Aerogel

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.

$$N_{p.e.} \simeq 55 \times L \left[ cm \right] \times \{1-(1/n\beta)^{2}\}$$ (1)

In the equation, L denotes radiator length, and for aerogel it is assumed to be 12cm, and for RICH (n=1.00041 for $CO_{2}$) 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.

図 11: Evaluated number of photo-electron for [thick line] n= 1.010, [dotted line] n = 1.015, and [dashed line] RICH ($CO_2$, n=1.00041) as a function of momentum. $N_{p.e.}$ is for the 12 cm thick of aerogel. For the thickness dependence, see section 7.4.

図 12: Difference of time-of-flight [ps] at 5 m vs. momentum, between pion and kaon [solid line], and between kaon and proton [dashed line].

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.