Seminar @ CUNPA 2013.10.18

1. Yoshitaro Takaesu
KIAS/KNRC
The Sensitivity to Mass Hierarchy
determination of Future Reactor
Neutrino experiments
In collaborationwith S.F. Ge, N. Okamura and K. Hagiwara
JHEP 1305:131,2013

2. Introduction
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3. Mass Hierarchy
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NH
IH

4. Reactor neutrino experiment
Detector
Reactors
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@ Detector

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

6. MH difference in spectrum
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NH
IH

7. Sensitivity
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8. Analysis method
Data
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MH = NH/IH
Fitting function Parameter constraints

9. Analysis method
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
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10. Sensitivity to the Mass hierarchy
The typical sensitivity curve of this experiment
Small flux
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Vvvv vvv

11. Effects of to the sensitivity
L = 30km
L = 50km
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0%
2.5%
-2.5%
10 20 30 40 50 60 70 80 90km

12. 12

13. Pull Factor
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14. Sensitivity to the Mass hierarchy
The typical sensitivity curve of this experiment
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15. Effect of Energy resolution
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16. Effect of Energy resolution 1
18kton 16.5GW 5yrs
Current value
NH
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17. Effect of Energy Resolution 2
18kton 16.5GW 5yrs
a = 3%a = 2%
b = 0 b = 1% Sensitivity 40%
Imrovementof b term is also important
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Current value

18. How to achieve better Energy Resolution?
Increase the photo-electron (p.e.)detected by PMT.
p.e.~ 200 pe/MeV ~ 2000 pe/MeV
Ex)
• Increase PMT coverage
• Increase QE of PMT
• More transparent LS
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~ 6% ~ 2%

19. 25m 35%
Energy Resolution (simulation)
J.S. Park (RENO)

20. Interference Effect
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21. E. Ciuffoli, J. Evslin, X. Zhang: 1302.0624
Y-F. Li, J. Cao, Y. Wang, L. Zhan: 1303.6733
ΔL = L1 – L2
Reactor1
Multi-reactor interference
L1 L2
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Reactor1 + Reactor2

22. multi-cores
Multi-reactor interference
16.5GW
18kton 5yrs
a = 3%, b = 0.5%
All Reactors
50 km
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250m

23. Parameter Measurement
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24. Parameter measurement
< 0.5% accuracy
can be measured accurately @ L ~ 50 km
L = 50km
1%
1%
1%
1%
* Effect of energy scale unc. Is not considered.

25. Summary
Future Reactor neutrino Experiment for MH determination
For > 3-sigma determination within 5 years
a < 3%
b < 0.5%
of Energy Resolution is required
with 16.5GW 18kton Reactor Complex.
Interference among reactor cores significantly affects
the sensitivity.
•Energy Scale uncertainty should be controlled very carefully.
arXiv: 0901.2976, 1208.1551, 1308.0591
* Neutrino parameters can be determined with < 1% accuracy.
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