Junji Haba

High Speed HPD for Photon Counting

We have succeeded in the development of a high-speed Hybrid Photodetector (HPD), by using a reduced electron lens and a newly developed avalanche diode (AD) with very low capacitance. The HPD shows fast time response of less than 500 ps in both rise and fall times, and good timing resolution of 26 ps (one sigma) for single photons at full illumination on a photocathode 8 mm in diameter. Limiting factors of the timing resolution were further investigated, and were found to be the transit time difference of electrons in vacuum along the photocathode and the jitter of the electronics. The timing resolution is 15 ps for illumination of less than 5 mm on the central part of the photocathode, which includes the jitter of 13 ps from the electronics. This resolution is the worlds highest for HPDs, and matches the resolution of MCP-PMTs. Both a GaAsP photocathode having close to 50% quantum efficiency in the visible and a bialkali photocathode having 34% QE in the UV were fabricated in view of making this device available for various applications. In this paper, we report the results of our evaluation, including discussion about the limiting factors of the timing resolution for the new HPD.

Development of a multi-pixel photon sensor with single photon sensitivity

Abstract A multi-pixel photon sensor with single-photon sensitivity has been developed. Based on a hybrid photo-detector (HPD) technology, it consists of a photocathode and a multi-pixel avalanche diode (MP-AD). The developed HPD has a proximity-focused structure, where the photocathode and MP-AD face each other with a small gap of 2.5xa0mm. The MP-AD, which has an effective area of 16xa0mm×16xa0mm, is composed of 8×8 pixel and has been specially designed for the HPD. The maximum gain of the HPD is 5×10 4 , sufficiently high to detect single photons with a timing resolution better than 100xa0ps. Up to four photoelectrons can be clearly identified as distinct peaks in a pulse-height spectrum, thanks to the low-noise characteristics of the HPD. It is also demonstrated that the HPD can be operated with good performance in a magnetic field as high as 1.5xa0T.

Development of a multi-pixel hybrid photodetector with high quantum efficiency and gain

A hybrid photo-detector (HPD) consisting of a photocathode and a multi-pixel avalanche diode (MP-AD) has been developed for these years. One of the features of the HPD is a good energy resolution, and it was shown in our previous study that the further improvement would be possible by reducing the fluctuation of charge loss in the dead layer at the entrance of the MP-AD. In this paper, we report on the result of the improvement with the newly developed HPD whose MP-AD encapsulated has a thinner dead layer than before. It is demonstrated that the new HPD has a much better energy resolution which enables the clear counting up to nine photoelectrons. Other features like a uniformity among the pixels or a photocathode sensitivity of the HPD are also presented.A hybrid photodetector (HPD) consisting of a photocathode and a multipixel avalanche diode (MP-AD) was developed a few years ago. Our previous studies showed that its inherent potential for high resolution photon counting could be further enhanced by reducing fluctuations in charge loss in the dead layer at the entrance of the MP-AD. In this paper, we report on the improvement with the newly developed HPD whose encapsulated MP-AD has a thinner dead layer than before. It is demonstrated that the new HPD has much better energy resolution, which enables clearer counting up to nine photoelectrons. Further enhancement of the photocathode sensitivity of the HPD is also discussed.

Magnetic field mapping of the Belle solenoid

The mapping of the magnetic field of the Belle detectors large superconducting solenoid is described. The mapping was done with the accelerator magnets located inside the Belle solenoid excited to their nominal field values. To cope with geometrical constraints, we developed a novel moving mechanism for the field probes that uses an ultrasonic motor located in the strong magnetic field.

Status of the Belle SVD detector

Abstract The Belle spectrometer was designed for studies of B meson decays at an asymmetric e + e − collider operating at the ϒ(4S) resonance. One of its crucial components, a silicon vertex detector (SVD), is placed just outside a cylindrical beryllium beam-pipe. After a year of Belle operation an upgraded version of SVD was installed during the regular summer shut-down. The new SVD follows the same design, with a few important improvements. Rad-soft readout electronics was replaced by rad-tolerant one, allowing for longer lifetime of the detector. A new radiation and temperature monitoring system was developed and implemented. A saw-shaped inner surface was introduced in the beam-pipe to prevent potential synchrotron radiation damage. The upgraded detector started operating successfully in October 2000.

Fine-Pixel Detector FPIX Realizing Sub-micron Spatial Resolution Developed Based on FD-SOI Technology

A Fine-PIXel detector (FPIX) with a pixel size of 8 × 8 μm has been developed using 0.2 μm fully-depleted silicon-on-insulator (FD-SOI) technology. With four FPIXs placed in a 120-GeV proton beam, the residual to reference track showed a Gaussian spread as small as 0.63 μm when three FPIXs other than the one under investigation were used to reconstruct the track. The point resolution corresponds to 0.59–0.83 μm. This is the first result showing that a sub-micron spatial resolution can be achieved by semiconductor detector.

Beam-beam effects observed at KEKB

At KEKB, a dedicated machine experiment on crab crossing has been carried out for about 4.5 months. Some of the beam-beam effects observed with crab crossing, which include a beam lifetime issue, are discussed in comparison with those with a finite crossing angle of plusmn11 mrad.