On the Connection Between the Stability of Multidimensional Positive Systems and the Stability of Switched Positive Systems

In this work, we study the connection of the stability of multidimensional positive systems with the stability of switched positive systems. In a previous work, we showed that the stability of a multidimensional positive system implies the stability of a related switched positive system. Here, we investigate the reciprocal implication

The monitoring system for the aerogel Cherenkov counter of the BELLE detector

We report on a design and performances of a monitoring system developed for the aerogel Cherenkov counters (ACC) of the BELLE detector. The system consists of blue LEDs, a diffuser box, and optical distributors which distribute the LED light to the ACC modules. The employed LED (NSPB series) has been observed to have high reliability on the long term stability and the temprature dependence. The diffuser box is employed to reduce the intrinsic non-uniformity of the LED light intensity. The overall performances of the present monitoring system on uniformity and intensity of the light output have been found to satisfy all the requirements for the monitoring.Comment: 24 pages, LaTeX, 13 eps figures, to be published in Nucl. Instrum. and Meth. A. Postscript file (4.5 MB) is available at http://www-hep.phys.saga-u.ac.jp/~murakami/paper/xxx_accmon.p

Results of the Excitation Test of the LHD Helical Coils Cooled by Subcooled Helium

Large helical device, the largest superconducting stellarator, has been operated for the research of fusion plasma since 1998. The toroidal field of almost 3 T is produced by a pair of pool-cooled helical coils, in the innermost layers of which a normal-zone had been induced several times at the bottom of the coil at higher currents than 11.0 kA. Since the field is not the highest there, the local cooling conditions are probably deteriorated by bubbles gathered by buoyancy. In order to improve the cryogenic stability by subcooling, an additional cooler with two-stage cold compressors was installed at the inlet of the coil in 2006. The inlet and outlet temperatures of the coils were successfully lowered to 3.2 K and 3.8 K, respectively, with a mass flow of 50 g/s. In spite of a half charging rate to reduce AC losses, a normal-zone was induced near the top of the coil at 11.45 kA. It propagated to one side and stopped near the inner equator, where the field is the highest. In comparison with the stability tests with a model coil, the local temperatures of the innermost layers near the top is considered to have been raised up to almost the saturated temperature of 4.4 K by charging. The excitation method was revised to waiting cool-down at 11.0 kA, and the excitations up to 11.5 kA have been attained

Monte-Carlo Simulation for an Aerogel Cherenkov Counter

We have developed a Monte-Carlo simulation code for an aerogel \v Cerenkov Counter which is operated under a strong magnetic field such as 1.5T. This code consists of two parts: photon transportation inside aerogel tiles, and one-dimensional amplification in a fine-mesh photomultiplier tube. It simulates the output photoelectron yields as accurately as 5% with only a single free parameter. This code is applied to simulations for a B-Factory particle-identification system.Comment: 40 pages, latex(article), 19 figure

Backward-angle photoproduction of π0\pi^0 mesons on the proton at EγE_\gamma = 1.5--2.4 GeV

Differential cross sections and photon beam asymmetries for $\pi^0$ photoproduction have been measured at $E_\gamma$ = 1.5--2.4 GeV and at the $\pi^0$ scattering angles, --1 $<$ cos$\Theta_{c.m.} <$ --0.6. The energy-dependent slope of differential cross sections for $u$-channel $\pi^0$ production has been determined. An enhancement at backward angles is found above $E_\gamma$ = 2.0 GeV. This is inferred to be due to the $u$-channel contribution and/or resonances. Photon beam asymmetries have been obtained for the first time at backward angles. A strong angular dependence has been found at $E_\gamma >$ 2.0 GeV, which may be due to the unknown high-mass resonances.Comment: 12 pages, 4 figures, submitted to PL

Near-threshold Lambda(1520) production by the gamma p -> K+Lambda(1520) reaction at forward K+ angles

Differential cross sections and photon-beam asymmetries for the gamma p -> K+ Lambda(1520) reaction have been measured with linearly polarized photon beams at energies from the threshold to 2.4 GeV at 0.6<cos(theta)<1. A new bump structure was found at W=2.11 GeV in the cross sections. The bump is not well reproduced by theoretical calculations introducing a nucleon resonance with J<=3/2. This result suggests that the bump might be produced by a nucleon resonance possibly with J>=5/2 or by a new reaction process, for example an interference effect with the phi photoproduction having a similar bump structure in the cross sections.Comment: 5 pages, 4 figures, published in Phys. Rev. Let

Measurement of the γ⃗p→K+Λ\vec{\gamma} p \to K^+ \Lambda Reaction at Backward Angles

Cross sections for the $\gamma p \to K^+ \Lambda$ have been measured at backward angles using linearly polarized photons in the range 1.50 to 2.37 GeV. In addition, the beam asymmetry for this reaction has been measured for the first time at backward angles. The $\Lambda$ was detected at forward angles in the LEPS spectrometer via its decay to $p\pi^-$ and the K^+ was inferred using the technique of missing mass. These measurements, corresponding to kaons at far backward angles in the center-of-mass frame, complement similar CLAS data at other angles. Comparison with theoretical models shows that the reactions in these kinematics provide further opportunities to investigate the reaction mechanisms of hadron dynamics.Comment: 6 figures, submitted to PRC rapid communication

Forward coherent ϕ\phi-meson photoproduction from deuterons near threshold

Differential cross sections and decay asymmetries for coherent $\phi$-meson photoproduction from deuterons were measured for the first time at forward angles using linearly polarized photons at $E_{\gamma}$= 1.5-2.4 GeV. This reaction offers a unique way to directly access natural-parity Pomeron dynamics and gluon exchange at low energies. The cross sections at zero degrees increase with increasing photon energy. The decay asymmetries demonstrate a complete dominance of natural-parity exchange processes, showing that isovector unnatural-parity $\pi$-meson exchange is small. Nevertheless the deduced cross sections of $\phi$-mesons from nucleons contributed by isoscalar t-channel exchange processes are not well described by the conventional Pomeron model.Comment: 14 pages, 6 figures. Final published versio