The Antarctic Muon And Neutrino Detector Array, AMANDA, is a Cherenkov detector deployed deep in the ice cap at the South Pole. Charged particles traveling faster than the speed of light in ice produce Cherenkov radiation that is detected by Photo-Multiplier Tubes. Using the information obtained by the Photo- Multiplier Tubes, the physical characteristics, such as direction and energy, can be reconstructed. High energy neutrinos of all flavors can produce particle cascades when interacting with matter. In ice, cascades are typically a few meters long, much smaller than the dimensions of AMANDA. Electron neutrinos produce cascades via both the charged and neutral current interactions. Muon and tau neutrinos produce cascades via the neutral current interaction. Isolated cascades are also produced by tau neutrinos via charged current interactions, because the resulting tau, at energies below a few hundred TeV, will travel only a few meters before decaying. Advantages of the cascade channel, compared to neutrino induced muons are better energy resolution and an order of magnitude lower background from atmospheric neutrinos when searching for extra terrestrial neutrinos. Data collected in 1997 were searched for high energy neutrino induced cascades. A total of 1.18 × 109 events were recorded for an effective live-time of 130.1 days. The overwhelming majority of the events recorded were produced by down-going cosmic-ray induced muons. Bright muon energy losses are the main background when searching for high energy extra- terrestrial neutrino induced cascades. The sensitivity of the detector to cascades has been studied using in-situ light sources. No evidence for the existence of a diffuse flux of high energy neutrinos has been found. Limits have been set for fluxes following an E -2 power law spectrum. For ne+n e the limit is<display-math> <fd> <fl>FE2<5.7-7.1×10- 6 Ge/Vdot s-1 dot sr-2 90%C.L.</fl> </fd> </display-math>For ne+n e+nm+n m+nt+n t the limit is<display-math> <fd> <fl>FE2<8.5- 10.5×10- 6Ge/Vdot s -1dot sr-2 90%C.L.</fl> </fd> </display-math>For both cases the limits are shown with and without the effect of systematic errors. The flux limits were obtained for neutrino energies between 5 TeV and 300 TeV. The effective detector volume has also been calculated for every neutrino flavor, allowing the calculation of fluxes for any neutrino flux model.
- Pub Date:
- August 2002
- Physics: Elementary Particles and High Energy, Physics: Astronomy and Astrophysics