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

Super-Kamiokande detector 39.3 m 42 m Water Cherenkov detector 1000 m underground 50,000 ton (22,500 ton fid.) 11, inch PMTs 1,885 anti-counter PMTs C Scientific American

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 Rebuilding Super-K acrylic vessel acrylic+(FRP or stainless steel)

Event classification of atmospheric ν e/  Fully Contained (FC)Partially Contained (PC) Upward through-going  Upward stopping    Contained event (sub-GeV, multi-GeV sample) E ν ～ 1 GeVE ν ～ 10 GeV E ν ～ 10 GeV (stop μ ） 100 GeV (through μ ）

Zenith angle distributions (FC+PC+up-μ) No oscillation (χ 2 =393.4/172 d.o.f) Best fit (  m 2 =2.5x10 -3 eV 2,sin 2 2  =1.00 χ 2 min =157.5/170 d.o.f) ν μ ⇔ ν τ 2-flavor oscillations ～ 15km ～ 13000km ～ 500km ～ 13000km ～ 500km

Combined allowed regions  →  Super-Kamiokande Best fit(Δm 2 =2.5×10 - 3,sin 2 2θ=1.0 χ 2 min=157.5/170 d.o.f) No oscillation (χ 2 =393.4/172 d.o.f) Δm 2 = (1.6 ～ 3.6)x eV 2 sin 2 2θ > 90%CL

ν μ ⇔ ν τ orν μ ⇔ ν sterile ? Using MSW effect and enriched NC sample  →  : No matter effect / NC interaction  → s : With matter effect / No NC interaction Neutrino oscillation in matter:  () = ( cos  m s sin  m - sin  m cos  m ) 1 2 () sin 2 2  m sin 2 2  = (  cos2    sin 2 2   =  2 G F n n E /  m 2 √ For sin 2 2  =  1 sin 2 2  m 1 ~    + 1 And for E = 30~100 GeV   ≫ 1 and sin 2 2  m   1 Suppression ! Test zenith angle of NC enriched events, high energy PC and through-going muon events.

Allowed region from FC single-ring sample

ν μ ⇔ ν τ orν μ ⇔ ν sterile ?  → s  →  E vis > 5 GeV =~25 GeV Zenith angle of high-E PC up/down ratio cosΘ  → s  →  １ checking matter effect (partially contained events) Up/down ratio of high-E PC Δm 2

ν μ ⇔ ν τ orν μ ⇔ ν sterile ?  → s  →  2 checking matter effect (upward through going μ) Zenith angle of up through μ cosΘ vertical/horizontal ratio  →   → s V/H ratio of up through μ Δm 2

ν μ ⇔ ν τ orν μ ⇔ ν sterile ?  → s  →  3 checking NC enriched sample (multi- ring events) Zenith angle of NC sample Up/down ratio of NC sample cosΘ up/down ratio  →   → s Δm 2

pure ν μ ⇔ ν sterile oscillations are disfavored with about 99% CL 99% CL excluded90% CL excluded Excluded region from three test samples

Neutrino Decay Neutrino Decay is a possible solution of the atmospheric neutrino problem (V.Barger et al.) Survival probability without neutrino oscillation(Δm 2 <<1) FC 1-ring + PC + up-μ data are consistent with neutrino decay scenario χ 2 min =147.0/152 dof

Neutrino Decay study with NC enriched sample Deficit of up-going NC events is expected for ν decay scenario perform χ 2 test to constrain neutrino decay parameters

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.

Update of neutrino crosssection (very preliminary) Update parameters G F = ×10 -5 sinθc=0.22 ↓ σ is increased by 5.8% (energy indep.) free proton target bound nucleon target blue new Magenta old blue new Magenta old

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 multi-GeV μmulti-GeV e sub-GeV μ

MACRO detector 76.6m×12m×9.3m streamer tubes liq. scintillation counters (TOF system)

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)

90% allowed region from MACRO χ -3 eV 2 ) νμ⇔ντνμ⇔ντ consistent with Super-K

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

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

HiRes event summary in Soudan 2 ν μ ν e Obs ± ±11.8 Obs.(Bgsub) 106.3± ±13.4 Exp.(Bartol) 158.5± ±4.4 (renorm. to ν e data) HiRes sample Recoil proton + lepton(>150MeV/c) single lepton(>600MeV/c) multiprong (Evis>700MeV and |Σp|>450MeV/c) R=(μ/e) data / (μ/e) MC =0.67±0.12

Soudan 2 allowed region χ -3 eV 2 ) consistent with Super-K

Summary of atmospheric ν observations Atmospheric neutrinos are measured using various techniques in SK, MACRO, Soudan 2 → all consistent with each other Δm 2 =1.6 ～ 3.6×10 -3, sin 2 2θ>0.9 for ν μ ⇔ ν τ sterile neutrino is disfavored as a prominent oscillation partner neutrino decay scenario with Δm 2 <<1 is excluded at 99% C τ likelihood distributions