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

・Need only smaller detector than other experiments

Advantages of reactor neutrino experiment

How to distinguish Mass Hierarchy ?

Mass Hierarchy difference

Max:

vanish:

MH difference in spectrum

analysis

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

Fitting parameters are

Penalty term

analysis – MH determination

MH is determined as the hierarchy which gives smaller . Ex)

MH is NH.

Sensitivity is estimated by

We claim that MH is determined with significane. accepted

MH

rejected MH

Sensitivity for MH determination

36 km (Max MH difference)

Max Sensitivity

Typical sensitivity curve as a function of Baseline length L

Sensitivity to the Mass hierarchy

Max. sensitivity

The typical sensitivity curve of this experiment

Reduction of sensitivity

Due to Small flux？

Effects of to the sensitivity

L = 30km

L = 50km

Baseline should be long enough

Effect of Energy Resolution

a = 0 a = 6%

Evergy Resolution affects the sensitivity significantly.

How good should be the energy resolution ?

Sensitivity to the Mass hierarchy

16.5GW 5kton 5yrs

Current value

NH

Optimized L ~ 50 km

２％ >３％ ~

Effect of Energy Resolution 2

16.5GW 5kton 5yrs

• Sensitivity is reduced by ~ 40%

• Optimized L is shortened by ~ 5 km

b = 0% b = 1%

a = 2% a = 3%

Multi-reactor interference

L1 L2

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

Baseline difference should be small.

ΔL = | L1 – L2 |

Multi-reactor interference 1

YongGwang only

Other reactor sitesinfluence the sensitivity.

All Reactors

16.5GW

5kton 10yrs

a = 3%, b = 0.5%

Multi-reactor interference 2All Reactors

Including Planned Reactors

Distributions ofEach Reactorsconsidered

The direction to RENO50 strongly affects the sensitivity.

16.5GW

5kton 10yrs

a = 3%, b = 0.5%

SummaryWe have discussed the sensitivity

of Medium Baselin Experiment

for MH determination.

For 16.5GW 5kton,

50km Optimal Baseline Length

a < 3%

b < 1% of Energy Resolution is requiredfor > 2-sigma determinationwithin 10 years.

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