Aerogel RICH Research Articles

Particle identification performance of the prototype aerogel RICH counter for the Belle II experiment

We have developed a new type of particle identification device, called an Aerogel Ring Imaging Cherenkov (ARICH) counter, for the Belle II experiment. It uses silica aerogel tiles as Cherenkov radiators. For detection of Cherenkov photons, Hybrid Avalanche Photo-Detectors (HAPDs) are used. The designed HAPD has a high sensitivity to single photons under a strong magnetic field. We have confirmed that the HAPD provides high efficiency for single-photon detection even after exposure to neutron and gamma-ray radiation that exceeds the levels expected in the 10-year Belle II operation. In order to confirm the basic performance of the ARICH counter system, we carried out a beam test at the DESY using a prototype of the ARICH counter with six HAPD modules. The results are in agreement with our expectations and confirm the suitability of the ARICH counter for the Belle II experiment. Based on the in-beam performance of the device, we expect that the identification efficiency at 3.5 GeV/c is 97.4% and 4.9% for pions and kaons, respectively. This paper summarizes the development of the HAPD for the ARICH and the evaluation of the performance of the prototype ARICH counter built with the final design components.

Impact of polishing on the light scattering at aerogel surface

Particle identification power of modern aerogel RICH detectors strongly depends on optical quality of radiators. It was shown that wavelength dependence of aerogel tile transparency after polishing cannot be described by the standard Hunt formula. The Hunt formula has been modified to describe scattering in a thin layer of silica dust on the surface of aerogel tile. Several procedures of polishing of aerogel tile have been tested. The best result has been achieved while using natural silk tissue. The resulting block has optical smooth surfaces. The measured decrease of aerogel transparency due to surface scattering is about few percent. This result could be used for production of radiators for the Focusing Aerogel RICH detectors.

A 144-channel HAPD for the Aerogel RICH at Belle II

A hybrid photo-detector (HAPD) has been developed for the aerogel RICH (ARICH) of the Belle II experiment. In the present contribution we report the performance tests in magnetic fields, results of the neutron and gamma irradiation studies, and of aging tests. We also review the production status and plans.

Aerogel for FARICH detector

We present our current experience in preparation of focusing aerogels for the Focusing Aerogel RICH detector. Multilayer focusing aerogel tiles have been produced in Novosibirsk by a collaboration of the Budker Institute of Nuclear Physics and Boreskov Institute of Catalysis since 2004. We have obtained 2–3–4-layer blocks with the thickness of 30–45mm. In 2012, the first samples of focusing blocks with continuous density (refractive index) gradient along thickness were produced. This technology can significantly reduce the contribution from the geometric factor of the radiator thickness to the resolution of the measured Cherenkov angle in the FARICH detector. The special installation was used for automatic control of reagents ratio during the synthesis process. The first samples were tested using the digital radiography method and on the electron beam with the FARICH prototype.

Readout ASIC and electronics for the 144ch HAPD for Aerogel RICH at Belle II

At the Belle II experiment, Aerogel RICH is used as the particle identification device that covers the forward end-cap part of the Belle II detector. We develop the readout system of Hybrid Avalanche Photo Detectors that are used as the photon sensors of the Aerogel RICH. We present overview of the readout system, and report the status of the mass production toward the Belle II experiment.

Beam test of FARICH prototype with digital photon counter

In June 2012 we tested a Focusing Aerogel RICH detector prototype based on Digital Photon Counters (DPC) by Philips at the CERN PS T10 beam line with a particle momentum up to 6GeV/c. The prototype comprises a 20×20cm2 photon detector with 48×48 DPC pixels. In order to reduce the dark count rate, the photon detector was cooled to −40°C in addition to disabling individual DPC's microcells. A four layer focusing aerogel radiator with 200mm focal distance was studied. We obtained a Cherenkov angle resolution of 3.61±0.04mrad. The mean number of photoelectrons in a ring is 12. Directly measured π/K separation at 6GeV/c momentum is 3.5σ, μ/π separation is 5.3σ at 1GeV/c. A comparison with a Monte Carlo simulation is presented as well.

Aerogel RICH for forward PID at Belle II

For the Belle II spectrometer we are preparing a proximity focusing RICH with aerogel as the radiator. It will be positioned in the forward direction of the spectrometer in the small space between the drift chamber and the electromagnetic calorimeter inside a strong magnetic field of 1.5T. The Hybrid Avalanche Photo Diode used as a photo sensor, is able to detect single photons with a high efficiency, can operate in the magnetic field and is resistant to the expected neutron and gamma fluxes in the detector. By detecting more than 11 photons per incident 4GeV/c pion, with 15mrad single photon Cherenkov angle resolution, the designed aerogel RICH should enable an efficient separation of kaons from pions in the wide range of particle momenta from 0.5GeV/c up to 4GeV/c.

Readout ASICs and Electronics for the 144-channel HAPDs for the Aerogel RICH at Belle II

Abstract The particle identification (PID) device in the endcap of the Belle detector will be upgraded to a ring imaging Cherenkov counter (RICH) using aerogel as a radiator at the Belle II experiment. We develop the electronics to read out the 70,000 channels of hit information from the 144-channel hybrid avalanche photodetectors (HAPD), of the aerogel RICH detector. A readout ASIC is developed to digitize the HAPD signals, and was used in a beam test with the prototype detector. The performance and plan of the ASIC is reported in this study. We have also designed the readout electronics for the aerogel RICH, which consist of front-end boards with the ASICs merger boards to collect data from the front-end boards. A front-end board that fits in the actual available space for the aerogel RICH electronics was produced.

Development of Ring Imaging Cherenkov counter for Belle II experiment at super KEKB

For the Belle II experiment at the superKEKB, we have been developing a proximity focusing ring imaging Cherenkov detector using a silica aerogel as a radiator. A 144-channel Hybrid Avalanche Photo-Detector which is developed with Hamamatsu Photonics K.K. was adopted as the photon detector for the Aerogel RICH counter. We have conducted beam tests in order to evaluate the particle identification performance for the A-RICH system. One of our current concern for the system is a radiation hardness of the HAPD. In order to realize the neutron hardness for 10-year Belle II operation, we have tried to make APDs with a thinner P-layer which is expected to help in reducing the leakage current. As a result, we actually confirmed effects of the improved APD. In this paper, we would alike to report the status of the A-RICH development, especially about the improvement of the HAPD.

Photonis MCP PMT as a light sensor for the Belle II RICH

We report about on-the-bench studies of Photonis multi anode micro-channel plate (MCP) PMTs, as candidate photodetectors for the aerogel RICH counter of the Belle II spectrometer. This photosensor is fast enough to be used also as a time-of-flight counter, which would complement the kinematic range of the aerogel RICH counter.

Status of aerogel production in Novosibirsk

Silica aerogel blocks are being produced for use in Cherenkov detectors by a collaboration of Boreskov Institute of Catalysis and Budker Institute of Nuclear Physics since 1986. Novosibirsk aerogel is used in several detectors; among them are KEDR, SND (BINP, Novosibirsk), LHCb (CERN, Geneva), AMS (for International Space Station mission) and others. Currently our investigations are going on in two directions: multilayer aerogels for Focusing Aerogel RICH and aerogels with high index of refraction. We have synthesized two-, three- and four-layer aerogel tiles with dimensions of 115 mm×115 mm. We have modernized the method of pinhole drying for preparation of aerogels with refractive index in the range of 1.07–1.20.

Focusing Aerogel RICH for particle identification and momentum measurement

The work is devoted to the development of the Focusing Aerogel RICH (FARICH). The option of the forward RICH for the SuperB project in Italy is presented. It features an aerogel-NaF radiator and MCP photodetectors. Monte Carlo simulation predicts the π / K separation at the level better than 3 σ from 0.2 to 7 GeV/ c, the μ / π separation—from 0.13 to 1.3 GeV/ c, and the kaon momentum measurement with an accuracy of about 1% at 1 GeV/ c. FARICH for the Super Charm-Tau Factory project in Novosibirsk is proposed. Monte Carlo simulation predicts μ / π separation at the level better than 3 σ for a momentum from 0.3 to 1.7 GeV/ c. A prototype will be tested on the new electron test beam facility at VEPP-4M collider.

Development of the readout ASIC for the 144ch HAPD for aerogel RICH

We have developed an ASIC for readout of a 144 channel HAPD (hybrid avalanche photo-detector), one of the candidate photo-detectors for use in the aerogel RICH detector of the Belle upgrade (Belle-II). The first series of ASICs for evaluation showed good performance, and have been used to successfully detect Cherenkov rings with a prototype aerogel RICH device. We are also developing a new version of the ASIC for real application at the Belle-II detector.

A multichannel compact readout system for single photon detection: Design and performances

Optimal exploitation of Multi Anode PhotoMultiplier Tubes (MAPMT) as imaging devices requires the acquisition of a large number of independent channels; despite the rather wide demand, on-the-shelf electronics for this purpose does not exist. A compact independent channel readout system for an array of MAPMTs has been developed and tested [1,2]. The system can handle up to 4096 independent channels, covering an area of about 20 × 20 cm 2 with pixel size of 3 × 3 mm 2 , using Hamamatsu H-9500 devices. The front-end is based on a 64 channels VLSI custom chip called MAROC, developed by IN2P3 Orsay (France) group, controlled by means of a Field Programmable Gate Array (FPGA) which implements configuration, triggering and data conversion controls. Up to 64 front-end cards can be housed in four backplanes and a central unit collects data from all of them, communicating with a control Personal Computer (PC) using an high speed USB 2.0 connection. A complete system has been built and tested. Eight Flat MAPMTs (256 anodes Hamamatsu H-9500) have been arranged on a boundary of a 3 × 3 matrix for a grand total of 2048 channels. This detector has been used to verify the performances of a focusing aerogel RICH prototype using an electron beam at the Frascati (Rome) INFN National Laboratory Beam Test Facility (BTF) during the last week of January 2009. Data analysis is ongoing: the first results are encouraging, showing that the Cherenkov rings are well identified by this system.

Study of an HAPD with 144 channels for the Aerogel RICH of the Belle upgrade

For the upgrade of the Belle detector at the KEKB collider, we are developing a proximity focusing ring imaging Cherenkov detector using aerogel as a radiator. A 144 channel HAPD (Hybrid Avalanche Photo-Detector) is one of the candidate photo-detectors. We have measured the performance of the HAPDs, and succeeded to read out signals from the HAPD corresponding to one photo-electron using ASICs that have been developed for this purpose. We have also performed a beam test with a 2 GeV electron beam, and succeeded to detect a Cherenkov ring from the aerogel radiator.

Long-term operational experience with the HERMES aerogel RICH detector

For nearly 10 years, from 1998 until the closure of the HERA ring last July, a focused RICH has been used in the HERMES experiment at DESY to measure the semi-inclusive deep-inelastic scattering of polarized electrons on polarized gaseous targets. The RICH utilized two radiators, a heavy fluorocarbon gas, and a wall of silica aerogel tiles. It has identified pions, kaons, and protons in the momentum range from 2 to 15 GeV/ c with a K / π separation of nearly 3 σ at 4 GeV/ c. The optical properties of the aerogel and the RICH performance related to this radiator are reviewed, and some parameters are sampled over the whole RICH operational period in order to test its long-term stability.

Development of an HAPD with 144 channels for the aerogel RICH of the Belle upgrade

For the upgrade of the Belle detector at the KEKB collider, we are developing a proximity focusing ring imaging Cherenkov detector using aerogel as a radiator. A 144 channel HAPD (Hybrid Avalanche Photo-Detector) is one of the candidate photo-detectors. We report on the performance of a recently delivered HAPD. We also discuss results of tests of a read-out ASIC which is being developed for the readout of the HAPD. Both the HAPD and the ASIC show good performance for detection of single photons.

Focusing aerogel RICH optimization

The method of improvement of Cherenkov angle resolution in RICH detectors using ‘focusing’ aerogel radiators (FARICH) is under investigation. The ‘focusing’ three-layer aerogel radiator was investigated using a digital radiographic device. The Monte Carlo calculations of velocity resolution based on measured variations of the refractive index in aerogel tile are presented. With the observed variations, π - and K-mesons can be separated up to 8.4 GeV/ c, π - and μ -mesons can be separated up to 1.6 GeV / c . We studied the use of sodium fluoride radiator in a RICH detector. NaF radiator extends the working momentum region for the π / K identification down to 0.6 GeV/ c. It has been shown that a RICH detector with NaF radiator can achieve a competitive velocity resolution up to 5 GeV/ c as compared to single-layer aerogel RICH.

Silicon photomultiplier as a detector of Cherenkov photons

A novel photon detector—i.e. the silicon photomultiplier—whose main advantage over conventional photomultiplier tubes is the operation in high magnetic fields, has been tested as a photon detector in a proximity focusing RICH with aerogel radiator. This type of RICH counter is proposed for the upgrade of the Belle detector at the KEK B-factory. Recently produced silicon photomultipliers show less noise and have larger size, which are important issues for a large area photon detector. We measured the single photon pulse height distribution, the timing resolution and the position sensitivity for different silicon photomultipliers (Hamamatsu MPPC HC025, HC050, and HC100). The silicon photomultipliers were then used to detect Cherenkov photons emitted by cosmic ray particles in a proximity focusing aerogel RICH. Various light guides were investigated in order to increase the detection efficiency.

Development of aerogel Cherenkov counters at Novosibirsk

The work on aerogel Cherenkov counters was started in Novosibirsk in 1986. Production of aerogels with refractive indices of 1.006–1.13 and thicknesses of blocks up to 50 mm was developed. The light absorption length at 400 nm is 5–7 m, the scattering length is 4–5 cm. By these parameters, the Novosibirsk aerogel is one of the best in the world. The ASHIPH Cherenkov counters with light collection on wavelength shifters have been developed. The ASHIPH system of the KEDR detector contains 1000 l of aerogel. The π / K separation is 4.5 σ . A project of ASHIPH counters for the SND detector has been developed. Aerogel RICH for LHCb gives a possibility to identify hadrons in the momentum range of 2–10 GeV/ c. The Novosibirsk group is developing an aerogel RICH for the endcap for the SuperBaBar project. Calculations performed by a group of physicists from Novosibirsk and DESY-Zeuthen have shown that aerogel radiators enable to achieve time resolution up to 20 fs.