Present status of oscillation studies by atmospheric neutrino experiments ν μ → ν τ 2 flavor...

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Present status of oscillation studies by a tmospheric neutrino experiments νμντ 2 flavor oscillations 3 flavor analysis Non-standard explanations Search for CC ντ events Future prospects Possible detectors Physics • Summary NuFact02, July 2002, London Takaaki Kajita ( ICRR, Univ. of Tokyo )

Transcript of Present status of oscillation studies by atmospheric neutrino experiments ν μ → ν τ 2 flavor...

• Present status of oscillation studies by atmospheric neutrino experiments

νμ→ντ 2 flavor oscillations 3 flavor analysis Non-standard explanations

Search for CC ντ events• Future prospects Possible detectors Physics• Summary

NuFact02, July 2002, London

Takaaki Kajita ( ICRR, Univ. of Tokyo )

Present status of oscillation studies by atmospheric neutrino experiments

Super-Kamiokande

Soudan-2

MACRO

Present status of atmospheric neutrino experiments

Super-Kamiokande

Soudan-2 : stopped data taking.

MACRO

Plastic container

Top

Side

New (almost final) data from Soudan-2• 5.9 kton ・ yr exposure• Partially contained events included.• L/E analysis with a “high resolution” sample• Total number of events: 403.6 (high resolution sample: 245.5 event

s, PC: 39.0)

Zenith angle L/E distribution

e

μ

Down-goingUp-going

(Final) MACRO data

or

νμ→ντ

Δm2 = 2.5×10-3

Consistent with oscillation.

L/E analysis with momentum measurement is also consistent with osc.

Super-Kamiokande data

• Whole SK-1 data have been analyzed.1489day FC+PC data + 1678day upward going muon data

1-ring e-like 1-ring μ-like multi-ring μ-like up-going μ

Up-going      Down-going

No osc.

Osc.

stopping

Through going

< 1.3GeV

> 1.3GeV

νμ→ντ oscillation results

Kamiokande

Soudan-2

MACRO

Super-K

sin22θ> 0.92 Δm2=(1.6 – 3.9)×10-3eV2

3 flavor analysis

●Assumption / Approximation

mν3

mν2

mν1

Δm12=02

Δm13 = Δm23 = Δm2 2 2

Δm , θ13, θ232

Matter effect !

Allowed parameter region

Pure, maximal νμ→ντ

90%CL

99%CL

No evidence for non-zero θ13. Consistent with reactor exp.

Super-K

(3 flavor, 1 mass scale dominance, normal mass hierarchy)

Oscillation to sterile neutrinos?Pure νμ→νs oscillation: (1) NC deficit & (2) Matter effect

NC enriched multi-ring events

Super-K 79ktyr

High E. PC

Through going μ

Super-K

Vertical / Horizontal ratio (through going μ)

MACRO

νμ→ντ

νμ→νs

νμ→νs 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).• . cossin

s

pure pure s sin2

Neutrino decay ?

Decay scenario can explain the CC data well. 2

min=141.5/152 dof @sin2= 0.33 m3/3=1.0x10-2GeV/km

Oscillation

decay

Log10[L/E(km/GeV)]

★Scenario (V.Barger et al., PLB 462 (1999) 109):

νμ=cosθν2 +sinθν3

       decay X               For Δm2→0;             P(ν→ν) = (cos2θ+ sin2θe-αL/2E)2

α=m/τ

Neutrino decay vs. NC data• NC data should also decrease due to decay into sterile state.

FC multi-ring NC enriched sample

The 99%CL allowed region by FC 1-ring+PC+up- samplesis almost excluded at 99%CL by the NC enriched sample.

Allowed and excluded parameter regions

Allowed (by CC data)

Excluded (by NC data)

Use Up/Down to test decay scenario

Search for CC ντ events

CC ντ events

ντ

ντ

τ

hadrons

● Many hadrons .... (But no big difference with other events . )

BAD τ- likelihood analysis

● Upward going only

GOOD Zenith angle

Only ~ 1.0 CC ντ FC events/kton ・ yr

(BG (other ν events) ~ 130 ev./kton ・ yr)

Tau likelihood analysis

Multi-ring Down-ward

Multi-ringUp-ward BG MC

+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)/ΣEi distance between interaction point and decay-e point max(P) Pt/Evis3/4 PID likelihood of most energetic ring

τ-like τ-like

Tau analysis results

B.G.

+BG

Independent analysis by Neural Network

Nτ= 145±44+11/-16

Nτexpected=86

Nτ= 99±39+13/-21

Consistent with νμ→ντ.

Max. likelihood analysis

Future atmospheric neutrino experiments

★ Really “oscillation”?

★ How accurate can sin 2θ23 and Δm23 be determined ?

★ Is θ13 measurable ?

★ Sign of Δm2 ?

Topics

2 2

Possible future atmospheric neutrino detectors

Magnetized large tracking detector (MONOLITH, ….)

Very large water Cherenkov detector (UNO, Hyper-Kamiokande, …..)

Really oscillation ?

Assume; Δm2=2×10-3eV2

2.8 Mton ・yr (UNO)

0.14 Mton ・yr (MONOLIT

H)

Use up-going events L = 2Rcosθ⇒ z

Large L Need to measure high-⇒energy events

Magnetized 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 sin22θ measurement

Standard SK analysis with the present SK systematics

0.11 Mton ・yr 0.23

0.9

90%C.L.

δ (sin22θ) = 3% Exposre(Mt

onyr)

Up sin22θ

Down 2= 1 - +ε

Systematic error related to Up/Down is small (2% @SK)

Precise determination of

sin22θ 90%

Accuracy of Δm2 measurement

L/E analysis

0.14 Mton ・yr

0.14 Mton ・ yr (MONOLITH)

Magnetized tracking detector

First minimum Δm2

δ(Δm2) = 6%

Measurement of θ13 ?

Matter effect !

Measurement of θ13 ?

Matter effect !

Reconstructed momentum (GeV/c)

CosΘ

Up

Down 2

1

(e-like)osc

(e-like)no-osc

1 10

Water Ch.

Reconstructed momentum (GeV/c)

0.9 Mton ・ yr

cosΘ < - 0.2 (up going)

sin θ13=0.0262

~ 4σ effect in 0.9 Mton ・ yr

1 10

Large water Ch. detector

Measurement of θ13 and sign of Δm ?

Matter effect

2

Charge identification (Magnetized tracking detector needed)

Determination of sign of Δm2 at 90%CL.

Δm2=2.5×10-3 sin2θ =0.0213

SummaryPresent status • All the data are consistent with pure νμ→ντ oscillations.

• No evidence for θ13.• No evidence for physics beyond standard neutrino osci.• Hint of τ appearance.

Future prospects• If much larger detectors and/or magnetized tracking dete

ctors are constructed, our understanding of neutrino masses and mixing will be improved significantly:

L/E, determination of oscillation parameters (23), θ13, sign of Δm , ….

sin22θ > 0.92 Δm2 = (1.6 – 3.9)×10-3 eV2

(SK, 90%CL)

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