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December 13 2004 11 51 FILE AMANDA DPF 2004 International Journal of Modern Physics A c World Scientific Publishing Company THE AMANDA NEUTRINO TELESCOPE ANDREA SILVESTRI for the AMANDA Collaboration Department of Physics and Astronomy University of California Irvine CA 92697 USA Received Day Month Year Revised Day Month Year We present recent results from the Antarctic Muon And Neutrino Detector Array AMANDA located at the South Pole in Antarctica AMANDA II commissioned in 2000 is a multipurpose high energy neutrino telescope with a broad physics and astrophysics scope We summarize the results from searches for a variety of sources of ultra high energy neutrinos TeV PeV diffuse sources by measuring either muon tracks or cascades neutrinos in excess of PeV by searching for muons traveling in the downgoing direction and point sources Keywords Neutrino Detector Neutrino Telescopes Neutrino Astronomy Antarctic Ice Ultra High Energy Neutrinos AMANDA Introduction AMANDA is the first neutrino telescope constructed in transparent ice and deployed between 1500 m and 2000 m beneath the surface of the ice at the geographic South Pole in Antarctica It is designed to search for neutrinos that originate in the most violent phenomena in the observable universe Galactic objects like Supernova Remnants and extragalactic objects such as Active Galactic Nuclei and gamma ray bursts GRB are expected to be the powerful engines accelerating protons and nuclei to the highest energies which eventually interact to generate neutrinos Although not explicitly discussed here the detector has measured atmospheric neutrinos and searched for neutrinos correlated with GRB1 1 The Detector The AMANDA II neutrino telescope2 is an array of 677 Optical Modules OM arranged in 19 strings The best sensitivity of the detector is achieved for neutrinos with E between 103 106 GeV Down going atmospheric s and up going s are the major contribution to the background The muon tracks are reconstructed with a maximum likelihood approach which models the arrival times and amplitudes of Cherenkov photons recorded by the photomultiplier tubes achieving an angular resolution of 1 5 2 5 Above a few PeV the Earth becomes opaque to neutrinos and only those moving down or horizontally can reach the detector Such events 1 December 13 2004 11 51 FILE 2 AMANDA DPF 2004 Andrea Silvestri need to be separated from large muon bundles from down going atmospheric air shower events 2 Search for Diffuse Neutrino Flux E2 dN dE 10 6 Gev s 1 cm 2 5 10 2 2 1 1 E e GeV cm s sr This section presents three different methods to search for the diffuse flux of neutrinos Fig 1 left summarizes the results of the two search methods sensitive to all flavors The experimental limits assume a 1 1 1 ratio of neutrino flavors at the Earth due to oscillation The dotted and dashed lines represent a sample of model predictions adjusted for oscillation if appropriate which have been excluded by these analyses see3 4 for details The leftmost rightmost solid line is the AMANDA limit obtained from the cascade UHE analysis The length of the experimental lines corresponds to the energy interval that contains 90 of the signal for a spectrum proportional to E 2 6 0 3 Time period 2000 2001 2002 2003 2000 2003 0 25 0 2 0 15 10 0 1 0 05 4 5 6 7 8 9 10 log10 E GeV 0 0 2 0 4 0 6 0 8 1 sin Fig 1 Left AMANDA II limits for the diffuse flux of all flavors calculated for an E 2 spectrum Right AMANDA II sensitivities from a point source as a function of declination angle for E 2 spectra above E 10 GeV at 90 C L Individual curves are presented for the indicated years of operation Bottom curve includes full data set The cascade analysis3 delivers excellent energy resolution of 0 1 0 2 in log E E and improved sensitivity to all flavors AMANDA is sensitive to induced cascades from any direction but with relatively modest angular resolution of 30 40 The diffuse flux limit from the cascade analysis is E2 all E 8 6 10 7 GeV cm 2 s 1 sr 1 derived for an E 2 spectrum at 90 confidence level C L As indicated in Fig 1 left 90 of the signal lies within the energy interval between 50 TeV E 5 PeV Strategies for the UHE analysis4 were developed to separate signal from background based on the large amount of Cherenkov light generated by interactions of neutrinos with E 1015 eV Five events were observed while 4 6 events were expected This corresponds to a flux limit for an E 2 spectrum of E2 all E 0 99 10 6 GeV cm 2 s 1 sr 1 at 90 C L in the energy range of 1 PeV E 3 EeV see Fig 1 left The energy spectrum of December 13 2004 11 51 FILE AMANDA DPF 2004 The AMANDA Neutrino Telescope 3 atmospheric s provides a third analysis tool5 to search for a diffuse source of high energy neutrinos The measured atmospheric E spectrum extends to 300 TeV and agrees with theoretical parameterizations Since the spectrum of observed events is consistent with atmospheric s it was used to set a preliminary limit on a potential extraterrestrial flux with spectral dependence of E 2 to E2 E 2 6 10 7 GeV cm 2 s 1 sr 1 at 90 C L in the energy range of 100 TeV E 300 TeV The combined systematic uncertainty is typically 30 although the value varies slightly with the analysis method 3 Search for Point Sources AMANDA II has surveyed the entire northern sky since 2000 for non statistical excesses in small regions of the sky6 None were found so far Fig 1 right summarizes the preliminary results of a 4 year combined analysis showing the expected sensitivity based on the assumption of no signal as a function of declination for E 2 spectra above E 10 GeV A final sample of 3369 events was observed which is in good agreement with the expected number of 3438 from atmospheric s An unbinned sky search was performed for statistical fluctuation No fluctuation exceeded 3 4 which is compatible with random fluctuation in the spatial distribution of atmospheric s Due to the large number of search bins a fluctuation of at least this magnitude would occur in 40 of similar data samples 4 Conclusion AMANDA has yet to observe an extraterrestrial neutrino source but she has demonstrated the cost effectiveness and robustness of the technique The detector is very versatile it addresses many different neutrino physics subjects and sets the most stringent upper limits on Galactic and extragalactic fluxes The improved search for diffuse fluxes which has ruled out several predictions along with the extended four year search for point sources has started to


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