Talk at Neutrino conference, Kyoto

1. Yoshitaro Takaesu
U. of Tokyo
Determination of mass hierarchy with
medium baseline reactor neutrino
experiments.

2. Reactor neutrino experiment
νe
Detector
Reactors
6 × 1023
νe/ 3GW/ 15min
2
PMT
Inside Detector (Inverse Beta Decay)

3. Reactor neutrino experiment
νe
Detector
Reactors
6 × 1023
νe/ 3GW/ 15min
3

4. Topics on medium baseline reactor ex.
4
• Optimum baselines
• Energy resolution (Energy scale uncertainty)
• Multiple reactor effects
• Geo neutrino
• Synergy with Long Baseline experiments
• Statistical test of hypothesis
• Fourier analysis vs. chi^2 analysis
• Nuclear recoil effect
etc…

5. survival prob. (Pee)
5
L ~ 1km
MH independent current reactor experiment
[DayaBay: Neutrino2014]
MH
[Minakata,Nunokawa,Parke,
Funchal: hep-ph/0701151]

6. Sensitivity to the Mass hierarchy
The typical sensitivity curve of this experiment
6

7. chi^2 analysis
We define
Naively, the significance of this
rejection is , but…(∆ χ2)min σ
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

8. Energy Resolution
8

9. Effect of Energy resolution
16.5GW 18kton 5yrs (RENO-50)
Current value
NH
δE
E
=
a
E/ MeV
2
+ b2
9
[Ge,Hagiwara,Okamura,
Takaesu:1210.8141]

10. How to achieve better Energy Resolution?
Increase the photo-electron (p.e.)detected by PMT.
p.e.~ 200 pe/MeV ~ 1000 pe/MeV
Ex)
• Increase PMT coverage
• Increase QE of PMT
• More transparent LS
•More Light yield
10
~ 6% ~ 3%

11. 11
[L.Wen: Neutrino 2014]

12. Multiple Reactor Effect
12

13. E. Ciuffoli, J. Evslin, X. Zhang: 1302.0624
Y-F. Li, J. Cao, Y. Wang, L. Zhan: 1303.6733
ΔL = L1 – L2
Reactor1
Multiple Reactor Effect
L1 L2
13
Reactor1 + Reactor2

14. multi-cores
Multiple Reactor Effect: RENO-50 case
16.5GW
18kton 5yrs
a = 3%, b = 0.5%
δE
E
=
a
√
E
2
+ b2
(∆ χ2)min
All Reactors
50 km
14
250m
[Y.Takaesu: International
workshop on RENO-50]

15. 15
[L.Wen: Neutrino 2014]

16. Geo-neutrino BG
16
KamLAND: 38.3 +- 10 TNU [1/(10^32 proton*yrs)]
Borexino: 38.8 +- 12 TNU
[Gando et.al 2011, Nature Geosci.]
[Ranucci: Neutorino 2014]
36 GW, 20 kton, 5 years, Eres=3% (JUNO)
arXiv:1006.1113

17. Summary
Future Reactor neutrino Experiment for MH determination
50km is the optimum baseline length
For > 3-sigma determination within 5 years (15GW 20kton)
3% of Energy resolution is required.
(Energy Scale uncertainty should be controlled carefully
arxiv:0901.2976, 1208.1551, 1308.0591)
Multiple reactor effect significantly affects the sensitivity.
Geo-neutrino may also become concern.
17