Mass hierarchy using medium baseline detector

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 is measured. • Reactor Experiments • can determine the Neutrino Mass Hierarchy . Advantages of reactor neutrino experiment ・Can determine MH independently from CP phase and matter effects ・ freeand well-studied source of neutrino • The sensitivity is studied • for determining the Mass Hierarchy

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

4. MH difference in spectrum

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

6. analysis We define tends to be Positive. NH is true: IH is true: tends to be Negative. NH is true case IH is rejected NH is rejected IH NH Naively, the significance of this rejection is , but… Not appropreate for the MH determination c.f.) Qian et.al. arXiv: 1210.3651 Evslin et.al. arXiv: 1305.5150

7. Interpretation of When we perform many pseudo-experiments, the approximately follows a Normal distribution. NH is true IH is true 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 Solid: Dashed: This is a frequentist approach to interpret . There are studies based on Bayesian approach. Qian et.al. arXiv: 1210.3651 Evslin et.al. arXiv: 1305.5150

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

10. Effect of Energy Resolution 2 b = 1% b = 0% 16.5GW 10kton 5yrs • Sensitivity is reduced by ~ 40% • Optimized L is shortened by ~ 5 km a = 2% a = 3%

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

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

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

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

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

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

20. Energy Distribution @ Detector far near

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 = 30km L = 50km Baseline should be long enough

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