Mass hierarchy using medium baseline detector

Yoshitaro Takaesu

KIAS/KNRC

In collaboration with S.F. Ge, N. Okamura and K. Hagiwara

arXiv: 1210.8141

Introduction

Reactor Experimentscan determine the Neutrino Mass Hierarchy .

The sensitivity is studied for determining the Mass Hierarchy

is measured.

・Can determine MH independently from CP phase and matter effects

・ free and well-studied source of neutrino

Advantages of reactor neutrino experiment

How to distinguish Mass Hierarchy ?

Mass Hierarchy difference

Max:

vanish:

MH difference in spectrum

analysis

The theoretical prediction is fitted to the Data,assuming NH or IH.

Fitting parameters are

Penalty term

analysisWe 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

IH is true

Interpretation of

When we perform many pseudo-experiments, the

approximately follows a Normal distribution.

0

NH is true

NH is true

When we perform an experiment and get a ,

we reject the IH assumptionwith the confidence of ( 1 – p ).

Interpretation of

Dashed:

Solid:

There are studies based on Bayesian approach.

This is a frequentist approach to interpret .

Qian et.al. arXiv: 1210.3651

Evslin et.al. arXiv: 1305.5150

Sensitivity to the Mass hierarchy

16.5GW 10kton 5yrs

Current value

NH

Effect of Energy Resolution 2

16.5GW 10kton 5yrs

• Sensitivity is reduced by ~ 40%

• Optimized L is shortened by ~ 5 km

b = 0% b = 1%

a = 2% a = 3%

Parameter measurement

< 0.5% accuracy

can be measured accurately @ L ~ 50 km

L = 50km

1%

1%

1%

1%

After mass hierarchy determination

Multi-reactor interference

L1 L2

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

Baseline difference should be small.

ΔL = L1 – L2

Multi-reactor interference 1

Other reactor sitesinfluence the sensitivity.

All Reactors

16.5GW

10kton 5yrs

a = 3%, b = 0.5%

YongGwang only

Multi-reactor interference 2All Reactors

Distributions ofEach Reactorsconsidered

The direction to RENO50 strongly affects the sensitivity.

16.5GW

10kton 5yrs

a = 3%, b = 0.5%

SummaryWe have discussed the sensitivity

of RENO50-like Experiment for MH determination.

With 16.5GW 10kton,

a < 3% (2%)

b < 0.5% (1%) of Energy Resolution is requiredfor > 80% probability of > 2-sigma (3-sigma)determination within 5 years.

Interference among reactor sites and reactor cores significantly affects the sensitivity.