Development of Pair Monitor

Figure 1: A schematic view of the forward region. The pair monitor will be located in front of the BeamCal, where is about 400 cm from IP. At ILC, measurement of the beam profile at IP is important to keep high luminosity of 2 × 10 cms. The beam size at IP is 639 nm, 5.7 nm, and 300 μm for horizontal (σX), vertical (σY), and longitudinal beam size (σZ), respectively. Since the beam size, especially σY, is very small, the beam profile monitor is required to measure the beam size within 1 nm accuracy. The pair monitor will be used to check the beam profile at the interaction point (IP), measuring the distribution of the electron-positron pairs generated during the beam crossing [2]. The generated electrons and positrons are scattered by the magnetic field produced by the oncoming beam, which is a function of the transverse size (σX, σY) and intensity of the beam. For that reason, the deflected particles should carry information of the transverse beam size, especially in their angular distribution. The pair monitor will be located at 400 cm from IP as shown in Fig. 1, where is in front of the BeamCal [3]. In our previous studies, the pair monitor has performance to measure the beam size with about 10% accuracy [4]. We have studied design of the pair monitor and developed the prototype of the readout ASIC. In this paper, test results of the readout ASIC and the future plan are reported.