To see the threshold momenta for the different indices of AEROGEL, the expected number of emitted photon are calculated through empirical equation 1, and plotted in 11.
In the equation, L denotes radiator length,
and for aerogel it is assumed to be 12cm, and
for RICH (n=1.00041 for ) it is 150 cm.
The constant is based on the beam test results
at KEK. For the aerogel, thickness dependence
is described in the section 7.4.
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Especially for the identification of kaon at the high momentum region (from 3.7 to 5.5 GeV/c), the matching is needed between the lowest threshold momentum (5.5 GeV/c) for pion rejection by RICH counter, and the lowest threshold (3.7 GeV/c for the n=1.010 with threshold at 10 % of maximum number of photoelectrons) of light emission in AEROGEL by kaon as well as by pion.