Laser Fiber Coupling Tests for Fiber Harp System in the Muon g-2 Experiment

With increased statistics and reduced systematic errors, the Muon g-2 experiment at Fermi National Accelerator Laboratory will improve the precision with which the muon's anomalous magnetic moment is known from 540 ppb to 140 ppb. Two diagnostic instruments, “fiber harps,” are installed at 180-degree and 270-degree positions of the g-2 storage ring. Each “harp” consists of seven 90 mm scintillating fibers with diameter of 0.5 mm, separated by 13 mm. The signals detected are guided through clear fibers to silicon photomultipliers (SiPM) and provide a measurement of the time dependence of the muon beam’s vertical and radial profiles. A previous challenge was coupling a laser fiber to each SiPM, and the “SiPM shield” has made this possible. The shield is a 3D printed, box-shaped component that fits on each SiPM. Each shield provides a round channel on the side of the SiPM. Through each channel, controlled light pulses from a diode laser are injected into the SiPM, to monitor the integrity of its signals and to determine its electronic impulse response function. We will present data on measured light intensity for the proposed designs that we compared.