The Anisotropy Search Program For the Pierre Auger Ob - servatory

The Pierre Auger Southern Observatory in Argentina has begun taking data as it is being developed up to a final enclosed area of 3000 square kilometres. A key aspect of the project is to provide information on the origin of the highest energy cosmic rays through understanding the arrival directions of those particles. To avoid claims of a spurious anisotropy detection because trials have not been properly accounted, the Auger Collaboration has agreed 'a priori' to the analysis prescription presented here. It specifies the following: 1. The accumulation time for the (future) data set to be analyzed. 2. The anisotropy 'targets', each assigned a chance probability level. 3. The analysis procedure for each trial. A positive result will be claimed for any target search only if its chance probability is less than its assigned level. The levels are chosen so that the total chance probability for one or more positive results is 0.001. Exploratory searches beyond this prescription will be encouraged, but the Auger Collaboration will not assign any confidence level to anisotropies that may be discovered that way. Any such discovery would identify a good target for a prescription to be used with a subsequent Auger data set.