119534509
Measurement of the average local energy spread of electron beam via coherent harmonic generation
The local energy spread of electron beam is a very important parameter for high-gain free-electron lasers (FELs), especially the seeded FELs. Highly accurate measurement of the extremely small local energy spread is rather challenging. In this paper, a simple method to accurately measure the average local energy spread based on the coherent harmonic generation is proposed. A one-dimensional analytical estimation is given to show the principle of this method, and three-dimensional simulation codes have been used to verify the theory. This method has been demonstrated on the Shanghai deep ultraviolet FEL, and the results show that the average local energy spread is about only 1.2 keV at the exit of the 136 MeV linac, which agrees well with the numerical simulations.
124860564
Short-pulse length effects of the seed laser in high-gain harmonic generation free-electron laser
In order to generate coherent hard x-ray free-electron laser ( FEL), cascading stages of high-gain harmonic generation ( HGHG) scheme usually employ seed pulse with longitudinal length down to tens of femtoseconds. Such a short pulse length ( SPL) seed laser, with broad bandwidth in the spectral domain, can no longer be characterized by monochromatic light in FEL equations. In this paper, a set of self-consistent, multifrequency FEL equations is derived to describe the interaction between the seed laser and the electrons in the modulator of HGHG. Moreover, the SPL effects of the seed laser on the electron beam's energy modulation, the output pulse length, the output peak power, and the output wavelength tuning in HGHG are theoretically and numerically investigated. Study demonstrates that the SPL seed laser seriously and significantly influences the HGHG performances, and these influences have to be taken into account in the design and optimization of the seeded FEL scheme.
73648727
Polarization control proposal for Shanghai deep ultraviolet free electron laser
In this paper, a fully coherent radiation option with controllable polarization is proposed for the Shanghai deep ultraviolet free electron laser (FEL) test facility. Intensive start-to-end simulation suggests that the two crossed planar undulators which generate the horizontal and vertical linear polarized FEL, should be placed as close as possible for avoiding the polarization performance degradation of the final combined FEL radiation. With the existence of the phase-shifter between the two crossed radiators. Fourier-Transform-Limited output radiation with 100 nJ order pulse energy, 5 Ps full pulse length and circular polarization degree above 90% could be achieved. (C) 2012 Elsevier B.V. All rights reserved.
120435997
High-pT hadronic trigger using electromagnetic calorimeter with the STAR detector
Abstract We derive a new method to improve the statistics of identified particles at high transverse momentum ( p T ) using online-triggered events by the STAR Barrel electro-magnetic-calorimeter (BEMC) detector. The BEMC is used to select charged hadrons ( π ± , K ± , and p ( p ¯ ) ) via hadronic shower energy deposited in the BEMC. With this trigger, the statistics of the high p T particles are significantly enhanced (by a factor of up to ∼ 100 for STAR) with trigger efficiency up to 20%. In addition, weak-decay V0s ( K S 0 and Λ ( Λ ¯ ) ) can be reconstructed by selecting the BEMC-trigger hadron as one of the decay daughters. We also show that the trigger efficiency can be obtained reliably in simulation and data-driven approaches, and final results from new method are compared with previous published results.
119369173
The Distinct Light Curve Shape of the Asteroid (469)
The observation light curves of the main belt asteroid (469) Argentina, obtained on March 9–11 2002 and August 10–11 2004, are presented in this paper. The complex light curve of the (469) suggests that it may be in NPA rotation. Using the Fourier analysis method, some prominent spectrum values are derived individually for two subset data. Among these period values, periods of 13.00 and 8.74 h are regarded as basic components. Other derived period values can be combined linearly with these two basic period values. If the (469) is in a free-force precession mode, the motion mode will be LAM (largest-axis mode) according the ratio of precession and rotation periods. And the minimum of I1/I3 (ratio of the largest and smallest principal momentum of inertial) is 3.05. Assuming an external torque releasing by a satellite forces the (469) to precess, the mass of satellite roughly is the same order as the primary’s on condition that the precession and rotation periods are two basic values. At present, we cannot draw an unambiguous conclusion on (469)’s motion for sparse data, So the further observations are necessary for understanding the (469)’s tumbling motion farther.
120276276
Surface versus volume emissions in photon–hadron correlations
High-pT photon–hadron correlations are studied within the next-to-leading order (NLO) perturbative QCD parton model with modified parton-jet fragmentation functions due to jet quenching in high-energy A+A collisions. In central A+A collisions, the away-side hadrons with large zT=pTh/pTγ are controlled mainly by the surface emission of the gamma-jet events, while a small zT region will be volume emission bias. In other words, gamma jets for a small-zT region probe the dense matter deeper than those gamma jets for a large-zT region, so the small-zT gamma jets are found to be slightly more sensitive to the properties of the dense matter than the large-zT gamma jets.
118402964
Higgs boson decays and production in the left–right twin Higgs model
The left-right twin Higgs model predicts one neutral Higgs boson �0 and it acquires mass m�0 � µr with the µ term, which can be lighter than half the SM-like Higgs boson mass in a portion of parameter space. Thus, the SM-like Higgs boson h can dominantly decay into a pair of light neutral Higgs bosons especially when mh is below the WW threshold. First, we examine the branching ratios of the SM-like Higgs boson decays and find that the new decay mode h ! �0�0 is dominant for the case of mh > 2m�0 . Then we study the production via gluon fusion followed by the decay into two photons or two weak gauge bosons and found that the production rate can be significantly suppressed for some
115768171
Preliminary Results of Mono‐energetic Electron Beams from a Laser‐plasma Accelerator Driven by 200 TW Femto Second Pulses
Relativistic mono‐energetic electron beams have been demonstrated by worldwide laser‐plasma accelerator experiments in the range of a few tens TW. Laser‐plasma accelerator experiment has been carried out with 200TW, 30fs Ti:Sapphire laser pulses focused on helium gas‐jets with F/8.7 optics. Intense mono‐energetic electron beams have been produced in the energy range of 30 to 150 MeV by controlling plasma length and density precisely. Images of Thomson scattering and fluorescence side scattering from plasma indicate highly relativistic effects such as a long self‐channeling and filamentation as well as energetic electron deflection and intense backward Raman scattering. Preliminary results of the first laser‐plasma accelerator experiment in the range of 200TW femto second pulses are presented.