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Review of experimental results on atmospheric neutrinos

Review of experimental results on atmospheric neutrinos. Univ. of Tokyo, Kamioka Observatory Masato Shiozawa. Introduction Super-Kamiokande MACRO Soudan 2 Summary. C Scientific American. Super-Kamiokande detector. Water Cherenkov detector. 1000 m underground

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Review of experimental results on atmospheric neutrinos

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  1. Jan.-2002 @CERN Review of experimental results on atmospheric neutrinos Univ. of Tokyo, Kamioka Observatory Masato Shiozawa Introduction Super-Kamiokande MACRO Soudan 2 Summary

  2. Jan.-2002 @CERN C Scientific American Super-Kamiokande detector Water Cherenkov detector • 1000 m underground • 50,000 ton (22,500 ton fid.) • 11,146 20 inch PMTs • 1,885 anti-counter PMTs 42 m 39.3 m

  3. Jan.-2002 @CERN Rebuilding Super-K • Phase-1 quick restart of K2K • rebuild SK with about half PMT density by autumn of 2002 • atmospheric ν, proton decay search • solar ν, SN watch with higher energy threshold • PMT vessel to prevent from chain reaction of explosion • Phase-2 full detector before the time of commissioning of JHF acrylic vessel acrylic+(FRP or stainless steel)

  4. Jan.-2002 @CERN Event classification of atmospheric ν Contained event (sub-GeV, multi-GeV sample) Upward through-going m Fully Contained (FC) Partially Contained (PC) m m e/m Upward stopping m Eν～ 1 GeV Eν～ 10 GeV Eν～ 10 GeV (stop μ） 　　　100 GeV (through μ）

  5. Jan.-2002 @CERN Zenith angle distributions(FC+PC+up-μ) νμ⇔ντ 2-flavor oscillations Best fit (Dm2=2.5x10-3eV2,sin22q=1.00 χ2min=157.5/170 d.o.f) No oscillation (χ2=393.4/172 d.o.f) ～ 13000km ～500km ～15km ～ 13000km ～500km

  6. Jan.-2002 @CERN Combined allowed regions nm→nt Super-Kamiokande Best fit(Δm2=2.5×10-3,sin22θ=1.0 χ2min=157.5/170 d.o.f) No oscillation (χ2 =393.4/172 d.o.f) Δm2 = (1.6～3.6)x10-3eV2 sin22θ > 0.9 @ 90%CL

  7. Jan.-2002 @CERN νμ⇔ντorνμ⇔νsterile? Using MSW effect andenriched NC sample nm→nt : No matter effect / NC interaction nm→ns : With matter effect / No NC interaction Neutrino oscillation in matter: ( ) ( ) ( ) cosqm sin22q nm sinqm n1 = sin22qm = ns - sinqm cosqm n2 (z-cos2q)2+sin22q z = - 2 GFnnEn / Dm2 √ 1 sin22qm ~ For sin22q = ~ 1 z2+ 1 And for En = 30~100 GeV z≫1 and sin22qm≪1 Suppression ! Test zenith angle of NC enriched events,　high energy PC and through-going muon events.

  8. Allowed region from FC single-ring sample

  9. Jan.-2002 @CERN νμ⇔ντorνμ⇔νsterile? １ checking matter effect (partially contained events) Zenith angle of high-E PC Up/down ratio of high-E PC nm→ns nm→ns up/down ratio nm→nt nm→nt Evis> 5 GeV <En>=~25 GeV 10-3 10-2 cosΘ Δm2

  10. Jan.-2002 @CERN νμ⇔ντorνμ⇔νsterile? 2 checking matter effect (upward through going μ) Zenith angle of up through μ V/H ratio of up through μ nm→ns nm→ns vertical/horizontal ratio nm→nt nm→nt 10-3 10-2 cosΘ Δm2

  11. Jan.-2002 @CERN νμ⇔ντorνμ⇔νsterile? 3 checking NC enriched sample (multi-ring events) Zenith angle of NC sample Up/down ratio of NC sample nm→nt nm→nt up/down ratio nm→ns nm→ns 10-3 10-2 cosΘ Δm2

  12. Excluded region from three test samples 90% CL excluded 99% CL excluded pure νμ⇔νsterile oscillations are disfavored with about 99% CL

  13. Jan.-2002 @CERN Neutrino Decay Neutrino Decay is a possible solution of the atmospheric neutrino problem (V.Barger et al.) Survival probability without neutrino oscillation(Δm2<<1) FC 1-ring + PC + up-μ data are consistent with neutrino decay scenario χ2min=147.0/152 dof

  14. Jan.-2002 @CERN Neutrino Decay study with NC enriched sample Deficit of up-going NC events is expected for ν decay scenario perform χ2 test to constrain neutrino decay parameters

  15. Jan.-2002 @CERN Result on neutrino decay study The 99%CL allowed region by FC 1-ring+PC+up-μ sample is excluded at 99%CL by the NC enriched sample.

  16. Jan.-2002 @CERN Update of neutrino crosssection(very preliminary) Update parameters GF=1.16639×10-5 sinθc=0.22 　　　　　　　　　　　　　↓ σ is increased by 5.8% (energy indep.) bound nucleon target free proton target blue new Magenta old blue new Magenta old

  17. Jan.-2002 @CERN Update of neutrino flux(very preliminary) HONDA 1D (official) Fluka 3D • HONDA 3D (new) • 3D calculation • dpmjet3 interaction model • primary flux from BESS/AMS • Ikenoyama effect sub-GeV e sub-GeV μ multi-GeV e multi-GeV μ

  18. Jan.-2002 @CERN MACRO detector 76.6m×12m×9.3m liq. scintillation counters (TOF system) streamer tubes

  19. Jan.-2002 @CERN Up throughgoing muons in MACRO Obs. 863ev Obs. 809ev(BG sub.) Exp. 1122ev.(Bartol) Obs./Exp.=0.721±0.026(stat)±0.043(sys)±0.123(th)

  20. Jan.-2002 @CERN 90% allowed region from MACRO νμ⇔ντ χmin@(1.0,2.5×10-3eV2) consistent with Super-K

  21. Jan.-2002 @CERN Low energy events in MACRO Obs. 154ev. Exp. 285ev. Obs./Exp. = 0.54±0.04(stat)±0.05(sys)±0.13(th) Obs. 262ev.(BG sub.) Exp. 375ev. Obs./Exp. = 0.70±0.04(stat)±0.07(sys)±0.17(th) consistent with up throughgoing muon results

  22. The Soudan 2 detector Mann@neutrino2000 ×224 Fiducial mass: 770 tons (Ar/CO2, 0.8cm/μsec)

  23. Jan.-2002 @CERN HiRes event summary in Soudan 2 • HiRes sample • Recoil proton + lepton(>150MeV/c) • single lepton(>600MeV/c) • multiprong (Evis>700MeV and |Σp|>450MeV/c) νμ νe Obs. 114.0±10.7 140.0±11.8 Obs.(Bgsub) 106.3±14.7 132.8±13.4 Exp.(Bartol) 158.5±4.8 132.8±4.4 (renorm. to νe data) R=(μ/e)data/ (μ/e)MC=0.67±0.12

  24. Jan.-2002 @CERN Soudan 2 allowed region χmin@(0.9,7.9×10-3eV2) consistent with Super-K

  25. Jan.-2002 @CERN Summary of atmospheric ν observations • Atmospheric neutrinos are measured using various techniques in SK, MACRO, Soudan 2 → all consistent with each other • Δm2=1.6～3.6×10-3, sin22θ>0.9 for νμ⇔ντ • sterile neutrino is disfavored as a prominent oscillation partner • neutrino decay scenario with Δm2<<1 is excluded at 99% Cτ likelihood distributions

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