PERFORMANCE OF A PROTOTYPE AEROGEL COUNTER READOUT BY FINE MESH PHOTO-TUBES

The BaBar experiment, in order to achieve its physics program, require s pion/kaon identification capability up to 4.3 GeV/c. The recent deve lopment of new processes has lead to the fabrication of low density si lica aerogel with high optical quality. An aerogel threshold counter u sing the combination of two refractive indices (1.055 and 1.007) can b e used to complete the angular coverage of the particle identification system in the forward region of the BaBar experiment. We present fina l test-beam results on a two-layer aerogel prototype, readout by Hamam atsu fine mesh photo-tubes, as required by the high magnetic field env ironment of the BaBar experiment, Several configurations have been tes ted, 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 achie ve the desired performances.