Limit on the diffuse flux of ultrahigh energy tau neutrinos with the surface detector of the Pierre Auger Observatory

THE PIERRE AUGER COLLABORATION, INCLUYE S. MOLLERACH

PHYSICAL REVIEW D

AMER PHYSICAL SOC

Año: 2009 vol. 79 p. 1 - 15

1550-7998

Data collected at the Pierre Auger Observatory are used to establish an upper limit on the diffuse flux of tau neutrinos in the cosmic radiation. Earth-skimming $ u_{ au}$ may interact in the Earth´s crust and produce a $ au$ lepton by means of charged-current interactions. The $ au$ lepton may emerge from the Earth and decay in the atmosphere to produce a nearly horizontal shower with a typical signature, a persistent electromagnetic component even at very large atmospheric depths. The search procedure to select events induced by $ au$ decays against the background of normal showers induced by cosmic rays is described. The method used to compute the exposure for a detector continuously growing with time is detailed. Systematic uncertainties in the exposure from the detector, the analysis and the involved physics are discussed. No $ au$ neutrino candidates have been found. For neutrinos in the energy range $2 imes10^{17}$ eV $< E_{ u}$ $<$ $2 imes10^{19}$ eV, assuming a diffuse spectrum of the form $E_{ u}^{-2}$, data collected between 1 January 2004 and 30 April 2008 yield a 90% confidence-level upper limit of $E_ u^{2} mathrm{d}N_{ u_ au}/mathrm{d}E_{ u} < 9 imes 10^{-8}$ GeV cm$^{-2}$ s$^{-1}$ sr$^{-1}$.