Upper Limit on the Diffuse $nu_mu$ Flux with the ANTARES Telescope

Nuclear Physics B Proceedings Supplement 00 (2021) 1–1 Nuclear Physics B Proceedings Supplement Upper Limit on the Diffuse νµ Flux with the ANTARES Telescope Simone Biagi for the ANTARES collaboration Dipartimento di Fisica dell’Universit`a and INFN, Viale Berti Pichat 6/2, 40127 Bologna, Italy Abstract A search for very-high energy cosmic muon neutrinos from unresolved sources is presented using data collected by the ANTARES neutrino telescope. Data corresponding to 334 days of equivalent live time show that the observed number of events is compatible with the expected number of background events. A 90% c.l. upper limit on the diffuse νµ flux is set at E2Φ90% = 5.3 × 10−8 GeV cm−2 s−1 sr−1 in the energy range 20 TeV – 2.5 PeV. Keywords: cosmic neutrinos, diffuse flux, underwater neutrino telescope The ANTARES neutrino telescope is a three- dimensional array of 885 photomultiplier tubes (PMT) distributed over 12 lines installed in the Mediterranean Sea [1]. A search for a diffuse flux of muon neutrinos using data collected from December 2007 to December 2009 is presented. Atmospheric muons and neutrinos are the main sources of background in a neutrino telescope. The former can be suppressed by applying requirements on Figure 1: The ANTARES 90% c.l. upper limit for a E−2 diffuse νµ +νµ flux, compared with the results obtained from other ex- periments and theoretical predictions. See [6] and references therein. the topology of the events, the latter is an irreducible background. As the spectrum of cosmic neutrinos is expected to be harder than that of atmospheric neutri- nos, the signal searched for corresponds to an excess of high energy events, produced by astrophysical sources, in the measured energy spectrum without any particular assumption on the source direction. A test signal spectrum ∝E−2 ν and the “conventional” atmospheric Bartol flux [2] were simulated. An energy estimator [3], based on the mean number of hit repeti- tions (R) on the PMTs, is used to separate the diffuse flux signal from the atmospheric νµ background. A cut over the R variable is optimized with the Model Rejec- tion Procedure [4] using Monte Carlo expectations only. Nine high energy neutrino candidates are found with an expected background of 10.7±2 events. The 90% c.l. upper limit on the diffuse νµ flux including systematic uncertainties is computed with the method of [5]: it is E2Φ90% = 5.3 × 10−8 GeV cm−2 s−1 sr−1 (1) in the energy range 20 TeV – 2.5 PeV. The result is com- pared with other experiments in Fig. 1. [1] G. Anton, these proceedings. [2] G.D. Barr et al., Phys. Rev. D70 (2004) 023006. [3] S. Biagi, PhD thesis (2010) http://antares.in2p3.fr/. [4] G.C. Hill and K. Rawlins, Astropart. Phys. 19 (2003) 393. [5] J. Conrad et al., Phys. Rev. D67 (2003) 012002. [6] T. Chiarusi and M. Spurio, Eur. Phys. J. C65 (2010) 649. arXiv:1101.2974v1 [astro-ph.HE] 15 Jan 2011

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