Yoshitaro TakaesuU. of Tokyo

Determination of mass hierarchy with medium baseline reactor neutrino

experiments.

Reactor neutrino experiment

νe

Detector

Reactors

6 × 1023 νe/ 3GW/ 15min

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PMT

Inside Detector (Inverse Beta Decay)

Reactor neutrino experiment

νe

Detector

Reactors

6 × 1023 νe/ 3GW/ 15min

3

Topics on medium baseline reactor ex.

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• Optimum baselines

• Energy resolution (Energy scale uncertainty)

• Multiple reactor effects

• Geo neutrino

• Synergy with Long Baseline experiments

• Statistical test of hypothesis

• Fourier analysis vs. chi^2 analysis

• Nuclear recoil effect

etc…

survival prob. (Pee)

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L ~ 1km

MH independent current reactor experiment

[DayaBay: Neutrino2014]

MH

[Minakata,Nunokawa,Parke,Funchal: hep-ph/0701151]

Sensitivity to the Mass hierarchy

The typical sensitivity curve of this experiment

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chi^2 analysisWe define

Naively, the significance of this rejection is , but…(∆ χ2)min σ

NHIH

Not appropreate for the MH determination

c.f.) Qian et.al. arXiv: 1210.3651

Evslin et.al. arXiv: 1305.5150

NH is true: tends to be Positive.

IH is true: tends to be Negative.

IH is rejectedNH is rejected

NH is true case

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Energy Resolution

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Effect of Energy resolution

16.5GW 18kton 5yrs (RENO-50)Current value

NH

δE

E=

a

E / MeV

2

+ b2

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[Ge,Hagiwara,Okamura,Takaesu: 1210.8141]

How to achieve better Energy Resolution?

Increase the photo-electron (p.e.)detected by PMT.

p.e.~ 200 pe/MeV ~ 1000 pe/MeV

Ex)

• Increase PMT coverage

• Increase QE of PMT

• More transparent LS•More Light yield

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~ 6% ~ 3%

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[L.Wen: Neutrino 2014]

Multiple Reactor Effect

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E. Ciuffoli, J. Evslin, X. Zhang: 1302.0624Y-F. Li, J. Cao, Y. Wang, L. Zhan: 1303.6733

ΔL = L1 – L2

Reactor1

Multiple Reactor Effect

L1 L2

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Reactor1 + Reactor2

multi-cores

Multiple Reactor Effect: RENO-50 case 16.5GW

18kton 5yrs

a = 3%, b = 0.5%δE

E=

a√

E

2

+ b2

(∆ χ2)min

All Reactors50 km

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250m

[Y.Takaesu: Internationalworkshop on RENO-50]

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[L.Wen: Neutrino 2014]

Geo-neutrino BG

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KamLAND: 38.3 +- 10 TNU [1/(10^32 proton*yrs)]

Borexino: 38.8 +- 12 TNU

[Gando et.al 2011, Nature Geosci.]

[Ranucci: Neutorino 2014]

36 GW, 20 kton, 5 years, Eres=3% (JUNO)

arXiv:1006.1113

SummaryFuture Reactor neutrino Experiment for MH determination

50km is the optimum baseline length

For > 3-sigma determination within 5 years (15GW 20kton)

3% of Energy resolution is required.

(Energy Scale uncertainty should be controlled carefully

arxiv:0901.2976, 1208.1551, 1308.0591)

Multiple reactor effect significantly affects the sensitivity.

Geo-neutrino may also become concern.

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