1. Mass hierarchy using medium baseline detector Yoshitaro Takaesu KIAS/KNRC In collaboration with S.F. Ge, N. Okamura and K. Hagiwara arXiv: 1210.8141

2. 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

3. How to distinguish Mass Hierarchy ? Mass Hierarchy difference Max: vanish:

4. MH difference in spectrum

5. analysis The theoretical prediction is fitted to the Data, assuming NH or IH. Fitting parameters are Penalty term

6. 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: 1210.3651 Evslin et.al. arXiv: 1305.5150 NH is true: tends to be Positive. IH is true: tends to be Negative. IH is rejected NH is rejected NH is true case

7. 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 ).

8. Interpretation of Dashed: Solid: There are studies based on Bayesian approach. This is a frequentist approach to interpre t. Qian et.al. arXiv: 1210.3651 Evslin et.al. arXiv: 1305.5150

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

10. Effect of Energy Resolution 2 16.5 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 %

11. Parameter measurement < 0.5 % accuracy can be measured accurately @ L ~ 50 km L = 50km 1%1% 1%1% 1%1% 1%1% After mass hierarchy determination

12. Multi-reactor interference L1 L2 E. Ciuffoli, J. Evslin, X. Zhang: 1302.0624 Y-F. Li, J. Cao, Y. Wang, L. Zhan: 1303.6733 Baseline difference should be small. ΔL = L1 – L2

13. 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

14. Multi-reactor interference 2 All Reactors Distributions of Each Reactors considered The direction to RENO50 strongly affects the sensitivity. 16.5 GW 10 kton 5 yrs a = 3 %, b = 0.5 %

15. 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.

16. Back Up Slides

17. Reactors in South Koreahttp://world- nuclear.org/info/Country- Profiles/Countries-O-S/South- Korea/#.UYzutiv24hx from World Neuclear Association http://world-nuclear.org/info/Country-Profiles/Countries-O-S/South-Korea/#.UYzutiv24hx

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

20. Energy Distribution @ Detector near far

21. Fourier Analysis has sensitivity for small. Don’t need accurate knowledge of or flux.

22. Pull Factors of fitting parameters

23. Effects of to the sensitivity L = 30 km L = 50 km Baseline should be long enough

24. Effect of Energy Resolution a = 0 a = 6 % Evergy Resolution affects the sensitivity significantly. How good should be the energy resolution ?