Shower power: isolating the prompt atmospheric neutrino flux using electronneutrinos

Abstract

At high energies, the very steep decrease of the conventional atmospheric component of theneutrino spectrum should allow the emergence of even small and isotropic components ofthe total spectrum, indicative of new physics, provided that they are less steeplydecreasing, as generically expected. One candidate is the prompt atmosphericneutrino flux, a probe of cosmic ray composition in the region of the knee as well assmall-x QCD, below the reach of collider experiments. A second is the diffuse extragalacticbackground due to distant and unresolved AGNs and GRBs, a key test of the nature of thehighest-energy sources in the universe. Separating these new physics components from theconventional atmospheric neutrino flux, as well as from each other, will be very challenging.We show that the charged-current electron neutrino ‘shower’ channel should be particularlyeffective for isolating the prompt atmospheric neutrino flux, and that it is moregenerally an important complement to the usually considered charged-currentmuon neutrino ‘track’ channel. These conclusions remain true even for the lowprompt atmospheric neutrino flux predicted in a realistic cosmic ray scenariowith heavy and varying composition across the knee (Candia and Roulet, 2003J. Cosmol. Astropart. Phys. JCAP09(2003)005). We also improve the correspondingcalculation of the neutrino flux induced by cosmic ray collisions with the interstellarmedium.