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TeV to PeV neutrinos and gamma-rays with Mountain SHALON Mirror Cherenkov Telescope
Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 451–454 www.elsevierphysics.com
TeV to PeV neutrinos and gamma-rays with Mountain SHALON Mirror Cherenkov Telescope V. G. Sinitsyna, T. P. Arsov, F. I. Musin, S. I. Nikolsky, V. Y. Sinitsyna, G. F. Platonova a
P.N.Lebedev Physical Institute, Leninsky prospect 53, Moscow, 119991, Russia
Problems in observation of extensive air showers generated by neutrinos are connected with an extremely small cross-section of inelastic collisions of neutrinos with nuclei. However, two facts allow to search for showers generated by neutrinos: (1) a hadron cascade with a primary energy of more than 10 13 eV leaves a mountain ridge to the atmosphere from a depth ∼ 300 g/cm 2 without any essential loss of the total energy in the hadron cascade, and (2) air Cherenkov radiation from such hadron cascades will be observed with a 7.5 km distant telescope over an area of more than 7 × 105 m2 . This partially compensates for the small cross-section of inelastic neutrino collisions. Observations have been carried out since 1992 at the high mountain Tien-Shan station using the SHALON Cherenkov mirror telescope with ∼ 11.2 m2 mirror area and image matrix of 144 PMT with full angle > 8◦ . The telescope characteristics allowed to start searching for local neutrino sources with energy 1013 − 1016 eV on EAS generated in the mountain-range located at some 7.5 and more kilometers from the gamma-telescope (in Russian the abbreviation SHALON means - the Extensive Air Showers from Neutrino).
1. Introduction The detection of Extraterrestrial Very High Energy Neutrinos by Atmospheric Cherenkov Telescopic System SHALON is discussed. The analysis of results of observation of extensive air showers at height of 3338 m above the sea level by means of gamma-telescope SHALON at zenith angles 72◦ , 76◦ , 84◦ , 97◦ are presented. The observed results are compared with the data of detection of showers according to the zenith direction. The observations have been carried out at Tien-Shan station using the SHALON gammatelescope. The SHALON telescope system has a mirror area of 11.2 m2 and 144 PMT matrix with < 0.1◦ angular resolution, that has the largest angular size (> 8◦ ) in the world. It allows to check the background of cosmic ray particle emission and the atmospheric transparency continuously during observation that gives an increasing observation efficiency. So it is the telescope characteristics that allows to start searching for local neutrino sources with energy 1013 − 1016 eV on EAS generated in mountain-range located at some 6 and more kilometers from gamma-telescope (in Russian the SHALON abbreviation means - the Extensive Air Showers from Neutrino)[1–5]. 0920-5632/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2007.11.050
A neutrino telescope detects the Cherenkov radiation generated in water or ice by passage of relativistic charged particles produced by neutrino collisions with nucleons in the detector volume. Because of weakness of neutrino interaction a very large detector volume is required. Some alternative approaches have been proposed. One of them is to use the earth or a mountain as a target volume for the converting neutrinos to leptons which then initiate extensive air shower (EAS) in the atmosphere detected by a Cherenkov telescope. Observations of neutrino initiated EAS in the mountain shadow seems attractive because of mountain valley screening from background showers of cosmic rays, and the only particles that can survive are neutrinos with energies > 1013 eV arriving from below the horizon. Cascades with energy 10 TeV are generated by neutrinos in the ground of mountain at a depth of < 300 g/cm2 . The Cherenkov radiation of the hadron cascades will be observed along the neutrino direction by a gamma-telescope placed about 7 kms from a mountain slope (fig. 1) over an area of more than 7 × 105 m2 . So, UHE neutrinos may be looked for at large zenith angles.
452
V.G. Sinitsyna et al. / Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 451–454
2. Extensive Air Showers at Large Zenith Angles
Figure 1. The geometry of down horizontal observation sessions.
Figure 2. left - The spectrum of Cherenkov radiation of extensive air showers by telescope SHALON observation. PMT amplitude arbitrary units are laid off along the abscissa. right - Examples of showers recorded in PMT matrix at different zenith angles. The amplitude of gray-scale shower images is proportional to the ADC count. The number, named CODE shows the range of detected signals in the ADC counts, which are proportional to shower energy. Table 1 The atmosphere depth at different zenith angles Zenith Atmosphere Number of Cherenkov angle, Θ◦ depth, g/cm2 bursts per hour 72◦ 2250 7 ± 1.14 76◦ 3000 1.8 ± 0.5 84◦ 5950 0.5 ± 0.01
The SHALON mirror telescope due to the trigger control of the detection of bursts of a shortrange (8 nsec) signal in 4 PMTs of the lightreceiver matrix allows one to know the number of observed bursts without observation of conditions of an angular picture of a Cherenkov burst. The telescope is calibrated using observations of EAS of cosmic ray at 0◦ zenith angle. The cosmic ray shower image detected in the SHALON telescope, is generally an elliptic spot in the light receiver matrix, written in the ADC counts (CODE). Observations at large zenith angles have been aimed at studying spectra of air showers induced by cosmic rays crossing through different atmospheric thicknesses and events accompanying the passage of EAS and cosmic ray particles near the horizon. Observations at large zenith angles (72◦ , 76◦ , 84◦ ) showed that the efficiency of Cherenkov light detection drops essentially as zenith angle increases, perhaps because of dissipation and absorption in the atmosphere. So, the comparison of observed results shows that at the zenith angle 84◦ the number of observed showers is ∼ 25 times less than expected neglecting the absorption and dissipation of Cherenkov photons in the atmosphere (table 1, fig. 2). The analysis of the observations allows one to make the following conclusion. Firstly, a night star sky does not produce any background events preventing the observation of electronphoton cascades coming from under the earth surface. Secondly, the observation of Cherenkov bursts from extensive air showers at large zenith angles, for example using horizontal extensive air showers, to investigate the energy spectrum of ultra-high energy cosmic rays is complicated by the absorption of Cherenkov photons in the large atmospheric thickness. 3. The observations of Cherenkov bursts at 97◦ zenith angle The SHALON Cherenkov mirror telescope is located at 3338 m a.s.l. The mountain range lies in the east direction, more than 4300 m a.s.l.
V.G. Sinitsyna et al. / Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 451–454
453
Figure 3. left - Cherenkov Radiation of EAS observed at 97◦ zenith angle by SHALON; right - Cherenkov Radiation of EAS observed at 0◦ zenith angle by SHALON. and about 20 km long. The thickness of matter in the telescopic field of view ranges from 2000 to 800 kms; the viewed mountain slope area is > 7 × 105 m2 . For the telescope located about 7 kms away from the mountain slope horizontally, the shadow of mountain is about 7◦ in elevation. In actual fact the distance from the telescope to the opposite side of the gorge is ∼ 7 km or ∼ 16.5 radiation lengths, quite sufficient for the development of an electromagnetic cascade characteristic for a rarified atmosphere. The purpose of observations was revealing of background conditions when anthropogenic sources of light are absent. During 246 hours of observations 5 events were detected which have expected angular characteristics of a light burst of an electron-photon cascade developing within the telescope observation angle. These showers have energy in the range of about 6 − 17.5 TeV. All the other 297 events detecting short-range light bursts in the atmosphere do not have a narrow angle light direction and are chaotically distributed along the whole matrix or
its part of a light-receiver (fig. 2). These events may be interpreted as a reflection of a Cherenkov burst from a snow mountain slope or as an ionization luminescence of the atmosphere when an extensive air shower transits within the telescope observation angle. 4. Metagalactic and galactic sources of very high-energy gamma-quanta and neutrinos with the mirror Cherenkov telescope SHALON Observations at 97◦ zenith angle were made on cloudless nights in the absence of artificial lights and in dry air. During 246 hours of observation 302 short-range bursts were recorded. The characteristics of 297 of these is a flash that chaotically or smoothly spreads along the whole or part of the matrix. These events may be interpreted as a reflection of EAS Cherenkov burst from a snow mountain slope or as ionization luminescence of the atmosphere if a vertical EAS transits within
454
V.G. Sinitsyna et al. / Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 451–454
the field of view. However, 5 events have characteristics similar to those observed at 0◦ zenith angle. These cascades look like normal extensive air showers generated in the atmosphere with narrow light shape. The shower energies are in the range of 6 - 17.5 TeV (fig. 3). The background for these events can be due to the reflection of cosmic ray EAS on the mountain slope. First of all it could be a reflection of showers initiated by particles born in interaction of very high energy cosmic rays and rock matter nucleons. The energy of detected showers is more than 6 TeV. There are no albedo particles of such high energies. Another source of particles with high transverse energy is jet production. The probability of hadronic jet production with the energy of the observed showers is ten orders of magnitude less than for detecting shower generated by secondary particles of UHE neutrino interaction. The estimated neutrino event rate is one shower per 100 hours for neutrinos of all flavours and fluxes expected by models. It corresponds to rate of ∼ 10−15 cm−2 s−1 which is comparable to fluxes of weak gamma-quantum sources presently observed by SHALON. 5. Conclusion It is supposed to overcome the main difficulty of observation of EAS, generated by neutrinos in conditions of high mountainous observations, connected with the small number of neutrinonuclei inelastic collisions. Two facts allow to carry out these experiments. Hadron cascades with energy > 1013 eV are generated by neutrinos in the ground of mountain at a depth of < 300 g/cm2 . The Cherenkov radiation of the hadron cascades will be observed along the direction of neutrino by a gamma-telescope placed at a distance about 7 kms from a mountain slope over an area of more than > 7 × 105 m2 . These cascades look like usual extensive air showers generated in the atmosphere with narrow light shape. Currently, the fluxes of galactic gammaquantum sources Cygnus X-3, Tycho’s SNR, Geminga of < 10−14 cm−2 s−1 are observed by SHALON.
The appearance of one shower per > 100 observation hours is expected if the neutrino flux from local sources is 10−15 cm−2 s−1 [6–14]. During 246 hours of observation 5 events (fig. 3) were detected which have the expected angular characteristics of a light burst of an electron-photon cascade developing within the telescope observation angle. REFERENCES 1. S. I. Nikolsky and V. G. Sinitsyna, VANT, Ser. TFE, 1331, (1987) 30. 2. V. G. Sinitsyna, Toward a Major Atmospheric Cherenkov Detector -II, ed. Lamb R. C. (Iowa State University, (1993) 91. 3. V. G. Sinitsyna, Nuovo Cim., 19C, (1996) 965. 4. V. G. Sinitsyna, S. I. Nikolsky, et al., Nucl. Phys. B (Proc.Suppl.), 75A, (2001) 352; 97, (2001) 215, 219. 5. S. I. Nikolsky and V. G. Sinitsyna, Physics of Atomic Nuclei, 67(10), (2004) 1900. 6. H. V. Klapdor-Kliengrothaus, K. Zuber, in Teilchenastrophysik, ed. Teubner B.G. (GmbH, Stuttgart, 2000). 7. L. K. Resvanis, Nucl. Phys. B (Proc. Suppl.), 122, (2003) 24. 8. B. Degrange, Toward a Major Atmospheric Cherenkov Detector-I, ed. Fleury P., Vacanti G. (Frontieres), (1992) 171. 9. E. V. Bugaev and Yu. V. Shlepin, Nucl. Phys. B (Proc. Suppl.), 122, (2003) 341. 10. D. Fargion, et. al., ApJ, 613, (2004) 1285. 11. V. S. Berezinsky, A. Z. Gazaev, JETP lett, 25(5), (1977) 276. 12. G. T. Zatsepin and V. S. Berezinsky, Neutrino Astrophysic Problems, 2, (INR, Russian Academy of Science, 1980) 172. 13. E. Waxman and J. Bahcall, Phys. Rev.Letters, 78, (1997) 2292. 14. J. Stecker and M. Salamon, Space Sci. Rev., 75, (1996) 341.
TeV to PeV neutrinos and gamma-rays with Mountain SHALON Mirror Cherenkov Telescope V. G. Sinitsyna, T. P. Arsov, F. I. Musin, S. I. Nikolsky, V. Y. Sinitsyna, G. F. Platonova a
P.N.Lebedev Physical Institute, Leninsky prospect 53, Moscow, 119991, Russia
Problems in observation of extensive air showers generated by neutrinos are connected with an extremely small cross-section of inelastic collisions of neutrinos with nuclei. However, two facts allow to search for showers generated by neutrinos: (1) a hadron cascade with a primary energy of more than 10 13 eV leaves a mountain ridge to the atmosphere from a depth ∼ 300 g/cm 2 without any essential loss of the total energy in the hadron cascade, and (2) air Cherenkov radiation from such hadron cascades will be observed with a 7.5 km distant telescope over an area of more than 7 × 105 m2 . This partially compensates for the small cross-section of inelastic neutrino collisions. Observations have been carried out since 1992 at the high mountain Tien-Shan station using the SHALON Cherenkov mirror telescope with ∼ 11.2 m2 mirror area and image matrix of 144 PMT with full angle > 8◦ . The telescope characteristics allowed to start searching for local neutrino sources with energy 1013 − 1016 eV on EAS generated in the mountain-range located at some 7.5 and more kilometers from the gamma-telescope (in Russian the abbreviation SHALON means - the Extensive Air Showers from Neutrino).
1. Introduction The detection of Extraterrestrial Very High Energy Neutrinos by Atmospheric Cherenkov Telescopic System SHALON is discussed. The analysis of results of observation of extensive air showers at height of 3338 m above the sea level by means of gamma-telescope SHALON at zenith angles 72◦ , 76◦ , 84◦ , 97◦ are presented. The observed results are compared with the data of detection of showers according to the zenith direction. The observations have been carried out at Tien-Shan station using the SHALON gammatelescope. The SHALON telescope system has a mirror area of 11.2 m2 and 144 PMT matrix with < 0.1◦ angular resolution, that has the largest angular size (> 8◦ ) in the world. It allows to check the background of cosmic ray particle emission and the atmospheric transparency continuously during observation that gives an increasing observation efficiency. So it is the telescope characteristics that allows to start searching for local neutrino sources with energy 1013 − 1016 eV on EAS generated in mountain-range located at some 6 and more kilometers from gamma-telescope (in Russian the SHALON abbreviation means - the Extensive Air Showers from Neutrino)[1–5]. 0920-5632/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysbps.2007.11.050
A neutrino telescope detects the Cherenkov radiation generated in water or ice by passage of relativistic charged particles produced by neutrino collisions with nucleons in the detector volume. Because of weakness of neutrino interaction a very large detector volume is required. Some alternative approaches have been proposed. One of them is to use the earth or a mountain as a target volume for the converting neutrinos to leptons which then initiate extensive air shower (EAS) in the atmosphere detected by a Cherenkov telescope. Observations of neutrino initiated EAS in the mountain shadow seems attractive because of mountain valley screening from background showers of cosmic rays, and the only particles that can survive are neutrinos with energies > 1013 eV arriving from below the horizon. Cascades with energy 10 TeV are generated by neutrinos in the ground of mountain at a depth of < 300 g/cm2 . The Cherenkov radiation of the hadron cascades will be observed along the neutrino direction by a gamma-telescope placed about 7 kms from a mountain slope (fig. 1) over an area of more than 7 × 105 m2 . So, UHE neutrinos may be looked for at large zenith angles.
452
V.G. Sinitsyna et al. / Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 451–454
2. Extensive Air Showers at Large Zenith Angles
Figure 1. The geometry of down horizontal observation sessions.
Figure 2. left - The spectrum of Cherenkov radiation of extensive air showers by telescope SHALON observation. PMT amplitude arbitrary units are laid off along the abscissa. right - Examples of showers recorded in PMT matrix at different zenith angles. The amplitude of gray-scale shower images is proportional to the ADC count. The number, named CODE shows the range of detected signals in the ADC counts, which are proportional to shower energy. Table 1 The atmosphere depth at different zenith angles Zenith Atmosphere Number of Cherenkov angle, Θ◦ depth, g/cm2 bursts per hour 72◦ 2250 7 ± 1.14 76◦ 3000 1.8 ± 0.5 84◦ 5950 0.5 ± 0.01
The SHALON mirror telescope due to the trigger control of the detection of bursts of a shortrange (8 nsec) signal in 4 PMTs of the lightreceiver matrix allows one to know the number of observed bursts without observation of conditions of an angular picture of a Cherenkov burst. The telescope is calibrated using observations of EAS of cosmic ray at 0◦ zenith angle. The cosmic ray shower image detected in the SHALON telescope, is generally an elliptic spot in the light receiver matrix, written in the ADC counts (CODE). Observations at large zenith angles have been aimed at studying spectra of air showers induced by cosmic rays crossing through different atmospheric thicknesses and events accompanying the passage of EAS and cosmic ray particles near the horizon. Observations at large zenith angles (72◦ , 76◦ , 84◦ ) showed that the efficiency of Cherenkov light detection drops essentially as zenith angle increases, perhaps because of dissipation and absorption in the atmosphere. So, the comparison of observed results shows that at the zenith angle 84◦ the number of observed showers is ∼ 25 times less than expected neglecting the absorption and dissipation of Cherenkov photons in the atmosphere (table 1, fig. 2). The analysis of the observations allows one to make the following conclusion. Firstly, a night star sky does not produce any background events preventing the observation of electronphoton cascades coming from under the earth surface. Secondly, the observation of Cherenkov bursts from extensive air showers at large zenith angles, for example using horizontal extensive air showers, to investigate the energy spectrum of ultra-high energy cosmic rays is complicated by the absorption of Cherenkov photons in the large atmospheric thickness. 3. The observations of Cherenkov bursts at 97◦ zenith angle The SHALON Cherenkov mirror telescope is located at 3338 m a.s.l. The mountain range lies in the east direction, more than 4300 m a.s.l.
V.G. Sinitsyna et al. / Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 451–454
453
Figure 3. left - Cherenkov Radiation of EAS observed at 97◦ zenith angle by SHALON; right - Cherenkov Radiation of EAS observed at 0◦ zenith angle by SHALON. and about 20 km long. The thickness of matter in the telescopic field of view ranges from 2000 to 800 kms; the viewed mountain slope area is > 7 × 105 m2 . For the telescope located about 7 kms away from the mountain slope horizontally, the shadow of mountain is about 7◦ in elevation. In actual fact the distance from the telescope to the opposite side of the gorge is ∼ 7 km or ∼ 16.5 radiation lengths, quite sufficient for the development of an electromagnetic cascade characteristic for a rarified atmosphere. The purpose of observations was revealing of background conditions when anthropogenic sources of light are absent. During 246 hours of observations 5 events were detected which have expected angular characteristics of a light burst of an electron-photon cascade developing within the telescope observation angle. These showers have energy in the range of about 6 − 17.5 TeV. All the other 297 events detecting short-range light bursts in the atmosphere do not have a narrow angle light direction and are chaotically distributed along the whole matrix or
its part of a light-receiver (fig. 2). These events may be interpreted as a reflection of a Cherenkov burst from a snow mountain slope or as an ionization luminescence of the atmosphere when an extensive air shower transits within the telescope observation angle. 4. Metagalactic and galactic sources of very high-energy gamma-quanta and neutrinos with the mirror Cherenkov telescope SHALON Observations at 97◦ zenith angle were made on cloudless nights in the absence of artificial lights and in dry air. During 246 hours of observation 302 short-range bursts were recorded. The characteristics of 297 of these is a flash that chaotically or smoothly spreads along the whole or part of the matrix. These events may be interpreted as a reflection of EAS Cherenkov burst from a snow mountain slope or as ionization luminescence of the atmosphere if a vertical EAS transits within
454
V.G. Sinitsyna et al. / Nuclear Physics B (Proc. Suppl.) 175–176 (2008) 451–454
the field of view. However, 5 events have characteristics similar to those observed at 0◦ zenith angle. These cascades look like normal extensive air showers generated in the atmosphere with narrow light shape. The shower energies are in the range of 6 - 17.5 TeV (fig. 3). The background for these events can be due to the reflection of cosmic ray EAS on the mountain slope. First of all it could be a reflection of showers initiated by particles born in interaction of very high energy cosmic rays and rock matter nucleons. The energy of detected showers is more than 6 TeV. There are no albedo particles of such high energies. Another source of particles with high transverse energy is jet production. The probability of hadronic jet production with the energy of the observed showers is ten orders of magnitude less than for detecting shower generated by secondary particles of UHE neutrino interaction. The estimated neutrino event rate is one shower per 100 hours for neutrinos of all flavours and fluxes expected by models. It corresponds to rate of ∼ 10−15 cm−2 s−1 which is comparable to fluxes of weak gamma-quantum sources presently observed by SHALON. 5. Conclusion It is supposed to overcome the main difficulty of observation of EAS, generated by neutrinos in conditions of high mountainous observations, connected with the small number of neutrinonuclei inelastic collisions. Two facts allow to carry out these experiments. Hadron cascades with energy > 1013 eV are generated by neutrinos in the ground of mountain at a depth of < 300 g/cm2 . The Cherenkov radiation of the hadron cascades will be observed along the direction of neutrino by a gamma-telescope placed at a distance about 7 kms from a mountain slope over an area of more than > 7 × 105 m2 . These cascades look like usual extensive air showers generated in the atmosphere with narrow light shape. Currently, the fluxes of galactic gammaquantum sources Cygnus X-3, Tycho’s SNR, Geminga of < 10−14 cm−2 s−1 are observed by SHALON.
The appearance of one shower per > 100 observation hours is expected if the neutrino flux from local sources is 10−15 cm−2 s−1 [6–14]. During 246 hours of observation 5 events (fig. 3) were detected which have the expected angular characteristics of a light burst of an electron-photon cascade developing within the telescope observation angle. REFERENCES 1. S. I. Nikolsky and V. G. Sinitsyna, VANT, Ser. TFE, 1331, (1987) 30. 2. V. G. Sinitsyna, Toward a Major Atmospheric Cherenkov Detector -II, ed. Lamb R. C. (Iowa State University, (1993) 91. 3. V. G. Sinitsyna, Nuovo Cim., 19C, (1996) 965. 4. V. G. Sinitsyna, S. I. Nikolsky, et al., Nucl. Phys. B (Proc.Suppl.), 75A, (2001) 352; 97, (2001) 215, 219. 5. S. I. Nikolsky and V. G. Sinitsyna, Physics of Atomic Nuclei, 67(10), (2004) 1900. 6. H. V. Klapdor-Kliengrothaus, K. Zuber, in Teilchenastrophysik, ed. Teubner B.G. (GmbH, Stuttgart, 2000). 7. L. K. Resvanis, Nucl. Phys. B (Proc. Suppl.), 122, (2003) 24. 8. B. Degrange, Toward a Major Atmospheric Cherenkov Detector-I, ed. Fleury P., Vacanti G. (Frontieres), (1992) 171. 9. E. V. Bugaev and Yu. V. Shlepin, Nucl. Phys. B (Proc. Suppl.), 122, (2003) 341. 10. D. Fargion, et. al., ApJ, 613, (2004) 1285. 11. V. S. Berezinsky, A. Z. Gazaev, JETP lett, 25(5), (1977) 276. 12. G. T. Zatsepin and V. S. Berezinsky, Neutrino Astrophysic Problems, 2, (INR, Russian Academy of Science, 1980) 172. 13. E. Waxman and J. Bahcall, Phys. Rev.Letters, 78, (1997) 2292. 14. J. Stecker and M. Salamon, Space Sci. Rev., 75, (1996) 341.