大気ニュートリノでの質量階層性決定の可能性

Kimihiro OKUMURA (ICRR, Univ. of Tokyo)
26th RCCN Neutrino Workshop

1Atmospheric neutrinosp, He      e   e        e   e  2

3 flavor oscillation
 e  100  cos 13  


0cos
sin
02323     i  0 sin  23 cos  23 sin 13e
大気ニュートリノ
加速器ニュートリノ

0 sin 13e i  cos 12 sin12 01  10  sin 12 cos 12 0 2  0 cos 13  001 3 

加速器ニュートリノ
原子炉ニュートリノ
大気ニュートリノ27.4 105  m12
 7.8 105 eV 20.30  sin2 12  0.32

22.24 103  m23
 2.44 103 eV 2

sin2 (223)  0.90

太陽ニュートリノ
原子炉ニュートリノ   ,  e
3

Nishikawa Neutrino2012 e appearance by T2K and MINOS
anti-e disappearance in reactor neutrino

sin 2 (213 ) ~ 0.14

Remaining problems of neutrino physics• CP violation (cp) search– accerlator neutrino （e.g. J-PARC to Hyper-K)• Mass hierarchy (MH)Mass hierarchy– Normal or Inverted

m3
m223

• To determine MH:

m212

m2

e   m 1
m2

m1– Reactor (medium baseline)– Double-beta decay（e.g. KamLAND）– Measurement using matter effectNormalm3

Inverted• very long baseline experiment（~1000km）• atmospheric neutrino5Sub-dominant effects in atm e flux ratio ofCHOOZ 13 and 13 =0

(e)/0(e) ( e )1 2P2 (r  c23 1) (1) r ~s  c~  sin 2 (cos 
13(1)0 ( e )13232
 2~s132 (r  s23
 1)

(2)

Pares and Smirnov
hep-ph/039312

CP R2  sin  CP  I 2 )
(2)

(3)

r : /e flux ratio (~2 at low energy)(3)(1) driven by m2sol sensitive to 23 octant(2) Interference
sensitive to CP(3) 13 resonance sensitive to 23, 13, MH
6  e enhancement by matter effecteResonance happens when :Zenith angle (cos)P(  e) for normal hierarchy, neutrino

2Acc  m23cos 213

  e enhanced in multi-GeV region
In case of Inverted hierarchy:m2  - m2

In case of anti neutrino :Nu. Energy (GeV)

ACC  - ACC

7

Inverted hierarchy
Normal hierarchy  eanti-  anti-e8Super-Kamiokande(front)
SK-I Acrylic+ FRP (back)11146 ID PMTs
(40% coverage)

SK-II

5182 ID PMTs
(19% coverage)

SK-III
11129 ID PMTs
(40% coverage)

SK-IV
Electronics
Upgrade1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012

SK-I
(1646days)SK-II(828days)

50kt water Cherenkov detector（FV22.5kt）

SK-III(636 days)

SK-IV（1097 days)

9

Neutrino interactions in multi-GeVQuasi-elastic  n  l  p

  p  l  nResonance region

Single-pion production  p  l  p     n  l  n     n  l  p   0

  p  l  n   0

  n  l  n     p  l  p   DIS  n  l  N  m   p  l  N  m   p  l  N  m   n  l  N  m 

Difficult to distinguish l- and l+ in Cherenkov detector
Try to probe  and anti- from pions10 e  n e   N'pions (*Total charge for the N’ and pion system is +1)
 e  p e  N'pions (*Total charge for the N’ and pion system is +2)
where       e    e    Decay e- e  p e  N'pions (*Total charge for the N’ and pion system is 0)
 e  n e  N'pions(*Total charge for the N’ and pion system is -1)
- is absorbed in water, no decay-electrons emitted• CCe has more delayed decay-e than CC anti-e• Tend to increase number of Cherenkov rings.

11

Kinematical tendency between CC  and anti-EeE’e-Hadrons

p or nyE  E'E• As Feynman y distribution is larger for CCe than CC anti-e,
CCe has small E’, hence:CC e

CC anti-e

MER (Most Energetic Ring)
momentum fraction

SmallerLarger

Number of identifiedCherenkov rings

MoreLess

Transverse momentum

LargerSmaller

Decay-electron

More

Less12

Statistical  / anti- separation
In case of single-ring ：sample divided by Ndcy

In case of multi-ring：
discriminate using Likelihood method e  n  e  n   CC  e

CC antie

レプトンエネルギーの割合

小大チェレンコフリング数

多少

横方向運動量

大

小

崩壊電子数

多少

13

Multi-GeV multi-ring e and anti-e separation likelihood(number of rings)
1.33 – 2.5 GeV

2.5 – 5.0 GeV

10 – 20 GeV> 20 GeV

5.0 – 10.0 GeV

CC eCC anti-e*area normalized
14

Multi-GeV multi-ring e and anti-e separation likelihood(Transverse momentum)
1.33 – 2.5 GeV

2.5 – 5.0 GeV

10 – 20 GeV> 20 GeV

5.0 – 10.0 GeV

CC e
CC anti-e*area normalized
15

Multi-GeV multi-ring e and anti-e separation likelihood(number of decay-electrons)
1.33 – 2.5 GeV

2.5 – 5.0 GeV

10 – 20 GeV> 20 GeV

5.0 – 10.0 GeV

CC e
CC anti-e*area normalized
16

Multi-GeV multi-ring e and anti-e enriched samples• The Multi-GeV Multi-ring e-like (MME) e and anti-e likelihood includes:

 Number of decay-electrons
 Number of identified Cherenkov rings
 Transverse momentum (divided by total momentum of rings)
Likelihood to separate e and anti- e(SK4)

Anti-e

Beforeseparation

e-likeAnti-e-like

CCe

56.1%

59.4%

53.1%

CC anti-e

19.5%

17.9%

21.0%

NC+ CC

24.5%

22.7%

25.9%

Nuber ofevents

341

161.9

168.1

eCC e
CC anti-eCC anti-

17Electron enhancement in zenith angle plot
sin213 =0.025, CP=40o(1-ring and multi-ring)(1-ring and multi-ring)

Normal、Invertedとも上向き方向に電子事象の超過が見られるが、e-likeとanti-e-likeでは増加量に違いがみられる。
18

Oscillation Effect (CP phase)cos 80
220

300

Livetime: 10 years

cos cos m212 = 7.6 x 10-5 eV2
m223 = 2.66 x 10-3 eV2
sin212=0.304
sin213 =0.025
192
sin 23 =0.425

Expected hierarchy sensitivity
Assumedm223

2.66 x 10-3 eV2

sin2

0.5



CP300 deg

sin213 =0.025 fixed(sin2213 =0.1)

Normal hierarchy

In case of NH :
2(IH)- 2(NH)= 1.06

Normal hierarchy
Inverted hierarchy

In case of IH :
2(NH)- 2(IH)= 0.9020

Fitting result assuming NH*sin213 fixed to be 0.025 (reactor)
m232

2
32
m32
 2.66  0.15
10eV
(1 )
0.40

sin2

0.425

0.380 - 0.628 (90%CL)

CP300All allowed at 90% C.L.

99% C.L.

90% C.L.
68% C.L.

2min = 556.7 / 477 dof
sin2

0.003

Free 13
Fixed reactor 13

0 - 0.0655

13 free
90% C.L.
99% C.L.

99% C.L.

90% C.L.
68% C.L.

90% C.L.
68% C.L.

68% C.L.

2121

Fitting result assuming IH*sin213 fixed to be 0.025 (reactor)

m232

2
32
m32
 2.66  0.17
10eV
(1 )
0.23

sin2

0.575

0.388 - 0.630 (90%CL)

CP


260

All allowed at 90% C.L.

2min = 555.5 / 477 dof
sin2

0.006

99% C.L.

90% C.L.
68% C.L.

Free 13
Fixed reactor 130 - 0.0944*13 free
90% C.L.
99% C.L.

99% C.L.

90% C.L.
68% C.L.

90% C.L.
68% C.L.

68% C.L.
2222Normal hierarchy: 2min = 556.7 / 477 dof
Inverted hierarchy: 2min = 555.5 / 477 dof
22c min(NH) - c min(IH) =1.2

(Sensitivity for mass hierarchy:
2(IH)- 2(NH) = 1.06
2(NH)- 2(IH) = 0.90)
Normal hierarchy
Inverted hierarchy

IH slightly favored ...
23

samples to provide large 2 for MH
Multi-GeV 1-ring anti-e-like(prefers NH)

Multi-GeV 1-ring -like(prefers IH)

cos cos dataNormal hierarchy

NH: sin223 = 0.425 (best fit)
IH: sin223 = 0.575 (best fit)

Inverted hierarchy
No osc*SK1+2+3+4 data

24

FUTURE POSSIBILITIES

25

Hyper-Kamiokande

26

Expected Effects : electron-like samples

27

Hyper-K sensitivity

10yrs, MHsin2(13)=0.098 fixedband : CP uncertainties

In 5 yrs, 3 sigma sensitivity for sin2(23)>0.5
In 10 yrs, 3 sigma sensitivity for sin2(23)>0.4
28

9ICAL at the India-based Neutrino Observatory (INO)
ResistivePlateChamber48mGlassPlates

50 kton Iron tracking Detector
 3 modules, 15 layers
 56 mm thick iron plates
 Resistive Plate Chambers (RPCs)
14m16m

Magnetized to 1.3 Tesla
 Can discriminate + vs  No sensitivity to e+,29 probability
E=7.5GeV, 13=10 degree

30

31

Mass hierarchy sensitivity with ICAL-INO

For sin2(23)=0.5, sin2(213)=0.1:

In 5 yrs (250kt-yr), 2 sigma sensitivity for MH
In 10 yrs (500kt-yr), 2.7 sigma sensitivity for MH
32

IceCube + DeepCore

PINGU

Digital Opitical
Module (DOM)` Higher phototube densities lower
the energy threshold of thedetector
 Less densely instrumented volume
can be used as a vetoIceCube

DeepCorePINGUPINGU-II~1 GeV~100 MeV

PMT density
Energy Threshold~100 GeV~10 GeV

Oscillation
sensitivity

Expected events for E vs cos :E. Kh. Akhmedov, S. Razzaque, A. Y. Smirnov.
arXiv: 1205.7071
Hierarchy asymmetry:Sij [ NijIH  NijNH ]NijNH

Smearing due to event reconstruction:
E = A E  = B (mp / E )1/2 ~ 0.5/E0.5

Asymmetry

Smearing
34

Total significanceS tot 2S
 ijijCould increasesignificance byimprovement ofreconstruction forneutrino energy anddirection

35

Summary• Mass hierarchy will be measured by atmospheric
neutrinos due to non-zero 13 and matter effect in theEarth– e resonance happens for either  or anti- dependingon MH• Super-K has ~1 sigma sensitivity by statistical  andanti- separation  Need more statistics !
• MH determination is promising in future experiments
using Mega-ton detector– Hyper-K– INO– IceCube/DeepCore/PINGU
36