R. Enomoto

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

Aerogel Cherenkov counter for the BELLE detector

In the BELLE experiment at the KEK B-factory, a threshold aerogel Cherenkov counter, with refractive index from 1.010 to 1.030, is used to provide p/K separation in the momentum region up to 3.5 GeV/c. The detector system has been constructed, installed into the BELLE detector, and then commissioned with cosmic rays and beams. This paper presents a brief explanation of the detector system and its performance obtained in early BELLE physics runs. ( 2000 Elsevier Science B.V. All rights reserved.

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 the inclusive cross section of jets in γγ interactions at TRISTAN

Abstract We have investigated the properties of jet production in almost real γγ collisions at √s=58 GeV with the TOPAZ detector at the TRISTAN e+e− collider. The data were analyzed with a jet-clustering method based on a cone algorithm. The jet rate shows evidence for a hard scattering effect of the hadronic constituents of a photon (resolved photon processes). We have also observed a substantial energy flow in the small-angle region, which is additional evidence for resolved photon processes. We present the transverse momentum dependence of the inclusive jet and two-jet cross sections and compare them with different model predictions.

Measurement of inclusive particle spectra and test of MLLA prediction in e+e− annihilation at s=58Gev

Abstract Inclusive momentum spectra are measured for all charged particles and for each of π ± , K ± , K 0 K 0 , and p p in hadronic events produced via e + e − annihilation at s =58 Gev . The measured spectra are compared with QCD predictions based on the modified leading log approximation (MLLA). The MLLA model reproduces the measured spectra well. The energy dependence of the peak positions of the spectra is studied by comparing the measurements with those at other energies. The energy dependence is also well described by the MLLA model.

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.

Search for SUSY Particles in e+ e- Annihilation at Tristan

Abstract The TOPAZ detector has accumulated about 11 pb−1 of data in the energy range s =52−57 GeV . Charged supersymmetric particles have been searched for. Assuming the photino to be massless, we place limits on the chargino of m χ GeV , on the scalar muon, tau, and quark of m μ GeV , m τ GeV , and m q GeV . The scalar electron can be excluded up to a mass of ∼ 28 GeV. Other cases are examined.

Measurement of the D ± Cross Section using a Soft-Pion Analysis in Two-Photon Processes

Abstract The differential cross section of dσ(e + e − → e + e − D ∗± X) dP T was measured using a soft-pion analysis D ∗± → π s ± D 0 (D 0 ) at TRISTAN. The average s was 58.7 GeV and the integrated luminosity used in this analysis was 198 pb − , respectively.

Direct CP violation in B meson decays via ϱ-ω interference

Abstract We investigate B ±,0 → ϱ 0 ( ω ) h ±,0 , where ϱ 0 ( ω ) decays to π + π − and h is any hadronic final state, such as π or K . We find large direct CP asymmetry in B meson decays via ϱ-ω interference. A possible method to determine weak phases, such as φ 2 = arg ( (V ud V ub ∗ ) (V td V tb ∗ ) ) and φ 3 = arg ( (V us V ub ∗ ) (V ts V tb ∗ ) ) , is also discussed. We show the feasibility to detect the CP asymmetries in these channels by assuming an asymmetric e + e − collider experiment. 10 9 B B events are required for the detection of this effect.

Measurement of the photon structure function F2γ and jet production at TRISTAN

Abstract We have measured the photon structure function F2γ in the reaction e+e− → e+e− hadrons for average Q2 values from 5.1 to 338 GeV2 by using data collected by the TOPAZ detector at TRISTAN. The data have been corrected for detector effects and are compared with theoretical expectations based on QCD. The structure function F2γ increases as ln Q2, as expected. A sample of events with one or two distinct jets has been identified in the final state. Although two-jet events can be explained solely by the point-like perturbative part, one-jet events require a significant hadron-like part in addition.