M. Takasaki

Radiation damage in silicon microstrip detectors

Abstract A radiation damage effect on silicon strip detectors of pn-junction type is investigated using a high energy proton beam. In order to clarify the cause of leakage current increase, several variations of strip detectors with different surface structures were made and tested. No appreciable differences in leakage current increase are observed among these samples. A strong temperature dependence on leakage current is observed. This can be explained by a formation of radiation induced trap energy levels in the bulk silicon. A moderate room temperature annealing is seen. A pulse height degradation of about 10–20% is observed at a few Mrad of radiation. Some implications of the present results are discussed for possible application of silicon semiconductor detectors in future high energy hadron colliders.

Precision positioning of SuperKamiokande with GPS for a long-baseline neutrino oscillation experiment

Abstract A positioning of the neutrino detector SuperKamiokande (SK) was made for a long-baseline neutrino oscillation experiment planned at KEK. For positioning, Global Positioning System (GPS) was employed. It has been demonstrated that GPS is of practical use for measuring the positions of SK and KEK, being 250 km distance from each other, to a better resolution. The geodetic coordinates at the SK center were obtained to be Lat. 36°25′32.5862″ N., Long. 137°18′37.1241″ E., H. 371.839 m in the global ellipsoidal coordinate system, WGS-84. The obtained coordinates are based on the coordinates given at a triangulation point at the KEK site. The present work will be fed back for constructing the neutrino beam line.

Optical design of beam lines at the KEK-PS new experimental hall

Abstract A new counter experimental hall [K.H. Tanaka et al., IEEE Trans. Magn. 28 (1992) 697] was designed and constructed at the KEK 12-GeV Proton Synchrotron (KEK-PS). The extracted proton beam from the KEK-PS is introduced to the new hall through the newly-prepared primary beam line, EP1, and hits two production targets in cascade. The upstream target provides secondary particles to the low momentum ( 0.4–0.6 GeV c ) separated beam line, K5, and the downstream target is connected to the medium momentum (0.6–2.0 GeV/c) separated beam line, K6. Several new ideas were employed in the beam optical designs of EP1, K5 and K6 in order to increase the number and the purity of the short-lived secondary particles, such as kaons and pions, under the limited energy and intensity of the primary protons provided by the KEK-PS. These new ideas are described in this paper as well as the first commissioning results.

New monochromatic muon beam channel using two body decay K+ → μ+v at rest in a production target

Abstract A new type of monochromatic μ + beam channel of high resolution was designed and constructed at the KEK 12 GeV proton synchrotron (KEK-PS). The principle of the channel is to transport 236 MeV/ c μ + emitted in the two body at rest decay of positive kaons, K + → μ + v , in the production target as a beam. In order to eliminate background μ + from in-flight π + decay, the channel has the following features. Firstly, the μ + beam is extracted at a backward angle of 147° from the direction of the 12 GeV primary proton beam, where the π + yield is relatively small. Secondly, the distance from the production target to the first bending magnet is designed to be as short as possible. Thirdly, the high momentum resolution of the beam channel also enables us to observe a very sharp peak in the μ + momentum spectrum, so that the background is efficiently subtracted. The typical intensity of the 236 MeV/ c monochromatic μ + is 3500 per 10 12 incident protons on a thin Pt target. The signal-to-background ratio finally achieved at the peak momentum was 60. This pure Kμ 2 muon beam was successfully utilized for an experiment designed to search for V + A currents in the weak interaction from a precise determination of the μ + longitudinal polarization.

The low-energy antiproton beam K4 at the KEK 12 GeV proton synchrotron

Abstract The beam K4 is designed to transport high-intensity, high-purity antiprotons in the momentum range between 0.4 and 0.8 GeV/c. Antiprotons are separated from unwanted pions, muons, and electrons by double-stage mass separation. The solid-angle momentum acceptance of the beam is 34.1 msr % ΔP P and the beam length is 28.5 m. The measured intensities of antiprotons at 450, 500, 580 and 650 MeV/c are 100, 210, 510 and 1100 per 1012 ppp; the corresponding π − μ − e − p ratios are 13.1, 7.7, 8.8 and 22.5, respectively. About 45% of the incomming antiprotons at 580 MeV stop or annihilate in flight in liquid hydrogen contained in a target cell with the dimension of 140 mm in diameter and 230 mm in length.

Neutron beam line at the KEK 12-GeV PS

A neutron beam line has been constructed at the KEK-proton synchrotron. Neutrons have been produced by the disintegration reactions of deuterons in a 6 cm thick beryllium target. Deuteron beams of 2–6 GeV have provided neutron beams of 1–3 GeV. The neutron flux increases with the deuteron energy. The typical beam intensities obtained were 1 × 108, 2 × 108, and 3 × 108 neutrons per 1011 deuterons of 2, 4, and 6 GeV, respectively. The neutron-momentum width, Δpp, was measured to be (4 ± 1) % in sigma at 1 GeV.

A superconducting secondary beam line in the 12 GeV proton synchrotron at KEK

Abstract Design and performance of a superconducting high energy secondary beam line, π1, are reported. The π1 beam line was constructed to transport an 8 GeV/c unseparated secondary beam to the experimental area of the 12 GeV proton synchrotron at KEK. The beam line has been operated for five years without any serious problems and was shut down in the summer of 1986. We describe its design, construction and operational results.

Present status of beam lines at KEK

The present status of the beam lines at KEK 12 GeV proton synchrotron is given. The accelerator recently has achieved successful operation to accelerate protons up to 10.4 GeV at the latest run. The time schedule of construction and the program of experiments are also given. A 4 GeV/c unseparated beam, π2, has been just installed at the internal targe area. A beam, Kl, up to 6 GeV/c from the fast extracted proton beam for the bubble chamber experiments is at the final stage of construction. Two experiments with the π2 beam and two experiments with the bubble chamber beam are approved for the initial phase of experiements. These experiments are expected to start in the middle of 1977. Two low momentum separated kaon beams, K2 and K3, up to 2 GeV/c as well as the splitting system of the slow extracted protons are now at the final stage of design and the construction has been partially started. The completion of these beam lines is scheduled in the spring of 1979. Three experiments utilizing the kaon beams a...

Magnet power supplies and beam line control for the KEK experimental halls

Abstract This paper describes the control system for magnet power supplies and many beam lines in two experimental halls at the 12 GeV proton synchrotron at KEK. In the experimental halls, many beam lines have been constructed, cleared away or modified every year since 1974. With this experience, in order to reduce construction time, cost, maintenance and manpower, we are now using a distributed control system, with the following features: - each power supply is equipped with a microprocessor and communications interface, - each beam line has an independent control system, - each beam line controller is connected to a central controller, providing a unified system.

CRYOGENIC SYSTEM OF 8-GeV/c PION BEAM LINE AT KEK

A cryogenic system of 8-GeV/c pion beam line, in which four superconducting bending magnets are installed, has been constructed at the KEK 12 GeV proton synchrotron and successfully operated for several months. This paper describes the components, the performance and the long term operation experience of the cryogenic system of 700W/200l/h at 4.4K.