensive program in calibration/monitoring of detectors

Previous best experimental limits from Chooz: sin2(213) <0.17 (m2

31=2.510-3 eV, 90% c.f.)

Daya Bay: Goal and Approach

Daya Bay:determine sin2213 with a sensitivity of 1%

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4 x 20 tons target mass at far site

Daya Bay: Powerful reactor by mountains

Far site1615 m from Ling Ao1985 m from DayaOverburden: 350 m

900 m

Daya Bay Near site363 m from Daya BayOverburden: 98 m

Ling Ao Near site~500 m from Ling AoOverburden: 112 m

465 m

295 m

810

m

22.9 GW

22.9 GW

(under construction) 22.9 GW in 2010

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Detection of e

Inverse -decay in Gd-doped liquid scintillator:

0.3b + Gd Gd* Gd + ’s(8 MeV) (t~30μs) + p D + (2.2 MeV) (t~180μs)

50,000b

nepe

Time, space and energy-tagged signal suppress background events.

Delayed Energy SignalPrompt Energy Signal

E Te+ + 1.8 MeV

1 MeV 8 MeV

6 MeV 10 MeV

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Antineutrino Detector

Cylindrical 3-Zone Structure separated by acrylic vessels:

I. Target: 0.1% Gd-loaded liquid scintillator, radius=half height= 1.55 m, 20 ton

II. -catcher: liquid scintillator, 42.5 cm thick

III. Buffer shielding: mineral oil, 48.8 cm thick

vertex

14%~ , 14cm

(MeV)

E E

11.6 %

12.5 cm for 8 MeV e-

With 192 PMT’s on circumference

and reflective reflectors on top and bottom:

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Calibrating Energy Cuts

Automated deployed radioactive sources to calibrate the detector energy and position response within the entire range.

68Ge (0 KE e+ = 20.511 MeV ’s) 252Cf (~4 neutrons/fission, 2.2 MeV n-p and 8 MeV n-Gd captures) LEDs (timing and PMT gains) R=1.35mR=0R=1.775 m

In addition, cosmogenic background (n and beta emitters) provide additional energy scale calibration sampled over the entire fiducial volume

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Muon Veto System

Surround detectors with at least 2.5m of water, which shields the external radioactivity and cosmogenic background

Water shield is divided into two optically separated regions (with reflective divider, 8” PMTs mounted at the zone boundaries), which serves as two active and independent muon tagger

Augmented with a top muon tracker: RPCs

Combined efficiency of tracker > 99.5% with error measured to better than 0.25%

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Backgrounds

DYB site LA site Far siteFast n / signal 0.1% 0.1% 0.1%9Li-8He / signal 0.3% 0.2% 0.2%

Accidental/signal <0.2% <0.2% <0.1%

Background = “prompt”+”delayed” signals that fake inverse-beta events

Three main contributors, all can be measured:

Background type Experimental Handle

Muon-induced fast neutrons (prompt recoil, delayed capture) from water or rock

>99.5% parent “water” muons tagged

~1/3 parent “rock” muons tagged9Li/8He (T1/2= 178 msec, b decay w/neutron emission, delayed capture)

Tag parent “showing” muons

Accidental prompt and delay coincidences Single rates accurately measured

B/S:

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Baseline Systematics Budget

Detector Related 0.38%

Reactor related 0.13%

Backgrounds 0.3% (Daya Bay near),

0.2% (Ling Ao near and far)

Signal statistics 0.2% (3 years of running)

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Daya Bay Sensitivity

90% confidence level, “baseline” detector uncertainties90% confidence level, “baseline” detector uncertaintiesUse rate and spectral shapeUse rate and spectral shape

Milestones DoE CD1 review, April 2007, approved Oct. 13 (Today!) Tunnel construction groundbreaking DoE CD2 review, Jan 2008 July 09 Deployment of the first pair of detectors Sept. 2010 Begin data taking with near-far

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Backup

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Detector-related

Baseline: currently achievable relative uncertainty without R&DGoal: expected relative uncertainty after R&DSwapping: can reduce relative uncertainty further