Progress on development of the new FDIRC PID detector
Introduction
The BaBar experiment has used very successfully the DIRC PID detector (DIRC=Detector of Internally Reflected Cherenkov light) [1]. The original DIRC had one weak point: its huge photon camera, filled with 6000 l of ultra-pure water, was sensitive to electromagnetic and neutron background. This needs to be improved as the SuperB luminosity will increase 100×. Therefore we have exchanged this simple pinhole camera at the heart of the DIRC detector into a focusing camera with sophisticated, solid fused-silica optics, while shrinking it to 1/25th of its former size and increasing its speed by a factor of 10 [2]. The new detector is called FDIRC (Focused Detection of Internally Reflected Cherenkov light). Each of the 12 FDIRC Photon cameras will have 48H-8500 MaPMTs, providing excellent timing capability for single photons (, TTS is a transit time spread). It is also necessary to implement new front-end electronics (FEE) with much higher timing precision (), higher hit rate capability (few MHz hit rate per pixel), and small dead time (less than 5% at 1 MHz rate) [3]. These improvements will compensate for the increase in luminosity (×100) and background between the two generations of experiments. A full scale FDIRC prototype module covering 1/12 of the barrel azimuth will be tested in the cosmic ray telescope (CRT) [4] at SLAC with 3D tracking using muons.
Section snippets
FDIRC design and construction
A very important design feature of FDIRC photon camera is to measure the Cherenkov angle with x–y pixels alone (the detector coordinate system where the y-direction is vertical and the x-direction is horizontal), i.e., a high resolution timing is not needed. Time is used, however, to cut the background, perform the chromatic correction by timing, and be part of PID maximum likelihood.
Fig. 1, Fig. 2 show the new FDIRC photon camera design. The camera was designed with one important constraint:
Choice of photodetectors and electronics
There were three Hamamatsu photon detectors under consideration, the H-8500 (64 pixels) and the H-9500 (256 pixels), and very recently R-11265-00-M64 (64 pixels) multi-anode PMTs (MaPMT) by Hamamatsu. At present, our nominal choice is a 12-stage H-8500 tube. It has a sufficient single electron timing spread (), it can be obtained with somewhat enhanced quantum efficiency QE of , it has more acceptable uniform gain response across its face (1:2.5), and it has been studied quite
A summary of R&D results up to now
It was very important to build a first FDIRC prototype with a single bar and oil-filled photon camera [10]. We learned how to operate new fast highly pixilated detectors [7], how to design a new optics, how to do the chromatic correction by timing (this was the very first RICH detector to achieve this). To be able to do such correction, one needs to achieve a timing resolution at a level of 200–250 ps per single photon, and the photon path length needs to be longer than 2–3 m. The fact that FDIRC
Expected performance of the final FDIRC
Contributions to the Cherenkov angle resolution per photon and per track are shown in Table 1. Fig. 8 shows the expected performance relative to the BaBar DIRC for various photodetector design choices. Fig. 7 shows MC simulation of FDIRC expected Cherenkov angle resolution in CRT for H-8500 tube with 6 mm pixels and no chromatic correction. Clearly, a small pixel size and high QE efficiency is crucial to obtain the best possible performance, although a nominal design with H-8500 tube and
Goals of the final FDIRC prototype test in CRT
The FDIRC prototype will be tested at SLAC in CRT using 3D tracks. The tracking system has an angular resolution of mrad, track position resolution of 5–6 mm, start time resolution of better than (with tracking corrections it may reach ), a 1.6 GeV muon low energy cut-off thanks to a 46 in.-thick iron absorber, and a large iron area of 55 in.×90 in. allowing to reach large range of dip angles. The 3D-tracking capability is very important to understand tails of the Cherenkov angle
Conclusion
We have clearly demonstrated that the photon camera, made of solid fused silica, is buildable. Its main advantage is the radiation hardness, small size, stability and practically no maintenance. It is more expensive compared to oil-based or water-based designs, but they require a long-term maintenance, which is at the end more expensive if one integrates over 10 years of operation. And fluid-based systems represent higher risk to other subsystems.
Acknowledgments
The authors would like to thank M. McCulloch for help in final assembly of the optics and prototype, M. Zago for the mechanical design of the Fbox and the Padova University mechanical workshop personnel for Fbox construction and assembly. We also thank M. Mongelli and V. Valentini of Bari for Fbox mechanical support structure design and M. Franco for helping to construct it. This work was supported in part by the Department of Energy, Contract DEAC02-76SF00515.
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Cited by (10)
DIRC: Internally reflecting imaging Cherenkov detectors
2020, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated EquipmentMicro-channel plates and vacuum detectors
2015, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated EquipmentCitation Excerpt :A first FDIRC prototype utilized a single quartz bar of the BaBar DIRC and a cylindrical mirror placed in a mineral oil expansion volume. Commercially-available MCP–PMTs and flat-panel multi-anode PMTs with 8×8 square pixels were investigated [42–44] and showed to fulfill the FDIRC requirements. A time-of-propagation (TOP) counter has been developed [45] to upgrade the barrel PID detector of the Belle-II experiment.
Design and performance of the focusing DIRC detector
2015, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated EquipmentCitation Excerpt :They each are attached to an individual wedge of approximately the same width as the bar, and all 12 bar assemblies are coupled to the bar box window. Fig. 1d and e shows the new optical components: a new wedge and a large focusing block (FBLOCK) [14]. The dimensions of the FBLOCK were nominally 560 mm height×217 mm length×422 mm width.
Optical properties of RICH detectors
2014, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated EquipmentCitation Excerpt :Fig. 21a shows the anatomy of the Cherenkov ring images for z-positions along the bar length. We tried to reduce the kaleidoscopic effect with various types of focusing with no success [33] (see Fig. 21b). Even non-focusing DIRC has it, uniformly spread along the ring.
Results from the FDIRC prototype
2014, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated EquipmentCitation Excerpt :It was the first RICH detector to successfully correct the chromatic error using timing. Here, we describe a FDIRC design developed for the SuperB experiment that was to be built in Fascati [5,6]. Fig. 1 shows a GEANT4 realized image of the FDIRC, indicating key components.
The PANDA Barrel DIRC detector
2014, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment