T. Omori

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.

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.

Modularized NaI(Tl) detectors in a half barrel configuration

We have constructed a modularized array of NaI(Tl) detectors in a half barrel configuration that is about 75 cm long with an inner radius of 25 cm. 96 NaI modules are surrounded by a layer of 48 modules of scintillating glass which have similar dimensions to the NaI modules. Each NaI crystal was shaped as a trapezoidal pyramid and encapsulated in a 1 mm thick aluminium container with dimensions of (43 × 94) × (110 × 94) × 377 mm3. The construction and performance are described along with the gain calibration and monitoring, the beam position sensitivity, the scattering between modules, etc. The fwhm energy resolution of a 5 × 5 array of NaI modules varied from 6.5% for incident electrons at 100 MeV to 3.6% at 1000 MeV

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.

Self-supporting cylindrical multiwire proportional chambers with two dimensional read-out

Abstract Cylindrical MWPCs have been constructed with anode diameters of 240–430 mm and a length of 750 mm. Cathode strips run helically with 38°–61° to the anode wires, and the induced charges were read out by ADC. Both the anode and the cathode efficiency were well above 99%. The resolution (σ) for the longitudinal position of the avalanche was 0.6 mm by the centre of gravity method, if the cathode was read out per 12 mm width by summing two adjacent cathode strips.

Performance of a scintillator glass calorimeter for 10.1–84.3 MeV photons

The performance of a scintillator glass (type: SCG1) calorimeter has been studied with tagged photons in the energy range from 10.1 to 84.3 MeV. The energy resolution (fwhm) is given as a function of the incident photon energy, 0.087√E(GeV), where E is the energy of the photons. The detection efficiency is 100% above a photon energy of 16.9 MeV. The results are compared with those of a lead glass (SF6) and an NaI(Tl) scintillator.

Liquid Hydrogen and Deuterium Target for Antiproton Annihilation at Rest

A 3.3 l liquid hydrogen and deuterium target cell of diameter 140 mm and length 230 mm constructed from 0.2 mm-thick stainless-steel sheet was used for an experiment on the annihilation of antiprotons at rest in the KEK 12 GeV Proton Synchrotron. The target cell was mounted deep inside the detector system, and the whole target system was designed for safety in case of breakage of the target cell, because the detector was contained in an enclosed room. The liquid level in the cell could be monitored well with carbon resistors distributed on its outer surface.

Antiproton-nucleon Annihilation into π oM and ηM with M=η, ω, ρ, and π in Antiproton-deuterium Annihilation at Rest

Using modularized NaI(Tl) detectors, we carried out a high-statistics measurement of inclusive π o and η spectra in antiproton annihilation at rest in a liquid D 2 target. We obtained the following two-meson yields (branching ratios) per \bar p N ( N = p or n ) annihilation: 0.19± 0.09% for π o ω, 1.07±0.19% for π o ρ o , 0.057±0.018% for π o η, 0.0123±0.0055% for π o π o , 0.02±0.02% for π o ρ - , 0.202±0.031% for π o π - , 0.49±0.12% for ηω, 0.45±0.15% for ηρ o , and 0.91±0.22% for ηρ - .

A large silicon detector to measure the antiproton range in a liquid hydrogen target

Abstract A large solid state detector Si(Li) has been developed for a low energy antiproton beam monitor. The size of the detector developed is 3 mm in thickness and 98 mm in diameter. The energy resolution is 50 keV (FWHM) for 976 keV electrons from a 207 Bi source. The stopping position of the incident antiproton in a liquid hydrogen target is determined for every event with an accuracy of 1.35 cm (σ) from the d E /d x information of the detector. Details of the characteristics of the solid detector are also described.

Performance of a BGO calorimeter below 1.6 GeV

Abstract An array of 7 bismuth germanate (BGO) modules, each being 17 or 20 cm long and having a hexagonal cross section with 50 mm across the parallel edges, has been tested with 0.2–1.6 GeV/ c electrons and pions. The fwhm energy resolution for 1 GeV electrons was 4.1% in agreement with the EGS calculations. The e/π separation for momentum analyzed particles at 1 GeV/ c was 1 500 with only the energy cut, and was improved to 1 2000 with an additional cut in the lateral energy spread. Finally a calorimeter has been constructed of 10 BGO modules surrounded with NaI slabs and successfully employed in KEK Experiment E68 to measure the γ ray energy spectrum in p p annihilation at rest. A fwhm resolution of 10% was obtained for 129 MeV γ rays.