arXiv subjects
Publications and source records attributed to S. Ogawa.
We present the result of a search for charge asymmetry in B^+ -> J/psi K^+ decays. The CP-violating charge asymmetry is measured to be A_CP(B^+ -> J/psi K^+) = [-0.76 +/- 0.50 (stat) +/- 0.22 (syst)]%.
We report a first measurement of inclusive B -> X_s eta decays, where X_s is a charmless state with unit strangeness. The measurement is based on a pseudo-inclusive reconstruction technique and uses a sample of 657 x 10^6 BB-bar pairs accumulated with the Belle detector at the KEKB e^+e^- collider. For M_{X_s} < 2.6 GeV/c^2, we measure a branching fraction of (26.1 +/- 3.0 (stat) +1.9 -2.1 (syst) +4.0 -7.1 (model)) x 10^-5 and a direct CP asymmetry of A_{CP} = -0.13 +/- 0.04 +0.02 -0.03. Over half of the signal occurs in the range M_{X_s} > 1.8 GeV/c^2.
The concept of low-voltage depletion and accumulation of electron charge in semiconductors, utilized in field-effect transistors (FETs), is one of the cornerstones of current information processing technologies. Spintronics which is based on manipulating the collective state of electron spins in a ferromagnet provides complementary technologies for reading magnetic bits or for the solid-state memories. The integration of these two distinct areas of microelectronics in one physical element, with a potentially major impact on the power consumption and scalability of future devices, requires to find efficient means for controlling magnetization electrically. Current induced magnetization switching phenomena represent a promising step towards this goal, however, they relay on relatively large current densities. The direct approach of controlling the magnetization by low-voltage charge depletion effects is seemingly unfeasible as the two worlds of semiconductors and metal ferromagnets are separated by many orders of magnitude in their typical carrier concentrations. Here we demonstrate that this concept is viable by reporting persistent magnetization switchings induced by short electrical pulses of a few volts in an all-semiconductor, ferromagnetic p-n junction.
This report summarises the conclusions from the detector group of the International Scoping Study of a future Neutrino Factory and Super-Beam neutrino facility. The baseline detector options for each possible neutrino beam are defined as follows: 1. A very massive (Megaton) water Cherenkov detector is the baseline option for a sub-GeV Beta Beam and Super Beam facility. 2. There are a number of possibilities for either a Beta Beam or Super Beam (SB) medium energy facility between 1-5 GeV. These include a totally active scintillating detector (TASD), a liquid argon TPC or a water Cherenkov detector. 3. A 100 kton magnetized iron neutrino detector (MIND) is the baseline to detect the wrong sign muon final states (golden channel) at a high energy (20-50 GeV) neutrino factory from muon decay. A 10 kton hybrid neutrino magnetic emulsion cloud chamber detector for wrong sign tau detection (silver channel) is a possible complement to MIND, if one needs to resolve degeneracies that appear in the $δ$-$θ_{13}$ parameter space.
We have studied charged nuclear fragments produced by 200 - 400 MeV/nucleon carbon ions, interacting with water and polycarbonate, using a newly developed emulsion detector. Total and partial charge-changing cross sections for the production of B, Be, and Li fragments were measured and compared with both previously published measurements, and model predictions. This study is of importance for validating and improving carbon ion therapy treatment planning systems, and for estimating the radiological risks for personnel on space missions, since carbon is a significant component of the Galactic Cosmic Rays.
A proximity focusing ring imaging Cherenkov detector, with the radiator consisting of two or more aerogel layers of different refractive indices, has been tested in 1-4 GeV/c pion beams at KEK. Essentially, a multiple refractive index aerogel radiator allows for an increase in Cherenkov photon yield on account of the increase in overall radiator thickness, while avoiding the simultaneous degradation in single photon angular resolution associated with the increased uncertainty of the emission point. With the refractive index of consecutive layers suitably increasing in the downstream direction, one may achieve overlapping of the Cherenkov rings from a single charged particle. In the opposite case of decreasing refractive index, one may obtain well separated rings. In the former combination an approximately 40% increase in photon yield is accompanied with just a minor degradation in single photon angular resolution. The impact of this improvement on the pion/kaon separation at the upgraded Belle detector is discussed.
A proximity focusing ring imaging Cherenkov detector using aerogel as the radiator has been studied for an upgrade of the Belle detector at the KEK-B-factory. We constructed a prototype Cherenkov counter using a 4 x 4 array of 64-channel flat-panel multi-anode PMTs (Hamamatsu H8500) with a large effective area. The aerogel samples were made with a new technique to obtain a higher transmission length at a high refractive index (n=1.05). Multi-channel PMTs are read-out with analog memory chips. The detector was tested at the KEK-PS pi2 beam line in November, 2002. To evaluate systematically the performance of the detector, tests were carried out with various aerogel samples using pion beams with momenta between 0.5 GeV/c and 4 GeV/c. The typical angular resolution was around 14 mrad, and the average number of detected photoelectrons was around 6. We expect that pions and kaons can be separated at a 4 sigma level at 4 GeV/c.
We study numerically the reconnection of quantized vortices and the concurrent acoustic emission by the analysis of the Gross-Pitaevskii equation. Two quantized vortices reconnect following the process similar to classical vortices; they approach, twist themselves locally so that they become anti-parallel at the closest place, reconnect and leave separately.The investigation of the motion of the singular lines where the amplitude of the wave function vanishes in the vortex cores confirms that they follow the above scenario by reconnecting at a point. This reconnection is not contradictory to the Kelvin's circulation theorem, because the potential of the superflow field becomes undefined at the reconnection point. When the locally anti-parallel part of the vortices becomes closer than the healing length, it moves with the velocity comparable to the sound velocity, emits the sound waves and leads to the pair annihilation or reconnection; this phenomena is concerned with the Cherenkov resonance. The vortices are broken up to smaller vortex loops through a series of reconnection, eventually disappearing with the acoustic emission. This may correspond to the final stage of the vortex cascade process proposed by Feynman. The change in energy components, such as the quantum, the compressible and incompressible kinetic energy is analyzed for each dynamics. The propagation of the sound waves not only appears in the profile of the amplitude of the wave function but also affects the field of its phase, transforming the quantum energy due to the vortex cores to the kinetic energy of the phase field.
We have observed $23.2 \pm 6.0_{-0.9}^{+1.0}$ purely-leptonic decays of $D_s^+ -> μ^+ ν_μ$ from a sample of muonic one prong decay events detected in the emulsion target of Fermilab experiment E653. Using the $D_s^+ -> ϕμ^+ ν_μ$ yield measured previously in this experiment, we obtain $B(D_s^+ --> μ^+ ν_μ) / B(D_s^+ --> ϕμ^+ ν_μ) =0.16 \pm 0.06 \pm 0.03$. In addition, we extract the decay constant $f_{D_s}=194 \pm 35 \pm 20 \pm 14 MeV$.