119485274
Covariant Light-Front Approach for s-wave and p-wave Mesons: Its Application to Decay Constants and Form Factors
We study the decay constants and form factors of the ground-state s-wave and low-lying p-wave mesons within a covariant light-front approach. Numerical results of the form factors for transitions between a heavy pseudoscalar meson and an s-wave or p-wave meson and their momentum dependence are presented in detail. In particular, form factors for heavy-to-light and B → D ∗∗ transitions, where D ∗∗ denotes generically a p-wave charmed meson, are compared with other model calculations. The experimental measurements of the decays B − → D ∗∗ π − and B → DD ∗∗ are employed to test the decay constants of D ∗∗ and the B → D ∗∗ transition form factors. The heavy quark limit behavior of the decay constants and form factors is examined and it is found that the requirement of heavy quark symmetry is satisfied. The universal Isgur-Wise (IW) functions, one for s-wave to s-wave and two for s-wave to p-wave transitions, are obtained. The values of IW functions at zero recoil and their slope parameters can be used to test the Bjorken and Uraltsev sum rules.
118628184
Model-independent analysis for determining mass splittings of heavy baryons
We study the hyperfine mass differences of heavy hadrons in the heavy quark effect theory. The effects of one-gluon exchange interaction are considered for the heavy mesons and baryons. Based on the known experimental data, we predict the masses of some heavy baryons in a model-independent way.
204174153
Combined chiral dynamics and MIT bag model study of strong Sigma(*) Q-->LambdaQpi decays
12196534
Mesonic form factors and the Isgur-Wise function on the light front
Within the light-front framework, form factors for P{r_arrow}P and P{r_arrow}V transitions (P denotes a pseudoscalar meson, V a vector meson) due to the valence-quark configuration are calculated directly in the entire physical range of momentum transfer. The behavior of the form factors in the infinite quark mass limit are examined to see if the requirements of heavy-quark symmetry are satisfied. We find that the Bauer-Stech-Wirbel-type light-front wave function fails to give a correct normalization for the Isgur-Wise function at zero recoil in P{r_arrow}V transition. Some of the P{r_arrow}V form factors are found to depend on the recoiling direction of the daughter mesons relative to their parents. Thus the inclusion of the nonvalence contribution arising from quark-pair creation is mandatory in order to ensure that the physical form factors are independent of the recoiling direction. The main feature of the nonvalence contribution is discussed. {copyright} {ital 1997} {ital The American Physical Society}
11335733
Charge radii of light and heavy mesons
Abstract. We calculate the electromagnetic (EM) form factors of the pseudoscalar mesons in the light-front framework. Specifically, these form factors are directly extracted from the relevant matrix elements, instead of choosing the Breit frame. The results show that the charge radius of the meson is related to both the first and second longitudinal momentum square derivatives of the momentum distribution function. The static properties of the EM form factors and the heavy quark symmetry of the charge radii are checked analytically in the heavy quark limit. In addition, we use the Gaussian-type wavefunction to obtain the numerical results.
1152504
Weak-field expansion for processes in a homogeneous background magnetic field
The weak-field expansion of the charged fermion propagator under a uniform magnetic field is studied. Starting from Schwinger's proper-time representation, we express the charged fermion propagator as an infinite series corresponding to different Landau levels. This infinite series is then reorganized according to the powers of the external field strength B. For illustration, we apply this expansion to $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}\ensuremath{\nu}\overline{\ensuremath{\nu}}$ and $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\nu}}\ensuremath{\nu}\ensuremath{\gamma}$ decays, which involve charged fermions in the internal loop. The leading and subleading magnetic-field effects to the above processes are computed.
16490248
A LONG LOOP COIL SYSTEM FOR INSERTION DEVICE MAGNET MEASUREMENT
The “dynamic scan” and “static scan” measurement methods, using the long loop coil system, have been designed for magnetic field measurements of the elliptically polarizing undulator (EPU) as well as any other insertion device magnet. The basic design concept is to build a reliable and high speed measurement system for characterizing the two transverse magnetic field components. The main features of this system are its high speed of measurement, high precision and accuracy. This system can perform the multipole field measurement within ten minutes by the “ static scan” method, and in one minute by the “ dynamic scan” method.
115015433
Effectiveness of a Shielding Cabinet on the Storage-Ring Septum Magnet of Taiwan Light Source
Abstract To avoid a parasitic magnetic field in the stored beam, the pulsed-magnet system of Taiwan Photon Source (TPS) requires the stray field to be minute: the stray field from the storage-ring (SR) injection septum is required to be less than 0.1 % of the main field in the gap. The most common method to protect against a parasitic magnetic field is to use a highly permeable and conductive material, such as mu-metal. A 300-ms half-sine-wave pulse up to a current maximum 9922 A is supplied to a septum and results in an eddy-current loss in a magnet and a conductor during rapid charging of a magnet. Competition between an eddy-current effect and the magnetic permeability would produce a complicated phenomenon inside the magnetic-shielding screen and affect the shielding performance. We examined the performance of magnetic shielding of a shielding screen with OPERA 2D for varied geometry and thickness of the screen.
54029089
Different kinds of analysis methods on a rectangular combined function bending magnet
Magnetic field features of a rectangular combined function bending magnet are different from the sector magnet. A strong edge focusing factor (i.e., thin lens effect) intrinsically exists at the two magnet edges for the rectangular bending magnet. Therefore, in this study, we develop two kinds of Hall probe mapping trajectory with four analysis methods to measure and analyze the bending magnet’s field behavior. A sufficient correlation among the four methods is an important feature. Those methods are individually used to derive the pole face tilt and bent, the effective magnetic length and to check the specification establish by the beam dynamics group. As for the two mapping methods, one is called “Radial Mapping” whose mapping trajectories in the longitudinal direction (s-axis) follow the different arc lengths of radius pkr and the transverse trajectories follow the radial displacement kr perpendicular to the arc trajectory. The other one is called “Lamination Mapping” whose mapping trajectories in the longitudinal direction follow the constant arc length of circle radius p and the transverse trajectories follow the transverse axis displacement 5.x parallel to the lamination direction. This study also discusses the differences between those two mapping methods. Results obtained from the harmonic field distribution along the longitudinal direction (including the fringing field) and the main components of the integral strength are compared. The subsequent error of the four analysis methods is 0.01% for the dipole strength and 0.3% for the quadrupole strength individually. According to the specifications, those analysis errors are acceptable. Meanwhile, the accuracies of different methods for the higher multipole strengths are all within tolerances. The peculiar sextupole held behavior at the two magnet edges from the different mapping methods is owing to the effective magnet pole face that will be discussed.
54200358
Control system for the superconducting insertion devices of NSRRC
To enhance hard X-ray production in the 1.5 GeV storage ring of NSRRC to serve the rapidly growing X-ray user community in Taiwan, the storage ring are planed to install up to five superconducting insertion devices. A 6 Tesla superconducting wavelength shifter was installed in mid-2002. A 3.2 Tesla superconducting multipole wiggler will be installed in the fall of 2003. The project for the other three multipole wigglers is launched. The control system had been implemented to support the operation of the superconducting insertion devices. The control system play a role to coordinate the operation of the main power supply and the trimming power supplies to charge/discharge the magnet and provide interlock protection for the magnet coils and vacuum ducts. A friendly user interface and various application programs are used to support routine operation. Design considerations and details of the implementation are also presented.
62901264
Experience of the Cryogenic System for Taiwan Light Source
In Taiwan light source a superconductive cavity and five superconductive magnets are installed in the storage ring. The cryogenic system provides liquid helium and liquid nitrogen with stable pressure. Failure events occurred on the components such as expansion turbine, compressor, and frequency inverter during the past years. A supervision system was developed to monitor the status of the cryogenic system and an automatic call out system was built to notify the operators when abnormal condition appears. To shorten the interruption period of liquid helium supply, the dewar keeps stable and continuous supply of liquid helium and the recovery compressor collets the evaporated helium gas from the cryostat for cases of several hours shutdown of the cryogenic system. Humidity, cleanness and helium leak tightness are items necessary to be well controlled before connecting new components or application devices to the cryogenic system. The matching between system cooling capacity and heat load is achieved via adjustment of turbine speed, precooling temperature, compressor speed, and heater power.