7967891
Beam-beam effect observed in the KEKB
This report summarizes observed phenomena related to the beam-beam effects in the KEKB collider. A general performance of the beam-beam effect is described. An em- phasis is put on the reduction of the specific luminosity with shorter bunch spacing. ible with the present maximum beam current. The scrub- bing effect of the chamber wall also possibly contributed to suppress the blowup. The present beam current limitation comes from a heating problem in the IR region. Another feature of the KEKB is that working points are very close to the half integer resonance particularly in the horizontal direction as is seen in the table. These horizon- tal tunes make the horizontal emittance large and the hori- zonal beta functions small to a large extent. This large emit- tance compensates the large bunch currents and contributes to stabilize the beams against the beam-beam effect. As is seen in the table, both of the horizontal and vertical tunes of the both rings are located above the half integer resonance, while the vertical tunes are above the integer resonance in the design. In the early days of the KEKB, the vertical tunes were above the integer resonance. In February 2001, the vertical tunes moved to above the half integer based on results of new beam-beam simulations. This change of the tunes brought some increase of the luminosity.
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.
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
8862999
Recent progress of KEKB
We summarize the machine operation of KEKB during past one year focusing on progress for this period.
122032423
Experiences at the KEK B-factory vacuum system
17883234
A Vertical Resonance of g-Mode Oscillations in Warped Disks and QPOs in Low-Mass X-Ray Binaries
Resonant oscillations in warped disks are examined in order to explain high-frequency QPOs and horizontalbranch QPOs in low-mass X-ray binaries. Different from our previous work, addressed to the same subjects, we relax in this paper the assumption that the disks are isothermal in the vertical direction. That is, the pressure, density, and temperature are assumed to be distributed in the vertical direction with a polytropic relation, and the polytropic index changes as the disk state changes. By this generalization and by some subsidiaries we can qualitatively explain, within the framework of our resonance model, observed large frequency variations in neutron-star QPOs and little variations in black-hole QPOs. We consider vertical resonances of g-mode oscillations, since they are most appropriate to explain observations.
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.
119688485
EVIDENCE FOR THE EXISTENCE OF A Z
2080857
A Resonance Model of Quasi-Periodic Oscillations of Low-Mass X-Ray Binaries
We try to understand the quasi-periodic oscillations (QPOs) in low-mass neutron-star and black-hole X-ray binaries by a resonance model in warped disks with precession. Our main concern is high-frequency QPOs, hectohertz QPOs, and horizontal-branch QPOs in the z sources and the atoll sources, and the corresponding QPOs in black-hole X-ray binaries. Our resonance model can qualitatively, but systematically, explain these QPOs by regarding hectohertz QPOs as a precession of warp.
118632115
An Attempt to Describe Frequency-Correlations among kHz QPOs and HBOs by Two-Armed Vertical p-Mode Oscillations: Case of No Magnetic Field
The trapping of two-armed (m = 2) vertical p-mode oscillations in relativistic disks is examined. The disks are assumed to be isothermal in the vertical direction, but are truncated at a certain height by the presence of corona. The same issues were examined in a previous paper (Kato 2012a). In this paper, unlike the previous paper, however, we do not use the approximation that the oscillations are nearly vertical, but limit to a simpler case of no magnetic field. As in the previous paper, the results suggest that the two basic oscillation modes [both are the fundamental (n = 1) in the vertical direction, but in the horizontal direction one is the fundamental (nr = 0) and the other the first overtone (nr = 1)] correspond to the twin kHz QPOs. Second, the oscillation mode, which is the first overtone (n = 2) in the vertical direction and the fundamental in the horizontal direction (nr = 0), will correspond to the horizontal branch oscillation (HBO) of Z-sources. The latter suggests that the horizontal branch of Z-sources is a sequence of temperature change in disks whose vertical thickness is strongly terminated. The temperature increases leftward along the sequence from the apex between the normal and horizontal branches.