Performance of a prototype aerogel counter readout by fine mesh photo-tubes

The BaBar experiment, in order to achieve its physics program, requires pion/kaon identification capability up to 4.3 GeV/c. The recent development of new processes has lead to the fabrication of low density silica aerogel with high optical quality. An aerogel threshold counter using the combination of two refractive indices (1.055 and 1.007) can be used to complete the angular coverage of the particle identification system in the forward region of the BaBar experiment. We present final test-beam results on a two-layer aerogel prototype, readout by Hamamatsu fine mesh photo-tubes, as required by the high magnetic field environment of the BaBar experiment, Several configurations have been tested, with different aerogels, photo-tubes and reflective materials. A comparison between data and a detailed Monte Carlo simulation is also presented. The result of the test shows that such a detector can achieve the desired performances.