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Study of salt neutrino detector forGZK neutrinos
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Masami Chiba
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Masami Chiba, Toshio Kamijo, Osamu Yasuda, Yuichi Chikashige*,
Tadashi Kon*, Yoshito Takeoka* and Ryo Yoshida*Tokyo Metropolitan
University, Tokyo Japan
International Workshop on Ultra High Energy Neutrino
TelescopeJuly 29-30, 2003Chiba University, Chiba, Japan
*Seikei University, Tokyo Japan
We present a study about a salt neutrino detector for
ultra-high-energy neutrinos. Transparency of rock salt for radio
wave is important for realization of SND. Radio wave attenuation
length in rock salt is measured and presented.
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Generation of UHE neutrinos (>1015eV)
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Direct generation in AGN, GRB, etc.Like an accelerator
experiment Incident beam: UHE protons, photons, neutrinos, etc.
Target: 2.7K cosmic microwave background, 1.9K cosmic neutrinos,
dark matter etc.
UHE n
UHE proton
UHE g
UHE n
Filled with 2.7K microwave, 1.9K neutrinos backgrounds, Dark
matter, etc.
13 B ly
0.02 B ly
2.7K microwave, GZK
1.9K neutrinos, Z bursts
UHE n
0.1 B ly
2.7K microwave
Star
Earth
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Astronomy in the highest energy region
Short interaction length 300Mpc to photons over 10TeV.
Protons propagate less than 50Mpc due to Greisen, Zatsepin and
Kuzmin (GZK) cut off process over 1020 eV.
Long-range astronomy, observing old universe, in the highest
energy region can be investigated by neutrinos exclusively.
GZK cut off process generates UHE neutrinos.p + (2.7K) + n + + p
e - e + e + e
5. GZK neutrino is probable to exist based on observed spectrum
of UHE cosmic rays with 2.7K cosmic microwave background.
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Neutrino flux and optimal detectorIt is natural to aim at GZK
neutrino at first. Additions are direct UHE neutrinos from AGN,
GRB, Topological Defects, etc. GZK neutrino flux is as low as
1(km-2 day-1).Large detector is needed with information of energy,
direction, time and flavor. For the energy measurement,
calorimetric detection is better than muon track detection.Radio
wave detection is suitable way to realize a large detector.
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CoherentCherenkovradiation in radio wave region Askaryan in
solid, 1961M.Fujii and J. Nishimura in air, 1969Electron or photon
beamElectrons are 20% excess over positrons in an electromagnetic
shower due to recoil electrons of Compton scattering etc.
Cherenkov radiation: dP/dn ~ ndn, P ~ n~ECoherent Cherenkov
radiation: P ~ n2~E2. Stronger radiation at UHE.Radio transparent
media should be used: rock salt, Lunar regolith, Ice, etc. Radio
wave can be detected over 1TeV shower near by and 1PeV shower 1km
apart by a 300K-noise receiver without absorption in the
material.
Rock SaltIn Phasen excess electrons
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Observation of the Askaryan EffectAskar effect is verified by
high energy photon beam at SLAC.M.Chiba
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Observation of the Askaryan Effect: Coherent Microwave Cherenkov
Emission from Charge Asymmetry in High-Energy Particle Cascades: D.
Saltzberg, P.Gorham et al., Phys. Rev. Lett. 86(2001)2802-2805.
simulated showercurve
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Properties of materials for UHE Neutrino DetectorRock salt: high
density, large refractive index and short radiation length(a)
Measurement of attenuation length L in situ ( P. Gorham et al. )(b)
Measurement of complex permittivity at laboratory ( our work )
Synthesized NaCl : ' = 5.9 , tan = 4.3 10-5 L= 1080m at 1GHz.
MaterialPropertiesAirSTP)IceH2O)Rock salt(NaCl)Lime
stone(CaCO3)Density (g/cm3)0.00120.9242.222.7Radiation length X0
(cm)304203910.19.0Refractive index n =
1.0002931.782.432.9Cherenkovangle (deg)1.38755.865.769.8Cherenkov
threshold energy(keV),,1075033
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World rock salt resourcesSALT DOMES, Gulf Region, United States
& Mexico, MICHEL T. HALBOUTY, Gulf Publishing Company, Book
Division, Houston, London, Paris, Tokyo, 1979Handbook of World Salt
Resources, Stanley J. Lefond, PLENUM PRESS, NEWYORK, 1969
M.Chiba
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3km 10kmRock salt is free from liquid and gas
permeationpetroleum or natural gas are likely to deposit around the
salt dome. Free from water permeation results good radio wave
transparency.Covered soil prevents surface radio wave to
penetrate.Penetrating cosmic rays underground are too spatially
disperse to generate coherent Cherenkov radiation effectively.Salt
neutrino detector installed in a salt domeSND Dow Earth Sciences,
Geol: J.Hertzing
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Underground Salt Neutrino Detector. Moderate number of radio
wave sensors could detect the neutrino interaction in the massive
rock salt. If the attenuation length L =1km, 216 antennas are set
at 400m intervals in 36 bore holes. It works as an imaging
calorimetric detector.Hockley salt mine, TexasArray of the
antennas0m2000m2000mnM.Chiba
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Requirements for the antennas
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OmnidirectionalWidebandCompact fitted in a bore holeHigh
efficiencyPolarization analyzability Small number of antennas for a
suite.g., loop antenna, fractal antenna, etc.
Loop antenna
Fractal antenna
Fractal Antenna Systems, Inc.
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Measurements of complex permittivity of rock salts and lime
stonesCavity perturbation methodAbsorption depends on the surface
condition of the samples, e.g. smoothness, stain etc. 9.4GHz TE107
Q=4000 Size: 23x10x155mm3
1GHz TM010Q=10000Size: 230mmf x 30mm
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Samples measured around 10GHzRock salt is fragile, so that it is
not easy to make small stick samples ( 1mm x 1mm x 10.2mm ). Lime
stone (especially Jura lime stone ) is rigid. The small stick
samples are obtained using a milling machine.
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Measurements of the suitability of large rock salt
formationsSimilar studies are done about UHE neutrino detector
utilizing rock salt. The results are consistent with
ours.M.Chiba
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Dielectric resonatorAttenuation lengthM.Chiba
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Nacl powder
Teflon
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in situ measurements
P.Gorham et al
NaCl, Dielectric Materials and Applications (A. R. von Hippel
ed.), 1954
tan=210-4
Rock salt Hockley mine, USA
Rock salt, Halstadt mine, Austria
NaCl synthesized
Lime stone, Kamaishi, Japan
Lime stone, Mt. Jura, France
Rock salt, Asse mine, Germany
Hippel 25GHz
1GHz cavity
5.5GHz
8.2GHz
11GHz
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GZK neutrino detection
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ConclusionsThe attenuation length of various rock salts and lime
stones are measured at 1-12GHz by the cavity perturbation method
with 10 times better precision than previous measurements at 10MHz
and 25GHz. Synthesized NaCl shows ' = 5.9 , tan = 4.3 10-5, L=
1080m at 1GHz. The tan is 5 times smaller than the upper limit
measured before at 10MHz.The attenuation length of rock salts in
Hockley mine, Texas is tan = 2.3 10-4, L= 180m at 1GHz. If the tan
is constant with respect to the frequency, L becomes 900m at
200MHz. L is long enough for the salt neutrino detector.We expect
to detect 10 GZK neutrinos/year by the salt neutrino detector with
the volume of 2kmx2kmx2km.
Astronomy of long distances in the highest energy region could
be investigated only by UHE neutrinos due to the short transport
length of photons and protons. GZK process generates UHE neutrinos.
Among UHE neutrinos, GZK neutrinos exist firmly due to the
observation of UHE cosmic ray and CMB.
At first GZK neutrino is a good target to detect. In addtion,
direct UHE neutrinos from AGN, etc.We need a large neutrino
detector since GZK flux is very low.The detector should provide the
possibility to know energy, direction and flavor of the
neutrinos.Radio wave detection is suitable way to realize.
Coherent Cherenkov radiation is calculated by Askaryan in solid,
1961 and M.Fujii and J.Nishimura in air, 1969.Askaryan effect is
proved by SLAC high energy photon beam.Among the materials, rock
salt and lime stone have good properties for short radiation length
and low Cherenkov threshold energy.Attenuation length in material
is proportional to radio wavelength emitted and inverse
proportional to tan. tanis the ratio of imaginary and real parts of
permittivity which represents the absorption.Recently, the
measurements have been done by P. Gorham et al. in situ
measurements and by us in the laboratory.Due to our measurements of
synthesized rock salt crystal, we get surprisingly large
attenuation has been got. It extends over 1km at 1GHz.It is enough
for SND if that of natural rock salt is the same.
Rock salt were made about 250 million years ago in Jura era. At
that time continents were not divided but one called Gondowana. A
closed sea water were evaporated by Sun shine and changed to a
solid. It was buried under the earth and turned into a rock. They
are distributed world wide. Unfortunately at the era Japan was
under the sea and has no chance to make rock salt. On the contrary,
Japan has a good resources of limestone. Geologically Japan was a
great barrier leaf to the continent.Typical salt dome in the gulf
region.
Underground salt neutrino detector. The size is 2kmx2kmx2km with
400m spacing antennas, in case of the attenuation length of 1km.
Excess electrons in the shower from the UHE neutrino interaction
generate coherent Cherenkov radiation with an emission angle of
56.
The attenuation length is measured as the absorption of radio
wave in the cavity. Two types of cavities are employed. Samples for
9.4GHz cavity.In situ measurements at Hockley salt mine, near
Houston, Texas was done by Peter Gorham, David Saltzberg.The
results shows the long attenuation length.Monte Carlo Design
Studies were done by D.Salzberg et al. The results are similar to
our work.Compilation of the attenuation lengths. 10MHz and 25GHz
are from Hippel 1954. Three data points are in situ Hockley salt
mine measurements.The rest are our measurements. Red points are
synthesized rock salt data. At 1GHz the attenuation length is over
1km. Pink points are Hockley mine. At 1GHz it is 180m. SND could
detect 10 events/year.The Hockley salt shows long enough
attenuation length for SND at 200MHz..10GZK neutrinos/year are
expected to be detected.