takaaki kajita (icrr, u.of tokyo) production of atmospheric neutrinos some early history (discovery...
TRANSCRIPT
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