This document discusses the sensitivity of a next generation reactor neutrino experiment to determine the neutrino mass hierarchy. It analyzes factors that affect the sensitivity such as baseline length, neutrino flux, detector size, energy resolution, and uncertainties in the neutrino oscillation parameters. With a 16.5GW thermal power reactor source, 18 kiloton detector, and 5 years of data taking, a reactor neutrino experiment could determine the mass hierarchy at over 3-sigma sensitivity if the energy resolution is less than 3% and 0.5% respectively. Other systematic uncertainties from multiple reactor sites, energy scale uncertainty, and oscillation parameters must also be carefully controlled to achieve this sensitivity.

1. 次世代原子炉ニュートリノ実験の質
量階層性への
Sensi'vity
Yoshitaro
Takaesu
KIAS/KNRC
In
collabora'on
with
S.F.
Ge,
N.
Okamura
and
K.
Hagiwara
JHEP
1305:131,2013

2. Introduc'on

3. Mass
Hierarchy
m1
m2
m3
Normal
Hierarchy
(NH)
m3
m1
m2
Inverted
Hierarchy
(IH)
m2
21
| m2
31|
2.3 10 3
eV2
7.5 10 5
eV2
m2
21
| m2
31|
m
3
netrinos
flavors
m2
21 = m2
2 m2
1 7.5 10 5
m2
21 < | m2
31| 2.3 10 3

4. PMT
Reactor
neutrino
experiment
e
Reactor
Detector
Inside
Detector
Evis
Inverse
Beta
Decay
(IBD)
2 1020
neutrinos/GW/sec
L

5. Energy
distribu'on
e
@
detector
e
near
dNfar
dEvis
=
NpT
4 L2
Ethr
dE (E ) Pee IBD G(E , Evis)
Pee
far
L
Neutrino
oscilla;on

6. How
to
dis'nguish
Mass
Hierarchy?
Detect
the
sign
of
( m2
32)m2
31
m1
m2
m3
m3
m1
m2
NH
IH
The
informa'on
of
mass^2
difference
are
in
Oscilla'on
Probabili'es.

7. MH
difference
in
spectrum
10000
20000
30000
40000
30 km NH
IH
2000
6000
10000
14000 40 km NH
IH
1000
3000
5000
7000
dN/dE[1/MeV]
50 km NH
IH
0
1000
2000
3000
4000
2 3 4 5 6 7 8
E [MeV]
60 km NH
IH
e

8. Sensi'vity

9.
analysis
2
The
theore;cal
predic;on
is
fiBed
to
the
Data,
assuming
NH
or
IH.
2
min(NH) 2
min(IH)
Nfit
i = dEvis
NpT
4 L2
Ethr
dE (E ) Pee IBD G(E , Evis)
FiFng
parameters
are
12, 13, m2
21, | m2
31|, fsys
Penalty
term
Nfit
i

10. 0
2
4
6
8
10
12
14
16
18
20
22
24
10 20 30 40 50 60 70 80 90 100
(2
)min
L [km]
a = 2% NH
3% NH
4% NH
5% NH
6% NH
Sensi'vity
to
the
Mass
hierarchy
16.5GW
10kton
5yrs
Current
value
NH
a 7%
E
E
=
a
E
2
+ b2
( m2
31)

11. Effects
of
to
the
sensi'vity
| m2
31|
L
=
30km
| m2
31|
| m2
31|
L
=
50km
Baseline
should
be
long
enough
| m2
31|+2
fit
2
fit | m2
31|+

12. 0
2
4
6
8
10
12
14
16
18
20
22
24
10 20 30 40 50 60 70 80 90 100
(2
)min
L [km]
a = 2% NH
3% NH
4% NH
5% NH
6% NH
Sensi'vity
to
the
Mass
hierarchy
16.5GW
10kton
5yrs
Current
value
NH
a 7%
E
E
=
a
E

13. Effect
of
Energy
Resolu'on
a
=
0
a
=
6%
Evergy
Resolu'on
affects
the
sensi'vity
significantly.
E = 0
E
E
=
a
E

14. Expected Energy Resolution
PMT coverage : 67% (15,000 20” PMTs)
PMT coverage : 67% (15,000 20” PMTs)
+ Attenuation length : 25 m
+ QE : 35%
J.S.
Park,
S.B.
Kim

15.
Effect
of
Energy
Resolu'on
2
16.5GW
10kton
5yrs
E
E
=
a
E
2
+ b2
•
Sensi'vity
is
reduced
by
~
40%
•
Op'mized
L
is
shortened
by
~
5
km
b
=
0%
b
=
1%
a
=
2%
a
=
3%
0
1
2
3
4
5
6
7
8
10 20 30 40 50 60 70 80 90 100
(
2
)min
L [km]
(a, b) = (3, 0) NH
(3, 0.5) NH
(3, 0.75) NH
(3, 1) NH
0
2
4
6
8
10
12
14
16
18
20
22
24
10 20 30 40 50 60 70 80 90 100
(
2
)min
L [km]
(a, b) = (2, 0) NH
(2, 0.5) NH
(2, 0.75) NH
(2, 1) NH

16. Other
Limicng
Factors

17. Mul'-­‐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

18. Mul'-­‐reactor
interference
Other
reactor
sites
influence
the
sensi'vity.
All
Reactors
16.5GW
10kton
5yrs
a
=
3%,
b
=
0.5%
E
E
=
a
E
2
+ b2
YongGwang
only
0
1
2
3
4
5
6
7
8
9
10
11
( 2)min

19. Mul'-­‐reactor
interference
All
Reactors
0
1
2
3
4
5
6
7
8
9
10
11
( 2
)min
16.5GW
10kton
5yrs
a
=
3%,
b
=
0.5%
E
E
=
a
E
2
+ b2
RENO
site
In
latest
RENO-­‐50
proposeal:
Site
changed
18
kton
detector

20. Energy
scale
uncertainty
Energy
scale
uncertainty
is
controlled
~
1%
for
RENO
detector.
J.
Evslin
et.al.
arXiv:
1308.0591
No
E
scale
Unc.
Unknown
E
scale
(worst
case)
Effect
of
E
scale
Uncertainty

21. Schedule
for
MH
determina'on
2010
2030
2020
RENO-­‐50
DayaBay
II
LBNE
LBNO
PINGU
INO
NOvA
（Opera;ng)
（Approved)
Hyper
K
2015
2025
*
rough
es;mate
2
sigma
3
sigma
4
sigma
5
sigma

22.
Summary
RENO50-­‐like
Experiment
for
MH
determina=on.
With
16.5GW
18kton,
a
<
3%
b
<
0.5%
of
Energy
Resolu=on
is
required
>
2
~
3-­‐sigma
determina;on
within
5
years.
E
E
=
a
E
2
+ b2
Interference
among
reactor
cores
significantly
affects
the
sensi;vity.
Energy
Scale
uncertainty
should
be
controlled
very
Carefully.
Many
Efforts
for
MH
determina;on
have
started
!