talk @ PPC at KIAS 2012.11.07
-
Upload
yoshitaro-takaesu -
Category
Science
-
view
95 -
download
0
Transcript of talk @ PPC at KIAS 2012.11.07
Determina)on of mass hierarchy with reactor neutrino experiment
Yoshitaro Takaesu
KIAS/KNRC
arXiv: 1210.8141 1
In collabora)on with S.F. Ge, N. Okamura and K. Hagiwara
PPC2012@KIAS Yoshitaro Takaesu
IntroducDon
• DayaBay and RENO observed large • There is a possibility that neutrino mass hierarchy is determined by observing reactor neutrino oscillaDon at km away
• In this talk, I discuss the sensiDvity of the future medium baseline reactor experiments for determining mass hierarchy
arXiv: 1210.8141 2
�13
O(10)
PPC2012@KIAS Yoshitaro Takaesu
Mass Hierarchy
arXiv: 1210.8141 3
If we assume there are 3 types of netrinos, there are 6 possible mass hierarchies.
We know
There are two possibiliDes leX, NH and IH.
Which one is realized in Nature?
Long standing and big ISSUE.
PPC2012@KIAS Yoshitaro Takaesu
�m221 = m2
2 �m21 � 7.5� 10�5
�m221 < |�m2
31| � 2.3� 10�3
m1
m2
m3
m1
m2
m3
Normal Hierarchy (NH)
Inverted Hierarchy (IH)
|�m231|
�m221
OscillaDon
arXiv: 1210.8141 4
Mass Hierarchy difference
�e � �e
PPC2012@KIAS Yoshitaro Takaesu
Reactor neutrino experiment
arXiv: 1210.8141 5
�e
PPC2012@KIAS Yoshitaro Takaesu
Flux @ Reactor Pee @ far detector �e
�e + p� e+ + n
Energy distribuDon @ far detector
arXiv: 1210.8141 PPC2012@KIAS Yoshitaro Takaesu 6
10000 20000 30000 40000
30 km NH IH
2000 6000
10000 14000 40 km NH
IH
1000 3000 5000 7000
dN /
dEi [
1/M
eV]
50 km NH IH
0 1000 2000 3000 4000
2 3 4 5 6 7 8
Ei [MeV]
60 km NH IH
�e
We want to observe the NH-‐IH difference in the energy distribuDon at a far detector
Let’s observe it!
… but There are obstacles…
Obstacle1:
arXiv: 1210.8141 PPC2012@KIAS Yoshitaro Takaesu 7
@ < 30 km, the NH-‐IH difference is totally absorbed by a small shiX of
within its uncertainty.
@ L > 30 km, the NH-‐IH difference cannot be totally absorbed.
We need a far detector at L > 30 km
There is the opDmal baseline length to determine mass hierarchy.
�|�m231|
�|�m231|
Obstacle2: finite Energy ResoluDon
arXiv: 1210.8141 PPC2012@KIAS Yoshitaro Takaesu 8
b: systematic error parta: statistical error part
AXer smearing with the detector Energy resoluDon, the NH-‐IH difference Can be absorbed again.
�E
E=
�����
a�E/MeV
�2
+ b2
Upper limit on the Energy ResoluDon
We esDmate – OpDmal baseline length
– Energy resoluDon required – Expected uncertainDes of neutrino parameters
Assuming an experiment with 20 GW 5kton (12% free proton) 5 years exposure.
arXiv: 1210.8141 PPC2012@KIAS Yoshitaro Takaesu 9
Analysis method
arXiv: 1210.8141 10 PPC2012@KIAS Yoshitaro Takaesu
We calculate the neutrino energy distribuDon for NH or IH,
Energy ResoluDon smearing (Gaussian)
We then perform the standard analysis to this “data” (next slide).
dNNH(IH)
dEobs=
NpT
4�L2
�dE�
dN
dE�Pee(L, E�)�IBD(E�)G(Etrue �Eobs, �E)
* corresponds to the averaged observed distribuDon. We don’t consider the fluctuaDon of data from experiment to experiment in this talk.
dNNH(IH)
dEobs
We introduce bining and prepare “data”, the number of events in each bin.
NNH(IH)i =
� Eobsi+1
Eobsi
dEobs dNNH(IH)
dEobs (i = 1, · · · , nbins)
�2
Analysis method cont.
arXiv: 1210.8141 11
The sensiDvity to determine MH:
PPC2012@KIAS Yoshitaro Takaesu
* We consider zero bin-‐size limit. The sensiDvity should be considered as the maximum sensiDvity.
Results
arXiv: 1210.8141 PPC2012@KIAS Yoshitaro Takaesu 12
SensiDvity for mass hierarchy
arXiv: 1210.8141 13
0
2
4
6
8
10
12
14
10 20 30 40 50 60 70 80 90 100
(6r
2 ) min
L [km]
b = 0
a = 2% NH IH
3% NH IH
4% NH IH
5% NH IH
6% NH IH
20 GW 5kton 5 years
a < 3% for
�E
E=
�����
a�E/MeV
�2
+ b2
OpDmal L ~ 50 km
PPC2012@KIAS Yoshitaro Takaesu
(��2)min > 9
SystemaDc Error of ResoluDon
arXiv: 1210.8141 14
0
2
4
6
8
10
12
14
10 20 30 40 50 60 70 80 90 100
(6r
2 ) min
L [km]
(a, b) = (2, 0) NH IH
(2, 0.5) NH IH
(2, 0.75) NH IH
(2, 1) NH IH
�E
E=
�����
a�E/MeV
�2
+ b2
b < 1% for
20GW 5kton 5 years
Larger b Shorter opDmal L
PPC2012@KIAS Yoshitaro Takaesu
(��2)min > 9
UncertainDes of Parameters
arXiv: 1210.8141 15
0.51.01.52.0
sin22e12
×10-2(a, b) = (3, 0.5) NH
IH(3, 1) NH
IH(6, 1) NH
IH
1234 sin22e13
×10-3
0.51.01.5
Sta
tist
ical
Unc
erta
inty
6m221
×10-6eV2
0246
10 20 30 40 50 60 70 80 90 100
L [km]
|6m231|
×10-5eV2
Parameter measurements are not sensiDve to the Energy resoluDon
PPC2012@KIAS Yoshitaro Takaesu
~ 0.5% level of uncertainDes can be achieved for sin2 2�12
|�m231|
�m221
Summary • We study the sensiDvity of a future medium baseline reactor neutrino experiment for MH determinaDon.
• For 20 GW 5kton 5 years exposure,
– opDmal baseline length ~ 50 km
– < 3% staDsDcal & < 1% systemaDc errors of Energy ResoluDon is required
– 0.5% level of accuracy for Neutrino Parameters
arXiv: 1210.8141 16 PPC2012@KIAS Yoshitaro Takaesu
* This study gives the minimum requirement for the energy resoluDon. * More realisDc study is very sensiDve to the environment, such as distribuDon of reactors within ~100 km from the far detector (J.Evslin et.al, arXiv:1209.2227).
arXiv: 1210.8141 17
Thank you
PPC2012@KIAS Yoshitaro Takaesu
arXiv: 1210.8141 18
-0.25 0
0.25 0.5 sin22e12
2% NH IH
3% NH IH
6% NH IH
-0.25 0
0.25 0.5 sin22e13
-0.25 0
0.25 0.5
pull
fact
or
6m221
-0.25 0
0.25 0.5
|6m231|
-0.25 0
0.25 0.5
10 20 30 40 50 60 70 80 90 100L [km]
fsys
PPC2012@KIAS Yoshitaro Takaesu
arXiv: 1210.8141 PPC2012@KIAS Yoshitaro Takaesu 19
-10 0 10 20 30
50
100
150
(��2)min
�E
E=
�����
2%�E/MeV
�2
+ (0.5%)2
L = 50km1000 experiments
(��2)min = 11.2
�(��2)min = 7.1
arXiv: 1210.8141 PPC2012@KIAS Yoshitaro Takaesu 20
-5
0
5
10
15
20
10 20 30 40 50 60 70 80 90 100
(6r2 ) m
in
L [km]
20GWth, 5kton (12.00% proton), 5 years, (bEvis/Evis)2 = ( (a / 3Evis)
2 + b2 )%
(a, b) = (2, 0.5) NH IH
arXiv: 1210.8141 21 PPC2012@KIAS Yoshitaro Takaesu
arXiv: 1210.8141 22 PPC2012@KIAS Yoshitaro Takaesu