28831321
Implementation of automatically sorting events with the Hough transformation for the DCBA experiment
The DCBA (Drift Chamber Beta-ray Analyzer) experiment is being conducted at KEK for experimentally confirming the neutrinoless double beta decay (0vßß). We have focused our attention on the charged-particle tracks in DCBA experiment, and proposed to use the Hough transformation in sorting events for analyzing the tracks quickly and efficiently. The Hough transformation is one of the methods used in general for detecting circles and lines in pictures. In this article, we report the present status of the sorting event method using the Hough transformation.
34322075
Development of 3D tracking detectors in the DCBA experiment for studies of double beta decays
DCBA(Drift Chamber Beta-ray Analyzer) experiment is aiming to search for neutrinoless double beta decay (0νββ). The DCBA detector is a momentum analyzer to measure individual electron energy from double beta decays. Since 0νββ is extremely rare, the detector must be low background and accommodate a lot of decays source. And also the excellent energy resolution is required at the Q-value to distinguish 0νββ from two-neutrino double beta decay (2νββ). The DCBA detector consists of drift chambers, a magnet and cosmic-ray veto counters. A test prototype DCBA-T2 has been constructed and operated with natural Mo source containing 9.6% 100Mo in order to solve operation problems. Another new prototype called DCBA-T3 is under construction at KEK. DCBA-T3 will have better performance than DCBA-T2 in view points of the energy resolution and the source accommodation volume. The results of the DCBA-T2 test operation and the DCBA-T3 status are described together with the future plan temporarily called Magnetic Tracking Detector (MTD), which is designed based on the experiences of DCBA-T2 and T3.
8370976
Fokker-Planck Models of Star Clusters with Anisotropic Velocity Distributions III. Multi-Mass Clusters
The evolution of globular clusters driven by two-body relaxation is investigated by means of numerical integration of the two-dimensional Fokker-Planck equation in energy--angular momentum space. The two- dimensional Fokker-Planck equation allows the development of velocity anisotropy. We include a spectrum of stellar masses in this paper. The radial anisotropy develops, that is, the radial velocity dispersion exceeds the tangential one, in the outer halo of multi-mass clusters as in single-mass clusters. However, the evolution of the velocity anisotropy depends significantly on the stellar mass in some cases. In fact the tangential velocity dispersion becomes dominant around the half-mass radius for massive components in clusters with a steep mass function. The development of this tangential anisotropy is closely related to the initial cooling of the massive components toward energy equipartition. Our simulation results indicate that multi-mass anisotropic King-Michie models are not always appropriate for describing the velocity anisotropy in globular clusters.
16812190
NUMERICAL EXAMINATION OF THE STABILITY OF AN EXACT TWO-DIMENSIONAL SOLUTION FOR FLUX PILE-UP MAGNETIC RECONNECTION
The Kelvin-Helmholtz (KH) and tearing instabilities are likely to be important for the process of fast magnetic reconnection that is believed to explain the observed explosive energy release in solar flares. Theoretical studies of the instabilities, however, typically invoke simplified initial magnetic and velocity fields that are not solutions of the governing magnetohydrodynamic (MHD) equations. In the present study, the stability of a reconnecting current sheet is examined using a class of exact global MHD solutions for steady state incompressible magnetic reconnection, discovered by Craig & Henton. Numerical simulation indicates that the outflow solutions where the current sheet is formed by strong shearing flows are subject to the KH instability. The inflow solutions where the current sheet is formed by a fast and weakly sheared inflow are shown to be tearing unstable. Although the observed instability of the solutions can be interpreted qualitatively by applying standard linear results for the KH and tearing instabilities, the magnetic field and plasma flow, specified by the Craig-Henton solution, lead to the stabilization of the current sheet in some cases. The sensitivity of the instability growth rate to the global geometry of magnetic reconnection may help in solving the trigger problem in solar flare research.
16053728
A detailed observational study of molecular loops 1 and 2 in the galactic center
Fukui et al. (2006) discovered two molecular loops in the Galactic center that are likely created by the magnetic flotation due to the Parker instability with an estimated field strength of ∼150 µG. Following the discovery, we present here a detailed study of the two loops based on NANTEN 12 CO(J=1–0) and 13 CO(J=1–0) datasets. The two loops are located in l = 355 ◦ – 359 ◦ and b = 0 ◦ – 2 ◦ at a velocity range of -20 – -180 km s −1 . They have a projected total length of ∼ 600 pc and heights of ∼250 – 300 pc from the Galactic disk at a distance of 8.5 kpc. They have loop-like filamentary distributions of 30 pc width and show bright foot points in the 12 CO emission in the edges of the loops at b ∼ 0.8 ◦ – 1.0 ◦ . These foot points are characterized by velocity dispersions of 50 – 100 km s −1 , much larger than those in the Galactic disk, supporting that the loops are located in the Galactic center within ∼1 kpc of Sgr A*. The loops also show large-scale velocity gradients of ∼30 – 50 km s −1 per ∼100 pc. We present an attempt to determine geometrical parameters and velocities of the loops by assuming that the loops having the same size are expanding and rotating at a constant radius R. The analysis yields that the loops are rotating at 50 km s −1 and expanding at 150 km s −1 at a radius of 670 pc from the center.
16609476
The Disruption of Globular Star Clusters in the Galaxy: A Comparative Analysisbetween Fokker-Planck and N-Body Models
Recent N-body simulations have shown that there is a serious discrepancy between the results of the N-body simulations and the results of Fokker-Planck simulations for the evolution of globular and rich open clusters under the influence of the galactic tidal field. In some cases, the lifetime obtained by Fokker-Planck calculations is more than 1 order of magnitude smaller than those obtained by N-body simulations. In this Letter, we show that the principal cause for this discrepancy is an oversimplified treatment of the tidal field used in previous Fokker-Planck simulations. We performed new Fokker-Planck calculations using a more appropriate implementation of the boundary condition of the tidal field. The implementation is only possible with anisotropic Fokker-Planck models, while all previous Fokker-Planck calculations rely on the assumption of isotropy. Our new Fokker-Planck results agree well with N-body results. Comparison of the two types of simulations gives a better understanding of the cluster evolution.
17562975
Fokker-Planck Models of Star Clusters with Anisotropic Velocity Distributions II. Post-Collapse Evolution
The evolution of a spherical single-mass star cluster is followed in detail up to core collapse by numerically solving the orbit-averaged two-dimensional Fokker-Planck equation in energy-angular momentum space. Velocity anisotropy is allowed in the two-dimensional Fokker-Planck model. Using improved numerical codes, the evolution has been followed until the central density increased by a factor of $10^{14}$ with high numerical accuracy. The numerical results clearly show self-similar evolution of the core during the late stages of the core collapse. When Plummer's model is chosen as the initial condition, the collapse time is about 17.6 times the initial half-mass relaxation time. This is longer than the collapse time for the isotropic model by about 13%. As the result of strong relaxation in the core, the halo becomes to be dominated by radial orbits. The degree of anisotropy monotonically increases as the radius increases.