Test Results

The beam test has been carried out at the $\pi2$ and T1 beam line of KEK-PS for the study of prototype performance. The beam composition is mainly pions and protons in the momentum range of 0.6 - 4.0 GeV/$c$. Particle identification of the beam has been done with time-of flight counters and two gas Cerenkov counters. Fig.24 shows a scatter plot between pulse height from an aerogel counter and TOF measured at 2 GeV/c. The aerogel counter is Belle type with index of 1.017. From the differences of TOF, particles can be identified. Clear separation of particles is demonstrated. For the performance study of the aerogel, we selected 2.0 GeV/$c$ positive pions.

図 23: $N_{pe}$ vs. mean of ADC at -1500 V for R6233.

図 24: Scatter plot of pulse height from Belle type versus TOF value at 2.0 GeV/$c$. PID can be done with TOF differences ($\pi ^{+}$, K, p, d, from left to right, respectively).

Typical pulse height distributions for 2.0 GeV/$c$ pions and protons observed with Belle type are compared in Fig.25. Pions (above threshold) and protons (below threshold), being identified with TOF, show clear difference in the aerogel; Pions show clear signal while protons gives pedestals only. With the beam composition at the test beam, aerogel cherenkov counter gives pion detection efficiency of 99.5 % and fake proton rate is 0.5 % with the threshold of 5.0 p.e.

Photoelectron yields have been measured as a function of incident momentum of pions. Belle type with index of 1.017 was used and the beam was injected onto the center of the box. As shown in Fig.26, number of photoelectrons increases with the momentum, which agrees well with the threshold curve as

$$N_{pe} \propto 1-\frac{1}{n^2}\frac{m^2+p^2}{p^2},$$ (2)

which is characteristic to the cherenkov emission.

図 25: Pulse height spectra in units of photoelectrons from one PMT of Belle type for 2.0 GeV/$c$ pions(above threshold) and protons(below threshold).

図 26: The number of photoelectrons for pions versus momentum. The curve shows the fit with Eq.2.