M. Koike

THE LARGE-ACCEPTANCE SPECTROMETER TAGX FOR PHOTOREACTION STUDIES AT THE 1.3-GEV TOKYO ELECTRON SYNCHROTRON

Abstract The study of photoreactions on light nuclei with the TAGX spectrometer started in 1987 using the 20% duty-cycle tagged-photon beam at the 1.3-GeV Tokyo electron synchrotron. TAGX is comprised of a π-sr magnetic spectrometer for detection of charged pions, kaons, and protons and a 0.85-sr time-of-flight spectrometer for neutrons. It has served in the past eight years as a unique medium-energy-resolution multi-particle spectrometer for coincidence experiments to detect such final states as pn, pp, π + π − , ppn, pp − , and pn π + π − : some of which were kinematically-complete measurements of three-particle and four-particle final states. Details of the detector components, their performance, data acquisition, event reconstruction analyses, and detector-acceptance calculations are described together with the results of experience acquired in those experiments. A TAGX improvement in the momentum resolution required for charged particle measurements in the 1-GeV photon energy region is also reported.

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.

High-count rate position-sensitive detectors for synchrotron radiation experiments

Abstract This paper describes several X-ray position-sensitive detectors developed for use in high-count rate experiments at synchrotron radiation sources; (1) a charge-integrating position-sensitive proportional counter, (2) an amorphous silicon photodiode array as an X-ray PSD, (3) a MWPC with a multiple delay-line encoder and (4) a MWPC with carbon-fiber anode wires. The performance of the detectors is demonstrated in two examples of the application: a time-resolved measurement of a kinetic diffraction diagram from contracting muscle and a two-dimensional diffraction measurement of a powder crystal are presented.

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.

Measurement of the 4He (γ, npp) n reaction in the Δ-resonance region

Abstract This is the first kinematically complete measurement of the 4He(γ, npp)n reaction in the energy range of 135–455 MeV. The ordered-momentum spectra and the double-differential cross sections are compared with the calculations which assume that photons are absorbed either on two- (np or pp), three- (npp), or four-nucleon systems. The ordered-momentum spectra below 400 MeV are reproduced well by pp and/or npp absorption but not by np absorption only.

A digital divider with extension bits for position-sensitive detectors

Abstract Digitizing errors produced in a digital divider for position-sensitive detectors have been reduced by adding extension bits to data bits. A relation between the extension bits and the data bits to obtain perfect position uniformity is also given. A digital divider employing 10 bit ADCs and 6 bit extension circuits has been constructed.

The total cross section for the 4He (γ, npp)n reaction in the Δ-resonance region

Abstract This is the first measurement of the total cross section σ( 4 He (γ npp)n) in the range of 135–455 MeV. The σ, which cannot be reproduced by any model, has similar E γ dependence to γ T (γ 4 He → all channels). The averaged ratio σ( 4 He(γ, npp)n)/ σ T (γ 4 He → all channels) = (2.3 ± 0.3)% is compared with a cascade-model calculation in which quasi-free pion production followed by pion reabsorption is assumed.

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.

A step-like rise in the 4He(γ,pn)2H cross section near the pion-production threshold

Abstract A kinematically complete 4He(γ,pn)2H measurement was carried out in the photon energy (Eγ) range 145–425 MeV. The total cross section (σα) forms a prominent structure whose peak lies at Eγ ∼ 245 MeV (the pnd invariant mass of 3960 MeV/c2). The ratio σ α σ d , where σd is the deuteron photodisintegration cross section, shows a step-like rise to a value of 6 at Eγ ∼ 140 MeV.

Simultaneous measurement of 3He(γ, pπ±) yields and model implications

Abstract 3 He(γ, pπ ± ) reactions are simultaneously measured for tagged photon energies of 380 ⩽ Eγ ⩽ 700 MeV. The yield ratio for the two channels, under the same kinematical and dynamical conditions, is found to be 0.90±0.07. Implications of this ratio in terms of the delta component in the ground state of 3He are examined. An alternate interpretation of this ratio as due to an admixture of isospin T = 1 2 and 3 2 transition amplitudes in a pure isovector interaction is also presented.