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Description
The geometrical configuration of the Einstein Telescope (ET) gravitational-wave observatory is one the most important design choices to be made for this future scientific facility. Two baseline configurations are currently being considered, a single triangle or 2 distant L-shaped detectors tilted by about 45◦. In this document we present a study of the scientific performance of the ET baseline configurations in both stand-alone mode and in the presence of either an L-shaped Cosmic Explorer detector with 40-km long arms located in the United States or the existing LIGO-Virgo-KAGRA network. We also include in the study an alternative ET configuration consisting of a triangle plus a distant L-shaped detector. We find that in stand-alone mode this alternative configuration performs better than the other two. The differences in performance between the ET configurations are reduced in the presence of the considered, additional non-ET detectors. We also study the impact on the ET scientific performance of the relative orientation of the future detectors in the network. We find that, while the options that include a triangular ET detector are basically insensitive to this orientation, a balanced compromise for the ET configuration consisting of two L-shaped detectors could be represented by a tilt angle between the two detectors of about 30◦.