田端 誠

Emission of muonium (μ +e-) atoms from silica aerogel into vacuum was observed. Characteristics of muonium emission were established from silica aerogel samples with densities in the range from 29 mg cm-3to 178 mg cm-3. Spectra of muonium decay times correlated with distances from the aerogel surfaces, which are sensitive to the speed distributions, and follow general features expected from a diffusion process, while small deviations from a simple roomtemperature thermal diffusion model are identified. The parameters of the diffusion process are deduced from the observed yields. © The Author(s) 2013.

This paper proposes a new X-ray radiographic technique for measuring density uniformity of silica aerogels used as radiator in proximity-focusing ring-imaging Cherenkov detectors. To obtain high performance in a large-area detector, a key characteristic of radiator is the density (i.e. refractive index) uniformity of an individual aerogel monolith. At a refractive index of n = 1.05, our requirement for the refractive index uniformity in the transverse plane direction of an aerogel tile is vertical bar delta(n-1)/(n-1)vertical bar < 4% in a focusing dual layer radiator (with different refractive indices) scheme. We applied the radiographic technique to evaluate the density uniformity of our original aerogels from a trial production and that of Panasonic products (SP-50) as a reference, and to confirm they have sufficient density uniformity within +/- 1% along the transverse plane direction. The measurement results show that the proposed technique can quantitatively estimate the density uniformity of aerogels. (c) 2012 Elsevier B.V. All rights reserved.

In order to understand the penetration process of projectiles into lower-density targets, we carry out hypervelocity impact experiments using low-density (60 mg cm(-3)) aerogel targets and various types of projectiles, and observe the track formation process in the targets using a high-speed camera. A carrot shaped track, a bulbous, and a "hybrid" one consisting of bulbous and thin parts, are formed. The results of the high-speed camera observations reveal the similarity and differences on the temporal evolution of the penetration depth and maximum diameter of these tracks. At very early stages of an impact, independent of projectile type, the temporal penetration depth is described by hydrodynamic models for the original projectiles. Afterward, when the breakup of projectiles does not occur, intact projectiles continue to penetrate the aerogels. In the case of the breakup of projectiles, the track expand: with a velocity of about a sound velocity of the aerogel at final stages. If there are large fragments, they penetrate deeper and the tracks become a hybrid type. The penetration of the large fragments is described by hydrodynamic models. Based on these results, we discuss the excavation near the impact point by shock waves. (C) 2012 Elsevier Inc. All rights reserved.

We present optical and X-ray radiographical characterization of silica aerogels with refractive index from 1.05 to 1.07 for a Cherenkov radiator. A novel pin-drying method enables us to produce highly transparent hydrophobic aerogels with high refractive index by shrinking wet-gels. In order to investigate the uniformity in the density (i.e., refractive index) of an individual aerogel monolith, we use the laser Fraunhofer method, an X-ray absorption technique, and Cherenkov imaging by a ring-imaging Cherenkov detector in a beam test. We observed an increase in density at the edge of the aerogel tiles, produced by pin-drying.

We present herein a characterization of a standard method used at the High Energy Accelerator Research Organization (KEK) to produce hydrophobic silica aerogels and expand this method to obtain a wide range of refractive index (n=1.006-1.14). We describe in detail the entire production process and explain the methods used to measure the characteristic parameters of aerogels, namely the refractive index, transmittance, and density. We use a small-angle X-ray scattering (SAXS) technique to relate the transparency to the fine structure of aerogels. (C) 2011 Elsevier B.V. All rights reserved.

A Mars Aero-flyby Sample Collection (MASC) mission has been proposed lately at Japan Aerospace Exploration Agency (JAXA). In order to improve the feasibility of this mission, the development of its sampling system during flying in the Martian dusty atmosphere to capture floating micron-sized dust particles is crucial. Since aerogel has been used as a capturing medium for micrometeoroids and space debris, it is also planned to be used for the MASC mission. In order to utilize aerogel as the capturing medium of hyperve-locity micron-sized dust particles during the Martian atmospheric flight, several unknown effects, such as aerodynamic heating of aerogel, impact on heated aerogel, and thermal alteration of micron-sized particles inside aerogel, need to be clarified. This work attempts to evaluate these effects by carrying out three types of experiments, (1) heating tests of aerogel in an arcjet wind tunnel, (2) two-stage light gas gun dust capture simulations, and (3) Van de Graaff micron-particle capture simulations. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc.

For the Belle II experiment at the superKEKB accelerator, we have been developing a proximity focusing ring imaging Cherenkov counter using silica aerogel as a radiator (ARICH). 144-channel Hybrid Avalanche Photo-Detectors (HAPD) developed with Hamamatsu Photonics K.K. were adopted as the Cherenkov photon detectors for the ARICH. We confirmed that the HAPD has sufficient performance for the ARICH photon detector by the bench test and carried out a test beam experiment with a prototype ARICH counter with six HAPDs, arranged as the actual ARICH configuration, at CERN in September 2011. As the result of the experiment, we succeeded in observing distinct Cherenkov images and confirmed that prototype ARICH had potentially 5.5σ K/π separation ability. One of our remaining concerns is radiation hardness of the HAPDs especially for γ-rays and neutrons. The HAPD is required the radiation hardness of the 10-year Belle II operation. From past studies of APDs for γ-ray and neutrons, we found the major cause of the radiation damage to the APD, and improved the structures of the APD. In order to confirm the improvement of HAPD for radiation hardness, we carried out a series of irradiation tests with various types of HAPDs using a 60Co facility and also a neutron beam facility. By understanding the reasons of the radiation damages in the APD, we have successfully improved radiation hardness of the APD by modification of electronic structure on it. In this paper, the latest status of HAPD development and the study of the radiation hardness for the HAPD are described. © 2012 IEEE.

We are developing a new Cherenkov counter using a silica aerogel for the LEPS (laser electron photon at SPring-8) experiment in order to veto background positron-electron events. The veto counter is important to investigate more interesting hadronic events. We are using aerogels with a refractive index (n) of 1.03 or 1.008 in the present counter. In this case, not only electrons but also pions are removed. For the research of pion events, it is necessary for aerogel Cherenkov counter (AC) not to remove pions. We focus on aerogels with n = 1.003 as a solution to this problem. In the current study, we propose a new AC possessing enough detection efficiency. By using this AC, only positron-electrons would be removed. © 2011 IEEE.

In modern elementary particle experiments, π/K identification is very important. In particular, a counter which works in any magnetic field is required. Currently we are working on a new silica aerogel Cherenkov counter with a wavelength shifting (WLS) fiber and a multi-pixel photon counter (MPPC, made by Hamamatsu Photonics K.K.), which is compact and resists the magnetic field. As a preliminary experiment, we performed a beam test at the LEPS (laser-electron photon at SPring-8) beam line to examine whether the WLS fiber can collect enough Cherenkov light. Based on the result, we propose to introduce new WLS fibers which increase the light yield and to construct a detection system which can collect Cherenkov light more effectively. If this new system works properly, the detection efficiency of pions is supposed to be more than 99%. © 2011 IEEE.

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. (C) 2012 Published by Elsevier B.V. Selection and/or peer review under responsibility of the organizing committee for TIPP 11.

For the Belle II experiment at the superKEKB accelerator, we have been developing a proximity focusing ring imaging Cherenkov counter using silica aerogel as a radiator (ARICH). 144-channel Hybrid Avalanche Photo-Detectors (HAPD) developed with Hamamatsu Photonics K. K. were adopted as the Cherenkov photon detectors for the ARICH. We confirmed that the HAPD has sufficient performance for the ARICH photon detector by the bench test and carried out a test beam experiment with a prototype ARICH counter with six HAPDs, arranged as the actual ARICH configuration, at CERN in September 2011. As the result of the experiment, we succeeded in observing distinct Cherenkov images and confirmed that prototype ARICH had potentially 5.5 sigma K/pi separation ability. One of our remaining concerns is radiation hardness of the HAPDs especially for gamma-rays and neutrons. The HAPD is required the radiation hardness of the 10-year Belle II operation. From past studies of APDs for gamma-ray and neutrons, we found the major cause of the radiation damage to the APD, and improved the structures of the APD. In order to confirm the improvement of HAPD for radiation hardness, we carried out a series of irradiation tests with various types of HAPDs using a Co-60 facility and also a neutron beam facility. By understanding the reasons of the radiation damages in the APD, we have successfully improved radiation hardness of the APD by modification of electronic structure on it. In this paper, the latest status of HAPD development and the study of the radiation hardness for the HAPD are described.

In this paper, we present recent progress in the development of hydrophobic silica aerogel as a Cherenkov radiator. In addition to the conventional method, the recently developed pin-drying method for producing high-refractive-index aerogels with high transparency was studied in detail. Optical qualities and large tile handling for crack-free aerogels were investigated. Sufficient photons were detected from high-performance aerogels in a beam test. (C) 2012 Published by Elsevier B. V. Selection and/or peer review under responsibility of the organizing committee for TIPP 11.

This paper presents the recent progress in the development of large-area hydrophobic silica aerogels for use as radiators in the aerogel-based ring-imaging Cherenkov (A-RICH) counter that will be installed in the forward end cap of the Belle II detector. The proximity-focusing A-RICH counter is designed to identify charged pions and kaons and to have a separation capability of more than 4 sigma at momenta up to 4 GeV/c. In a focusing-dual-layer radiator with different refractive indices, a prototype A-RICH counter satisfied the required performance using our conventional aerogel tiles with refractive indices n of 1.045 and 1.055, transmission lengths AT of 30-40 mm, and designed final dimensions of 18 x 18 x 2 cm(3). Moreover, we achieved better pi/K separation performance using n similar to 1.06 aerogels with relatively small dimensions but long transmission length (Lambda(T) > 50 mm) produced by a novel pin-drying method. We need to fill the large end cap area of 3.5 m(2) with two-layer aerogel tiles and to minimize the number of tiles with realistic dimensions to reduce the tile boundaries, at which the number of detected photoelectrons decreases. Therefore, we studied large area aerogel production by both conventional and pin-drying methods as a key to achieving high performance over the actual detector. This paper discusses the crack-free yield, optical transparency, and uniformity in refractive index within a monolith of recently produced large area aerogels.

A large number of cometary dust particles were captured with low-density silica aerogel during the NASA Stardust mission. The dust particles penetrated into the aerogel and formed various track shapes. To estimate the properties of the dust particles, such as density and size, based on the morphology of the tracks, we carried out systematic experiments testing impacts into low-density aerogel at 6 km s(-1) using projectiles of various sizes and densities. We found that the maximum track diameter and the ratio of the track length to the maximum track diameter in aerogel are good indicators of projectile size and density, respectively. Based on these results, we estimated the size and density of individual dust particles from comet 81P/Wild 2. The average density of the "fluffy" dust particles and the bulk density of all dust particles were obtained as 0.35 +/- 0.07 and 0.49 +/- 0.18 g cm(-3), respectively. These statistical data provided the content of monolithic and coarse grains in the Stardust particles, similar to 30 wt%. Combining this result with some mid-infrared observational data, we found that the content of crystalline silicates is similar to 50 wt% or more of non-volatile material.

A new hybrid avalanche photo-detector has been developed as a photon sensor for the Belle II RICH counter. Single-photon response was investigated in the presence of a magnetic field and excellent performance was demonstrated. In addition, the radiation damage due to the neutron dose was studied. By building a prototype consisting of six photo-detectors, a test beam experiment was carried out. We successfully obtained a single-photon Cherenkov resolution of 13.5 mrad with 15.3 photoelectrons and achieved a pi/K separation of more than 6 sigma at 4 GeV/c. (C) 2010 Elsevier B.V. All rights reserved.

Optical quality of silica aerogel with refractive index values greater than 1.06 has been remarkably improved by introducing a new fabrication technique, called "pinhole drying method". This technique allows to produce ultra-high index aerogel up to 1.26 with excellent transparency. The transmission length of the aerogel tile with index of 1.06, obtained with the new method, was found to be doubled compared to that with conventional production. To evaluate the optical performance as a Cherenkov radiator, a prototype RICH counter was built and a test beam experiment was carried out. A clear Cherenkov ring has been observed and significant increase in the detected light yield has been confirmed. (C) 2010 Elsevier B.V. All rights reserved.

Hydrophobic silica aerogels with ultra-low densities have been designed and developed as cosmic dust capture media for the Tanpopo mission which is proposed to be carried out on the International Space Station. Glass particles as a simulated cosmic dust with 30 _m in diameter and 2.4 g/cm³ in density were successfully captured by the novel aerogel at a velocity of 6 km/s. Background levels of contaminated DNA in the ultra-low density aerogel were lower than the detection limit of a polymerase chain reaction assay. These results show that the manufactured aerogel has good performance as a cosmic dust collector and sufficient quality in respect of DNA contamination. The aerogel is feasible for the biological analyses of captured cosmic dust particles in the astrobiological studies.

For the upgrade of the Belle detector at the KEKB collider, we are developing a proximity focusing ring imaging Cherenkov detector using a silica aerogel as a radiator. An array of 144 channel HAPD (Hybrid Avalanche Photo Detector) will be used as the photo-detector. We have measured performance of the HAPDs, and succeeded to read out single-photon signals from the HAPD using custom-made ASICs that have been developed for this purpose. We have also performed a beam test with a 2 GeV/c electron beam and demonstrated more than 4 sigma K/pi separation performance at 4 GeV/c. (C) 2010 Elsevier B.V. All rights reserved.

In modern elementary particle experiments, pi/K identification is very important. In particular, a counter which works in any magnetic field is required. Currently we are working on a new silica aerogel Cherenkov counter with a wavelength shifting (WLS) fiber and a multi-pixel photon counter (MPPC, made by Hamamatsu Photonics K.K.), which is compact and resists the magnetic field. As a preliminary experiment, we performed a beam test at the LEPS (laser-electron photon at SPring-8) beam line to examine whether the WLS fiber can collect enough Cherenkov light. Based on the result, we propose to introduce new WLS fibers which increase the light yield and to construct a detection system which can collect Cherenkov light more effectively. If this new system works properly, the detection efficiency of pions is supposed to be more than 99%.

We are developing a new Cherenkov counter using a silica aerogel for the LEPS (laser electron photon at SPring-8) experiment in order to veto background positron-electron events. The veto counter is important to investigate more interesting hadronic events. We are using aerogels with a refractive index (n) of 1.03 or 1.008 in the present counter. In this case, not only electrons but also pions are removed. For the research of pion events, it is necessary for aerogel Cherenkov counter (A C) not to remove pions. We focus on aerogels with n = 1.003 as a solution to this problem. In the current study, we propose a new AC possessing enough detection efficiency. By using this AC, only positron-electrons would be removed.

We can produce highly transparent silica aerogels with high refractive index by using the novel pin-drying method. In this paper, we present characterization studies of aerogels with refractive indices of 1.05 to 1.07 for a Cherenkov radiator. We use the laser Fraunhofer method, an X-ray absorption technique, and a ring imaging Cherenkov detector on a beam test to investigate the uniformity of density (i.e., refractive index) of an aerogel tile. We observed an increase in density at the edge of pin-dried aerogel tiles.

We can produce highly transparent silica aerogels with high refractive index by using the novel pin-drying method. In this paper, we present characterization studies of aerogels with refractive indices of 1.05 to 1.07 for a Cherenkov radiator. We use the laser Fraunhofer method, an X-ray absorption technique, and a ring imaging Cherenkov detector on a beam test to investigate the uniformity of density (i.e., refractive index) of an aerogel tile. We observed an increase in density at the edge of pin-dried aerogel tiles. © 2011 IEEE.

JAXAが検討している火星探査において，生命探査を行う意義について述べ，具体的方法を提案した。

微生物の惑星間移動および地球外有機物の地球への伝搬を検証するための宇宙実験「たんぽぽ」について，その目的と準備状況について述べた。

A new hybrid avalanche photo-detector has been developed for the Belle RICH counter. The basic features of this device were examined with and without a magnetic field. By constructing a RICH prototype counter using 6 photo-detectors, we carried out a test beam experiment to confirm the performance. We obtained a single photon Cherenkov angle resolution of 12.8 mrad with 4.6 photoelectrons in our experimental setup, demonstrating that 4 sigma pi/K separation at 4 GeV/c was achieved. (C) 2010 Elsevier B.V. All rights reserved.

We have succeeded in developing hydrophobic silica aerogels over a wide range of densities (i.e. refractive indices). A pinhole drying method was invented to make possible producing highly transparent aerogels with entirely new region of refractive indices of 1.06-1.26. Obtained aerogels are more transparent than conventional ones, and the refractive index is well controlled in the pinhole drying process. A test beam experiment was carried out in order to evaluate the performance of the pinhole-dried aerogels as a Cherenkov radiator. A clear Cherenkov ring was successfully observed by a ring imaging Cherenkov counter. We also developed monolithic and hydrophobic aerogels with a density of 0.01 g/cm(3) (a low refractive index of 1.0026) as a space dust capturer for the first time. Consequently, aerogels with any refractive indices between 1.0026 and 1.26 can be produced freely. (C) 2010 Elsevier B.V. All rights reserved.

For the Belle II experiment, we are developing a proximity focusing ring imaging Cherenkov counter using a silica aerogel as a radiator. Recently, a new aerogel fabrication method, called pin-hole drying, was invented and remarkably improved optical transparency has been realized in the region of refractive index larger than 1.05. For the photo-detector, we have developed a 144-channel Hybrid Avalanche Photo-Detector with Hamamatsu Photonics K. K. The HAPD has excellent single photon detection performance, 5 5 mm2 position resolution and immunity to magnetic field. The tolerance to the neutron irradiation up to 5 1011 neutron/cm2 has been confirmed. In November 2009, we have performed a test beam experiment at KEK for a prototype A-RICH counter with 6 HAPDs and aerogel tiles produced by the pin-hole drying method. We successfully observed a clear Cherenkov ring image and obtained the single photon Cherenkov angle resolution of 13.5 mrad and 15.3 detected photoelectrons. This result corresponds to more than 6 K/ separation at 4 GeV/c and fulfills the requirement for the Belle II. © 2010 IEEE.

For the Belle-II detector, we are conducting R&amp D on proximity focusing ring imaging Cherenkov (RICH) detector using a silica aerogel as a radiator. A 144-channel HAPD (Hybrid Avalanche Photo Detector) is adopted as a photo-detector for the Aerogel-RICH. Because the typical gain of HAPDs is lower than conventional photomultipliers, we need high-gain and low-noise electronics for readout of the HAPD. In addition, the electronics system should be sufficiently compact. For these reasons, we have designed and fabricated readout chips for the HAPD signal processing, based on ASIC (Application Specific Integrated Circuit) technique. We performed a test beam experiment of a prototype Aerogel RICH counter. In this test, it is found that Cherenkov rings are well reconstructed with the developed electronics system, and the ASIC shows excellent performance to be used for the aerogel RICH system. A present concern is a neutron tolerance of HAPDs. We have been studying how much possible radiation damage caused by neutrons can be reduced by optimizing the ASIC parameters without decreasing sensitivity for Cherenkov photons. It has been found that the radiation damage by neutrons considered in the Belle-II can be cured by shortening the shaping time of the amplifier in the ASIC. In this paper, we will report the performance of the ASIC chips that were used in the beam test and new version that is under development will be also explained. © 2010 IEEE.

For the Belle-II experiment, a proximity focusing RICH counter with silica aerogel radiator will be employed as a new particle identifier in the forward endcap region. The detector makes use of a novel radiator concept, a multilayer radiator stack in a focusing configuration. The central element of the counter is a reliable single photon detector which can be operated at 1.5 T, has a sufficiently fine granularity and compact size. A novel hybrid avalanche photo-detector (HAPD) has been developed with Hamamatsu to satisfy these conditions. We have studied the device on the bench, and in beam tests, and have shown that it can be successfully operated in a high axial magnetic field.

For the Belle II experiment, we are developing a proximity focusing ring imaging Cherenkov counter using a silica aerogel as a radiator. Recently, a new aerogel fabrication method, called "pin-hole drying", was invented and remarkably improved optical transparency has been realized in the region of refractive index larger than 1.05. For the photo-detector, we have developed a 144-channel Hybrid Avalanche Photo-Detector with Hamamatsu Photonics K. K. The HAPD has excellent single photon detection performance, 5 x 5 mm(2) position resolution and immunity to magnetic field. The tolerance to the neutron irradiation up to 5 x 10(11) neutron/cm(2) has been confirmed. In November 2009, we have performed a test beam experiment at KEK for a prototype A-RICH counter with 6 HAPDs and aerogel tiles produced by the "pin-hole drying" method. We successfully observed a clear Cherenkov ring image and obtained the single photon Cherenkov angle resolution of 13.5 mrad and 15.3 detected photoelectrons. This result corresponds to more than 6 sigma K/pi separation at 4 GeV/c and fulfills the requirement for the Belle II.

For the Belle-II detector, we are conducting R&D on proximity focusing ring imaging Cherenkov (RICH) detector using a silica aerogel as a radiator. A 144-channel HAPD (Hybrid Avalanche Photo Detector) is adopted as a photo-detector for the Aerogel-RICH. Because the typical gain of HAPDs is lower than conventional photo-multipliers, we need high-gain and low-noise electronics for readout of the HAPD. In addition, the electronics system should be sufficiently compact. For these reasons, we have designed and fabricated readout chips for the HAPD signal processing, based on ASIC (Application Specific Integrated Circuit) technique. We performed a test beam experiment of a prototype Aerogel RICH counter. In this test, it is found that Cherenkov rings are well reconstructed with the developed electronics system, and the ASIC shows excellent performance to be used for the aerogel RICH system. A present concern is a neutron tolerance of HAPDs. We have been studying how much possible radiation damage caused by neutrons can be reduced by optimizing the ASIC parameters without decreasing sensitivity for Cherenkov photons. It has been found that the radiation damage by neutrons considered in the Belle-II can be cured by shortening the shaping time of the amplifier in the ASIC. In this paper, we will report the performance of the ASIC chips that were used in the beam test and new version that is under development will be also explained.

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. (C) 2009 Elsevier B.V. All rights reserved.

We have developed the new production methods of silica aerogel with the refractive indices between 1.15 and 1.25. Since the velocity of the photoelectric electron from the 511keV photon is 0.866c and the maximum velocity of the Compton electron is 0.8c, only photoelectric electrons occurs the Cherenkov light inside the radiator with n-1.2. We are constructing the simple prototype PET detectors using these silica aerogels. Since there are no efficiency for the Compton events, the pulse height measurements are not need. The data acquisition system becomes very simple. ©2009 IEEE.

We have developed the new production methods of silica aerogel with the refractive indices between 1.15 and 1.25. Since the velocity of the photoelectric electron from the 511keV photon is 0.866c and the maximum velocity of the Compton electron is 0.8c, only photoelectric electrons occurs the Cherenkov light inside the radiator with n similar to 1.2. We are constructing the simple prototype PET detectors using these silica aerogels. Since there are no efficiency for the Compton events, the pulse height measurements are not need The data acquisition system becomes very simple.

In the LEPS (Laser Electron Photon at Spring-8) experiment [1], we use a photon beam which is generated through laser induced backward Compton scattering with the circulating 8GeV electron beam in the synchrotron radiation ring. The energy range of the photons is between about 1.5 GeV and 3.0 GeV, and the typical intensity is 10(6) photons/sec. This photon beam makes a huge number of electron-positron pairs, which prevents us to study hadronic events we are interested in. In order to exclude the pair creation events, we use a silica aerogel Cherenkov counter. Since we can handle only 10(3) events/see by the DAQ at most, the event rate must be reduced by three orders of magnitude using the aerogel counter as the veto at the trigger level.

A proximity focusing RICH using aerogel as a Cherenkov radiator has been developed for the upgrade of the Belle detector. We have considered the idea to accumulate multiple aerogel radiators so that Cherenkov photons front each tile organize a unified ring image on a photo-detector plane. Advancing this idea, we have developed aerogel in which the refractive index varies continuously. We report the production method of the silica aerogel with refractive index gradient and he result of test beam experiment.

We have been developing a proximity focusing ring imaging Cherenkov counter (RICH) with aerogel radiator, to extend the hadron identification capabilities in the forward endcap region of the Belle detector at the KEK B factory. This paper presents our recent studies on possible improvement of the RICH performance by using precise timing information. Cherenkov photons emitted in the aerogel radiator as well as in the entrance window of the PMT were used for the time-of-flight (TOF) measurement. A beam test using the Burle 85011 MCP PMT showed an excellent resolution of about 3 5 ps for Cherenkov photons from the PMT window. Such TOF measurement would supplement the RICH performance, and allow to positively identify particles below the Cherenkov threshold in aerogel, such as kaons and protons in the region around 1 GeV/c. (C) 2008 Elsevier B.V. All rights reserved.

Highly transparent silica aerogel has been developed for a Cherenkov radiator in a RICH detector to be installed into the Belle forward end-cap apparatus. We have improved the aerogel optical properties for a wide range of refractive indices around 1.03-1.07. The parameters that control a synthesis process in the aerogel production were successfully optimized, and the obtained transmission length for this index range was almost doubled. A prototype was constructed using newly produced aerogel samples in order to carry out a test beam experiment, and a remarkable increase in the Cherenkov light yield was confirmed. The uniformity of refractive index in an aerogel block was examined using an X-ray tomography device and the deviation was found to be sufficiently small. Furthermore, the production of a monolithic aerogel consisting of two layers with different refractive indices is also described. (C) 2008 Elsevier B.V. All rights reserved.

In the LEPS (Laser Electron Photon at Spring-8) experiment [1], we use a photon beam which is generated through laser induced backward Compton scattering with the circulating 8GeV electron beam in the synchrotron radiation ring. The energy range of the photons is between about 1.5 GeV and 3.0 GeV, and the typical intensity is 106 photons/sec. This photon beam makes a huge number of electron-positron pairs, which prevents us to study hadronic events we are interested in. In order to exclude the pair creation events, we use a silica aerogel Cherenkov counter. Since we can handle only 103 events/sec by the DAQ at most, the event rate must be reduced by three orders of magnitude using the aerogel counter as the veto at the trigger level. ©2008 IEEE.

A proximity focusing RICH using aerogel as a Cherenkov radiator has been developed for the upgrade of the Belle detector. We have considered the idea to accumulate multiple aerogel radiators so that Cherenkov photons from each tile organize a unified ring image on a photo-detector plane. Advancing this idea, we have developed aerogel in which the refractive index varies continuously. We report the production method of the silica aerogel with refractive index gradient and he result of test beam experiment ©2008 IEEE.

It is need threshold type Cherenkov counters with the refractive index of about 1.1 to identify protons from kaons and pions in the momentum range of 1-2 GeV/c in a trigger stage. There were no materials having such refractive indices in ordinary temperature and ordinary pressure. But we found the production method of silica aerogel with high refractive indices. (2005NSS N14-191) By our research and development works of two years, production parameters were modified and transmission length at the wavelength of 400nm achieved more than 20mm at index range of 1.08&lt n&lt 1.25. We will perform the beam test experiments with the electron beams (LNS, Tohoku Univ.) in May and September, and the proton beams (HIMAC, NIRS) in this autumn. We will report the results in this presentation. © 2007 IEEE.

A proximity focusing RICH with aerogel radiator has been studied to extend the pion-kaon separation power in the forward region of the Belle spectrometer. Such a proximity focusing RICH counter is also a very fast detector, in particular if a micro-channel plate (MCP) PMT is used as the photon detector. With its excellent timing properties, the same device could also serve as a time-of-flight counter and thus supplement other identification methods, in particular for low momentum tracks. Cherenkov photons emitted in the radiator medium (aerogel) as well as in the entrance window of the PMT could be used for the time-of-flight measurement. A prototype of this novel device using BURLE 85011 64-anode, microchannel plate PMT, was tested on the bench and in the test beam at KEK. Excellent performance of this counter could be demonstrated. In particular, a good separation of pions and protons was observed in the test beam data with a time-of-flight resolution of about 35 ps (rms) for Cherenkov photons produced in the PMT window. ©2006 IEEE.

A proximity focusing RICH using aerogel as the Cherenkov radiator is being developed as a new particle identification device for the Belle detector upgrade. A prototype counter was constructed with recently produced aerogel samples, arranged in a focusing configuration, and a test beam experiment was carried out in order to evaluate the performance of the apparatus. With this device we have achieved a ir-K separation that exceeded 5σ at 4 GeV/c, with ≈ 9 detected photoelectrons per track. We have also studied the influence of various parameters like radiator refractive index combinations on the performance of the apparatus. © 2006 IEEE.