54716814
Performance of KEKB with crab cavities
20 years after they were initially proposed, in February 2007 crab cavities are for the first time installed in an operating collider, KEKB. The commissioning of KEKB with crab cavities is reported, and the performance of the collider is compared with the performance without crab cavities and with the beam-beam simulation. Operational experience of the crab cavities with beams is described.
122032423
Experiences at the KEK B-factory vacuum system
24439340
Direct electron acceleration by stochastic laser fields in the presence of self-generated magnetic fields.
A simple direct acceleration model is proposed, taking into account the stochastic phase disturbance of the coherent driving laser fields. A relativistic single particle simulation shows that plasma electrons are efficiently accelerated far above the ponderomotive energy. The energy and momentum distributions of the accelerated electrons are derived to examine the effects of the self-generated magnetic field on the characteristics of the electron beams. In addition to the beam collimation effect, the magnetic field is found to further enhance the electron acceleration, resulting in the generation of ultrahigh energy electrons.
121897579
Study of timing degradation and light attenuation in long plastic scintillation rods for time-of-flight counters in relativistic heavy ion experiments
Abstract We have studied the timing and light yield characteristics of long and thin scintillator samples of various sizes. Both the light yield and the time resolution degrade exponentially with respect to the distance from one end; the inverse slope parameters for the time resolutions are found to be twice those of the light yield. This is interpreted in terms of a photoelectron statistics picture, which can also explain the observed position dependence of time resolution for time-of-flight counters.
8862999
Recent progress of KEKB
We summarize the machine operation of KEKB during past one year focusing on progress for this period.
86865953
Present Status of KEKB Vacuum System
The commissioning of KEKB (KEK B-factory) started in December 1998. The vacuum system has been working almost satisfactorily. The photon stimulated gas desorption coefficient of copper beam chamber is decreasing steadily and reached to about 2 - 4 × 10 -6
123323389
Multiwire Proportional Chambers in a 1 GeV/c Magnetic Spectrometer
A set of four multiwire proportional chambers with 612 wires has been constructed for an experiment on proton Compton scattering and π0 photoproduction with the 1.3 GeV electron synchrotron at Institute for Nuclear Study, University of Tokyo. It is located inside the 1 GeV/c Magnetic Spectrometer together with the wire spark chambers. Precise particle trajectories against a high background can be determined by the use of the multiwire proportional chambers. The construction of the chambers and electronics, and the performance of the system are described.
119286608
Resonant excitation of tilt mode in tidally deformed disks
In a previous paper (Kato 2013b), we have shown that in deformed disks a pair of trapped oscillation modes can be resonantly excited through couplings with disk deformation. In this paper we examine in what cases tilts are excited on tidally deformed disks by the above-mentioned wave-wave resonant process. The results show that tilts can be excited in various evolutional stages of tidally deformed disks, although the wave mode which becomes the pair to the tilt and the mode of tidal waves contributing to the resonance change by change of disk stages.
121673805
Polarimeter System for High-Energy Protons Using Carbon Plate and Liquid Hydrogen
In order to measure recoil proton polarization for the reaction γ+p→π°+p in a wide energy range, a polarimeter system has been constructed using carbon plate and liquid hydrogen as the scatterer. It consists of multi-wire proportional chambers, wire spark chambers, scintillation counter hodoscopes, and scatterers. Carbon plates for lower energy protons and liquid hydrogen for higher-energy protons were used as scatterers. The liquid-hydrogen polarimeter has worked reliably in continuous operation for a long time. The performance of the system in the experiment is described.
17631509
Quasi-Periodic Oscillations Resonantly Induced on Spin-Induced Deformed-Disks of Neutron Stars
We consider the situation where a spin-induced wavy perturbation is present on disks of neutron-star low-mass X-ray binaries. By non-linearly coupling with the perturbation, some modes of disk oscillations resonantly interact with the disks. We examine the resonant conditions under the assumption that the disks are vertically isothermal. The results show that when the spin frequency has some particular values, resonant coupling occurs at some radii. The modes and frequencies of these resonant oscillations are summarized. Some of these resonant oscillations seem to explain the frequencies of the observed kHz QPOs in objects of which the spin frequency is known.
124095029
Measurement of large-angle cross-sections for coherent pion photoproduction on deuteron
SummaryCoherent pion photoproduction from deuteron is studied by measuring the differential cross-sections at c.m. angles between 90° and 130° in a photon energy range from 500 to 1000 MeV. The experimental data are compared with a model calculation which takes into account two kinds of contributions, the nonresonant contribution consisting of pion photoproduction from single nucleons and pion rescattering and that from the dibaryon resonances3F3(2.26) and1G4(2.51). The model predictions for the photon asymmetry σ and the deuteron polarizationiT11 are also presented.RiassuntoSi studia la fotoproduzione coerente del pione dal deuterone misurando le sezioni d'urto differenziali ad angoli del centro di massa compresi tra 90° e 130° in un intervallo d'energia dei fotoni pari da 500 a 1000 MeV. Si confrontano i dati sperimentali con un calcolo di un modello che consideri due tipi di contributi, il contributo non risonante che consiste nella fotoproduzione di pioni da singoli nucleoni e rescattering di pioni., e quello dalle risonanze del dibarione3F3(2.26) e1G4(2.51). Si presentano anche le previsioni del modello per l'asimmetria σ dei fotoni e la polarizzazione dei deuteroniiT11.--РезюмеИсследуется когерентное фоторождение пионов на дейтоне, посредством измерения поперечных сечений в области углов от 90° до 130° в системе центра масс и в области энергий фотонов от 500 до 1000 МэВ. Экспериментальные данные сравниваются с модельными вячислениями, которые учитывают два типа вкладов: нерезонансный вклад, состоящий из фоторождения пионов на отдельных нуклонах, и перерассеяние пиона и вклад от дибарионных резонансов3F3(2.26) и1G4(2.51). Так же приводятся модельные предсказания для фотонной асимметрии σ и поляризации дейтонаiT11.