Mass hierarchy using medium baseline detector Yoshitaro Takaesu KIAS/KNRC In collaboration with S.F. Ge, N. Okamura and K. Hagiwara arXiv:

Introduction Reactor Experiments can 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

analysis We define Naively, the significance of this rejection is, but… NH IH Not appropreate for the MH determination c.f.) Qian et.al. arXiv: Evslin et.al. arXiv: NH is true: tends to be Positive. IH is true: tends to be Negative. IH is rejected NH 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 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 interpre t. Qian et.al. arXiv: Evslin et.al. arXiv:

Sensitivity to the Mass hierarchy 16.5 GW 10 kton 5 yrs Current value NH

Effect of Energy Resolution GW 10 kton 5 yrs 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 L ~ 50 km L = 50km 1%1% 1%1% 1%1% 1%1% After mass hierarchy determination

Multi-reactor interference L1 L2 E. Ciuffoli, J. Evslin, X. Zhang: Y-F. Li, J. Cao, Y. Wang, L. Zhan: Baseline difference should be small. ΔL = L1 – L2

Multi-reactor interference 1 Other reactor sites influence the sensitivity. All Reactors 16.5 GW 10 kton 5 yrs a = 3 %, b = 0.5 % YongGwang only

Multi-reactor interference 2 All Reactors Distributions of Each Reactors considered The direction to RENO50 strongly affects the sensitivity GW 10 kton 5 yrs a = 3 %, b = 0.5 %

Summary We have discussed the sensitivity of RENO50-like Experiment for MH determination. With 16.5 GW 10 kton, a < 3% (2%) b < 0.5 % (1%) of Energy Resolution is required for > 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 Association

PMT Reactor neutrino experiment Reactor Detector Inside Detector Inverse Beta Decay (IBD)

Energy 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 = 30 km L = 50 km 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 ?