2656324
Radiative leptonic decays of heavy mesons in heavy quark limit
We study the radiative leptonic decays of heavy mesons within the covariant light-front model. Using this model, both the form factors FV and FA have the same form when the heavy quark limit is taken. In addition, the relation between the form factor FV and the decay constant of a heavy meson FH is obtained. The hadronic parameter β can be determined by the parameters appearing in the wave function of the heavy meson. We find that the value of β is not only quite smaller than the one in the non-relativistic case, but also insensitive to the value of the light quark mass mq. These results mean that the relativistic effects are very important in this work. We also obtain that the branching ratio of B→lνlγ is about (1.40–1.67)×10-6, in agreement with the general estimates in the literature.
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}
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.
204174153
Combined chiral dynamics and MIT bag model study of strong Sigma(*) Q-->LambdaQpi decays
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.
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.
58914659
SUBPICOSECOND LASER SLICING X-RAY SOURCE FOR TIME- RESOLVED RESEARCH AT TPS
The feasibility of using a high intensity short pulse laser to produce ultrafast x-ray pulses from the Taiwan Photon Source (TPS) by bunch slicing is being investigated. In our study, a modulator wiggler with period length of 25 cm is placed in one 7 m straight section and is operated at low field strength to minimize possible side-effects that may limit the performances of the low emittance TPS ring. With proper beam separation technique, undulators in straight sections at downstream of the modulator wiggler can be used to produce ultrafast soft and hard x-ray 100 fs pulses at moderate flux. This installation will offer the opportunity to study ultrafast phenomena of condensed matters at atomic resolution.
49387430
DESIGN AND FABRICATION OF MULTIPOLE CORRECTOR MAGNET
Abstract Taiwan Light Source (TLS) started operating using top-up mode injection in October 2005. The Elliptically Polarized Undulator (EPU5.6) operated very well in decay mode; however, partial beam loss occurred when the top-up injection was executed at the magnet gap and array phase, which are fixed at the minimum gap and π (vertical polarization mode), respectively. This work presents a novel multipole corrector magnet installed downstream of the EPU5.6 to compensate for multipole field error and eliminate partial beam loss. This multipole magnet provides normal and skew components of the dipole, quadrupole, sextupole, octupole, and dectupole field components. A changeable multipole field component mechanism was designed using an electrical circuit. Additionally, the measurement system of Hall probe was used to measure magnet field quality.
121586206
Comparison of two superconducting elliptical undulators for generating circularly polarized light
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.
122858718
Features of the magnetic field of a rectangular combined function bending magnet
Magnetic field features of the combined function bending magnet with dipole and quadrupole field components are essential for the successful operation of the electron beam trajectory. These fields also dominate the photon beam quality. The vertical magnetic field B/sub y/(x,y) calculation is performed by a computer code "MAGNET" at the magnet center (s=0). Those results are compared with the 2-D field measurement by the Hall probe mapping system. Also detailed survey has been made of the harmonic field strength and the main features of the fundamental integrated strength, effective length, magnetic symmetry, tilt of the pole face, offset of the field center and the fringe field. The end shims that compensate for the strong end negative sextupole field to increase the good field region for the entire integrated strength are discussed. An important physical feature of this combined function bending magnet is the constant ratio of dipole and quadrupole strength /spl int/Bds//spl int/Gds which is expressed as a function of excitation current in the energy range 0.6 to 1.5 GeV.