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Takaaki Kajita, ICRR, Univ. of Tokyo

XII International Workshop on Neutrino Telescopes March, 2007, Venice. T2KK,: What is new?. Takaaki Kajita, ICRR, Univ. of Tokyo. ◆Introduction ◆T2KK: Venice last year ◆T2KK: What is new? - L dependence, - Higher energy option, - Octant of q 23 , - Others ◆Summary.

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Takaaki Kajita, ICRR, Univ. of Tokyo

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  1. XII International Workshop on Neutrino Telescopes March, 2007, Venice T2KK,: What is new? Takaaki Kajita, ICRR, Univ. of Tokyo ◆Introduction ◆T2KK: Venice last year ◆T2KK: What is new? - L dependence,- Higher energy option, - Octant of q23, - Others ◆Summary

  2. Introduction • mass and mixing parameters: q12, q23, q13, d, Dm122, Dm132(=Dm232) Known: q12, Dm122 sin22q23, |Dm232| nenmnt n3 n2 n1

  3. Goals for the future neutrino oscillation exp’s Near future reactor, LBL exp’s Unkown In addition, If q23 ≠p/4, is it >p/4 or <p/4 ? q13 Sign of Dm232 nenmnt n3 nenmnt n3 or n2 or n1 n3 CP ? How much will T2KK contribute to these measurements?

  4. T2KK: Venice last year Detector in Korea ?

  5. Possible experimental setup Total cost must be similar to the original Hyper-K design. 0.27Mton 0.27Mton 2.5 deg. off axis (or smaller off-axis Angle) 2.5 deg. off axis Distance from the target (km) JPARC 0754MW 2.5deg.off-axis beam @Kamioka Fig. from Senda NP04 Off-axis angle

  6. Bi-probability plots for Kamioka and Korea sin22q13=0.05 BG: almost identical  both 2.5 deg. off axis beam

  7. Expected signal, BG and 2 signal BG 4yrs n + 4yrs anti-n sin22q13=0.1, d=p/2 n and anti-n × Kamioka and Korea 5 energy bins syst. Errors: 5% BG (overall) 5% BG (energy dep.) 5% signal efficiency +(Korea-Kamioka flux diff.in recent analysis)

  8. T2K-II(0.54 Mt) vs. T2KK(0.27+0.27 Mt) Kamioka+Korea n4yr + anti-n4yr T2K-II n2yr + anti-n6yr Truth 68,90,99%CL 

  9. Expected sensitivity hep-ph/0504026 Total mass of the detectors = 0.54 Mton fid. mass 4 years neutrino beam + 4 years anti-neutrino beam Mass hierarchy CP violation (sind≠0) 3 s (thick) 2 s (thin)

  10. T2KK: What is new?

  11. What is new ? (1)- 1050km: a magic baseline ? - K.Okumura, 2nd T2KK workshop, Seoul 2006 2.5 degree off-axis beam with L between 1000km and 1250km is available. Checked if the sensitivity depends strongly on the baseline length. sin22q13 Kam only L=1000km Sensitivity to mass hierarchy (True = normal hierarchy) L=1050km L=1100km L=1150km  The sensitivity does not depend strongly on L ! L=1200km L=1250km d 3s sensitivity

  12. What is new ? (2): higher energy option Mass hierarchy hep-ph/0607177 3 L=1300km, Wide band beam 2 3 Kamioka + Korea T2K II (Kamioka) T2KK ‘s sensitivity on mass hierarchy is still limited compared with the US studies…  Higher energy better ?

  13. Higher energy beam Flux (arb. unit) 1.0 to 2.5 degree off axis beam available in Korea. P(nmne) En (GeV)

  14. Maximum likelihood analysis T2K electron appearance selection is based on several cuts. This set of cuts cannot be used directly in higher energy beams, since the cut position depends on energy.  Maximum likelihood (with 8 variables). Likelihood distributions Cut at L=0.

  15. Signal and BG for various off-axis beams 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: Low E BG more serious. (2nd osc. Max. difficult to see.) But larger matter effect at the 1st osc. Max..

  16. 3s sensitivities for various OA angles F.Dufour, 2nd T2KK workshop, July 2006, Seoul (Updated) Mass hierarchy CP violation Preliminary 3 Could be slightly too optimistic for OA angle less than 2.5 degrees (The syst errors are assumed to be fully correlated between 2 detectors) Kam only (OA2.5) Kam + Korea OA1.0 Kam + Korea OA1.5 Kam + Korea OA2.0 Kam + Korea OA2.5 Mass hierarchy: OA1.0 @Korea gives the best sensitivity CP violation: Sensitivity depends weekly on the beam option

  17. What is new ? (3): 8 fold degeneracy In the previous study, maximal q23 mixing (q23=p/4) was assumed. However, q23 might not be p/4. In this case, there should be additional ambiguity in the parameter measurements (especially in that of sin2q13) due to the ambiguity in the octant of q23 (i.e., q23 >45 or <45 deg.). It will be very nice if the same setup can solve the octant ambiguity of q23. Resolving 8 fold parameter degeneracy in T2KK

  18. Oscillation probabilities and the signal P(nmne) by the solar Dm2 is proportional to sin22q12・cos2q23 Solar oscillation effect visible in a very long baseline (or very large L/E) experiment. sin22q12・cos2q23 effect visible Atm. + CP terms BG events Solar term ○sin2 q23= 0.4, sin2 2q13= 0.01 ●sin2 q23= 0.6, sin2 2q13= 0.0067 (sin2q23・sin22q13 is equal in the two cases.) Dm2: positive, d=p3/4

  19. Parameter 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 parameter degeneracies.

  20. sin22q13 Sensitivity to octant of q23 sin22q23=0.96 hep-ph/0609286 OA 2.5 degree for both Kamioka and Korea sin22q23=0.99 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). Could resolve the 8 hold degeneracy of the oscillation parameters.

  21. Other recent studies (1) In T2KK, do we need 40% photo-coverage (200,000 PMTs)? Or 20% photo-coverage (100,000 PMTs) can be OK? F. Dufour, 2nd T2KK workshop, Seoul 2006 Likelihood distributions (red: BG, black: CC ne, green: CC QE ne) 20% photo-coverage looks OK (as far as LBL experiments are concerned).

  22. Other recent studies (2)Hybrid Photo-Detector R&D H.Aihara, 2nd T2KK workshop

  23. Summary If non-zero q13 is observed…. • We hope to proceed to the next phase of experiment with higher power beam and larger detector(s). • Goals: discovery of leptonic CP violation, and determination of mass hierarchy and octant of q23. (+ Various non-LBL physics). • T2KK can be one of the serious possibilities. • We will continue the studies.

  24. End

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