Yoshitaro TakaesuKIAS/KNRC

The Sensitivity to Mass Hierarchy determination of Future Reactor

Neutrino experiments

In collaboration with S.F. Ge, N. Okamura and K. HagiwaraJHEP 1305:131,2013

Introduction

2

Mass Hierarchy

3

NHIH

Reactor neutrino experiment

Detector

Reactors

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@ Detector

Reactor neutrino experiment

Detector

Reactors

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PMT

Inside Detector (Inverse Beta Decay)

MH difference in spectrum

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NHIH

Sensitivity

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Analysis method

Data

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MH = NH/IH

Fitting function Parameter constraints

Analysis methodWe define

Naively, the significance of this rejection is , but…

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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Sensitivity to the Mass hierarchy

The typical sensitivity curve of this experiment

Small flux

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Vvvv vvv

Effects of to the sensitivity

L = 30km

L = 50km

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0%

2.5%

-2.5%10 20 30 40 50 60 70 80 90 km

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Pull Factor

13

Sensitivity to the Mass hierarchy

The typical sensitivity curve of this experiment

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Effect of Energy resolution

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Effect of Energy resolution 1

18kton 16.5GW 5yrs

Current value

NH

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Effect of Energy Resolution 2

18kton 16.5GW 5yrs

a = 3%a = 2%

b = 0 b = 1% Sensitivity 40%

Imrovement of b term is also important17

Current value

How to achieve better Energy Resolution?

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

p.e.~ 200 pe/MeV ~ 2000 pe/MeV

Ex)

• Increase PMT coverage

• Increase QE of PMT

• More transparent LS

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~ 6% ~ 2%

25m 35%

Energy Resolution (simulation)

J.S. Park (RENO)

Interference 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

Multi-reactor interference

L1 L2

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Reactor1 + Reactor2

multi-cores

Multi-reactor interference 16.5GW

18kton 5yrs

a = 3%, b = 0.5%

All Reactors50 km

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250m

Parameter Measurement

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Parameter measurement

< 0.5% accuracy

can be measured accurately @ L ~ 50 km

L = 50km

1%

1%

1%

1%

* Effect of energy scale unc. Is not considered.

SummaryFuture Reactor neutrino Experiment for MH determination

For > 3-sigma determination within 5 years

a < 3%

b < 0.5%

of Energy Resolution is required

with 16.5GW 18kton Reactor Complex.

Interference among reactor cores significantly affects the sensitivity.

•Energy Scale uncertainty should be controlled very carefully.arXiv: 0901.2976, 1208.1551, 1308.0591

* Neutrino parameters can be determined with < 1% accuracy.

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