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Takaaki Kajita, ICRR, Univ. of Tokyo

NuFact04, Osaka, July 2004. Atmospheric Neutrinos; - Present and future -. Takaaki Kajita, ICRR, Univ. of Tokyo. Outline. Atmospheric neutrino beam Atmospheric neutrinos: Present L/E analysis Atmospheric neutrinos: Future sub-dominant oscillations ?

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Takaaki Kajita, ICRR, Univ. of Tokyo

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  1. NuFact04, Osaka, July 2004 Atmospheric Neutrinos; - Present and future - Takaaki Kajita, ICRR, Univ. of Tokyo

  2. Outline • Atmospheric neutrino beam • Atmospheric neutrinos: Present L/E analysis • Atmospheric neutrinos: Future sub-dominant oscillations ? • Summary Only 2 and 3 flavor neutrino oscillations

  3. Cosmic Ray Atmospheric neutrinos p, K Atmosphere μ e nm nm ne nm ne Neutrinos from the other side of the Earth.

  4. Total nm+nm flux Flux × En2 En(GeV) Atmospheric neutrino beam Measured cosmic ray proton flux Zenith angle: nm ne

  5. Event classification Fully Contained (FC) (E ~1GeV) Partially Contained (PC) (E ~10GeV) Stopping  (E~10GeV) Through-going (E~100GeV)

  6. Atmospheric neutrinos: Present Soudan-2 (1kton tracking detector) 9.3m 76m Super-Kamiokande (50,000ton water Ch. Detector) MACRO (large muon detector) 12m

  7. Super-K atmospheric neutrino data CC ne CC nm 1489day FC+PC data + 1646day upward going muon data

  8. Soudan2 • 5.9 kton・yr exposure • Partially contained events included. • L/E analysis with the “high resolution” sample Reconstructed Lν/ Eν dist. Zenith angle Phys.Rev. D68 (2003) 113004 e e μ μ Up-going Down-going No osc. nm ntosc.

  9. Multiple scattering Em En or MACRO PLB 566 (2003) 35 Oscillation Δm2 =2.5×10-3 L /E Upward horizontal

  10. Neutrino oscillation parameters nm nt 90%CL Soudan-2 Super-K MACRO

  11. m-like multi-GeV + PC SK collab. hep-ex/0404034 L/E analysis New ! oscillation decoherence decay Should observe this dip! • Further evidence for oscillations • Strong constraint on oscillation parameters, especially Dm2

  12. FC single-ring m-like Full oscillation 1/2 oscillation D(L/E)=70% Selection criteria Select events with high L/E resolution (D(L/E) < 70%) Following events are not used: ★horizontally going events ★low energy events 2121 FC m-like and 605 PC Similar cut for: FC multi-ring m-like, OD stopping PC, and OD through-going PC

  13. 1489 days FC+PC (Super-K) L/E distribution Mostly up-going MC (no osc.) Decoh. Decay Osc. Mostly down-going • Evidence for oscillatory signature Decay and decoherence disfavored at 3.4 and 3.8s level, respectively.

  14. Allowed neutrino oscillation parameters 90% CL 1.9x10-3 < Dm232 < 3.0x10-3 eV2 0.90 < sin22q23(90% C.L.) SK L/E analysis Kam. c2min=37.9/40 d.o.f @ Dm2=2.4x10-3,sin22q=1.00 (sin22q=1.02, c2min=37.8/40 d.o.f) Soudan2 K2K MACRO SK Zenith angle analysis  Stronger constraint on Dm2  Consistent with that of the standard zenith angle analysis

  15. Matter effect cosQ En(GeV) Search for non-zero q13 (Dm122=0 assumed) MC, SK 20yrs 1+multi-ring, e-like, 2.5 - 5 GeV Electron appearance s213=0.05 s213=0.00 null oscillation cosQ Electron appearance in the 5 – 10GeV upward going events.

  16. Super-K e-like data Multi-GeV, single-ring e-like Multi-GeV, multi-ring e-like (special) No evidence for excess of upward-going e-like events

  17. prelim. n2 n3 n1 n2 n3 n1 3 flavor analysis from Super-K Normal Inverted

  18. Atmospheric neutrinos: Future Present: Study of dominant oscillation channel (nm nt) Future: Study of sub-dominant oscillations ★q13? ★Mass hierarchy? ★Solar oscillation effects? nenmnt Normal mass hierarchy is assumed. n3 ν mass n2 n1

  19. Possible future atmospheric n detectors Very large water Cherenkov detector UNO Hyper-K (1Mton) Mton class detector at Frejus Magnetized large tracking detector MONOLITH, INO (India-based Neutrino Observatory, …

  20. Importance of s2q23>0.5; S.Pascoli et al., hep-ph/0305152 TK noon2004 Sensitivity to non-zero q13 Multi-GeV electron appearance SK 20yr MC Water Cherenkov detector 450 kton・yr (SK 20 years) 3s 3s 3s ～ Present bound on sin2q13 (Dc2 ∝～ exposure)

  21. P(nmne) n2 n3 n1 n2 n3 n1 cosQ En(GeV) Sign of Dm23(13)2 ? How can we discriminate positive and negative Dm2 ? Real Dm232 =positive assumed Real Dm232 = negative assumed P(nmne) cosQ En(GeV) (No resonance for anti-neutrinos) (No resonance for neutrinos)

  22. Measurement of sign of Dm2 in large magnetized detectors Δm2=2.5×10-3 sin2θ =0.02 13 Determination of sign of Δm2 at 90%CL. NPB (proc suppl) 91 (2001) 147, hep-ex/0106252

  23. TK NOON2004 Measurement of sign of Dm2in water Cherenkov detectors ? Use differences in s and ds/dy Dm2: fixed, q23: free, q13: free, positive Dm2 Exposure: 1.8Mtonyr (SK 80yr or HK ～3.3 yr) 3s 3s 3s

  24. Solar oscillation effects Solar neutrino oscillation: LMA (Dm122 = 7×10-5eV2) Expected number of sub-GeV e-like events in SK. Peres, Smirnov NPB 680 (2004) 479 10 1 The number of e-like events changes as a function of sin2q23 (NOT sin22q23).  Discrimination of >45 and <45 q23 might be possible. (However, the effect is very small for s22q23=1.00.) P.Lipari NOON2004

  25. Summary • Atmospheric neutrinos have been playing major role in the neutrino oscillation studies. • The present data are nicely explained by nm nt oscillations with; Dm2=1.9 – 3.0 × 10-3 eV2 sin22q > 0.90 (SK L/E analysis) • Recent L/E analysis has shown evidence for “oscillatory” signature. • Future atmospheric neutrino experiments is likely to continue to contribute to the neutrino oscillation physics (q13, sign of Dm232 ….) (If (a) much larger detector, (b) relatively large q13.)

  26. End

  27. Specials in L/E analysis 1.5m from top & bottom FC single-ring, multi-ring m-like 22.5kt →26.4kt Expand fiducial volume 1m from barrel More statistics for high energy muons observed charge / expectation from through-going PC OD through-going OD stopping Classify PC events using OD charge OD through-going MC • OD stopping • OD through going Different L/E resolution OD stopping MC

  28. Energy and angular resolution of neutrinos

  29. m m L/E cuts Full osc. Half osc.

  30. Sensitivity to other models (determination of L/E resolution cut) 70% 80% n decoherence n decay n decay n decay 70% 80% n decoherence n decoherence L/E resolution cut at 70%

  31. Event summary of L/E analysis Fractions of FC and PC samples in L/E distribution FC Data MC CC nm single-ring multi-ring stopping through-going 1619 2105.8 (98.3%) 502 813.0 (94.2%) 114 137.0 (95.4%) 491 670.4 (99.1%) PC

  32. Check of the observed dip in L/E distribution (1) Other L/E resolution cuts

  33. Check of the observed dip in L/E distribution (2) FC e-like (Flat L/E distribution is expected.)

  34. Check of the observed dip in L/E distribution (3) zenith angle :cosq  -cosq (Zenith angle of each event is inverted. Because of the wrong assignment of L, no dip is expected.)

  35. Sensitivities to alternative models and the data n decoherence obtained Dc2 n decay L/E resolution cut at 70%

  36. Neutrino decay and decoherence models ? c2min=37.9/40 d.o.f c2min=49.1/40 d.o.f  Dc2 =11.3 c2min=52.4/40 d.o.f  Dc2 =14.5 Oscillation Decay Decoherence ndecay disfavored at3.4s ndecoherence at3.8s First dip observed in the data cannot be explained by alternative hypotheses  Evidence for oscillatory signature

  37. c2 as a function of sin2q13 Inverted Normal

  38. CC ne CC ne How can we discriminate neutrino and anti-neutrino interactions ? Simple answer: No. It is not possible to discriminate event by event in water Cherenkov experiments. However, s(total) and ds/dy are different. Single-ring e-like Multi-ring e-like Others Others CC ne CC ne  Try to discriminate positive and negative Dm2 using these events.

  39. Electron appearance for positive and negative Dm2 in a water Chrenkov detector Dm2=0.002eV2 s2q23 = 0.5 s2q13 = 0.05 (SK 20yrs) Single-ring e-like Multi-ring e-like Relatively high anti-ne fraction Lower anti-ne fraction Positive Dm2 Negative Dm2 null oscillation cosQ cosQ

  40. c2 difference (inverted-normal) True= normal mass hierarchy assumed. Dm2: fixed, q23: free, q13: free Exposure: 1.8Mtonyr (SK 80yr or HK ～3.3 yr) 3s 3s 3s

  41. c2 difference (normal – inverted) True= inverted mass hierarchy assumed. Dm2: fixed, q23: free, q13: free Exposure: 1.8Mtonyr (SK 80yr or HK ～3.3 yr) 3s 3s 3s

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