Takaaki Kajita (ICRR, U.of Tokyo)

• Production of atmospheric neutrinos• Some early history (Discovery of atmospheric

neutrinos, Atmospheric neutrino anomaly)• Discovery of neutrino oscillations• Studies of atmospheric neutrino oscillations• Sub-dominant oscillations –present and future-

Atmosphere

Calculating the atmospheric neutrino Calculating the atmospheric neutrino beambeam

Flu

x ×

E2

E(GeV)

Measured cosmic ray proton flux

Total flux+ geomagnetic field

+ (p+Nucleon) int.

+ decay of or K

+ ……

Some features of the beam (1)Some features of the beam (1)

(+ )/(e+ e)(+ )/(e+ e)

/e ratio is calculated to an accuracy of better than 3% below ～ 5GeV.

/e ratio is calculated to an accuracy of better than 3% below ～ 5GeV.

Some features of the beam (2)Some features of the beam (2)

Zenith angleZenith angle

Up-going Downcoszenith

Up/down ratio very close to 1.0 and accurately calculated (1% or better) ab

ove a few GeV.

Up/down ratio very close to 1.0 and accurately calculated (1% or better) ab

ove a few GeV.

＠ Kamioka (Japan)

Comment: Geomagnetic field and the fluxComment: Geomagnetic field and the flux

Assume a detector in Kamioka (Japan)

Calculate the minimum momentum of a cosmic ray proton directing to Kamioka arriving at the atmosphere.

Do

wn

-goi

ng

Up

-goi

ng

For this location, flux(up) > flux(down) in the low-energy rangeFor this location, flux(up) > flux(down) in the low-energy range

GeV/c

Comment: Flux in the horizontal directionComment: Flux in the horizontal directionnow 10 years ago…

3D calculation 1D calculation

Horizontal enhancementHorizontal enhancement

νC.R.(1D)

Target area(1D, 3D)

C.R.(3D)

3D1D

G. Battistoni et al., Astropart. Phys. 12, 315 (2000)

Syst error better than 5%

Below 10GeV, the flux is predicted to better than 10%. Above 10GeV the flux calculation must be improved.

(This statement is for Honda04 flux.)

Below 10GeV, the flux is predicted to better than 10%. Above 10GeV the flux calculation must be improved.

(This statement is for Honda04 flux.)

How accurate is the absolute normalization How accurate is the absolute normalization of the flux ?of the flux ?

Neutrino interactionsNeutrino interactions

Eν(GeV)

E/Quasi-elastic

1 productionDeep inelastic

CC total

lepton

N N’

Quasi-elastic

lepton

N N*

N’

1 production

lepton

N N’

Deep inelastic

Event classificationEvent classification

Fully Contained (FC) (E ~1GeV)

Partially Contained (PC) (E ~10GeV)

Through-going (E~100GeV)

Stopping (E~10GeV)

Comment: upward-going muons Comment: upward-going muons

∝E

Range∝∝

Wide energy range

Discovery of atmospheric neutrinos Discovery of atmospheric neutrinos

(NX)(NX)

At the depth of 3200 meters (8800 meters water equivalent) in South Africa First observed on Feb. 23, 1965By F.Reines et al.

At the depth of 2400 meters (7500 meters water equivalent) in India (Kolar Gold Field)First published on Aug. 15, 1965By C.V. Achar et al.

photo of the South Africa experiment

Detector for the KGF experiment

Zenith angle distribution Zenith angle distribution (updated data from the South Africa experiment)(updated data from the South Africa experiment)

Vertical (going up or

down)

Horizontal going

Neutrino induced

muons

Neutrino induced

muons

Cosmic ray muonsCosmic r

ay muons

PRD18, 2239 (1978)

The first hint ? The first hint ? (South Africa experiment, 1978)(South Africa experiment, 1978)

Vertical Horizontal

Neutrino induced

muons

Neutrino induced

muons

Cosmic ray muons

Cosmic ray muons

4.06.1

Data

CarloMonte Deficit of muon dataDeficit of muon data

PRD18, 2239 (1978)

“We conclude that there is fair agreement between the total observed and expected neutrino induced muon flux …”

Proton decay experimentsProton decay experimentsGrand Unified Theories p=1030±2 years

NUSEX (130ton)

Frejus (700ton)

Kamiokande (1000ton)

IMB (3300ton)

These experiments observed many contained atmospheric neutrino events (background for proton decay).

These experiments observed many contained atmospheric neutrino events (background for proton decay).

Selection of atmospheric neutrinos Selection of atmospheric neutrinos Example: Kamiokande

At 1000m underground,

cosmic ray : 0.3/sec/detector

Atmospheric : 0.3/day/1000ton

Fiducial region

n

2.7m

3.5m

anti-counteranti-

counter

ν

Charged particle

Photomultiplier tube (PMT)

50cm φ 　　(Super-K)

20cm φ 　　

n

1cos

n (refractive index)=1.34 in water

θ=42deg. for β=1

Number of Ch. photons with λ=300-600 nm emitted by a relativistic particle per cm = 340.

Need an efficient detection of the photons. Large PMTs

Detecting Cherenkov photonsDetecting Cherenkov photons

Charged particle PMT

Detecting Cherenkov photons and event reconstrDetecting Cherenkov photons and event reconstructionuction

Time: vertex position

direction

Pulse height (number of pe’s): energy

Color: timing

Size: pulse height

Super-K

Too few muon decaysToo few muon decays

Kamiokande: J.Phys.Soc.Jpn 55, 711 (1986)

IMB: PRL57, 1986 (1986)

Proton decay background papers:Proton decay background papers:

vNX, =2.2sec)e

or

Nlepton+++X, ++, +e+

On the other hand,… On the other hand,… several “no evidence” for atmospheric several “no evidence” for atmospheric

neutrino oscillation papersneutrino oscillation papers

Boiliev et al, (Baksan), Sov J. Nucl. Phys. 34, 787 (1981)

J.M. LoSecco et al. (IMB), PRL 54, 2299 (1985)

R.M. Bionta et al., (IMB), PRD 38, 768 (1988)

/e ratio measurement in Ka/e ratio measurement in Kamiokandemiokande

1983 (Kamiokande construction)

electronics

Water system

Electrons and muonsElectrons and muons

muon-like events

electron-like events

KamiokandeKamiokande

Super-KSuper-K

Particle identificationParticle identificationelectron-like event

muon-like event

2

deg70 ..

2 )(..)'.(.

ep

ore expectedepdobsepParticle ID

e: electromagnetic shower, multiple Coulomb scattering

: propagate almost straightly, loose energy by ionization loss

Difference in the event patternDifference in the event pattern

Particle ID performanceParticle ID performance

Cosmic ray μ e from μ decay

ε=99%@Super-K (98% @Kamiokande)

(figures from Super-K)

First result on the First result on the /e ratio /e ratio (1988)(1988)

Kamiokande(3000ton Water Ch. 　　　　　　

　　　　～ 1000ton fid. Vol.)

2.87 kton ・ year

Data MC prediction

e-like ( ～ CC e)

93 88.5

-like ( ～ CC )

85 144.0

“We are unable to explain the data as the result of systematic detector effects or uncertainties in the atmospheric neutrino fluxes. Some as-yet-unaccoundted-for physics such as neutrino oscillations might explain the da

ta.”

K. Hirata et al (Kamiokande ） Phys.Lett.B 205 (1988) 416.

However, …However, …Let’s write the atmospheric deficit by (/e)data/(/e)MCLet’s write the atmospheric deficit by (/e)data/(/e)MC

First supporting evidence for small First supporting evidence for small /e/e

IMB experiment also observed smaller (/e) in 1991 and 1992.

However, …However, …Let’s write the atmospheric deficit by (/e)data/(/e)MCLet’s write the atmospheric deficit by (/e)data/(/e)MC

Atmospheric Atmospheric neutrinos and neutrinos and

neutrino neutrino oscillations oscillations

Cosmic ray p, He, ……

Cosmic ray p, He, ……

Detector

　 osci

llation

Detect down-going and up-going

Atmosphere

Down-going

Up-going

Zenith angle distributionsZenith angle distributions

Consistent with no zenith angle dependence...

Kamiokande (Evis <1.3 GeV) IMB (<1.5GeV)

Angular correlation Angular correlation

(CC e samples)

(CC sample)

Lepton momentum (MeV/c)

leptonNucleon(MN= 1GeV/c2)

Next: zenith angleNext: zenith angle…(Kamiokande,1994)…(Kamiokande,1994)

multi-GeV -like

events

multi-GeV -like

events

Deficit of upward-going -like events

m2=1.6 ・ 10-2eV2

Up/Down=0.58 (2.9 σ)+0.13 -0.11

Up-going Down-going

No oscillation

Super-Kamiokade detectorSuper-Kamiokade detector50,000 ton water Cherenkov detector (22,500 ton fiducial volume)

１０００ｍ underground

11200 PMT(Inner detector)

1900 PMT(Outer detector)

Exit

３９ｍ

４２

ｍ

Around Super-K

Entrance to the mine

Super-Kamiokande Super-Kamiokande (under construction, Dec. 1994)(under construction, Dec. 1994)

Super-Kamiokande detector under constructionSuper-Kamiokande detector under construction

Early summer 1995

Water filling in Super-Kamiokande Water filling in Super-Kamiokande

Jan. 1996

Kamiokande

Event type and neutrino energyEvent type and neutrino energy

Fully Contained (FC)

Partially Contained (PC)

Through-going

Stopping

Various types of atmospheric neutrino events (1)Various types of atmospheric neutrino events (1)

FC (fully contained)

・ Both CC e and (+NC)

・ Need particle identification to separate e and

Single Cherenkov ring electron-like event

Single Cherenkov ring muon-like event

Color: timing

Size: pulse height

Outer detector (no signal)

Various types of atmospheric neutrino events (2)Various types of atmospheric neutrino events (2)

PC (partially contained)

・ 97% CC

Signal in the outer detector

Various types of atmospheric neutrino events (3)Various types of atmospheric neutrino events (3)

Upward going muon

ν

・ almost pure CC

Upward stopping muon

Upward through-going muon

Atmospheric Atmospheric neutrinos and neutrinos and

neutrino neutrino oscillations oscillations

Cosmic ray p, He, ……

Cosmic ray p, He, ……

Detector

　 osci

llation

Detect down-going and up-going

Atmosphere

Down-going

Up-going

Super-Kamiokande Super-Kamiokande @Neutrino98@Neutrino98

SK concluded that the observed zenith angle dependent deficit (and the other supporting data) gave evidence for neutrino oscillations.

Fully contained, 1-ring events

with Evis > 1.33GeV

plus partially contained events

Super-Kamiokande data nowSuper-Kamiokande data now@Neutrino98

(535 day)@Neutrino98

(535 day)

Now (2293 day)

Now (2293 day)

No oscillation

oscillation

Up-going Down-going

Results from the other atmospheric Results from the other atmospheric neutrino experimentsneutrino experiments

Soudan-2MACRO

MINOS(first data in 2005)

Soudan2Soudan2

CC quasi-elastic

e CC CC deep inelastic

Soudan2Soudan2

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• Upward stopping muons included. hep-ex/0507068

Zenith angle

e

μ

e μ

Up-going

Down-going

Upward stopping muons

MACROMACROUpward

through-going

Upward through-going

Upward-going PC

Upward-going PC

Upward stopping + down-

going PC

Upward stopping + down-

going PC

Down-going cosmic ray Upward

through-going

Upward through-going

or

MACROMACRO

Upward horizontal

PLB 566 (2003) 35 EPJ C36(2004)323

OscillationΔm2 =2.5×10-3

No osc.

Osc.

No osc.

MINOSMINOSPRD73, 072002 (2006) 6.18 kton ・ yr (418d

ays)

zenith-angle

L/E

Separation of and anti-

oscillation parametersoscillation parameters

Soudan-2

MACRO

Super-K

90%CL

MIN

OS

(a

tmo

sph

eric

)

Also, consistent results from long baseline experiments (K2K & MINOS) D.Harris’s lecture

Summary of Atmospheric Neutrino-1Summary of Atmospheric Neutrino-1

• Experimental studies of atmospheric neutrinos started in the mid. 1960’s.

• Different type of atmospheric neutrino experiments started in the 1980’s (proton decay experiments).

• Study of the background for proton decay found unexpected atmospheric deficit.

• In 1998, the deficit was concluded as evidence for neutrino oscillations.

End