Production of atmospheric neutrinos

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Atmospheric neutrinos
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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Production of atmospheric neutrinos
Atmosphere
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(No Transcript)
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Calculating the atmospheric neutrino beam
geomagnetic field (pNucleon) int. decay of
p or K
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Some features of the beam (1)
nm/ne ratio is calculated to an accuracy of
better than 3 below 5GeV.
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Some features of the beam (2)
_at_Kamioka (Japan)
Zenith angle
cosqzenith
Up-going
Down
Up/down ratio very close to 1.0 and accurately
calculated (1 or better) above a few GeV.
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Comment 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.
GeV/c
Down-going
Up-going
For this location, flux(up) gt flux(down) in the
low-energy range
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Comment Flux in the horizontal direction
now
10 years ago
1D calculation
3D calculation
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Horizontal enhancement
G. Battistoni et al., Astropart. Phys. 12, 315
(2000)
1D
3D
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How accurate is the absolute normalization of the
flux ?
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.)
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Neutrino interactions
Quasi-elastic
CC total
Deep inelastic
1p production
E?(GeV)
Quasi-elastic
1p production
Deep inelastic
n
n
lepton
lepton
n
lepton
p
p
p
N
N
N
N
N
N
N
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Event classification
Fully Contained (FC) (E? 1GeV)
Partially Contained (PC) (E? 10GeV)
Stopping ?? (E??10GeV)
Through-going ? (E??100GeV)
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Comment upward-going muons
s(nN) ?En Range ?Em, ltEmgt ? En Wide energy range
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Some early history (discovery of atmospheric
neutrinos)
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Discovery of atmospheric neutrinos
At the depth of 3200 meters (8800 meters water
equivalent) in South Africa First observed on
Feb. 23, 1965 By F.Reines et al.
At the depth of 2400 meters (7500 meters water
equivalent) in India (Kolar Gold Field) First
published on Aug. 15, 1965 By C.V. Achar et al.
photo of the South Africa experiment
(nmN?mX)
Detector for the KGF experiment
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Zenith angle distribution (updated
data from the South Africa experiment)
PRD18, 2239 (1978)
Cosmic ray muons
Neutrino induced muons
Vertical (going up or down)
Horizontal going
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(Atmospheric neutrino anomaly)
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The first hint ?
(South Africa experiment, 1978)
PRD18, 2239 (1978)
Cosmic ray muons
Neutrino induced muons
Vertical
Horizontal
Deficit of muon data
We conclude that there is fair agreement between
the total observed and expected neutrino induced
muon flux
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Proton decay experiments
Grand Unified Theories ? tp10302 years
Kamiokande (1000ton)
IMB (3300ton)
NUSEX (130ton)
Frejus (700ton)
These experiments observed many contained
atmospheric neutrino events (background for
proton decay).
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Selection of atmospheric neutrinos
Example Kamiokande At 1000m underground, cosmic
ray m 0.3/sec/detector Atmospheric n
0.3/day/1000ton
n
2.7m
3.5m
Fiducial region
m
anti-counter
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Detecting Cherenkov photons
Charged particle
Photomultiplier tube (PMT)
50cm f (Super-K)
?
20cm f
n (refractive index)1.34 in water ?42deg.
for ß1
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Detecting Cherenkov photons and event
reconstruction
Super-K
Color timing Size pulse height
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Too few muon decays

Proton decay background papers
IMB PRL57, 1986 (1986)
Kamiokande J.Phys.Soc.Jpn 55, 711
(1986)
vmN?mX, m(t2.2msec)?enn or nN?leptonpX,
p?mn, m?enn
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On the other hand, several no evidence for
atmospheric neutrino 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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m/e ratio measurement in Kamiokande
electronics
Water system
1983 (Kamiokande construction)
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Electrons and muons
Kamiokande
muon-like events
electron-like events
Super-K
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Particle identification
electron-like event
muon-like event
e electromagnetic shower, multiple Coulomb
scattering
m propagate almost straightly, loose energy by
ionization loss
Difference in the event pattern
Particle ID
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Particle ID performance
(figures from Super-K)
e from µ decay
Cosmic ray µ
e99_at_Super-K (98 _at_Kamiokande)
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First result on the m/e ratio (1988)
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.
Kamiokande (3000ton Water Ch. 1000ton
fid. Vol.) 2.87 ktonyear
K. Hirata et al (Kamiokande)Phys.Lett.B 205
(1988) 416.
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However,
Lets write the atmospheric nm deficit by
(m/e)data/(m/e)MC
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First supporting evidence for small m/e
IMB experiment also observed smaller (m/e) in
1991 and 1992.
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However,
Lets write the atmospheric nm deficit by
(m/e)data/(m/e)MC
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Atmospheric neutrinos and neutrino oscillations
Cosmic ray p, He,
Detector
Detect down-going and up-going n
nm?nt oscillation
Cosmic ray p, He,
Down-going
Atmosphere
Up-going
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Zenith angle distributions
Kamiokande (Evis lt1.3 GeV)
IMB (lt1.5GeV)
Consistent with no zenith angle dependence...
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Angular correlation
n
(CC ne samples)
lepton
(CC nm sample)
Nucleon (MN 1GeV/c2)
q
Lepton momentum (MeV/c)
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Next zenith angle(Kamiokande,1994)
multi-GeV m-like events
Up-going
Down-going
Deficit of upward-going m-like events
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Discovery of neutrino oscillations
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Super-Kamiokade detector
50,000 ton water Cherenkov detector (22,500 ton
fiducial volume)
Exit
11200 PMT(Inner detector) 1900 PMT(Outer detector)
42m
39m
1000m underground
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Around Super-K
Entrance to the mine
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Super-Kamiokande (under construction, Dec. 1994)
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Super-Kamiokande detector under construction
Early summer 1995
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Water filling in Super-Kamiokande
Jan. 1996
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Event type and neutrino energy
Fully Contained (FC)
Partially Contained (PC)
Stopping ?
Through-going ?
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Various types of atmospheric neutrino events (1)
Both CC ne and nm (NC) Need particle
identification to separate ne and nm
FC (fully contained)
n
Outer detector (no signal)
Single Cherenkov ring electron-like event
Single Cherenkov ring muon-like event
Color timing Size pulse height
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Various types of atmospheric neutrino events (2)
Signal in the outer detector
PC (partially contained)
n
97 CC nm
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Various types of atmospheric neutrino events (3)
Upward going muon
almost pure CC nm
?
Upward stopping muon
Upward through-going muon
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Atmospheric neutrinos and neutrino oscillations
Cosmic ray p, He,
Detector
Detect down-going and up-going n
nm?nt oscillation
Cosmic ray p, He,
Down-going
Atmosphere
Up-going
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Super-Kamiokande _at_Neutrino98
Fully contained, 1-ring events with Evis gt
1.33GeV plus partially contained events
SK concluded that the observed zenith angle
dependent deficit (and the other supporting data)
gave evidence for neutrino oscillations.
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Super-Kamiokande data now
_at_Neutrino98 (535 day)
Now (2293 day)
No oscillation
nm?nt oscillation
Down-going
Up-going
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Results from the other atmospheric neutrino
experiments
Soudan-2
MACRO
MINOS (first data in 2005)
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Soudan2
nm CC quasi-elastic
ne CC
nm CC deep inelastic
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Soudan2

• 5.9 ktonyr exposure
• Partially contained events included.
• L/E analysis with the high resolution sample
• Upward stopping muons included. hep-ex/0507068

Phys.Rev. D68 (2003) 113004
Zenith angle
Reconstructed L?/ E? dist.
e
µ
e
Up-going
Down-going
µ
No osc.
nm ? nt osc.
Upward stopping muons
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MACRO
Upward through-going m
Upward-going PC
Down-going cosmic ray m
Upward through-going m
Upward stopping m down-going PC
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MACRO
PLB 566 (2003) 35 EPJ C36(2004)323
No osc.
Osc.
No osc.
Upward
horizontal
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MINOS
PRD73, 072002 (2006) 6.18 ktonyr
(418days)
nm zenith-angle
L/E
Separation of nm and anti-nm
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nm?nt oscillation parameters
nm ? nt
90CL
Soudan-2
MACRO
MINOS (atmospheric)
Super-K
Also, consistent results from long baseline
experiments (K2K MINOS) ?
D.Harriss lecture
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Summary of Atmospheric Neutrino-1

• Experimental studies of atmospheric neutrinos
  started in the mid. 1960s.
• Different type of atmospheric neutrino
  experiments started in the 1980s (proton decay
  experiments).
• Study of the background for proton decay found
  unexpected atmospheric nm deficit.
• In 1998, the nm deficit was concluded as evidence
  for neutrino oscillations.

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End