This document discusses the sensitivity of a medium baseline reactor neutrino experiment to determine the neutrino mass hierarchy. It finds that: 1) For a 16.5GW reactor flux, 5kton detector, and 5 year run time, an optimal baseline length of around 50km could determine the mass hierarchy at over 2-sigma significance with an energy resolution of less than 3%. 2) The energy resolution is crucial, as a resolution of 3% reduces sensitivity by around 40% compared to 2%, and shortens the optimal baseline length by about 5km. 3) Interference from other reactor sites and cores significantly impacts the sensitivity, so their locations and flux distributions must be carefully considered in the experiment design.

1. Mass hierarchy
using medium baseline detector
Yoshitaro Takaesu
KIAS/KNRC
In collaborationwith 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 fromCP phase and matter effects
・Need only smaller detector than other experiments
Advantages of reactor neutrino experiment

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

4. MH difference in spectrum

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

6. 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

7. Sensitivity for MH determination
36 km (Max MH difference)
Max Sensitivity
Typical sensitivity curve as a function of Baseline length L

8. Sensitivity to the Mass hierarchy
Max. sensitivity
The typical sensitivity curve of this experiment
Reduction of
sensitivity
Due to Small flux？

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

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

11. Sensitivity to the Mass hierarchy
16.5GW 5kton 5yrs
Current value
NH
Optimized L ~ 50 km
２％ >
３％ ~

12. 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%

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

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

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

17. Summary
We 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 required
for > 2-sigma determination
within 10 years.
Interference among reactor sites and/or reactor cores
significantly affects the sensitivity.