9/14/2007 TAUP 2007, Sendai 1

The Daya Bay Reactor Neutrino Experiment

Shaomin Chen (for the Daya Bay collaboration)Tsinghua University, Beijing, China

TAUP 2007, Sendai, Japan

9/14/2007 TAUP 2007, Sendai 2

CP violation in lepton sector

cos sin cossin cos cos sin

cos si

sin

s n sn oi c

1

2

12 12 13

12 12 23 23

12 23 2

3

13 3

10 0 1 0 0 0 00 0 1 0 0 0 0

0 0 1 0 0 0 0 1

φδ

φ

δ

θ

θ

θ θ θθ θ θ θ

θ θ θ

− ⎛ ⎞⎛ ⎞⎛ ⎞⎛ ⎞⎜ ⎟⎜ ⎟⎜ ⎟⎜ ⎟− ⎜ ⎟⎜ ⎟⎜ ⎟⎜ ⎟

⎜ ⎟ ⎜ ⎟⎜ ⎟ ⎜ ⎟−⎝ ⎠ ⎝ ⎠⎝ ⎠ ⎠− ⎝

ii

i

i

e ee

e

θ13 is the gateway of CP violation in lepton sector!

2 0.0312 0.04sin 2 0.86θ +

−= CL213sin 2 0.19, 90%θ < = 2

23sin 2 0.92θ >

Three-neutrino oscillation ( )3

1, ,l i

ili l eUν ν μ τ

=

= =∑To incorporate CP violation into the three-light-neutrino model

Pontecorvo-Maki-Nakagawa-Sakata Matrix

CP violation parameters: Dirac phase δ, Majorana phases φ1, φ2

1 2 0 and could be manifested in extremely hard to measure !φ φ νββ ⇒may be accessible through oscillation sea rches.δ

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Theoretical predictions for θ13

10–4M-Theory model0.03—0.04Renormalization group enhancement

>0.04Anarchy0.043×2 see-saw

4×10–4—0.15Textures0—0.15Flavor symmetries

4×10–4—0.04SO(10)+Texture1.2×10–6—0.18SO(10)+Flavor Symmetry

0.04Orbifold SO(10)0.13Minimal SO(10)

sin22θ13Model(s)

A precise θ13 measurement is helpful in understanding the physics beyond the Standard Model.

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How to measure θ13?Disappearance searches at reactors:

Appearance searches at accelerators:

Reactor experiments provide a clean environment to measure θ13.Accelerator experiments give access to both θ13 and δ values.

13

2 2 2 212 13 31

2 2 2

4 2 2 212 13 12

212 13 3

21

2

cos sin 2 sin (1.267 )

sin sin 2 sin (1.2

cos sin 2 sin (1.26

67 )

7 )dis P

LmE

P m

LE

LE

m

P θ

θ

θ θ

θ

θ ⋅ Δ ⋅

= + =

+

+ ⋅ Δ ⋅

⋅ Δ ⋅

22 2 2 2 2 2 223 23 23 113

21

2

1

2

3 3

1sin sin (1.267 ) cos sin sin (1.26sin

cos s( sinin

)

)

7appL Lm m

AE E

P

ρ

θ

θ θ δ

θ θ θ≈ Δ + Δ

−

213sin 2 0.1θ =

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Current knowledge on θ13

Direct search (PRD 62, 072002) Global fit (hep-ph/0506083)

A small θ13(e.g. sin22θ13<0.02) would make accelerator experimental searches for CP violation become a kind of “Mission: Impossible”.

At Δm231 = 2.5 × 10−3 eV2,

sin22θ13 < 0.17

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How to reach 1% precision?Increase statistics:

Need intensive neutrino flux from powerful nuclear reactorsUtilize larger target mass, hence larger detectors

Reduce systematic uncertainties:Reactor-related:

Optimize baseline for best sensitivity and smaller residual errorsNear and far detectors to minimize reactor-related errors

Detector-related:Use “Identical” pairs of detectors to do relative measurementComprehensive program in calibration/monitoring of detectorsInterchange near and far detectors (optional)

Background-relatedGo deeper to reduce cosmic-induced backgroundsEnough active and passive shielding

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Daya Bay nuclear power plant

4 reactor cores, 11.6 GW2 more cores in 2011, 5.8 GW Mountains near by55 km to Hong Kong

55 km

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Signature of a signal

0

0

( >2 =1.022MeV)

Reaction:

Prompt signal:

Delayed signal: ( ~ 8MeV, ~ 28 )

( 2.2MeV, ~ 1

2 '

80 )Delayed signal

'

:

e

ee

e n

e

n

p

E m

G

e

Gd d E s

s

n d

s

E spγ

γ

ν

τ

γ

γ μ

γ τ μ

+

+

−+

+ → +

+ →

′+ → +

+ → + =∑

Neutrino energy:

++ +−++≅epnne

mMMTTE )(ν

Threshold=1.8 MeV

Antineutrino Interaction Rate(events/day per 20 ton module)Daya Bay near site 960 Ling Ao near site 760 Far site 90

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Origins of backgroundAccidental coincidences Stop muons

Fast neutrons Two accidental coincidences

CHOOZCHOOZ

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Primary design considerationsIdentical near and far detectors to cancel reactor-related errorsMultiple modules for reducing detector-related errors and cross checksThree-zone detector modules to reduce detector-related errors Overburden and shielding to reduce backgroundsMultiple muon detectors for reducing backgrounds and cross checksMovable detectors for swapping

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Baseline and target mass

flux, oscillation and energy spectrumSystematic uncertainties of reactors and detectorsOverburden, ambient background and uncertainties

depend

Input to the p

ent rates and

ro

sp

ces

ect

-

r

s:

a of cos

---

e

e

ν

+ 8mogenic neutrons and Li

1.8 km 80 tons

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Experimental LayoutFar site1615 m from Ling Ao1985 m from Daya BayOverburden: 350 mLing Ao Near site~500 m from Ling AoOverburden: 112 mDaya Bay Near site363 m from Daya BayOverburden: 98 m

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Anti-neutrino detector designThree zones modular structure:

I. Target: 20t, 1.6m Gd-loaded scintillatorII. γ-catcher: 20t, 45cm normal scintillator III. Buffer shielding: 40t, 45cm oil

Reflector at top and bottom192 8”PMT/modulePMT coverage: 12%(with reflector)

σE/E = 12%/√E σr = 13 cm

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Gd-loaded liquid scintillatorLinear Alkyl Benzene (LAB) doped with organic Gd complex (0.1% Gd mass concentration)

Gd-LS and LS mixed in storage pool and distributed to all sites

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AD modules in far site

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Calibrations and monitoring

Full manual calibration procedures

Automated calibration procedures

And maybe more calibration procedures to come…

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Muon veto detector designMultiple muon veto detectors:

RPC’s at the top as muon trackerWater pool as

Cherenkov counter has inner/outer regionsCombined eff.> (99.5 ± 0.25) %

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Estimated efficiencies

Neutron detection efficiency is a product of 85% Gd fraction and 93% energy cut.

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Summary of uncertainties

0.32% (Daya Bay near)0.22% (Ling Ao near)0.22% (far)

Backgrounds

0.2%Signal statistics

0.38% (baseline)0.18% (goal)

Detector (per module)

0.087% (4 cores)0.13% (6 cores)

Neutrinos from Reactor

Uncertainty Sources

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Goal to be reached at Daya Bay

The sensitivity of ≤ 0.01 for sin22θ13 will be reached in 2013.

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This needs a team effort!

North America (14)BNL, Caltech, 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,

George Mason Univ.

Asia (18)IHEP, CIAE,Tsinghua Univ.

Zhongshan Univ.,Nankai Univ.Beijing Normal Univ., Nanjing Univ.

Chengdu Univ. Tech., Shandong Univ.Shenzhen Univ., Hong Kong Univ.USTC,Chinese Hong Kong Univ.Taiwan Univ., Chiao Tung Univ.,National United Univ.,CGNPG,

Dongguan Univ. Tech.

Europe (3)JINR, Dubna, Russia

Kurchatov Institute, RussiaCharles University, Czech Republic

~ 160 collaborators

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Recommendations

第250次香山科学会议简报 (2005)Meeting brief for the 250th Xiangshan Scientific Meeting…2．中微子混合角θ13是自然界的基本参数之一，…是一个急需解决的关键问题。Neutrino mixing angle θ13 is one of the fundamental parameters in nature,…a key issue to be resolved. 3．…条件已经基本成熟，而且实验得到了大亚湾核电站有关方面的大力支持。…准备充分，完全有能力和实力完成这项实验。…have mature technology and get strong support from Daya Bay Nuclear Power Plant. … get preparations well done and have capability and strength to complete this experiment. 4．确定θ13…在国际上竞争激烈，…项目在年内立项是赢得国际竞争的关键。International competition in determining θ13 is very vigorous,…getting the project approved promptly is a key to win the competition.…

This is an usual way to initiate a giant research project in China.

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Roadmap

Passed DOE scientific review Oct. 2006CDR released (hep-ex/0701029) Jan. 2007Passed US CD-1 review April 2007Passed final nuclear safety review in China April 2007Received funding from Chinese agencies April 2007TDR to PAP released Sept. 2007Ground breaking ceremony Oct. 2007Anticipate US CD-2/3a review Nov. 2007Deployment of the first detector July 2009Data taking with final configuration Sept. 2010

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Summary

An ultimate sensitivity of ≤ 0.01 for sin22θ13 is designed to be reached at the Daya Bay experiment.Detector design is close to complete.

Received commitment from Chinese funding agencies.

US CD-2/3a Physics Review scheduled for Nov. 2007.

Civil construction will start from Oct. 2007, detectors will be deployed in 2009, and full operation expected in 2010.

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And more…

We already know GuangDong province is a place forproviding one of the most delicious foods and the cheapest “Made in China” products in the world.

We are anticipating it will also be an excellent place for us to have the most precise “Made in China” θ13 .

Thank you!

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Back-up slides

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Reactor neutrino spectrumReactor neutrino rate and spectrum depends on:

The fission isotopes and their fission rate, uncorrelated ~ 1-2%Fission rate depends on thermal power, uncorrelated ~ 1%Energy spectrum of weak decays of fission isotopes, correlated ~ 1%

Three ways to obtain reactor neutrino spectrum:Direct measurement at near siteFirst principle calculationSum up neutrino spectra of 235U, 239Pu, 241Pu(from measurement) and 238U(from calculation, ~ 1%)

They all agree well within 3%

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Calibrating Energy CutsAutomated deployed radioactive sources to calibrate the detectorenergy and position response within the entire range.

68Ge (0 KE e+ = 2×0.511 MeV γ’s)60Co (2.506 MeV γ’s)238Pu-13C (6.13 MeV γ’s, 8 MeV n-capture)

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Estimated event rates

The total event rate in each site is less than 3.5 kHz and istherefore affordable in the readout-every-hit scheme.

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FEE and trigger system

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Sources of systematics Detector-related

Reactor-related

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Reactor-related uncertainties

Assuming 30 cm precision in core position

2 2 2Far =

( ) ( ) ( )nearr r r

DB LA fr r rr r rL L L

φ φ φα⎡ ⎤

+⎢ ⎥⎣ ⎦∑ ∑ ∑

2 22 1

2 21 2

( ) ( )( ) ( )

LA f LA fDB LA

DB f DB fLA DB

L L L LL L L L

α− −

− −

⋅ − ⋅=

⋅ − ⋅

Far site

Daya Bay(near site)

Ling Ao(near site)

1DBL 2

LAL2DBL

1LAL

1fL 2

fL

1 2

1φ 2φ

fDBL

fLAL

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Background-related errorsUncorrelated backgrounds: U/Th/K/Rn/neutronSingle gamma rate @ 0.9MeV < 50HzSingle neutron rate < 1000/day

Correlated backgrounds:Fast Neutrons: double coincidence8He/9Li: neutron emitting decays