T. Sumiyoshi

Study of a threshold Cherenkov counter based on silica aerogels with low refractive indices

Abstract To identify π ± and K ± in the region of 1.0−2.5 GeV/ c , a threshold Cherenkov counter equipped with silica aerogels has been investigated. Silica aerogels with a low refractive index of 1.013 have been successfully produced using a new technique. By making use of these aerogels as radiators, we have constructed a Cherenkov counter and checked its properties in a test beam. The results obtained demonstrated that our aerogel was transparent enough to make up for loss of the Cherenkov photon yield due to a low refractive index. Various configurations for the photon collection system and some types of photomultipliers, such as the fine-mesh type, for a read out were also tested. From these studies, our design of a Cherenkov counter dedicated to π K separation up to a few GeV/ c with an efficiency greater than 90% was considered.To identify π ± and K ± in the region of 1.0 ∼ 2.5 GeV/c, a threshold Cherenkov counter equipped with silica aerogels has been investigated. Silica aerogels with a low refractive index of 1.013 have been successfully produced using a new technique. By making use of these aerogels as radiators, we have constructed a Cherenkov counter and have checked its properties in a test beam. The obtained results have demonstrated that our aerogel was transparent enough to make up for loss of the Cherenkov photon yield due to a low refractive index. Various configurations for the photon collection system and some types of photomultipliers, such as the fine-mesh type, for a read out were also tested. From these studies, our design of a Cherenkov counter dedicated to π/K separation up to a few GeV/c with an efficiency greater than 90 % was considered. 1 Introduction Recently, asymmetric e + e − colliders with high luminosities to explore CP violation in B meson system(B-factory) have been proposed[1, 2]. In a B-factory detector, an identification of the particle species is an important issue. In particular, the separation of π ± and K ± in the momentum region of 1.0 ∼ 2.5 GeV/c is indispensable for studying many B meson decay channels[1]. For this purpose, Cherenkov counter equipped with silica aerogels having a low refractive index is one of the most promising devices since it has been widely used in high energy experiments[3]. Furthermore, the use of an aerogel Cherenkov counter enables us to reduce the material for a particle identification device which is located in front of an electromagnetic calorimter. The requirements imposed on our aerogel Cherenkov counter are: (i) The refractive index of aerogel(n) should be in the 1.010 ∼ 1.015 range in order to to achieve a π/K separation capability in the region of 1.0 ∼ 2.5 GeV/c. (ii) The optical transparency of the aerogel should be high. Notice that Cherenkov photons emitted by an injected particle becomes significantly small in our case because the Cherenkov light yields are proportional to 1 − 1/n 2. Therefore, the loss of photons in the aerogel due to absorptions and scatterings should be minimized. (iii) Efficient photon collection and detection under a

Silica aerogels in high energy physics

Abstract Low-refractive-index silica aerogel is the most convenient radiator for threshold Cherenkov counters, used for particle identification in high energy physics. For the BELLE detector at the KEK B-Factory we have produced about 2 m 3 of hydrophobic silica aerogels of n =1.01–1.03. Particle identification capability of the aerogel Cherenkov counters was tested and 3 σ pion/proton separation has been achieved at 3.5 GeV/c. Radiation hardness of the aerogels was confirmed to 9.8 Mrad. Thanks to the improved transparency, aerogels prepared by the two-step method can be used as radiators for not only threshold type but also for Ring Imaging type Cherenkov counters.

Measurement of R and search for new heavy quarks in e+e- annihilation at 50 and 52 GeV centre-of-mass energies

Abstract The total cross section for the process of the e+e- annihilation into hadrons has been measured at the centre-of-mass energies of 50 GeV and 52 GeV and a search has been made for new heavy quarks. The ratios R = σ(e+e- → hadrons)/σpoint(e+e- → μ+μ-) obtained are 4.4±0.5 at 50 GeV and 4.7±0.3 at 52 GeV, respectively. An additional systematic uncertainty is 10%. From the event shape analysis we found no evidence for a new quark with charge 2 3 e .

Beam tests of a Fast-RICH prototype with VLSI readout electronics

Abstract In this report we discuss the Fast Ring Imaging Cherenkov technique that we have developed for application to proximity-focused LiF (or CaF2) solid radiator and multiwire chamber photon detector with cathode-pad readout using TEA in CH4 as photosensor. We describe the full-scale Prototype of 12 000 pads (5.334 × 6.604 mm2) we have built, and briefly the dedicated VLSI readout electronics we have developed. We report in detail the investigations we have performed in a hadron test beam at the CERN PS, and compare the results obtained to the expected performances. The maximum momentum for π/K separation at 3σ achieved in these tests is 2.86 GeV/c for LiF (2.39 GeV/c for CaF2). The experimentally achieved Cherenkov merit factors, after correction for azimuthal angle acceptance, are N0 = 65.5 cm−1 (57.7 cm−1), to be compared with 53.8 cm−1 (50.2 cm−1) from Monte Carlo calculations. Operation of the detector over several months has proven the technique reliable and robust, and suitable for application in high-luminosity hadron colliders like LHC, as well as e+e− B-Factories like KEK (Japan), SLAC (USA), and Cornell (USA).

Feasibility Study of Single-Photon Counting Using a Fine-mesh Phototube for an Aerogel Readout

The fine-mesh phototube is one type of photodetector which can be used under a strong magnetic field. For an aerogel readout, the single-photon detection efficiency should be close to 100% in order to identify particle species. We carried out a feasibility study of single-photon counting using fine-mesh phototubes, and obtained a possible solution.The fine-mesh phototube is one type of photodetector which can be used under a strong magnetic field. For an aerogel readout, the single-photon detection efficiency should be close to 100% in order to identify particle species. We carried out a feasibility study of single-photon counting using fine-mesh phototubes, and obtained a possible solution.

Performance of the VENUS lead-glass calorimeter at TRISTAN

Abstract The initial performance of the VENUS barrel electromagnetic calorimeter at TRISTAN is described. The calorimeter is composed of 5160 lead-glass counters in a semi-tower arrangement. An energy resolution of 3.8% was obtained for 26 GeV Bhabha events. The neutral pions in the hadronic events were reconstructed with a mass resolution of σ = 16 MeV. The gain of the lead-glass counters was stable within 2% during a four months operation at TRISTAN.

Measurement of the proton-antiproton pair production from two-photon collisions at TRISTAN

Abstract The cross section of the γγ → p p reaction was measured at two-photon center-of-mass energy (Wγγ) between 2.2 and 3.3 GeV, using the two-photon process at an e+e− collider, TRISTAN. The Wγγ dependence of the cross section integrated over a c.m. angular region of | cos θ ∗ | is in good agreement with the previous measurements and the theoreticalv prediction based on diquark model in the high Wγγ region.

STUDY ON FINE-MESH PMTS FOR DETECTION OF AEROGEL CHERENKOV LIGHT

Abstract Most recent fine-mesh photomultipliers (FM-PMTs), with 19 dynode stages, have been tested for application to a threshold aerogel Cherenkov counter. Two properties, the gain and the pulse height resolution, have been particularly studied in a magnetic field of up to 1.5 T. The obtained results show that a FM-PMT is a suitable device for detection of aerogel Cherenkov light.

Monte-Carlo simulation for an aerogel Cherenkov counter

We have developed a Monte-Carlo simulation code for an aerogel v Cerenkov Counter which is operated under a strong magnetic field such as 1.5T. This code consists of two parts: photon transportation inside aerogel tiles, and one-dimensional amplification in a fine-mesh photomultiplier tube. It simulates the output photoelectron yields as accurately as 5% with only a single free parameter. This code is applied to simulations for a B-Factory particle-identification system.Abstract We have developed a Monte-Carlo simulation code for an aerogel Cherenkov counter which is operated under a strong magnetic field such as 1.5T. This code consists of two parts: photon transportation inside aerogel tiles, and one-dimensional amplification in a fine-mesh photomultiplier tube. It simulates the output photo-electron yields as accurately as 5% with only a single free parameter. This code is applied to simulations for a B-factory particle identification system.

Determination of the QCD scale parameter ΛMS with QCD cascade on the basis of the next-to-leading logarithmic approximation

Abstract The relative production ratio of 3-jet events to the total number of hadronic events was studied in e+e− annihilations at centre-of-mass energies between 54 and 61.4 GeV. The QCD scale parameter has been determined to be Λ MS =254 −47 +55 ±56 MeV on the basis of a QCD cascade with the next-to-leading logarithmic approximation.