Recent results on prototype aerogel threshold counters for particle identification in the region 0.5-4.3 GeV/c

The recent development of new processes has led to the fabrication of small density silica aerogel with high optical quality. The BaBar experiment, in order to achieve its physics program, requires a good pion/kaon identification capability up to 4.3 GeV/c able to work inside a 1.5 T magnetic field. 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. Different detector geometries read out by two photodetector types (fine mesh phototubes and hybryd photodiodes) have been considered and tested in a CERN beam test.