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-

III International Pontecorvo Neutrino Physics SchoolAlushta, Ukraine, Sep. 2007

Atmosphere

(Sign of the particles are neglected in this figure.)

Calculating the atmospheric Calculating the atmospheric neutrino beamneutrino beam

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)

above a few GeV.

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

above a few GeV.

＠ Kamioka (Japan)

Comment: Geomagnetic field and the Comment: Geomagnetic field and the fluxflux

Let’s 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: Horizontal fluxComment: Horizontal fluxnow 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)

For simplicity, let’s assume that the direction of the secondary particles are isotropic (reasonable at low E.)

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

Enhanced sensitivity to high energy neutrinos

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 (from the South Africa experiment 1978)(from the South Africa experiment 1978)

Vertical (going up or

down)

Horizontal going

Neutrino induced

muons

Neutrino induced

muons

Cosmic ray

muons

Cosmic ray

muons

PRD18, 2239 (1978)

Idea to study oscillations with atmospheric neutrinos: Bilenky & Pontecorvo, Phys. Rep. 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 (in the late 1970’s) 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 Detecting Cherenkov photons and event reconstructionreconstruction

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+

/e ratio measurement in /e ratio measurement in KamiokandeKamiokande

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 data.”

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) (1991, 1992).

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

Atmospheric Atmospheric neutrinos neutrinos

and neutrino and neutrino oscillations oscillations

Cosmic ray p, He, ……

Cosmic ray p, He, ……

Detector

oscillation

Detect down-going and up-going

Atmosphere

Down-going

Up-going

E

LmP

222 27.1

sinsin1)(

Zenith angle distributionsZenith angle distributions

Consistent with no zenith angle dependence...

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

e-like -like

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

Not high enough statistics to conclude …Not high enough statistics to conclude …

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 under constructionSuper-Kamiokande under construction

Early summer 1995

Super-Kamiokande with pure waterSuper-Kamiokande with pure water

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 neutrinos

and neutrino and neutrino oscillations oscillations

Cosmic ray p, He, ……

Cosmic ray p, He, ……

Detector

oscillation

Detect down-going and up-going

Atmosphere

Down-going

Up-going

Up/down ratio measurement is essentially free from systematicsUp/down ratio measurement is essentially free from systematics

Super-K Super-K @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 (2290 day)

Now (2290 day)

No oscillation

oscillation

Up-going Down-going

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

Soudan-2MACRO

MINOS(Atmospheric neutrinos only in this lecture)

Soudan2Soudan2

CC quasi-elastic

e CC

CC deep inelastic

1 kton fine grain tracking calorimeter

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

MACROMACRO

Upward 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

77m

12m

10m

or

MACROMACRO

Upward horizontal

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

OscillationΔm2 =2.5×10-3

No osc.

Osc.

No osc.

MINOS MINOS (atmospheric)(atmospheric)PRD73, 072002 (2006)

6.18 kton ・ yr (418days)

zenith-angle

L/E

Separation of and anti-

5.4 kton tracking detector with

magnetic field

hep-ex/0701045

oscillation parametersoscillation parameters

Also, consistent results from long baseline experiments (K2K & MINOS) Lecture by K.Nishikawa

MINOS (Atmospheric)

Soudan-2

MACRO

Super-K

Kamiokande

, 90%C.L.

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.

• Various atmospheric neutrino experiments give consistent results.

End