9083411
Improved analysis for the baryon masses to order Lambda(QCD) / m(Q) from QCD sum rules
We use the QCD sum rule approach to calculate the masses of the Lambda_Q and Sigma_Q baryons to the Lambda_{QCD}/m_Q order within the framework of heavy quark effective theory. We compare the direct approach and the covariant approach to this problem. Two forms of currents have been adopted in our calculation and their effects on the results are discussed. Numerical results obtained in both direct and covariant approaches are presented. The splitting between spin 1/2 and 3/2 doublets derived from our calculation is {\Sigma_Q^*}^2-\Sigma_Q^2\simeq 0.35\pm 0.03 GeV^2 which is in good agreement with the experiment.
121216453
Heavy quark effective theory sum rules for higher excited charmed mesons: With a view on D(sJ)(2632)
Mass of the excited (1{sup -},2{sup -}) (2{sup -},3{sup -}) and (2{sup +},3{sup +}) cs states is calculated to the 1/m{sub Q} order within the framework of the heavy quark effective theory using QCD sum rule method. The obtained kinetic energy is comparable to the c-quark mass, thus results in large 1/m{sub Q} correction for the c-quark case. With the sum rules for the chromomagnetic interaction term, the mass splitting for the three doublets is presented. Based on the predicted mass spectrum the exotic D{sub sJ}(2632) state, if really exists, is unlikely to be a conventional orbitally higher excited cs state, although the experimental center lies within the range for the mass of the 1{sup -} meson.
118399148
Light cone QCD sum rules for the semileptonic decay Lambda(b) -> p l anti-nu
The exclusive semileptonic heavy baryon decay \Lambda_b\to p l\bar\nu is investigated using light-cone sum rule method in both full QCD and HQET. The form factors describing the decay are calculated and used to predict the decay width and differential distribution. The total decay width obtained from full QCD is in agreement with the previous theoretical predictions while the HQET result are typically one order smaller. Both results are consistent with the experimental upper limit and can be compared to the refined experimental data in the future.
119432190
Semileptonic decay Lambda(c) ---> Lambda l+ nu from QCD light-cone sum rules
We present the study of the semileptonic decay \Lambda_c to \Lambda\ell^+\nu by using the light-cone sum rule approach. Distribution amplitudes (DAs) for the \Lambda baryon are discussed to the leading order conformal spin, and QCD sum rule estimate for the corresponding parameters is presented. The form factors describing the decay are calculated and used to predict the decay width and the decay asymmetry parameter \alpha. With the inclusion of twist-3 contributions the calculated decay width \Gamma=(7.2+/-2.0)X10^{-14} GeV as well as asymmetry \alpha=-(0.88+/-0.03) is found in good agreement with the experimental data, while there are appreciable deviations from experiment values when the higher twist contributions are included.
53997503
A PERMANENT MAGNET PHASE SHIFTER FOR THE EUROPEAN X-RAY FREE ELECTRON LASER
In undulator systems with adjustable gaps phase shifters are needed to exactly control the phase retardation between electrons and the radiation field over the entire length of an undulator system. A phase shifter based on Permanent Magnet technology for the use in the European XFEL has been developed and tested. Specifications are given. This paper will explain its magnetic principle and design. Magnetic test results are presented and thoroughly discussed. Special attention is given to the operation in the XFEL.
2277847
OPTIMIZATION AND MODELING OF THE ACCELERATOR FOR THE FERMI @ ELETTRA FEL
Design studies are in progress to use the existing FERMI{at}Elettra linear accelerator for a seeded harmonic cascade free-electron laser (FEL) facility [1]. This accelerator will be upgraded to 1.2 GeV and equipped with a low-emittance RF photocathode gun, laser heater, two bunch compressors, and a beam delivery system. We present an optimization study of all the components downstream of the gun, aimed at achieving the high peak current, low energy spread and low emittance electron beam necessary for the FEL. Various operational scenarios are discussed. Results of accelerator simulations including effects of space charge, coherent synchrotron radiation and wakefields are reported.
54869476
OPTIMAL RF SYSTEMS FOR LIGHTLY LOADED SUPERCONDUCTING STRUCTURES
one meter cavity would therefore need to supply only 300 W to meet these demands. Recent developments in the field of RF accelerators have created a demand for power amplifiers that can support very high accelerating gradients, 15-25 MV/m, in superconducting structures with extremely low losses. Free electron lasers with modest beam current, I<10 uA, or those based on energy recovery linacs may have intrinsic power demands of less than 1 kW/m. We present a design concept for an amplifier and external tuner system that will efficiently meet this requirement. A likely amplifier for this application is the Inductive Output Tube (IOT) which offers high AC/RF efficiency, flexible power output and switching capability without the need for external modulation. The use of solid state amplifiers is also considered. The external tuner circuit makes use of low loss RF components, include waveguide, circulators and ferrite phase shifters to create a moderate quality standing wave between the amplifier and the superconducting cavity. The potential effective Qext exceeds 3×10 7 .
1202782
DESIGN OPTIMIZATIONS OF X-RAY FEL FACILITY AT MIT
In recent years, a number of short wavelength FEL experiments have demonstrated key technologies and obtained good agreement between experiment and theory. The x-ray FEL at MIT(1) is one example of a design for a new generation linac-based light source. Such a new machine requires very high quality electron beams. Besides the usual requirements on beam quality such as emittance, energy spread, peak current, etc., there are new challenges emerging in the design studies, e.g., the precise arrival timing of electron beam at lower tens of femtoseconds level to ensure the laser seed overlap the desired sections of electron bunch in the multiple-stage HGHG process. In this paper we report the progress on design optimization towards high quality and low sensitivity beams. INTRODUCTIONS The proposed MIT x-ray laser incorporates design features that take advantage of many recent developments. It blends proven technologies into a powerful new instrument that combines the high power, coherence, and ultrashort timescale probe of a laser with the energy reach and spatial resolution of synchrotron x-rays. It is a primary goal to integrate the instruments and experimental methods from the laser and synchrotron radiation communities at the earliest stages of design. Integrated high-harmonic generation laser technology will seed the electron beam and generate photon beams with high longitudinal coherence and pulse lengths significantly below 100 femtoseconds, perhaps below 1 femtosecond. The FEL itself will use the high gain harmonic generation (HGHG) method to produce multiple harmonics of the tunable input seed. The output radiation has the full longitudinal and transverse coherence and stability of the seed laser, providing substantial improvement over performance based solely on SASE. A sketch of linac layout is shown in Figure 1. The major components are the superconducting electron linac of length ~300 m, plus undulator tunnels and experimental halls. The production of x-ray laser pulse begins with generation of the electron beam in the RF photoinjector. The photoelectrons are produced by a conventional laser striking the photocathode contained in a high field RF cavity, producing 200 pC to 1 nC pulses that are about 10 to 25 picoseconds long. The superconducting linac will accelerate electron beam to up to 4 GeV energy. At about 200 MeV and 900 MeV, the beam enters the first and second magnetic chicane, which compress the pulse length to between 100 to 1000 femtoseconds and increase the bunch current from a few tens of amps to a few thousand amps.
117533820
Longitudinal kinetic energy spread from focusing in charged particle beams
A charged particle beam can be given a longitudinal kinetic energy spread through focusing by magnetic solenoid lenses. Measurements of energy spread are reported and are compared with the results of computer simulations, which include several known sources of energy spread. These sources are discussed. The results of the measurements and the simulations agree, giving energy spreads which are two orders of magnitude larger than the initial thermal energy spread.<<ETX>>