16596210
A Consistent treatment for pion form-factors in space - like and time - like regions
We write down some relevant matrix elements for the scattering and decay processes of the pion by considering a quark-meson vertex function. The pion charge and transition form factors $F_\pi$, $F_{\pi\gamma}$, and $F_{\pi\gamma^*}$ are extracted from these matrix elements using a relativistic quark model on the light-front. We found that, the form factors $F_\pi$ and $F_{\pi\gamma}$ in the space-like region agree well with experiment. Furthermore, the branching ratios of all observed decay modes of the neutral pion, that are related to the form factors $F_{\pi\gamma}$ and $F_{\pi\gamma^*}$ in the time-like region, are all consistent with the data as well. Additionally, $F_\pi$ in the time-like region, which deals with the nonvalence contribution, is also discussed.
204174153
Combined chiral dynamics and MIT bag model study of strong Sigma(*) Q-->LambdaQpi decays
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.
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.
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.
55115813
Measurement of Field Inaccuracy and Shim Simulation of a 130-Pole Superconducting Undolator
A superconducting undulator (length 975.2 mm, with 130 poles) was wound and trained, and its field measured, at National Synchrotron Radiation Research Center. The NbTi wires were excited to 1.36 T at 497 A after 28 cycles. A Hall probe (length 2.50 m) was used to characterize the distribution of the magnetic field of arrays in the magnetic gap (width 5.6 mm). The measurement region of the Hall probe in the vertical dewar is greater than 1 m. The shrinkage or expansion of the Hall probe depends on the thermal variation at both its ends. The length of the Hall probe must be evaluated in the long region. The reproducibility of the measurement system was verified in the same experiment. A shim method involving a trim pole piece was developed to correct for deviations of the magnetic field. This paper discusses the source of measurement inaccuracy with the Hall probe and present results of the simulation of shimming the trim poles.
55387450
PROGRESS IN INSERTION DEVICES FOR TPS IN PHASE I
Taiwan Photon Source (TPS) with beam energy 3 GeV and beam current 500 mA is a third-generation synchrotron radiation facility of medium energy. In the initial commissioning stage of TPS, the machine will be equipped with ten insertion devices (ID) and serve seven beamlines in phase I. Of these, three long straight sections configured as a double-minimum betay function lattice design with minimized beam influence of emittance are used for the installation of a pair of insertion devices in a straight section, two undulators of APPLE-II type and four in-vacuum undulators (IU), to produce great brilliance and coherent X-rays with great flux. The details of these insertion devices are explained herein.
126037008
Spectrum Property Analysis of a Wiggler-like Undulator
A wiggler with the property of low total radiation power and that maintains a large photon flux in the hard x-ray region, 5-20 keV, which is necessary for the special demand of users, was investigated to decrease the difficulty of the design of optical components in the beam line and to decrease the load of RF cavity power. Such an insertion devise is called a wiggler-like undulator. The spectrum of this wiggler-like undulater was investigated with a code of which the algorithm is based on a compromising between useful photon flux and total radiation power of insertion devices for spectrum optimization. The properties of the spectrum of the wiggler-like undulator are discussed herein. Furthermore, the power distribution is somehow also discussed.
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.
56094745
The construction of a 9-pole prototype for SRRC U-10 undulator
A 9-pole undulator prototype with a magnetic period length of 10 cm was designed and constructed to examine the mechanical and magnetic field performance. The hybrid permanent magnet structure was optimized by using 2D "PANDIRA" and 3D "TOSCA" magnetostatic codes. A half period magnet model was also fabricated to verify the magnetic field strength on-axis and the transverse field roll-off within 0.1 % in the good field region of /spl plusmn/10 mm at a minimum gap minimum gap of 22 mm. The end pole configurations, as equipped with either two tunable permanent magnetic rotators or steering coil correctors were designed for minimizing the deviation of the magnetic field strength integrals. The magnet structures were mounted on a 2 meter long C-frame support structure in which the gap could be moved in parallel and phase motion. The field characteristics and measurement results between the adjustable gap undulator (AGU) and the hybrid adjustable phase undulator (APU) were also presented.