Takaaki Kajita (ICRR, U.of Tokyo)
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Transcript of Takaaki Kajita (ICRR, U.of Tokyo)
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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-
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Atmosphere
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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
+ ……
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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.
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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)
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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
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Comment: Flux in the horizontal directionComment: Flux in the horizontal directionnow 10 years ago…
3D calculation 1D calculation
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Horizontal enhancementHorizontal enhancement
νC.R.(1D)
Target area(1D, 3D)
C.R.(3D)
3D1D
G. Battistoni et al., Astropart. Phys. 12, 315 (2000)
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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 ?
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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
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Event classificationEvent classification
Fully Contained (FC) (E ~1GeV)
Partially Contained (PC) (E ~10GeV)
Through-going (E~100GeV)
Stopping (E~10GeV)
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Comment: upward-going muons Comment: upward-going muons
∝E
Range∝∝
Wide energy range
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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
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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)
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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 …”
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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).
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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
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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
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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
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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+
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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)
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/e ratio measurement in Ka/e ratio measurement in Kamiokandemiokande
1983 (Kamiokande construction)
electronics
Water system
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Electrons and muonsElectrons and muons
muon-like events
electron-like events
KamiokandeKamiokande
Super-KSuper-K
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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
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Particle ID performanceParticle ID performance
Cosmic ray μ e from μ decay
ε=99%@Super-K (98% @Kamiokande)
(figures from Super-K)
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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.
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However, …However, …Let’s write the atmospheric deficit by (/e)data/(/e)MCLet’s write the atmospheric deficit by (/e)data/(/e)MC
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First supporting evidence for small First supporting evidence for small /e/e
IMB experiment also observed smaller (/e) in 1991 and 1992.
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However, …However, …Let’s write the atmospheric deficit by (/e)data/(/e)MCLet’s write the atmospheric deficit by (/e)data/(/e)MC
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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
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Zenith angle distributionsZenith angle distributions
Consistent with no zenith angle dependence...
Kamiokande (Evis <1.3 GeV) IMB (<1.5GeV)
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Angular correlation Angular correlation
(CC e samples)
(CC sample)
Lepton momentum (MeV/c)
leptonNucleon(MN= 1GeV/c2)
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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
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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
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Around Super-K
Entrance to the mine
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Super-Kamiokande Super-Kamiokande (under construction, Dec. 1994)(under construction, Dec. 1994)
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Super-Kamiokande detector under constructionSuper-Kamiokande detector under construction
Early summer 1995
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Water filling in Super-Kamiokande Water filling in Super-Kamiokande
Jan. 1996
Kamiokande
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Event type and neutrino energyEvent type and neutrino energy
Fully Contained (FC)
Partially Contained (PC)
Through-going
Stopping
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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)
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Various types of atmospheric neutrino events (2)Various types of atmospheric neutrino events (2)
PC (partially contained)
・ 97% CC
Signal in the outer detector
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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
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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
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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
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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
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Results from the other atmospheric Results from the other atmospheric neutrino experimentsneutrino experiments
Soudan-2MACRO
MINOS(first data in 2005)
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Soudan2Soudan2
CC quasi-elastic
e CC CC deep inelastic
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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
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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
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or
MACROMACRO
Upward horizontal
PLB 566 (2003) 35 EPJ C36(2004)323
OscillationΔm2 =2.5×10-3
No osc.
Osc.
No osc.
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MINOSMINOSPRD73, 072002 (2006) 6.18 kton ・ yr (418d
ays)
zenith-angle
L/E
Separation of and anti-
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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
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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.
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End