July 29, 2003; M.Chiba1 Study of salt neutrino detector for GZK neutrinos

July 29, 2003; M.Chiba2 Generation of UHE neutrinos (>10 15 eV)

July 29, 2003; M.Chiba3 Astronomy in the highest energy region 1.Short interaction length 300Mpc to photons over 10TeV. 2.Protons propagate less than 50Mpc due to Greisen, Zatsepin and Kuzmin (GZK) cut off process over eV. 3.Long-range astronomy, observing old universe, in the highest energy region can be investigated by neutrinos exclusively. 4.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.

July 29, 2003; M.Chiba4 Neutrino flux and optimal detector 1.It is natural to aim at GZK neutrino at first. 2.Additions are direct UHE neutrinos from AGN, GRB, Topological Defects, etc. 3.GZK neutrino flux is as low as 1(km -2 day -1 ). 4.Large detector is needed with information of energy, direction, time and flavor. For the energy measurement, calorimetric detection is better than muon track detection. 5.Radio wave detection is suitable way to realize a large detector.

July 29, 2003; M.Chiba5 Coherent Cherenkov radiation in radio wave region Askar’yan in solid, 1961 M.Fujii and J. Nishimura in air, 1969 Electron or photon beam Electrons are 20% excess over positrons in an electromagnetic shower due to recoil electrons of Compton scattering etc. 1.Cherenkov radiation: dP/d  d  P   n   2.Coherent Cherenkov radiation: P   n 2   2. Stronger radiation at UHE. 3.Radio transparent media should be used: rock salt, Lunar regolith, Ice, etc. 4.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 Salt In Phase n excess electrons

July 29, 2003; M.Chiba6 Observation of the Askar’yan Effect Askar’ effect is verified by high energy photon beam at SLAC. M.Chiba

July 29, 2003; M.Chiba7 Properties of materials for UHE Neutrino Detector Material Properties Air （ STP) Ice （ H 2 O ) Rock salt (NaCl) Lime stone (CaCO 3 ) Density ρ (g/cm 3 ) Radiation length X 0 (cm) Refractive index n = Cherenkov angle (deg) Cherenkov threshold energy(keV) ２, ０６０, ４ ０７ Rock salt: high density, large refractive index and short radiation length (a) Measurement of attenuation length L α in situ ( P. Gorham et al. ) (b) Measurement of complex permittivity ε at laboratory ( our work ) Synthesized NaCl : ε' = 5.9, tanδ = 4.3× L α = 1080m at 1GHz.

July 29, 2003; M.Chiba8 World rock salt resources ・ SALT DOMES, Gulf Region, United States & Mexico, MICHEL T. HALBOUTY, Gulf Publishing Company, Book Division, Houston, London, Paris, Tokyo, 1979 ・ Handbook of World Salt Resources, Stanley J. Lefond, PLENUM PRESS, NEWYORK, 1969 M.Chiba

July 29, 2003; M.Chiba9 3km 10km 1.Rock salt is free from liquid and gas permeation ： petroleum or natural gas are likely to deposit around the salt dome. 2.Free from water permeation results good radio wave transparency. 3.Covered soil prevents surface radio wave to penetrate. 4.Penetrating cosmic rays underground are too spatially disperse to generate coherent Cherenkov radiation effectively. Salt neutrino detector installed in a salt dome SND Dow Earth Sciences, Geol: J.Hertzing

July 29, 2003; M.Chiba10 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 α =1km, 216 antennas are set at 400m intervals in 36 bore holes. It works as an imaging calorimetric detector. Hockley salt mine, Texas Array of the antennas 0m 2000m M.Chiba

July 29, 2003; M.Chiba11 Requirements for the antennas

July 29, 2003; M.Chiba12 Measurements of complex permittivity of rock salts and lime stones Cavity perturbation method Absorption depends on the surface condition of the samples, e.g. smoothness, stain etc. 9.4GHz TE107 Q=4000 Size: 23x10x155mm 3 1GHz TM010 Q=10000 Size: 230mm  x 30mm

July 29, 2003; M.Chiba13 Samples measured around 10GHz Rock 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.

July 29, 2003; M.Chiba14 Measurements of the suitability of large rock salt formations Similar studies are done about UHE neutrino detector utilizing rock salt. The results are consistent with ours. M.Chiba

July 29, 2003; M.Chiba15 Dielectric resonator Attenuation length M.Chiba

July 29, 2003; M.Chiba16 GZK neutrino detection

July 29, 2003; M.Chiba17 Conclusions 1.The 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. 2.Synthesized NaCl shows ε' = 5.9, tanδ = 4.3× 10 -5, L α = 1080m at 1GHz. The tanδ is 5 times smaller than the upper limit measured before at 10MHz. 3.The attenuation length of rock salts in Hockley mine, Texas is tanδ = 2.3× 10 -4, L α = 180m at 1GHz. If the tanδ is constant with respect to the frequency, L α becomes 900m at 200MHz. L α is long enough for the salt neutrino detector. 4.We expect to detect 10 GZK neutrinos/year by the salt neutrino detector with the volume of 2kmx2kmx2km.