The document discusses the potential of the T2KK and T2KO experiments to measure neutrino mass hierarchy and the Dirac CP violating phase using a 100 kiloton water Cherenkov detector placed in Korea or Oki Island, respectively, with the Super-Kamiokande detector also used. It finds that the mass hierarchy could be determined at over 3 sigma significance with T2KK in 5 years, while T2KO may require some luck within 5 years. Both experiments could improve constraints on the CP violating phase, measuring it to 20-50 degrees accuracy. The neutrino beam experiments are important to fully determine the neutrino mass hierarchy and CP phase in the coming decade.

1. T2KK/T2KO 実験での質量階層性、
CP 位相測定の可能性
1
Yoshitaro Takaesu
U of Tokyo

2. Introduction

3. Questions in neutrino physics
• Dirac or Majorana?
• mass scale & its origin?
• Sterile neutrinos?
• CP violation in the lepton sector?
• Majorana CP phase?
• Dirac CP phase?
• mass hierarchy?
3

4. Questions in neutrino physics
• Dirac or Majorana?
• mass scale & its origin?
• Sterile neutrinos?
• CP violation in the lepton sector?
• Majorana CP phase?
• Dirac CP phase?
• mass hierarchy?
4
Fix unknowns as possible as we can.
We know them.
But really don’t know them.

5. Further motivations for MH and Dirac CP phase
• Needed for determination of neutrino mass in
hierarchical case from cosmology and beta decay exp.
results.
• Define scope for future neutrinoless double beta decay
experiments.
• Reduce uncertainty for CP phase measurements
significantly.
5
⌃imi m2
= ⌃i|Uei|2
m2
i
Mass hierarchy
Dirac CP phase
• provide a solution for CP violation source in Leptogenesis.
• via flavour dependent CP asymmetry
for M1 << 10^12 GeV.
• Constrain flavor symmetry models for neutrino mixing pattern.
[Perke, Petcov, Riotto, PRD and NPB 2007]

6. Our knowledge on neutrino sector
Three light flavor mixing
Mass differences
normal inverted
Mass hierarchy: NH or IH
[PDG:Phys.Rev. D86 (2012) 010001] 6
U =
Majorana phase
Unknown
irrelevant to neutrino
oscillation

7. Hints on MH and Dirac CP phase
around 90° seems to be
disfavoured
by T2K + reactor (theta_13).
MINOS favours around 90°
but lower statistics.
MH and Dirac CP phase are still less constrained.
1403.0867
Global Fit
Forero et.al
1205.4018
7
1502.01550

8. • T2K (LBL, 22.5kt WC) (2011 ~ )
• Nova (LBL, 14kt LAr) (2014 ~ )
• INO (atm, 50kt Iron) (2018 ~ )
• JUNO (react, 20kt LSci) (2020 ~ )
• RENO50 (react, 18kt LSci) (2020 ~ )
• ORCA (atm, 3Mt Ocean) (2020 ~ )
• PINGU (atm, 3Mt Ice) (2021 ~ )
• DUNE (LBL, 40kt LAr) (2024 ~ )
• T2HK (LBL, 560kt WC) (2025 ~ )
• ESSnuSB (LBL, 500kt WC) (2030 ~ )
Oscillation Experiments for MH / Dirac CP phase
T2K/T2HK&
DUNE%
Nova%
PINGU&
INO
RENO50
ESSnuSB
Operating
Approved
Proposed
8

9. Neutrino Beam Exp.

10. We assume POT/year ( sec)
with 40 GeV proton beam.
focusing beamνµ (νµ )
p
Neutrino beam is produced by colliding protons on target.
The total neutrino flux is expressed by POT (Protons On Target).
( like Luminosity @ collider )
0.64 MW
(Talk by T.Nakaya @Flavor of New Physics (2015.3.9))
Current: 0.32 MW
Plan: 0.75 MW in 5years
10

11. Oscillation Probability: disappearance mode
(Up to linear terms of are retained in A and B)
CP phase sensitive terms are subdominant.
-> almost insensitive to CP phase
Effect of Mass hierarchy (sign of Delta_31) is too small
comparing to 1 -> almost insensitive to Mass hierarchy
However, this mode is important to constrain
using its large number of events.
sin ✓23
11

12. Matter effect terms enhances sign difference of .
Oscillation Probability
(Up to linear terms of are retained in A and B)
Amplitude
correction
Phase
correction
Matter Effect
12

13. term typically has larger coefficient than term.
LBL exp. are more sensitive to than .
Oscillation Probability
Ae
' 0.2
✓
¯⇢
3 g/cm3
◆ ✓
E
GeV
◆
0.47
✓
L/1000 km
E/GeV
◆
sin CP
Be
' 0.28
✓
¯⇢
3 g/cm3
◆ ✓
L
1000 km
◆
+0.23
✓
L/1000 km
E/GeV
◆
cos CP
Higher neutrino E has better sensitivity to the mass hierarchy
for a fixed baseilne L.
The sensitivity to CP phase is increased for lower E.
-> Need to cover lower neutrino energy/higher peaks.
±

14. Oscillation Probability

15. T2KK / T2KO
15
As an Example of next generation neutrino beam experiments

16. T2KK and T2KO
16
T2KK: 100 kton in Korea and SK [hep-ph/0410229, 0504026, 0901.1517,
1001.5165]
T2KO: 100 kton in Oki island and SK [0804.2111, 1209.2763]
* SK (22.5kton) is also used as a second detector
SK
T2K
(250 km)
22
• Longer baseline than T2K to enhance sensitivity to the MH
• Wide band beam for sensitivity to (phase)
as well as (amplitude).

17. T2KK and T2KO
17
T2KK: 100 kton in Korea and SK [hep-ph/0410229, 0504026, 0901.1517,
1001.5165]
T2KO: 100 kton in Oki island and SK [0804.2111, 1209.2763]
* SK (22.5kton) is also used as a second detector
SK22
• Longer baseline than T2K to enhance sensitivity to the MH
• Wide band beam for sensitivity to (phase)
as well as (amplitude).
T2KO
(650 km)
100

18. T2KK and T2KO
18
T2KK: 100 kton in Korea and SK [hep-ph/0410229, 0504026, 0901.1517,
1001.5165]
T2KO: 100 kton in Oki island and SK [0804.2111, 1209.2763]
* SK (22.5kton) is also used as a second detector
SK22
• Longer baseline than T2K to enhance sensitivity to the MH
• Wide band beam for sensitivity to (phase)
as well as (amplitude).
T2KK
(1000 km)
100

19. Beam profiles
νµ beam
Korea and Oki detectors cover wider energy range than SK.
sensitive to term (phase) as well as term (Amp.).
But more NC π0 BG from the high energy tail
K.Hagiwara, T.Kiwanami, N.Okamura, K.Senda hep-ph/1209.2763
Flux * Cross section

20. Energy distributions: νe appearance mode (NH)
Total events
CCQE signal
non-CCQE signal
NC π0 BG
miss-ID neutrino BG
SK
T2KO
T2KK
T2KK and T2KO
can observe the
2nd oscillation peak
as well as the 1st peak.

21. Energy distributions: νe appearance mode (IH)
Total events
CCQE signal
non-CCQE signal
NC π0 BG
miss-ID neutrino BG
SK
T2KO
T2KK
T2KK and T2KO
can observe the
2nd oscillation peak
as well as the 1st peak.

22. Mass Hierarchy
22

23. Sensitivity to Mass Hierarchy
T2KK 2.5°OAB@SK
T2KO
MH can be determined with > 3 sigma for T2KK in 5 years run.
We need luck to determine MH with T2KO in 5 years run.
Sensitivity strongly depends on CP phase and 2-3 angle.

24. Sensitivity of other experiments to MH
1311.1822
1401.2046

25. Sensitivity of other experiments to MH
DUNE
Full 5yrs run
25
PINGUORCA
Nova +T2K
ESSnuSB 2+8yrs
Hyper-K 10yrs

26. Sensitivity of other experiments to MH
RENO-50INO

27. Dirac CP phase
27

28. T2K122 (just for comparison with T2KK and T2KO)
28
T2K122: 100 kton added to SK
SK22
• Longer baseline than T2K to enhance sensitivity to the MH
• Wide band beam for sensitivity to (phase)
as well as (amplitude).
T2K122
(295 km)
100

29. degeneracy in
Sensitivity to CP phases (global picture)
The sensitivity to the CP phase measurement is fully expressed in
test vs. true plane.
4 9
Exclusion contours
corresponds to
CP measurement accuracy
in previous slides
T2KK
3°OAB
T2KK
2.5°OAB
T2KO T2K122
sin CP

30. T2KK & T2KO have better sensitivity than T2K122
around ±60°, ±120°.
CP measurement with and beam
Longer baseline helps to resolve degeneracy in
termdue to
Poor accuracy
due to the
degeneracy
T2KK
3°OAB
T2KK 2.5°OAB
T2KO T2K122

31. Using around 2.5:2.5 beam ratio, CP phase can be measured
with 20° - 50° (T2KK) and 20° - 45° (T2KO) accuracy.
T2KK 3°OAB T2KK 2.5°OAB
T2KO T2K122
CP measurement with and beam

32. Sensitivity of LBL experiments to Dirac CP phase
T2KK (10yrs)
T2K+Nova
T2KK (5yrs)
T2KK/T2KO-like experiment can fill gap
btw Nova/T2K and Hyper-K/DUNE, if realized.
(DUNE)
T2KO
* modified plot
in 1309.7022

33. for 45% of (T2KK)
for 25% of (T2KO)
for 33% of (T2K122)
Sensitivity to CP violation detection
The region of the CPV
detection is also clearly seen.
4 9
Exclusion contours
CPV
CPV detection with
Sensitivity to CPV in 5years
T2KK
3°OAB
T2KK
2.5°OAB
T2KO T2K122
Statistics matters
CPV sensitivity:
T2K122 > T2KO > T2KK

34. Sensitivity of LBL experiments to CPV
34
DUNE 10yr
ESSnuSB 2+8 yr: 1309.7022
Hyper-K 10yrs

35. Summary
There are many on-going efforts to determine the neutrino mass hierarchy
and Dirac CP violating phase in the lepton sector.
Mass hierarchy will be determined with 3-5 sigma.
We discussed sensitivity of neutrino beam experiments
to MH and CP phase, considering T2KK/T2KO like experiment
as an example.
CP phase will be measured with 20° - 50° accuracy.
MH will be fixed in the next decade, but it will take more time to
measure CP phase accurately and establish CPV.
Using 100kton WC detector at ~1000 km distance
with 5*10^21 POT neutrino beam flux,
(atm. & react. exp. can also contribute.)
(Neutrino beam exp. plays a crucial role.)