Study of salt neutrino detector forGZK neutrinos

Masami Chiba

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.

Generation of UHE neutrinos (>1015eV)

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

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.

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.

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

Observation of the Askaryan EffectAskar effect is verified by high energy photon beam at SLAC.M.Chiba

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

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

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

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

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

Requirements for the antennas

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.

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

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.

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

Dielectric resonatorAttenuation lengthM.Chiba

Nacl powder

Teflon

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

GZK neutrino detection

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.