Search for UHE Neutrinos with AMANDA Stephan Hundertmark University of California, Irvine Methodical Aspects of Underwater/Ice Neutrino Telescopes Hamburg, 15 & 16 August 2001

Introduction Identification of point like or diffuse sources Muon range well above ~10 km for Eµ>10^16 eV Large volume can be monitored But: Upgoing neutrinos are absorbed by the earth Downgoing limited by ice overburden Signal concentrated around the horizon

Length of UHE muons Shown is the length of 10^16 and 10^20 eV muons and the availible pathlength to the ice surface for the AMANDA array 10^20 eV 10^16 eV Length (km) Probability Zenith (degree) Length to surface (km)

Relative Muon Flux from Isotropic 10^16 eV Neutrino Flux Absorption of the ä 's Limited overburden for ä  µ conversion

Predicted µ Fluxes AGN (S) AGN (P) Gelmini Charm (pQCD) Charm (SM) Number of events per year for hypothetical 0.5 km² detecor:

MC Background EventMC Signal Event

Data Sets 1997 Experimental Data (B10 array); 75 days livetime Corsika; 0.84 days livetime HE-Corsika (E prim > 80 TeV) for p,Fe... Signal E^-1; 10^15-10^20 eV single muons plane & volume simulation

Definition of used Variables 1. NCH Number of hit channels 2. NH Number of hits for all channels 3. F1H Fraction of hit channels with exactly one hit 4. MA Mean amplitude for hit channels 5.  FG) Zenith angle for first guess. 6.  LR) Zenith for likelihood reconstruction 7. L Likelihood for LR A. NN1 Neural Net using 3., 5., 6. and 7. B. NN2 Neural Net using 1., 2., 3. and 4.

Definition of Levels Level 0: 1. Calibration, cleaning of cross-talk, cleaning of unstable OMs 2. Rejecting events with NCH R 95 or NCH(B4)<4 3. Rejecting events caused by electronic noise Level 1: 4. Rejecting events with F1H S 0.65 Level 2: 5. NN1>0.37 Level 3: 6. NN1>0.85 and NN2>0.7

Results Level Experiment Corsika MC Signal 0 2,405,055 35,560 10, ,096 (6.32) 2,005 (5.64) 9,261 (87.7) 2 2,192 (0.09) 37 (0.1) 8,406 (79.6) ,279 (59.4) Good agreement in passing rates for exp. data and Corsika Signal efficency remains high

Nitrogen Laser Simulation -Laser used to test detector answer to bright events - Significant amount of effort went into understanding these events - Amasim improved to simulate N 2 events

Energy of Air Shower Primaries -Cosmic ray primaries become significantly higher energetic throughout the analysis -Enables efficent simul- ation of the bgr. events

Composition at different Levels Level Protons Helium Iron Total events Trigger 71 % 23 % <1 % 5.1e % 30 % 17 % % 35 % 17 % 71 The analysis selects events of heavier primaries

Level 0: Exp. Data 3 Background MC F1H Good agreement between exp. and bgr. MC Signal shows distinct behavior

Level 1: Exp. Data 3 Background MC Good agreement between exp. and bgr. MC Cut choosen so that ~10 % signal is lost

Level 2: Definition of Final Cut Signal Background Signal and Background is seperated Background MC is in same area as exp. data Spase trigger can be found in the whole bgr. area

Effective Area for Final Level D Dip is simulation artefact !

µ-Flux Limit from Volume Simulation Non observation of events within 75 days gives Preliminary Limit for E-2 muon flux:  µ(10^15-20 eV) = 9 x 10^8 E-2 (GeV km² y sr)¯¹

Summary A method for a search for UHE events in the upper hemisphere was developed Within 75 days no candidates were found A preliminary muon flux limit was derived More work is in progress to establish this limit and convert it in a neutrino limit The remaining data for 97 will be analysed We are close to start rejecting models