123208138
PRESENT STATUS OF THE KEKB B-FACTORY
The KEKB B-factory is an energy-asymmetric e+edouble-ring collider at KEK. It has been operated since December 1998, and has recently marked the peak luminosity of 7.35 /nb/s which is the highest value in the history of colliders. By several improvements such as solenoid windings in LER, new moving-chamber masks in HER, etc., the luminosity performance of KEKB has been significantly upgraded last year. This paper mainly describes the progress after the summer shutdown in 2001. 1 OVERVIEW The luminosity performance of KEKB, both peak and integrated luminosities, has been almost doubled in a year, as shown in Fig. 1. The main beam parameters at the peak record are listed in Table 1, compared with those about a year ago. While the main optical parameters, ex, β ∗ x,y, σz, and the number of bunches were almost unchanged, the beam-beam parameters increased as the bunch current increased. The total beam currents are now mainly limited by heating of the IR masks closest to the IP, due to both HOM and synchrotron light.
122032423
Experiences at the KEK B-factory vacuum system
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
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.
17623960
Frequency Correlation of QPOs Based on a Resonantly Excited Disk-Oscillation Model
In previous papers, we have proposed a model that the high-frequency quasi-periodic oscillations (HF QPOs) observed in black-hole and neutron-star X-ray binaries are inertial-acoustic oscillations that are resonantly excited on a one-armed deformed disk by nonlinear couplings between the oscillations and the disk deformation. In this paper we show that in addition to the inertial-acoustic waves, one-armed corrugation waves are also excited in the deformed disks. They are low-frequency oscillations. We examine frequencies and their correlations among the inertial-acoustic oscillations and the corrugation waves that are excited, in order to know whether they can describe observed frequency correlations among kHz QPOs and low-frequency QPOs (LF QPOs) in neutron-star X-ray binaries. The results seem to well describe the observed correlations in Cir X-1, if we adopt $M= 1.5\sim 2.0 M_\odot$ and $a_* \sim 0.8$, where $M$ is the mass of the central star and $a_*$ is the dimensionless spin parameter of the metric. Finally, assumptions involved in this disk-oscillation model are briefly summarized and discussed.
121162987
Polarization of recoil protons from proton Compton scattering in the region of the second πN resonance
Abstract The polarization of recoil protons from proton Compton scattering has been measured at an angle of 90° c.m.s. in the region of the second nucleon resonance. The scattered photons were detected by a telescope which consisted of a lead plate converter, scintillation-counter hodoscopes and a Cerenkov counter, The angles and momenta of recoil protons were analyzed by a magnet with four spark chambers. The polarization of protons was obtained from the asymmetry in the elastic scattering of protons on carbon in a spark chamber. The polarization of recoil protons from proton Compton scattering are − 0.36 ± 0.29 and − 0.13 ± 0.29 at incident photon energies of 700 ± 50 and 800 ± 50 MeV, respectively. The polarization of recoil protons from neutral pion photoproduction is also obtained and the results are in good agreement with the previous data. A calculation of the polarization of recoil protons in the proton Compton scattering has been made by using an isobar model. The results of the calculation are consistent with the experimental data.
120413457
Coherent bremsstrahlung from the internal target of the 1.3 GeV electron synchrotron
Abstract A Si single crystal has been mounted on the conventional internal target holder of the 1.3 GeV electron synchrotron at the Institute for Nuclear Study, Tokyo. The energy spectrum measured with the pair spectrometer has a clear enhancement due to the coherent bremsstrahlung process. The linear polarization of the photon beam thus obtained is estimated to be 27% and 10% at the photon energy of 200 and 540 MeV, respectively.
108290141
Thermal Instability of Advection-Dominated Disks against Local Perturbations
The thermal stability of advection-dominated accretion disks against local perturbations is re-examined in order to correct some errors in our previous paper. Thermal perturbations which are local in the radial direction are found to also be local in the vertical direction. Because of this, the using of vertically integrated quantities was irrelevant in analyzing the stability of local thermal perturbations when the disks are geometrically thick. Our new results, obtained by correcting the error, show that if the turbulence acts as a diffusion process in thermal energy transport, it strongly dampens the thermal perturbations. In these cases when the diffusion process is weak, however, perturbations grow due to a variation of the viscous heating associated with the perturbations. One such example of growth is in the case where radiation pressure greatly dominates the gas pressure.
15347243
NONLINEAR RESONANCE IN THE ACCRETION DISK OF A MILLISECOND PULSAR
Two simultaneous frequencies of quasi-periodic millisecond modulation of the X-ray flux (twin kilohertz quasiperiodic oscillations) have recently been detected in an accreting 2.5 ms X-ray pulsar. Their difference, equal to about of the neutron star spin rate, clearly indicates that resonant oscillations of the accretion disk have been 1 2 observed. Similar nonlinear resonances may be spontaneously excited in the accretion disk in the absence of a pulsar, e.g., in black holes. We identify modes of disk oscillations whose frequencies are in agreement with the two observed ones when the rotating neutron star is modeled with realistic equations of state. Subject headings: stars: neutron — X-rays: general On-line material: color figures