arXiv subjects

Y. Watanabe

Publications and source records attributed to Y. Watanabe.

60 records · Page 4Linked to original sources

arXiv2003

Semiclassical Distorted Wave Model Analysis of Backward Proton Emission from $(p,p^{\prime}x)$ Reactions at Intermediate Energies

A semiclassical distorted wave (SCDW) model with Wigner transform of one-body density matrix is presented for multistep direct $(p,p^{\prime}x)$ reactions to the continuum. The model uses Wigner distribution functions obtained in methods which include nucleon-nucleon correlations to a different extent, as well as Woods-Saxon (WS) single-particle wave function. The higher momentum components of target nucleons that play a crucial role in reproducing the high-energy part of the backward proton spectra are properly taken into account. This SCDW model is applied to analyses of multistep direct processes in $^{12}$C$(p,p^{\prime}x)$, $^{40}$Ca$(p,p^{\prime}x)$ and $^{90}$Zr$(p,p^{\prime}x)$ in the incident energy range of 150--392 MeV. The double differential cross sections are calculated up to three-step processes. The calculated angular distributions are in good agreement with the experimental data, in particular at backward angles where the previous SCDW calculations with the WS single-particle wave function showed large underestimation. It is found that the result with the Wigner distribution function based on the coherent density fluctuation model provides overall better agreement with the experimental data over the whole emission energies.

nucl-th↗

arXiv2000

Design, fabrication and measurement of the first rounded damped detuned accelerator structure (RDDS1)

As a joint effort in the JLC/NLC research program, we have developed a new type of damped detuned accelerator structure with optimized round-shaped cavities (RDDS). This paper discusses some important R&D aspects of the first structure in this series (RDDS1). The design aspects covered are the cell design with sub-MHz precision, HOM detuning, coupling and damping technique and wakefield simulation. The fabrication issues covered are ultra-precision cell machining with micron accuracy, assembly and diffusion bonding technologies to satisfactorily meet bookshelf, straightness and cell rotational alignment requirements. The measurements described are the RF properties of single cavities and complete accelerator section, as well as wakefields from the ASSET tests at SLAC. Finally, future improvements are also discussed.

physics.acc-ph↗

arXiv2000

Fabrication Process of Rounded Damped Detuned Structure

Following the successful design and fabrication of Damped Detuned Structures (DDS), the JLC/NLC linear collider project advanced to Rounded Damped Detuned Structures (RDDS) with curved cross section of the cavity shape for increased shunt impedance. Various advanced techniques for fabricating RDDS1 disks comparing to those for DDS were established to satisfy the dimension accuracy of +-1 micron over the entire surface made by ultra-precision turning. These disks were assembled with almost the same stacking and bonding jigs and processes as those of DDS3 assembly. In consequence, the assembly showed little disk-to-disk misalignment within 1 micron before and after the process. Though, it had 200 micron smooth bowing, which was subsequently corrected as DDS3, and flares at both ends.

hep-ex↗

arXiv2000

Meeting Tight Frequency Requirement of Rounded Damped Detuned Structure

Following successful design and fabrication of damped detuned structures, the R&D for the accelerating structures of the NLC/JLC linear collider project proceeded to studies of Rounded Damped Detuned Structure with curved cross section of the cavity shape for increased shunt impedance. The important features of the structure are the accurately tuned accelerating mode frequency and the distribution of the first dipole modes smooth and close to the design distribution. These requirements were met based on the high-accuracy diamond turning with its capability to realize the periphery tolerance of two microns. The lowest dipole mode frequencies scattered by 0.6 MHz RMS. The error in the accelerating mode frequency averaged over a structure was 0.1 MHz by applying a feed-forward method.

hep-ex↗

arXiv1995

Study of the levels in $^{17}$C above the $^{16}$C + neutron threshold

The $β$-delayed neutron decay of $^{17}$B was studied using a radioactive ion beam. The neutron energies, measured via time-of-flight, give information on states in $^{17}$C above the $^{16}$C + neutron threshold. States in $^{17}$C were found at excitation energies of 2.25(2) MeV, 2.64(2) MeV and 3.82(5) MeV, and possibly at 1.18(1) MeV. These low lying states are of possible interest for nuclear physics as well as for astrophysics.

nucl-ex↗

arXiv1995

A search for massive neutral bosons in orthopositronium decay

We have searched for an exotic decay of orthopositronium into a single photon and a short-lived neutral boson in the hitherto unexplored mass region above 900 ${\rm keV}/{\it c}^{2}$, by noting that this decay is one of few remaining candidates which could explain the discrepancy of the orthopositronium decay-rate. A high-resolution measurement of the associated photon energy spectrum was carried out with a germanium detector to search for a sharp peak from this two-body decay. Our negative result provides the upper-limits of\mbox{ }$2.0 \times 10^{-4}$ on the branching ratio of such a decay in the mass region from 847 to 1013 ${\rm keV}/{\it c}^{2}$, and excludes the possibility of this decay mode explaining the discrepancy in the orthopositronium decay-rate.

hep-ex↗