S. Kasai

Bio: S. Kasai is an academic researcher from Hiroshima University. The author has contributed to research in topics: Synchrotron & Spectrometer. The author has an hindex of 6, co-authored 8 publications receiving 66 citations.

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.

Total cross section for the γ d → π − pp reaction between 380 and 840 MeV

Abstract: The total cross section for the \ensuremath{\gamma}d\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$pp reaction has been measured for incident photon energies from 380 to 840 MeV in steps of 10 MeV, with the best energy resolution attained so far. A large-acceptance detector was used to observe the reaction products. Overall uncertainties in the deduced cross sections are less than 9% (\ensuremath{\sim}4% statistical and \ensuremath{\sim}8% systematic). The results are in excellent agreement with previous bubble chamber measurements and do not show any statistically significant structure which can be interpreted as evidence for the formation of dibaryon resonances. An upper limit at 95% confidence level of ${\mathrm{\ensuremath{\sigma}}}_{\mathrm{peak}}$\ensuremath{\Gamma}230 \ensuremath{\mu}b MeV is obtained for a resonance in the vicinity of photon energy 700 MeV (mass\ensuremath{\sim}2490 MeV).

The reaction γ +d → π+ + π− +p + n between 570 and 850 MeV andΔ ++ Δ − production

Abstract: The reaction γ+d → π++π−+p + n has been measured in a kinematically complete way at incident photon energies from 570 to 850 MeV in steps of 40 MeV. From detailed comparison of measured data with results of event simulations, it is concluded that three different mechanisms, the quasi-free, double-delta and phase space productions, contribute to the reaction. Each of the cross sections corresponding to these mechanisms is determined separately.

Detection of recoil electrons in triplet photoproduction

Abstract: In order to study the feasibility of a new type of gamma-ray polarimeter, we have constructed a scintillation counter system for detecting the recoil electrons in the triplet photoproduction. It has been tested by using tagged photons in the energy range between 120 and 400 MeV and proved to be capable of identifying the triplet photoproduction events with recoil electron momenta between 1.92 and 10 MeV/c.

A honeycomb sandwich structure vacuum jacket for cryogenic targets

Abstract: Cryogenic targets (H 2 , D 2 and 4 He) have been built for use in the study of photonuclear reactions with a π sr spectrometer, TAGX, at the 1.3 GeV Tokyo electron synchrotron. A new type of vacuum jacket, fabricated from plastic honeycomb core and Mylar skins, has been used in the target system for more than 5000 hours. The average radiation thickness and the average density of this jacket are measured to be 3.3 × 10 −3 X 0 and 0.15 g/cm 3 , respectively.

The CEBAF large acceptance spectrometer (CLAS)

Abstract: The CEBAF large acceptance spectrometer (CLAS) is used to study photo- and electro-induced nuclear and hadronic reactions by providing efficient detection of neutral and charged particles over a good fraction of the full solid angle. A collaboration of about 30 institutions has designed, assembled, and commissioned CLAS in Hall B at the Thomas Jefferson National Accelerator Facility. The CLAS detector is based on a novel six-coil toroidal magnet which provides a largely azimuthal field distribution. Trajectory reconstruction using drift chambers results in a momentum resolution of 0.5% at forward angles. Cherenkov counters, time-of-flight scintillators, and electromagnetic calorimeters provide good particle identification. Fast triggering and high data-acquisition rates allow operation at a luminosity of 10 34 nucleon cm −2 s −1 . These capabilities are being used in a broad experimental program to study the structure and interactions of mesons, nucleons, and nuclei using polarized and unpolarized electron and photon beams and targets. This paper is a comprehensive and general description of the design, construction and performance of CLAS.

Double pion photoproduction on nucleon and deuteron

Abstract: Photoproduction of two pions on nucleon and deuteron is studied for photon energies from threshold up to Eγ = 1.5 GeV. For the elementary operator an effective Lagrangian approach is used with resonance and Born contributions. The model parameters are fixed by resonance decay widths and multipole analyses of single-pion photoproduction. A satisfactory description of total cross sections of two-pion production on the proton for various charge channels is achieved, except for π0π0 production for which a significant underestimation is found near threshold. The operator then serves for the evaluation of this reaction on the deuteron in the impulse approximation. In addition, NN rescattering in the final state is taken into account, but πN and ππ rescatterings are neglected. Results are presented for total cross sections and target asymmetries.

Incoherent pion photoproduction on the deuteron in the first resonance region

Abstract: Incoherent pion photoproduction on the deuteron is studied in the first resonance region. The unpolarized cross section, the beam asymmetry, and the vector and tensor target asymmetries are calculated in the framework of a diagrammatic approach. Pole diagrams and one-loop diagrams with $\mathit{NN}$ scattering in the final state are taken into account. An elementary operator for pion photoproduction on the nucleon is taken in various on-shell forms and calculated using the SAID and MAID multipole analyses. Model dependence of the obtained results is discussed in some detail. A comparison with predictions of other works is given. Although a reasonable description of many available experimental data on the unpolarized total and differential cross sections and photon asymmetry has been achieved, in some cases a significant disagreement between the theory and experiment has been found. Invoking known information on the reactions $\ensuremath{\gamma}d\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}d$ and $\ensuremath{\gamma}d\ensuremath{\rightarrow}\mathit{np}$ we predict the total photoabsorption cross section for deuterium. We find that our values strongly overestimate experimental data in the vicinity of the \ensuremath{\Delta} peak.