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K2K far detector analysis

K2K far detector analysis. ICRR, Univ. of Tokyo Kenji Kaneyuki for the K2K collaboration. oscillation analysis strategy SK data oscillation analysis conclusion. neutrino oscillation probability. atmospheric n observation. zenith angle distribution : L dependence @ each energy.

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K2K far detector analysis

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  1. K2K far detector analysis ICRR, Univ. of Tokyo Kenji Kaneyuki for the K2K collaboration • oscillation analysis strategy • SK data • oscillation analysis • conclusion

  2. neutrino oscillation probability atmospheric n observation zenith angle distribution : L dependence @ each energy K2K Long baseline experiment L =250km : fixed reduction of events spectrum distortion En

  3. K2K oscillation analysis strategy n flux, spectrum n interaction @ ND number of n events pm, qm measurement @ ND ND Far/Near ratio SK number of n events reconstructed En observation @ SK • flux, spectrum expectation • @ SK • oscillation analysis (sin22q, Dm2)

  4. F1 ( En < 500) = 0.78  0.36 F2 ( 500 En < 750) = 1.01  0.09 F3 ( 750 En <1000) = 1.12  0.07 F4 (1500 En <2000) = 0.90  0.04 F5 (2000 En <2500) = 1.07  0.06 F5 (2500 En <3000) = 1.33  0.17 F6 (3000 En ) = 1.04  0.18 nQE/QE = 1.02  0.10 c2=638.1 for 609 d.o.f 10-6 1.0 2.0 measured flux @ ND (previous talk) Far/Near flux ratio beam MC confirmed by PION monitor En (GeV)

  5. Super-Kamiokande (Far detector on K2K) 50kt total volume 22.5kt fiducial volume 20’PMT photocathode coverage SK-I 11,146 40% SK-II 5,182 19% 41.4m 1000m underground 39.3m

  6. Summary of SK-2 absolute energy calibration various sources (decay-e, p0, low-energy m, high energy m) are used to estimate the energy uncertainty. data agree with MC within ±1.9% time variation : ±0.9% total uncertainty : ±2.1%

  7. event reconstruction on K2K-II likelihood distribution for ring counting likelihood distribution for PID 1-ring ≥2-ring e-like m-like atmospheric n data MC exp. w/ osc. sub-GeV Evis>500MeV/c sub-GeV Likelihood distribution of atmospheric neutrino data agree with MC. (dis-agreements are taken into account to the systematic error.)

  8. SK event selection TOF (0.83ms) cut using GPS Decay electron cut. 500msec 20MeV Deposited Energy No OD activity, fiducial volume, Evis  30MeV 1.6BG events within 500msec 5msec 108 FC events in fiducial volume

  9. SK event summary K2K-I(47.9×1018POT), K2K-II(41.2×1018POT)

  10. K2K oscillation analysis • Total Number of events • Enrec spectrum shape of FC-1ring-m events • Systematic error term Poisson prob. for FC events shape for Enrec for 1ring m event systematic error f x : Systematic error parameters normalization, spectrum, nQE/QE, Far/Near, SK systematic uncertainty

  11. Best fit 1.00 All parameter region (sin22q, Dm2)=(1.53, 2.12x10-3) In physical region (sin22q, Dm2)=(1.00, 2.73x10-3) DlogL=0.64 2.73 sin22q≥1.53 can be occurred by statistical fluctuation with 14.4%. shape : KS prob.=52% data w/o osc. • NSKobs=108 • NSKexp (best fit)=104.8 oscillated expectation Best fit expectation reproduce data well.

  12. nm-nt oscillation allowed region K2K-I+II 8.9x1019POT best fit (sin22q, Dm2) =(1.53, 2.12x10-3) (all) =(1.00, 2.73x10-3) (phys.) 1.7×10-3 ≤Δm2 ≤3.5×10-3 (90%C.L.) @ sin22q=1.0

  13. number of events v.s. En shape distortion number of events En shape Dm2[eV2] Dm2[eV2] sin22q sin22q Oscillation analysis results based on number of events and the En spectrum distortion are consistent.

  14. K2K-I vs K2K-II Enrec K2K-I K2K-II data w/o osc. best fit oscillated expectation allowed region K2K-I and K2K-II results are consistent.

  15. Oscillation analysis results based on neutrino interaction model (CC 1p re-weighted and no coherent p) oscillation results are robust to n interaction assumption.

  16. nm-nt oscillation allowed region K2K SK-I 2flavor SK-I L/E K2K result is consistent with SK-I results.

  17. Null oscillation probability (DlnL) Both number of events and En spectrum distortion are consistent with neutrino oscillation. K2K confirmed neutrino oscillation discovered in Super-Kamiokande atmospheric neutrinos at 3.86s.

  18. Conclusion K2K confirmed neutrino oscillation at 3.86s. Both number of events and En spectrum distortion are consistent with neutrino oscillation. number of events 2.94s En spectrum distortion 2.53s Allowed region for nm dis-appearance is 1.7×10-3 ≤Δm2 ≤3.5×10-3 (90%C.L.) @ sin22q=1.0

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