2008 Vol. 32, No. 3
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The lightest new gauge boson BH with mass of hundreds GeV is predicted in the littlest Higgs model. BH should be accessible in the planned ILC and the observation of such particle can strongly support the littlest Higgs model. The realization of γγ and e－γ collisions would open a wider window to probe BH. In this paper, we study the new gauge boson BH production processes e－γ→e－γ
BH and e－γ→e－ZBH at the ILC. Our results show that the production cross section of the process e－γ→e－ZBH is less than 0.1fb in most parameter spaces allowed by the electroweak precision data while the cross section of the process e－γ→e－γBH can be over one fb in the favorable parameter spaces. With the high luminosity, the enough typical signals could be produced via ee－γ→e－γBH.
Because the final electron and photon beams can be easily identified and the signal can be easily distinguished from the backgrounds produced by Z and H decaying, e－γ→e－γBH is a promising process to probe BH.
We improve the isospin dependent quantum molecular dynamical model by including isospin effects in the Skyrme potential and the momentum dependent interaction to obtain an isospin dependent Skyrme potential and an isospin dependent momentum interaction. We investigate the isospin effects of Skyrme potential and momentum dependent interaction on the isospin fractionation ratio and the dynamical mechanism in intermediate energy heavy ion collisions. It is found that the isospin dependent Skyrme potential and the isospin dependent momentum interaction produce some important isospin effects in the isospin fractionation ratio.
The interacting boson model with isospin (IBM-3) has been used to study the isospin excitation states and electromagnetic transitions for 24Mg nucleus. The mixed symmetry states at low spin are also analyzed. The theoretical calculations are in agreement with experimental data. The present calculations indicate that the 31+ state is the lowest mixed symmetry state.
The Langevin equation including particle emission was used to reproduce the recently measured spin distribution of evaporation residue cross sections in the reaction 16O+184W at beam energies of 84, 92, 100, 108, 116 and 120MeV. By comparing the theoretical calculations with the experimental data, the validity of the stochastic approach to dissipative fission is verified. Moreover, a pre-saddle nuclear viscosity coefficient of 5×1021s－1 is extracted.
A new charge measurement method, time over threshold (TOT), has been used in some gas detectors lately. Here TOT is studied for TOF system, made of plastic scintillator counter, which can simplify the electronics of the system. The signal characteristics are measured and analyzed with a high quality oscilloscope, including noise, pedestal, signal amplitude, total charge, rise time and the correlation between them. The TOT and charge are related and can be fitted by some empirical formula. The charge measurement resolution by TOT is given and this will help the design of TOF electronics.
We develop an empirical formula to parameterize the 3-dimension
(3D) distribution of electromagnetic showers in the Alpha Magnetic
Spectrometer Ⅱ electromagnetic calorimeter(ECAL). The formula was
verified by ECAL test beam data in 2002 and found to perform well.
The distribution of electron showers in the ECAL are well
described by the formula, which has parameters that allow one to
determine the 3D shape of electromagnetic showers in the ECAL. We
use this formula to correct for lateral energy leakage and dead
channels in the ECAL; good results are obtained.
The chamber production and installation of the BESⅢ MUON identifier system have been finished. The cosmic ray test result after installation shows that the average efficiency is bigger than 95% and can meet the requirement of the design report. A database including all the chamber parameters and performance data has been constructed and is accessible online. The quality control procedures during the production and the database are described.
The Monte-Carlo samples of pion, kaon and proton generated from 0.3GeV/c to 1.2GeV/c by the `tester' generator from SIMBES which are used to simulate the detector of BESⅡ are identified with the Bayesian neural networks (BNN). The pion identification and misidentification efficiencies are obviously better at high momentum region using BNN than the methods of χ2 analysis of dE/dX and TOF information. The kaon identification and misidentification efficiencies are obviously better from 0.3GeV/c to 1.2GeV/c using BNN than the methods of χ2 analysis. The proton identification and misidentification efficiencies using BNN are basically consistent with the ones of χ2 analysis. The anti-proton identification and misidentification efficiencies are better below 0.6GeV/c using BNN than the methods of χ2 analysis.
Superconducting deflecting cavities can be used in synchrotron light source to generate subpico-second X-ray pulses while the impedance of the lower order modes (LOM) and higher order modes (HOM) in the cavity should be kept below an accepted level to avoid beam instability. These modes can be damped by adding waveguide on beam pipe. Detailed simulation of Q in CST Microwave
Studio is introduced and experiment results on an aluminum model cavity with damping waveguide are reported to make a comparison.
In this paper, the nonlinear transport of intense bunched beams in electrostatic quadrupoles is analyzed using the Lie algebraic method, and the results are briefly presented of the linear matrix approximation and the second order correction of particle trajectory in the state space. Beam having K-V distribution and Gaussian distribution approximation are respectively considered. A brief discussion is also given of the total effects of the quadrupole and the space charge forces on the evolution of the beam envelope.
A 3+1/2cell DC-SC photo-injector for PKU-FEL facility is under development，which is an upgrade design of the successful 1+1/2cell DC-SC photo-injector. The Lorentz detuning and tuning structure for the 3+1/2cell superconducting cavity is presented in this paper. The Lorentz force detuning coefficient is 1.2Hz/(MV/m)2 with double stiffening rings for the half cell and single stiffening rings between the adjacent TESLA cells. With the special stiffening structure, the 3+1/2cell whole cavity needs only one tuner. The influences of the tuning on frequency shift, field flatness and average gradient are discussed in this paper. The simulation results show that the stiffening rings' design is successful.
BEPCⅡ is an electron-positron collider designed to run under multi-bunches and high beam current condition. The accelerator consists of an electron ring, a positron ring and a linear injector. In order to achieve the target luminosity and implement the equal bunch charge injection, the Bunch Current Monitor (BCM) system is built on BEPCⅡ. The BCM system consists of three parts: the front-end circuit, the bunch current acquisition system and the bucket selection system. The control software of BCM is based on VxWorks and EPICS. With the help of BCM system, the bunch current in each bucket can be monitored in the Central Control Room. The BEPCⅡ timing system can also use the bunch current database to decide which bucket needs to refill to implement ``top-off'' njection.
A backward wave oscillator (BWO) is introduced in the paper. On the accelerator of Sinus-700, it is experimentally investigated. Under the condition that the electron energy is 740keV, the beam current is 7kA and the guiding magnetic field is at 0.68T, the performance of 1.15GW microwave output power at. 9.1GHz microwave frequency with 22ns pulse width and 22% conversion efficiency are reached.
The design of the China Spallation Neutron Source (CSNS) low-energy beam transport (LEBT) line, which locates between the ion source and the radio-frequency quadrupole (RFQ), has been completed with the TRACE3D code. The design aims at perfect matching, primary chopping, a small emittance growth and sufficient space for beam diagnostics. The line consists of three solenoids, three vacuum chambers, two steering magnets and a pre-chopper. The total length of LEBT is about 1.74m. This LEBT is designed to transfer 20mA of H-pulsed beam from the ion source to the RFQ. An induction cavity is adopted as the pre-chopper. The electrostatic octupole steerer is discussed as a candidate. A four-quadrant aperture for beam scraping and beam position monitoring is designed.
With the development of free electron laser (FEL) and the international linear collider (ILC), the electron bunch length is getting smaller and smaller. The traveling-wave transverse RF deflecting structure is an important part of the RF deflecting method for bunch length measurement and phase space diagnostics. The operation mode in RF deflector is the ``TM11-like'' mode. Since the TM11-like mode in this structure has a pair of degenerate dipole modes, two additional holes are provided on either side of each iris to stabilize the mode. The simulation and optimization have been done. A prototype has been fabricated and tested. The cold test results have been compared with the simulations of the first three modes.
Cascading stages of high gain harmonic generation free electron laser (FEL) seem to be a feasible way to generate short wavelength radiation. With help of the analytical estimates, we design a two-stage cascading scheme to achieve 131nm DUV radiation on the basis of the Shanghai deep ultraviolet free electron laser test facility. Detailed studies on the FEL performance, the stability and the sensitivity of the output power to parameter variation have been achieved by GENESIS1.3, and design of the lattice structure is presented.
The Beijing intense slow positron beam facility is based on the 1.3GeV linac of Beijing Electron-Positron Collider (BEPC) aiming to produce mono-energetic intense slow positron beam for material science investigation. The plugged-in 22Na based slow positron beam section has been newly constructed to supply continuous beam time for the debugging of positron annihilation measurement stations and improve the Beijing intense slow positron beam time using efficiency. Performance testing result of the plugged-in 22Na based slow positron beam facility are reviewed in this paper, with the measurement of the beam transport efficiency, the view of beam spot, the adjustment of beam position, the measurement of beam intensity and energy spread etc. included.
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