Present status of oscillation studies by atmospheric neutrino experiments 2 flavor oscillations 3 flavor analysis Non-standard explanations Search for CC eventsFuture prospects Possible detectors PhysicsSummaryNuFact02, July 2002, London

Takaaki Kajita ( ICRR, Univ. of Tokyo )

Present status of oscillation studies by atmospheric neutrino experimentsSuper-Kamiokande Soudan-2MACRO

Present status of atmospheric neutrino experimentsSuper-Kamiokande Soudan-2 : stopped data taking.MACROPlastic containerTopSide

New (almost final) data from Soudan-25.9 ktonyr exposurePartially contained events included.L/E analysis with a high resolution sampleTotal number of events: 403.6 (high resolution sample: 245.5 events, PC: 39.0)Zenith angleL/E distributioneDown-goingUp-going

(Final) MACRO dataor m2 = 2.510-3Consistent with oscillation.L/E analysis with momentum measurement is also consistent with osc.

Super-Kamiokande dataWhole SK-1 data have been analyzed.1489day FC+PC data + 1678day upward going muon data 1-ring e-like 1-ring -like multi-ring -like up-going Up-goingDown-going No osc.Osc.stoppingThrough going< 1.3GeV> 1.3GeV

oscillation resultsKamiokandeSoudan-2MACROSuper-Ksin22> 0.92 m2=(1.6 3.9)10-3eV2

3 flavor analysisAssumption / Approximationm3m2m1m12=02m13 = m23 = m222m , 13, 232Matter effect !

Allowed parameter regionPure, maximal 90%CL99%CLNo evidence for non-zero 13. Consistent with reactor exp.Super-K(3 flavor, 1 mass scale dominance, normal mass hierarchy)

Oscillation to sterile neutrinos?Pure s oscillation: (1) NC deficit & (2) Matter effect NC enriched multi-ring eventsSuper-K 79ktyrHigh E. PC Through going Super-KVertical / Horizontal ratio (through going )MACROs s is disfavored > 99%.(1) NC deficit(2) Matter effect

Oscillation to sterile neutrinos?Use all the SK data (including NC, up-through-going-muons and High-E PC)..

nm g cosxnt + sinxn s pure nm g nt pure nm g ns sin2x

Neutrino decay ?Decay scenario can explain the CC data well. c2min=141.5/152 dof @sin2q = 0.33 m3/t3=1.0x10-2GeV/kmOscillationdecayLog10[L/E(km/GeV)]Scenario (V.Barger et al., PLB 462 (1999) 109):=cos2 +sin3 decay X For m20; P() = (cos2+ sin2e-L/2E)2=m/

Neutrino decay vs. NC dataNC data should also decrease due to decay into sterile state.FC multi-ring NC enriched sampleThe 99%CL allowed region by FC 1-ring+PC+up-m samplesis almost excluded at 99%CL by the NC enriched sample. Allowed and excluded parameter regionsAllowed (by CC data)Excluded (by NC data)Use Up/Down to test decay scenario

Search for CC eventsCC eventshadrons Many hadrons (But no big difference with other events ) BAD - likelihood analysis Upward going only GOOD Zenith angle Only 1.0 CC FC events/ktonyr

(BG (other events) 130 ev./ktonyr)

Tau likelihood analysisMulti-ring Down-wardMulti-ringUp-wardBG MC t+BG MC Selection Criteria multi-GeV, multi-ring most energetic ring is e-like log(likelihood) > 0 (multi-ring) > 1 (single-ring)

total energy number of rings number of decay electrons max(Ei)/Ei distance between n interaction point and decay-e point max(Pm) Pt/Evis3/4 PID likelihood of most energetic ring-like-like

Tau analysis resultsB.G. t+BGIndependent analysis by Neural NetworkN= 14544+11/-16Nexpected=86N= 9939+13/-21Consistent with .Max. likelihood analysis

Future atmospheric neutrino experiments

Really oscillation? How accurate can sin 223 and m23 be determined ? Is 13 measurable ? Sign of m2 ? Topics22

Possible future atmospheric neutrino detectorsMagnetized large tracking detector (MONOLITH, .)Very large water Cherenkov detector (UNO, Hyper-Kamiokande, ..)

Really oscillation ?Assume; m2=210-3eV22.8 Mtonyr (UNO)0.14 Mtonyr (MONOLITH)Use up-going events L = 2Rcosz Large L Need to measure high-energy eventsMagnetized detectorVery large detector

Super-K may not be too small..70 year MC (1.6Mtonyr)First osc. mim.Use only high L/E resolution events

Accuracy of sin22 measurementStandard SK analysis with the present SK systematics 0.11 Mtonyr0.23 0.990%C.L. (sin22) = 3% Exposre(Mtonyr) Up sin22Down 2= 1 - +Systematic error related to Up/Down is small (2% @SK)Precise determination of sin2290%

Accuracy of m2 measurementL/E analysis0.14 Mtonyr0.14 Mtonyr (MONOLITH)Magnetized tracking detectorFirst minimum m2(m2) = 6%

Measurement of 13 ?Matter effect !

Measurement of 13 ?Matter effect !Reconstructed momentum (GeV/c)CosUpDown21 (e-like)osc (e-like)no-osc1 10Water Ch.Reconstructed momentum (GeV/c)0.9 Mtonyr cos < 0.2 (up going)sin 13=0.02624 effect in 0.9 Mtonyr1 10Large water Ch. detector

Measurement of 13 and sign of m ?Matter effect 2Charge identification (Magnetized tracking detector needed)Determination of sign of m2 at 90%CL. m2=2.510-3 sin2 =0.0213

SummaryPresent status All the data are consistent with pure oscillations.

No evidence for 13.No evidence for physics beyond standard neutrino osci.Hint of appearance.

Future prospectsIf much larger detectors and/or magnetized tracking detectors are constructed, our understanding of neutrino masses and mixing will be improved significantly: L/E, determination of oscillation parameters (23), 13, sign of m , .sin22 > 0.92 m2 = (1.6 3.9)10-3 eV2(SK, 90%CL)2