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)


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.


�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


Reactor neutrino experiment

arXiv: 1210.8141 5

�e


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:


@ < 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


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.


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:


* We consider zero bin-‐size limit. The sensiDvity should be considered as the maximum sensiDvity.

Results


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


(��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


(��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


~ 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


* 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


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



-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


-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

talk @ PPC at KIAS 2012.11.07

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Transcript of talk @ PPC at KIAS 2012.11.07