39233375
Beam-beam experience at KEKB
KEKB has achieved the peak luminosity of 4.1 x 10{sup 33} cm{sup -2} sec{sup -1} and the present capability for delivering integrated luminosity is 224 pb{sup -1}/day. This paper describes (1) the recent performance and the problems of KEKB and (2) the comparison of beam-beam simulations with experiments at KEKB.
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.
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.
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
122032423
Experiences at the KEK B-factory vacuum system
123010857
Recoil proton polarization of neutral pion photoproduction from protons in the energy range between 400 MeV and 1142 MeV
The recoil proton polarization of the reaction γp → π0p was measured at a c.m. angle of 100° for incident photon energies between 451 and 1106 MeV, and at an angle of 130° for energies from 400 to 1142 MeV. One photon, decayed from a π0 meson, and a recoil proton were detected in coincidence. Two kinds of polarization analyzer were employed. In the range of proton kinetic energy less than 420 MeV and higher than 346 MeV, carbon plates and liquid hydrogen were used for determining the polarization, respectively. The data given by the two polarimeter systems are in good agreement. Results are compared with recent phenomenological analyses. From the comparison between the present data and the polarized target data, the invariant amplitude A3 can be estimated to be small.
118590299
Trapped, Two-Armed, Nearly Vertical Oscillations in Disks with Toroidal Magnetic Fields II: Effects of Finite Thickness
We examine the radial trapping of two-armed (m = 2) vertical p-mode oscillations in geometrically thin relativistic disks that are vertically isothermal, but terminated at a certain height by the presence of hot and low-density corona. The disks are assumed to be subject to toroidalmagneticfields. The oscillationsare classified by n, anumber related to the node number of oscillations in the vertical direction, and starting from n = 1. In modes with n = 1, the frequencies of trapped oscillations depend little on the height of termination, but in modes with n = 2, 3, ��� the frequencies decrease and the radial extentions of the trapped region become wide, as the termination height decreases. This study is a preparation to examine whether these oscillations can describe kilo-hertz quasi-periodic oscillations (kHz QPOs), horizontal branch oscillations (HBOs), and their correlations.
17039539
Resonant Excitation of Disk Oscillations in Two-Armed-Deformed Disks and Application to High-Frequency QPOs
In previous papers we showed that in one-armed deformed disks, p-mode and g-mode oscillations are resonantly excited by horizontal resonance, and applied it to high-frequency quasi-periodic oscillations (QPOs) observed in lowmass X-ray binaries. In that model, the observed time variation of kHz QPOs is regarded as being the result of a timedependent precession of the deformation. In this paper we consider another possible cause of the time variation of kHz QPOs. That is, we demonstrate that in two-armed deformed disks, p-mode and g-mode oscillations are excited by a vertical resonance, not by a horizontal resonance (horizontal resonance dampens them). Furthermore, we show that in the case of a vertical resonance, the frequencies of excited disk oscillations can vary with time if the vertical disk structure changes with time. A brief application of these results to the time variation of observed kHz QPOs is discussed.
118562535
Recoil proton polarization of proton compton scattering in the resonance region
SummaryThe recoil proton polarization of proton Compton scattering (γp→γp) was measured in the photon energy range from 500 MeV to 1000 MeV atθ∗=100° and from 400MeV to 800 MeV atθ∗=130°. A recoil proton and a scattered photon were detected in coincidence with a magnetic spectrometer and a photon detector. The recoil proton polarization was measured with a carbon polarimeter. The results are compared with a phenomenological analysis based on an isobar model and a dynamical analysis based on the dispersion relation.RiassuntoÈ stata misurata la polarizzazione del protone di rinculo nello scattering di Compton del protone (γp→γp) nell'intervallo d'energia del fotone da 500 a 1000 MeV perθ∗=100°, e da 400 a 800 MeV perθ∗=130°. Sono stati individuati un protone di rinculo e un fotone diffuso contemporaneamente con uno spettrometro magnetico e un rivelatore di fotoni. La polarizzazione del protone di rinculo è stata misurata con un polarimetro a carbonio. Si confrontano i risultati con un'analisi fenomenologica basata su un modello a isobare e con un'analisi dinamica basata sulla relazione di disperisone.РезюмеПроведено измерение поляризации протонов отдачи при комптоновском рассеянии на протонах в области энергий фотонов от 500 МэВ до 1000 МэВ приθ∗=100° и от 400 МэВ до 800 МэВ приθ∗=130°. Протон отдачи и рассеянный фотон детектируются на совпадение с помощяю магнитного спектрометра и детектора фотонов. Поляризация протона отдачи измеряется с помщью углеродного поляриметра. Полуенные результаты сравниваются с феноменологическим анализом, основанным на изобарной модели, и динамическим анализом, основанным на дисперсионном соотношении.
120142226
Polarization of recoil neutrons from single-pion photoproduction off protons in the resonance region
Abstract The polarization of the recoil neutrons from the reaction γ p→ π + n was measured at a c.m. angle of 105° for incident photon energies between 675 and 1125 MeV. A scattered π + meson and a recoil neutron were detected in coincidence with a magnetic spectrometer and a neutron polarimeter system using liquid hydrogen. Results are compared with recent phenomenological analyses and the other existing data measured by the double polarization measurement technique.