14344162
Consistent treatment for valence and nonvalence configurations in semileptonic weak deacys
Abstract We discuss the semileptonic weak decays of P → P ( P denotes a pseudoscalar meson). In these timelike processes, the problem of the nonvalence contribution is solved systematically as well as the valence one. These contributions are related to the light-front quark model (LFQM), and the numerical results show the nonvalence contribution of the light-to-light transition is larger than of the heavy-to-light one. In addition, the relevant CKM matrix elements are calculated. They are consistent with the data of Particle Data Group.
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.
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.
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}
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.
120445064
Superconducting wiggler with semi-cold beam duct at Taiwan light source
Abstract A 3.2 T superconducting wiggler with a periodic length of 6 cm and 32 poles was designed and fabricated as an X-ray source. The beam duct of this magnet is a semi-cold, ultra-high vacuum chamber that consists of an aluminum and stainless steel taper. The number of poles in this magnet design is even, to minimize the integral strengths of the multipole components. Two measurement systems—involving room-temperature and cryogenic Hall probes—were set up to measure the field of the superconducting wiggler. A cryogenic plant that supplied liquid helium and nitrogen to the superconducting wiggler has already been established. The performance of magnet construction is good and the commissioning of the superconducting wiggler in the storage ring has been successful. No trim coil compensation on the magnet is required to adjust the electron beam orbit. Furthermore, the electron beams exhibit no loss and remain highly stable after the superconducting wiggler has been quenched.
119106630
Evidence for Aharony duality for orthogonal gauge groups
We study the Aharony duality for three dimensional $ \mathcal{N} = 2 $ supersymmetric gauge theories for orthogonal gauge groups with matters in vector representation. We provide the evidence for the duality by working out the partition function on S3 and the superconformal index, which show perfect agreement.
55844721
FIELD ERROR CORRECTION FOR A SUPERCONDUCTING UNDULATOR
To reach higher photon energies in the region of soft or hard x-rays from 1 to 10 keV with high photon beam brightness in low energy storage rings, superconducting undulators with very short period length and high magnetic field strength are required. Because undulator radiation comes in a line spectrum, photons up to the 7 th harmonic are desired. This requires to correct the undulator for errors in period length and magnetic field strength. The photon brightness (or photon flux density) in such harmonics is strongly dependent on perfect periodicity of the magnetic field. Small changes in field strength and phase from period to period can cause destructive interference which reduces the photon intensity dramatically, especially at higher harmonics. Such imperfections also appear in conventional permanent material undulators, which can be corrected by well developed and efficient shimming. Unfortunately, this method cannot be applied to superconducting undulators. Therefore, we present a new approach to field corrections by modification of the magnetic field saturation in each pole. By this correction, not only the magnetic field error but also greatly improves phase (period length) errors from period to period. The proposed method works quite local with only small perturbations in neighbouring poles. The tunability is preserved for most of the field excitations and is reduced only at extreme parameters.
122890200
Core-level and valence-band study using angle-integrated photoemission on LaFeAsO(0.9)F(0.1)
Using angle-integrated photoemission spectroscopy we have probed the novel LaFeAsO{sub 0.9}F{sub 0.1} superconductor over a wide range of photon energies and temperatures. We have provided a full characterization of the orbital character of the valence-band (VB) density of states (DOS) and of the magnitude of the d-p hybridization energy. Finally, we have identified two characteristic temperatures: 90 K where a pseudogap-like feature appears to close and 120 K where a sudden change in the DOS near E{sub F} occurs. We associate these phenomena with the spin density wave magnetic ordering and the structural transition seen in the parent compound, respectively. These results suggest the important role of electron correlation, spin physics, and structural distortion in the physics of Fe-based superconductors.