1. Report of the T2KK Workshop
NNN07 at Hamamatsu, Oct. 2-5, 2007
Report of the T2KK Workshop
Soo-Bong Kim, Seoul National University,

2. 1st & 2nd Workshops on T2KK http://T2KK.snu.ac.kr

3. Summary of the 1st & 2nd Workshops
T2KK motivation:
- T2K-II with HK needs to resolve the degeneracy in the measured CP
phase based on the longer L and the larger matter effects
Location of the detector(s):
- ~2000 m.w.e. depth for most of physics (H.Sobel, T2KK05)
- a candidate site at Kamioka (K.Nakamura, T2KK05)
- mountains of 1,200 meters in height are found almost everywhere in
the interesting region of Korea (D.Son, T2KK05, C.Ryu, T2KK06)
Resolving the oscillation parameter degeneracy:
- mass hierarchy & CP phase (H.Minakata, N.Okamura, E.J.Jeon, T2KK05
S.K.Kang, H.Minakata, K.Senda, T2KK06)
- sensitivity as a function of off-axis angle at far detector (N.Okamura, T2KK05/06,
F.Dufour, T2KK06, K.Okumura, T2KK06, A.Rubbia, T2KK05/06)
- liquid Ar sensitivity (A.Rubbia, T2KK05/06)
Probing non standard physics:
- NSI (P.Ko, H.Sugiyama, T2KK06)
- test of unitarity (B.Gavela, T2KK06)

4. 3rd Workshop on T2KK University of Tokyo, Tokyo 9/30-10/1, 2007
Site study for HK and one in Korea
(N. Wakabayashi, C. Ryu)
BNL-Fermilab LBL/J-PARC /Systematics at Superbeam exp.
(M. Diwan, T. Ishida, P. Huber)
Oscillation parameter degeneracy
(S.K. Kang, J. Valle)
T2KK sensitivity in resolving degeneracy
(F. Dufour, C. Ishihara, N. Okamura,
K. Okumura, A. Rubbia, K. Senda)
NSP/Test of Unitarity (P. Ko, K. Kimura)
4th workshop at KIAS, Seoul
fall, 2008

5. Site Study for Hyper-Kamiokande
Site studies and cavern analyses by Mitsui Mining & Smelting Co. Ltd. (K. Nakamura, T2KK05)
Study on the joint rock mass by Shimizu Corporation (N. Wakabayashi, T2KK07)

6. Site Study for the Korean Detector
mountains of 1,200 meters in height are found almost everywhere in
the interesting region of Korea → Search for a candidate site
(D.Son, T2KK05, C.Ryu, T2KK06/07)

7. Oscillation Parameter Degeneracy
Resolving the octant degeneracy
(H. Minakata, T2KK05/06, S.K.Kang T2KK06/07)
q13
Sign of Dm232
If q23 ≠p/4,
is it >p/4 or <p/4 ?
ne nm nt n3 or
ne nm nt n3 n2 n1 or n3
CP ?
How much can T2KK contribute to these measurements?

8. How to solve the octant degeneracy?
H. Minakata, T2KK06
Strategy: Use information which are not proportional to sin2223 x sin2213
Detect solar m2 effect (∝ cos223)
Requires very long baseline (or very large L/E)
OK even at small 13
(S. Nakayama T2KK06)
Combining reactor measurement of 13
Requires great precision in reactor 13 measurement
Powerful at large 13
(N. Okamura T2KK06)
Very large L/E + Reactor 13 (C. Ishihara, N. Okamura, A. Rubbia, T2KK07)

9. Sensitivity of Mass Hierarchy
C. Ishihara, T2KK07

10. Resolving the degeneracy: T2K-II vs. T2KK
T2K-II (Kamioka only)
T2KK (Kamioka + Korea)
Octant of q23
not resolved
Mass hierarchy not determined
T2KK has a good sensitivity to resolve the parameter degeneracies.

11. Sensitivity to the Octant of 23
S. Nakayama, T2KK06
sin22q23=0.96
OA 2.5 degree for both Kamioka and Korea
sin22q23=0.99
sin22q13 2s 3s
Octant ambiguity of q23 can be resolved at 2s if sin22q23 < ~0.97 (almost independent of the value of sin22q13 and mass hierarchy).
T2KK could resolve the 8 hold degeneracy of the oscillation parameters.

12. Sensitivity on Off-axis Angles of the Korea Detector
N.Okamura, T2KK05/07
Suggested that the higher energy beam is better due to the larger matter effect.
1.0 to 3.0 degree off-axis beam available in Korea.
However, background might be a serious issue for higher energy beam.
Detailed Monte Carlo study (F.Dufour, T2KK06)
Liquid Argon detector (A.Rubbia, T2KK05/06)

13. Sensitivity on Baseline of the Korea Detector
K. Okumura, T2KK06
2.5 degree off-axis beam with L between
1,000km and 1,250km is available.
Kamioka only
L=1000km
L=1050km
L=1100km
3 s sensitivity to mass hierarchy
(True = normal hierarchy) d
sin22q13
L=1150km
L=1200km
L=1250km
The sensitivity does not depend strongly on L !
Potentially many candidate sites !

14. Beam Energy Profiles at Sites in Korea
A. Rubbia, T2KK07
1.0 to 3.0 degree off-axis beam available in Korea.

15. Signal & BG for Various Off-axis Beams
F.Dufour, T2KK06
Korea
Kamioka
1.5 degree
1.0 degree
2.5 degree
signal
signal BG BG
sin2(2q13)=0.1 d=1/2p
4 year neutrino run
4MW beam
2.5 degree
2.0 degree
Smaller off-axis angle:
Larger matter effect at the 1st osc. Max..
 Low E BG more serious.
(2nd osc. Max. difficult to see.)

16. T2KK Sensitivities for Various OA Angles
F.Dufour, T2KK06/07
Mass hierarchy
CP violation

17. Sensitivity of Mass Hierarchy
A. Rubbia, T2KK07
The longer baseline & higher rate improves mass hierarchy determination

18. Liquid Ar Detector Quasi-elastic Deep inelastic
A. Rubbia, T2KK05/06/07
Quasi-elastic
Deep inelastic
Possibility to study exclusive final states also in Multi-GeV range
Detector behaves as a very fine-grained “tracking-calorimeter”
Very small NC and other ne background even with the multi-GeV beam.
 Good for near on-axis beam.

19. Sensitivity of Liquid Ar Detector
A. Rubbia, T2KK05/06/07
OA 1.0 deg, 28×1021pot, 100 kton mass
Very high sensitivity, especially
in the very small sin22q13 region.
sin22q13=0.006
Mass Hierarchy CP

20. Probing Non-standard Neutrino Physics
P. Ko, T2KK06/07
Quantum Decoherence:
Lorentz Symmetry/CPT Violation:
Flavor nonuniversal neutrino interactions with matter:
See their upcoming paper….

21. Summary
T2KK is an interesting option to resolve the oscillation parameter degeneracy based on the longer baseline and an additional, identical detector in Korea.
For the best experiment, T2KK needs further tuning of some of parameters such as baseline, off-axis angle, detector mass, etc.
T2KK needs a study of more physics opportunities.