Mass hierarchy using medium baseline detector

Yoshitaro Takaesu KIAS/KNRC

In collaboration with S.F. Ge, N. Okamura and K. HagiwaraarXiv: 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…

NH IH

Not appropreate for the MH determinationc.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 assumption with 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: 1210.3651Evslin et.al. arXiv: 1305.5150

Sensitivity to the Mass hierarchy16.5GW 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 5yrsa = 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 5yrsa = 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.

Back Up Slides

Reactors in South Koreahttp://world-nuclear.org/info/Country-Profiles/Countries-O-S/South-Korea/#.UYzutiv24hx

from World Neuclear Associationhttp://world-nuclear.org/info/Country-Profiles/Countries-O-S/South-Korea/#.UYzutiv24hx

PMT

Reactor neutrino experiment

Reactor Detector

Inside Detector

Inverse Beta Decay (IBD)

Energy Distribution

@ Detector

near far

Fourier Analysis

• has sensitivity for small . • Don’t need accurate knowledge of or flux.

Pull Factors of fitting parameters

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 ?