Atmospheric Neutrinos

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Atmospheric Neutrinos
Primary Cosmic-ray interaction
p
in the atmosphere.

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From Neutrino Astrophysics J. Bahcall
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Possible Reasons for the Deficit of solar
neutrinos

• The solar model is wrong.
• The experiments are wrong.
• 3. Electron neutrinos are changing to
• another flavor in leaving the sun and
• getting to the earth. -neutrino oscillations

Recent data provides evidence that Reason 3 is
correct.
SuperK Flux low electron energy spectrum
restricted the possible oscillation parameters.
SNO Separately measured fluxes of electron
neutrinos and of all neutrinos. Flux of all
neutrinos agrees with solar model predictions for
electron neutrinos.
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Kamland Measured anti-neutrinos from several
nearby (130km) nuclear reactors. Found flux
deficit as predicted by oscillation parameters
allowed by SuperK.
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Add two waves of different frequency
Get beats of frequency
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Frequency is related to energy
h is Plancks constant.
If a quantum mechanical state is a superposition
of two states with different energies, quantum
beats occur, with beat frequency
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Example 1-dimensional box with a particle.
Probability distributions for lowest two energy
states separately.
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Now combine the two states
Oscillation frequency is proportional to
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Why
?
Special relativity
(c1)
(Taylor exp)
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Complications

• Traversal of matter, in the Sun or
• Earth provides extra stimulation of the
• oscillations.

(Mikelaev, Smirnov, Wolfenstein)

• Oscillations occur among 3 neutrinos.
• (But the couplings are generally unequal, and
  2-neutrino
• oscillations are a good approximation.

• 4 neutrinos?

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More on the Detection of Neutrinos
1) Scattering by electrons (SuperK, SNO)
(1)
(1/6)
Rates can be calculated the second reaction
rate is 1/6 of first.
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2) Deuterium Interactions (SNO)
The second reaction rate has a unique signature
delayed gamma.
N
Other Neutrino Experiments

• Accelerator-produced neutrino
• beams. Long-baseline (100s of
• km) experiments. K2K (KEK accelerator to SuperK
  detector), and MINOS (Fermilab to Soudan Mine)
• Now running. First results consistent with
  oscillations.

• Detectors of very high energy
• neutrinos from astrophysical sources (see below).

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Super-Kamiokande
Super-Kamiokande is a 50,000 ton water detector
at a depth of 1600 meters in the Kamioka Mozumi
mine in Japan.
This followed the pioneering work of M.
Koshiba et al. at the Kamiokande detector in the
same mine.
Designed to detect solar , atmospheric,
and supernova neutrinos, and proton decay.
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Super-K Site in Japan
Mozumi
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The Super-K Detector
Designed to detect solar, atmospheric and
super-nova ns

• Detector Characteristics
• 41 m h x 39 m dia.
• 50,000 ton (22,000 ton fiducial)
• 11,200 20 PMTs inner detector
• 1,850 8 PMTs anti-detector
• 40 photo-cathode coverage

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Photomultiplier tube Sensitive to very small
light pulses
Can detect, with about 30 efficiency, a single
photon.
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Mine entrance
After accident
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When a boat moves faster than the speed of the
surface waves, a wake is created.
Similarly, when a charged particle Moves through
a transparent medium with speed gt c/n a shock
wave is created. The shock wave is Cerenkov
radiation.
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Cerenkov Event Reconstruction
e or m

• Pattern of Hits
• Where the event occurred
• ID of particle (e or m)
• Amount of Light
• Energy of particle

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Low Energy Electron
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Solar Neutrinos
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Finding Oscillation Parameters from the data

• 1.Pick values of beat frequency
• and coupling strength.
• 2.Predict the experimental results
• on zenith angle and energy
• distributions with these values.
• 3. Compare data with predictions.
• If they disagree, the values are
• excluded.
• Make a map of allowed
• values.

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SuperK also found strong evidence for neutrino
oscillations in atmospheric neutrinos.
There is also evidence that this oscillation is
from
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Sudbury Neutrino Observatory (SNO)
Uses D2O instead of water.
About 1/50 SuperK size, but detection rate about
the same.
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SNO Results
1. Flux from
-only reaction
is less by appropriate amount than SuperK flux
for

• Flux of all-flavor neutrinos
• agrees with solar model calculations.

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Kamland Detector
Also in Mozumi mine. At site of original
Kamiokande experiment.
Detector is liquid scintillator, in which a
moving charged particle produces a light flash.
Radioactivity background a serious Problem which
was overcome.
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Kamland detected reactor-produced anti-neutrinos.
Average distance 130 km.
The e annihilation was detected, and, after some
delay, the g from the reaction
produced an electron-positron pair.
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Kamland Energy Spectrum
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Kamland oscillation parameters
Agrees with one of the SuperK-allowed parameters!
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SuperKamiokande Solar
Oscillation parameters determined from energy
spectrum and day-night difference
Blue and green regions are allowed.
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Orbital Eccentricity
(For solar neutrinos)
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SuperK also found strong evidence for neutrino
oscillations in atmospheric neutrinos.
There is also evidence that this oscillation is
from
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Atmospheric neutrinos
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Muon - Electron Identification
e-like
mu-like
For atmospheric neutrino scattering
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L/E Distribution of Atmospheric Neutrinos
The dashed lines show the expected shape for nm?
nt at Dm22.2 x 10-3 eV2 and sin2 2q 1.
Phys. Rev. Lett. 81 (1998) 1562-1567
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Conclusions

• The standard solar model is
• basically correct.
• 2. Neutrino oscillations exist.
• 3. Neutrinos have mass.

Current and planned accelerator experiments will
address interesting and complex questions about
coupling strengths, and make more precise mass
measurements.
More data from solar and atmospheric Experiments
will further confirm and extend the current
results.
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Very High Energy Neutrinos from Astrophysical
Sources
Cosmic rays have energies as high As 1020
eV. There may be localized sources of protons or
nuclei with very high energies. If these
interact, the secondaries will produce neutrinos
which reach the earth. Fluxes much lower than
solar, but the neutrino interaction
probability increases with energy.
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In addition to compact sources , a diffuse
high-energy flux is expected. This is due to
interactions of EeV cosmic rays with the CMB.
Observation Methods

• Large arrays of PMTs
• In ice at the South Pole. (Amanda, IceCube)
• In Mediterranean (Antares, Nestor, Nemo)
• In Lake Baikal
• 2) Detection of radio emission from
• Cascades.

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Detector in Lake Baikal
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PMT strings inserted in winter, when lake is
frozen.
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Antares assembling digital optical module
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n telescope point source search
Prototype experiment AMANDA
Preliminary

• Search for clustering in northern hemisphere
• compare significance of local fluctuation to
• atmospheric n expectations
• un-binned statistical analysis
• no significant excess

2000-2003 (807 days) 3329 n from northern
hemisphere 3438 n expected from atmosphere
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South Pole
Hot water hose for melting ice
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Lowering PMT string
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To make high energy neutrinos, an accelerated
proton beam hits some outside matter,
producing pions.
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A muon event in IceCube.
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Neutrino mixing will create a flux of tau
neutrinos.
Tau neutrino (a) makes a tau lepton (b) Then tau
lepton decays.
Double-bang event.
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• Also
• Nestor (water Cerenkov)
• Nemo (water Cerenkov)
• Goldstone (radio antenna, looks at moon.
• RICE (radio antennae, looks at neutrino
• interactions in antarctic ice.)
• 5. ANITA (radio, balloon package.)