S. Kurokawa

Overview of the KEKB accelerators

An overview of the KEKB accelerators is given as an introduction of the following articles in this issue, first by summarizing the basic features of the machines, and then describing the improvements of the performance since the start of the physics experiment.

Search for a rare decay mode K+ → π+νv and axion

Abstract Using stopped kaons, rare decay modes K + → π + ν v and K + → π + a 0 is the light pseudoscalar meson (axion), have been measured. The upper bound of the branching ratio was found to be 1.4 × 10 −7 for K + → π + ν v and 3.8 × 10 −8 for K + → π + a 0 .

Search for a Rare Decay Mode K+ ---> pi+ Neutrino anti-neutrino and Axion

Abstract Using stopped kaons, rare decay modes K + → π + ν v and K + → π + a 0 is the light pseudoscalar meson (axion), have been measured. The upper bound of the branching ratio was found to be 1.4 × 10 −7 for K + → π + ν v and 3.8 × 10 −8 for K + → π + a 0 .

Radiation damage of BGO crystals due to low energy γ rays, high energy protons and fast neutrons

Abstract Results are presented on the effects of radiation on BGO crystals. It is shown that BGO has more than two orders of magnitude higher resistance against low energy γ rays than SF5 lead glass. Darkening of the crystal is hardly visible even after an irradiation of 3.6 × 10 6 R. The darkening faded by more than one half after several days and it has almost completely disappeared after much longer periods. The tolerable rate of synchrotron radiation on BGO calorimeters is 100 R/h in a conservative estimate if the degradation in transmittance is required to be less than 1 % over a depth of 20 radiation lengths. In BGO calorimeters, the degradation of scintillation efficiency is less important than that of the transmittance, 99.999% pure crystals have a two orders of magnitude better resistance than 99.99% pure ones. Sample darkening caused by 12 GeV protons or fast neutrons is an order of magnitude more severe than that by low energy γ rays. Moreover, the recovery is not complete even after a period of more than 100 days. Some data on sample activation are also presented.

Search for narrow peaks in inclusive π0 spectra from pp annihilation at rest

Abstract By using modularized NaI(Tl) detectors, we carried out a high statistics measurement of inclusive π0 spectra from p p annihilation at rest. We did not observe any narrow π0 peaks arising from baryonium production, p p →π 0 B . The σ upper limit of the yield varied between 10−2 and 10−4 depending on the mass and oncharge multiplicity. Three narrow peaks at 2 σ levels were seen at approximately the same masses as in the previous measurement of p p → γ B .We also derived the yield of p p annihilation into π0M forM = o, η′, ω, ϱ0, η and π0.

The TRISTAN control system

The 8 GeV accumulation ring and the 30 GeV main ring of TRISTAN, an accelerator-storage ring complex at KEK, are controlled by a highly computerized control system. Twenty-four minicomputers are linked by optical fiber cables to form an N-to-N token ring network. The transmission speed on the cables is 10 Mbps. From each minicomputer, a CAMAC serial highway extends to the controlled equipment. At present, twenty minicomputers are connected to the network and are used to control the accumulation ring. The software system is based on the NODAL language devised at the CERN SPS. The KEK NODAL system retains main features of the original NODAL: the interpretive scheme, the multi-computer programming facility, and the data-module concept. In addition, it has the following features: (1) fast execution due to the compiler-interpreter method, (2) a multi-computer file system (3), a full-screen editing facility, and (4) a dynamic linkage scheme for data modules and NODAL functions. The accelerators are operated through five operator consoles, each of which is managed by one minicomputer in the network. An operator console contains two 20-inch high-resolution color graphic displays, a pair of touch-panels, and ten small TV monitors. One touch-panel is used to select a program and a piece of equipment to be controlled; the other is used mainly to perform the console actions.

A new experimental limit for the decay K+ → π+γγ

Abstract A search for K + → π + γ, π + γγ, π + γγγ was made detecting pions from stopped kaons in the kinetic energy region between 117 MeV and 127 MeV. New Limits of 1.4 ×10 −6 , 8.4 × 10 −6 and 1.0 × 10 −4 for the branching ratio were obtained assuming a phase-space spectrum on the pion energy. The first limit also aplies to another process K + → π + + a, where a is a light meson with mass smaller than 100 MeV/ c 2 and decays into n γs with lifetime less than 10 −9 s.

A bismuth germanate scintillator as a total absorption shower detector

Abstract A bismuth germanate crystal (BGO; 58 mm in diameter, 120 mm in length) was irradiated by 35–175 MeV positrons, in order to examine the possibility of its use in high energy experiments. The energy resolution (fwhm) varies from 32% at 35 MeV to 13.5% at 175 MeV. Uniformity of the light yield with respect to the longitudinal and transverse positions is excellent, when measured with a collimated γ ray from 132 Cs.

Search for narrow states by detection of monochromatic gamma rays in p̄p annihilation at rest

Abstract An inclusive γ ray spectrum in pp annihilation at rest has been measured with modularized NaI(Tl) detectors with statistics several times higher than before. The aim of the experiment was to search for baryonium B in pp → γB by detection of narrow lines in the γ ray spectrum. We have not observed any narrow state B with yield greater than 1.5 × 10 −3 per annihilation and with statistical significance higher than 2σ.

Low-energy separated beam K3 at KEK

The design and the performance of the K3 beam at the KEK 12 GeV Proton Synchrotron are reported. The beam line provides separated kaons up to a maximum momentum of 0.8 GeV/c and separated antiprotons up to 1.1 GeV/c. The beam can be operated in two different modes: a high-intensity mode, K3-S, and a high-momentum-resolution mode, K3-L. The solid-angle momentum acceptance and the beam length of K3-S are 48.4 msr Δ PP and 14.45 m, respectively, and those of K3-L are 13.3 msr%ΔPP and 16.3 m. Measured optical parameters of K3-S agreed with the designed values. Measured intensity of K+ per 1012 protons and the π+μ+e+K ratio were 1.96 × 104 and 4.2 at 500 MeV/c, 3.12 × 104 and 3.0 at 540 MeV/c, and 5.18 × 104 and 2.6 at 600 MeV/c.