Takaaki Kajita, ICRR, Univ. of Tokyo

NuFact04, Osaka, July 2004

Outline

• Atmospheric neutrino beam

• Atmospheric neutrinos: Present

L/E analysis

• Atmospheric neutrinos: Future

sub-dominant oscillations ?

• Summary

Only 2 and 3 flavor neutrino oscillations

Atmospheric neutrinos Cosmic Ray

, K

e

e

Atmosphere μ

Neutrinos from the other side of the Earth.

e

Atmospheric neutrino beam

Zenith angle:F

lux

× E2

E(GeV)

Measured cosmic ray proton flux

e

Total flux

Event classificationFully Contained (FC) (E ~1GeV)

Partially Contained (PC) (E ~10GeV)

Through-going (E~100GeV)

Stopping (E~10GeV)

Super-Kamiokande (50,000ton water C

h. Detector)

Soudan-2 (1kton tracking detector)

MACRO (large muon detector)

76m

12m

9.3m

Super-K atmospheric neutrino data

1489day FC+PC data + 1646day upward going mu

on data

CC e CC

Soudan2

Reconstructed Lν/ Eν dist.

No osc. osc.

Phys.Rev. D68 (2003) 113004

• 5.9 kton ・ yr exposure• Partially contained events included.• L/E analysis with the “high resolution” sample

Zenith angle

e

μDown-going

Up-going

e μ

or

MACRO

OscillationΔm2 =2.5×10-3

Upward horizontal

L /E

Multiple scattering

E

E

PLB 566 (2003) 35

Neutrino oscillation parameters

Soudan-2

MACRO

Super-K

92.02sin

)(104.35.1

23

2

23223

eVm

90%CL

oscillation

decoherence

decay

Further evidence for oscillations Strong constraint on oscillation parameters, especially m2

-like multi-GeV + PC

Should observe this dip!

New !

SK collab. hep-ex/0404034

Selection criteria

Following events are not used:

★horizontally going events

★low energy events

Select events with high L/E resolution

((L/E) < 70%)

FC single-ring -like

Full oscillation 1/2

oscillation

(L/E)=70%

Similar cut for: FC multi-ring -like,

OD stopping PC, and

OD through-going PC

2121 FC -like and

605 PC

L/E distribution

MC (no osc.)

1489 days FC+PC (Super-K)

Evidence for oscillatory signature

Mostly down-going

Mostly up-going

Osc.

Decay

Decoh.

Decay and decoherence disfavored at 3.4 and 3.8 level, respectively.

Allowed neutrino oscillation parameters

2min=37.9/40 d.o.f

@ m2=2.4x10-3,sin22=1.00(sin22=1.02, 2

min=37.8/40 d.o.f)

1.9x10-3 < m232 < 3.0x10-3 eV2

0.90 < sin2223 (90% C.L.)

Stronger constraint on m2

Consistent with that of the standard zenith angle analysis

SK L/E analysis

90% CL

SK Zenith angle analysis

K2K

Soudan2

MACRO

Kam.

Search for non-zero 13

Electron appearance in the 5 – 10GeV upward going events.

E

LmP e

2232

13

2

23

2 27.1sinsinsin)(

s213=0.05 s213=0.00 null oscillation

MC, SK 20yrs

Electron appearance

1+multi-ring, e-like, 2.5 - 5 GeV

cosE(GeV)

cos

)( eP

Matter effect

(m122=0 assumed)

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

3 flavor analysis from Super-K

Normal

Inverted

3

21

3

21

prelim.

Present: Study of dominant oscillation channel ( )

Future: Study of sub-dominant oscillations

ν m

ass

23

2

)13(23

m

12

2

12 (small)m

(small)13

2

)23(13

m

e

Normal mass hierarchy is assumed.

★ 13?

★Mass hierarchy?

★Solar oscillation effects?

Possible future atmospheric detectors

Magnetized large tracking detector

Hyper-K (1Mton)

Very large water Cherenkov detector

MONOLITH, 　

INO (India-based Neutrino Observatory, …

Mton class detector at Frejus

UNO

Water Cherenkov detector 450 kton ・ yr (SK 20 years)

3 3 3

Importance of s223>0.5; S.Pascoli et al., hep-ph/0305152

TK noon2004

2 ∝ ～ exposure) ～ Present bound on sin213

Multi-GeV electron appearance

Sensitivity to non-zero 13

SK 20yr MC

How can we discriminate positive and negative m2 ?

Real m232 = positive

assumed

(No resonance for anti-neutrinos)

Real m232 = negative

assumed

(No resonance for neutrinos)

E(GeV)

cos

P(e)

E(GeV)

cos

P(e)

Sign of m23(13)2 ?

3

21

3

21

Measurement of sign of m2

in large magnetized detectors

Determination of sign of Δm2 at 90%CL.

Δm2=2.5×10-3 sin2θ =0.0213

NPB (proc suppl) 91 (2001) 147, hep-ex/0106252

Measurement of sign of m2

in water Cherenkov detectors ?

3 3 3

m2: fixed, 23: free, 13: free, positive m2

Exposure: 1.8Mtonyr (SK 80yr or HK ～ 3.3 yr)

Use differences in and d/dy

TK NOON2004

Solar oscillation effectsSolar neutrino oscillation: LMA (m12

2 = 7×10-5eV2) Expected number of sub-GeV e-like events in SK.

Peres, Smirnov NPB 680 (2004) 479

The number of e-like events changes as a function of sin223 (NOT sin2223).

Discrimination of >45 and <45 might be possible. (However, the effect is very small for s2223=1.00.)

P.Lipari NOON2004

10

1

• Atmospheric neutrinos have been playing major role in the neutrino oscillation studies.

• The present data are nicely explained by oscillations with;

m2=1.9 – 3.0 × 10-3 eV2

sin22 > 0.90 (SK L/E analysis)• Recent L/E analysis has shown evidence for “oscillatory”

signature.• Future atmospheric neutrino experiments is likely to conti

nue to contribute to the neutrino oscillation physics (13, sign of m23

2 ….)

(If (a) much larger detector, (b) relatively large 13.)

End

Specials in L/E analysis

1.5m from top & bottom

1m from barrel

22.5kt

→26.4ktExpand fiducial volume

More statistics for high energy muons

Classify PC events using OD charge

I. OD stoppingII. OD through going

Different L/E resolution

FC single-ring, multi-ring -like

PC

observed charge / expectation from through-going

OD stopping

OD through-going

OD through-going MC

OD stopping MC

Energy and angular resolution of neutrinos

L/E cuts

Full osc.

Half osc.

Sensitivity to other models (determination of L/E resolution cut)

70% 80%

80%70%

decay decay

decoherence decoherence

decay

decoherence

L/E resolution cut at 70%

Event summary of L/E analysis

Fractions of FC and PC samples in L/E distribution

1619 2105.8 (98.3%)

502 813.0 (94.2%)

114 137.0 (95.4%)

491 670.4 (99.1%)

single-ring

multi-ring

stopping

through-going

FC

PC

Data MC CC

Check of the observed dip in L/E distribution (1)

Other L/E resolution cuts

Check of the observed dip in L/E distribution (2)

FC e-like

(Flat L/E distribution is expected.)

Check of the observed dip in L/E distribution (3)

zenith angle : cos-cos

(Zenith angle of each event is inverted. Because of the wrong assignment of L, no dip is expected.)

Sensitivities to alternative models and the data

decay

decoherence

L/E resolution cut at 70%

obtained2

Neutrino decay and decoherence models ?

Oscillation

Decay

Decoherence

2min=37.9/40 d.o.f

2min=49.1/40 d.o.f 2 =11.3

2min=52.4/40 d.o.f 2 =14.5

decay disfavored at 3.4

decoherence at 3.8

First dip observed in the data cannot be explained by alternative hypotheses

Evidence for oscillatory signature

2 as a function of sin213

Normal Inverted

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, (total) and d/dy are different.

Try to discriminate positive and negative m2 using these events.

CC e

CC e

CC e

CC e

Others Others

Single-ring e-like Multi-ring e-like

Electron appearance for positive and negative m2 in a water

Chrenkov detector

Single-ring e-like Multi-ring e-like

Positive m2

Negative m2

null oscillation

cos cos

Relatively high anti-e fraction

Lower anti-e fraction

m2=0.002eV2

s223 = 0.5 s213 = 0.05(SK 20yrs)

2 difference (inverted-normal)

m2: fixed, 23: free, 13: free

Exposure: 1.8Mtonyr (SK 80yr or HK ～ 3.3 yr)

3 3 3

True= normal mass hierarchy assumed.

2 difference (normal – inverted)

m2: fixed, 23: free, 13: free

Exposure: 1.8Mtonyr (SK 80yr or HK ～ 3.3 yr)

3 3 3

True= inverted mass hierarchy assumed.