2011 Vol. 35, No. 10

Knockout reaction induced by 6He at 61.2 MeV/u
YE Yan-Lin, JIANG Dong-Xing, HUA Hui, ZHENG Tao, LI Zhi-Huan, GE Yu-Cheng, LI Xiang-Qing, LOU Jian-Ling, CAO Zhong-Xin, SONG Yu-Shou, XIAO Jun, LI Qi-Te, QIAO Rui, YOU Hai-Bo, CHEN Rui-Jiu, XU Hu-Shan, WANG Jian-Song, GUO Zhong-Yan, ZHANG Xue-Ying, LI Chen, HU Zheng-Guo, CHEN Ruo-FU, WANG Meng, XU Zhi-Guo, YUE Ke, TANG Bin, ZANG Yong-Dong, ZHANG Xue-Heng, YAO Xiang-Wu, CHEN Jin-Da, BAI Zhen
2011, 35(10): 891-895. doi: 10.1088/1674-1137/35/10/001
A knockout reaction induced by 6He at 61.2 MeV/u was carried out at the HIRFL-RIBLL radioactive beam line. The α core fragments at forward angles were detected in coincidence with the recoiled protons at large angles. From this coincident measurement the valence nucleon knockout mechanism and the core knockout mechanism can be separated according to the polar angle correlation between the core fragments and the recoiled protons. It is demonstrated that, when reconstructing the resonant state of a weakly bound nucleus, the contamination resulting from the core knockout mechanism should be eliminated in order to obtain the correct structure information.
Particle and field theory
Scalar meson spectroscopy with a fine lattice
FU Zi-Wen, Carleton DeTar
2011, 35(10): 896-901. doi: 10.1088/1674-1137/35/10/002
With sufficiently light u and d quarks the isovector (a0) and isosinglet (f0) scalar meson propagators are dominated at large distances by two-meson states. In the staggered fermion formulation of lattice QCD, taste-symmetry breaking causes a proliferation of multihadron states that complicates the analysis of these channels. Of special interest is the bubble contribution, which makes a considerable contribution to these channels. Using numerical simulation we have measured the correlators for both a0 and f0 channels in the “Asqtad” improved staggered fermion formulation in a MILC fine (a=0.09 fm) lattice ensemble. We analyze those correlators using rooted staggered chiral perturbation theory (rSχPT) and achieve chiral couplings that are well consistent with previous determinations.
Gluon number fluctuations with heavy quarks at HERA
ZHU Xiang-Rong, ZHOU Dai-Cui
2011, 35(10): 902-907. doi: 10.1088/1674-1137/35/10/003
We study the effect of gluon number fluctuations (Pomeron loops) on the proton structure function at HERA. It is shown that the description of charm and bottom quarks and longitudinal structure functions are improved, with χ2/d.o.f,=0.803 (fluctuations) as compared with χ2/d.o.f,=0.908 (without fluctuations), once the gluon number fluctuations are included. We find that in the gluon number fluctuation case the heavy quarks do not play an important role in the proton structure function as the saturation model. The successful description of the HERA data indicates that the gluon number fluctuation could be one of the key mechanisms to describe the proton structure function at HERA energies.
Searching for a neutral top-Higgs in association with top-quark pairs at an e+e- collider in the TC2 model
LI Bing-Zhong, HAN Jin-Zhong
2011, 35(10): 908-913. doi: 10.1088/1674-1137/35/10/004
We investigate the associated production of the neutral top-Higgs ht0 with a pair of top-quarks in the context of the topcolor-assisted technicolor (TC2) model at the future e+e- Linear Colliders (LC) i.e. e+e- → tt ht0. We calculate the production rate and present the distributions of the transverse momenta of top-Higgs and top-quarks. The results show that the total cross section is typically of the order of 1.0-7.5 fb in the energy range between 1000 GeV and 2000 GeV of the LC for the whole top-Higgs mass region of interest. It should be distinctly possible that hundreds or even thousands of ht0 signals can be produced per year at the LC given the luminosity L=500 fb-1.
particle and nuclear astrophysics and cosmology
Kinematics in Randers-Finsler geometry and secular increase of the astronomical unit
2011, 35(10): 914-919. doi: 10.1088/1674-1137/35/10/005
Kinematics in Finsler space is investigated. It is shown that the result based on the kinematics with a special Finsler structure is in good agreement with the reported value of the secular trend in the astronomical unit, dAU/dt=15±4[m/century]. The space deformation parameter λ in this special structure is very small, with a scale of 10-6, and should be a constant. This is consistent with the reported value of an anomalous secular eccentricity variation of the Moon's orbit.
Constraints of gravitational baryo/leptogenesis on Cardassian expansion
2011, 35(10): 920-924. doi: 10.1088/1674-1137/35/10/006
In this paper, proceeding from the relation between the Cardassian model and the accelerated expansion of the universe, adopting a parametric method which does not depend on a precise mechanism for gravitational baryo/leptogenesis and using the model parameter of CPT-violating interaction, we study the role of the modified Friedmann equation which plays a role in the matter asymmetry of the early epoch and the accelerated expansion of the present universe. Thus the appropriate Cardassian component in the radiation-dominated era or in the matter-dominated universe can be obtained. The results indicate that early CPT-violation is included in the Cardassian term. In the same way, the present Cardassian term that belongs to a quintessence-like model can drive the universe towards a flat, matter-dominated and accelerating expansion.
Nuclear and ion Physics
Shape phase transition in neutron-rich even-even light nuclei with Z=20-28
BAI Hong-Bo, LI Xiao-Wei
2011, 35(10): 925-929. doi: 10.1088/1674-1137/35/10/007
The E-Gamma Over Spin (E-GOS) analysis method is applied to the study of the shape phase transition of neutron-rich even-even light nuclei with Z=20-28. Some valuable results are gained through analysing E-GOS curves of Ca, Ti, Cr, Fe and Ni nuclei.
Multi-modal calculations of prompt fission neutrons from 238U(n, f) at low induced energy
ZHENG Na, ZHONG Chun-Lai, FAN Tie-Shuan
2011, 35(10): 930-934. doi: 10.1088/1674-1137/35/10/008
Properties of prompt fission neutrons from 238U(n, f) are calculated for incident neutron energies below 6 MeV using the multi-modal model, including the prompt fission neutron spectrum, the average prompt fission neutron multiplicity, and the prompt fission neutron multiplicity as a function of the fission fragment mass υ(A) (usually named “sawtooth” data) The three most dominant fission modes are taken into account. The model parameters are determined on the basis of experimental fission fragment data. The predicted results are in good agreement with the experimental data.
Medium modified fragmentation function: equivalence of the ACSX and QW formalisms in the high-Q2 region
WANG Meng-Liang, ZHOU Dai-Cui
2011, 35(10): 935-939. doi: 10.1088/1674-1137/35/10/009
We study the medium modified fragmentation function in high-energy heavy-ion collisions. We show that the ACSX and QW formalisms are equivalent to each other in the high-Q2 limit in both theoretical and numerical aspects.
Detection Technology and Methods
A novel simulation method to evaluate the collection performance of a monolithic active pixel sensor
FU Min, TANG Zhen-An
2011, 35(10): 940-945. doi: 10.1088/1674-1137/35/10/010
A novel simulation method is presented in this paper to evaluate the collection performance of monolithic active pixel sensor (MAPS) devices for minimum ionizing particle tracking. A simplified 3D matrix pixel structure is built using the computer aided design software Sentaurus. The virtual device is then divided into hundreds of parts and an independent customized X photon model is involved in each part to simulate the conditions under 55Fe radiation. After data processing and analysis, charge collection efficiency, collection time and diffusion conditions can be estimated in detail. In order to verify the reliability of the method, comparisons are made between the simulations and experiments. Although there are some defects, it can be concluded that the proposed idea is a feasible method for the evaluation of the MAPS collection performance.
Cosmic ray test for a T0 detector
FU Zai-Wei, QIAN Sen, NING Zhe, LIU Shu-Dong, CHEN Xiao-Hui, HENG Yue-Kun, WANG Yi-Fang, QI Ming, YANG Shuai, SUN Yong-Jie, SHAO Ming, LI Cheng, ZHENG Yang-Heng
2011, 35(10): 946-951. doi: 10.1088/1674-1137/35/10/011
The endcap of time-of-flight (ETOF) detector in BES (Beijing Spectrometer) III is planned to be upgraded by using multi-gap resistive plate chambers (MRPCs) and the designed time resolution of the MRPCs is around 50 ps. Thus a time-zero (T0) detector needs to be built to offer a high quality reference time for the MRPCs beam test. So a T0 detector is built using plastic scintillator tiles (BC420) to couple with four fast phototubes (PMTs, Hamamatsu H6533). The timing properties of the detector is studied by using a cosmic ray test and factors related to the time resolution, such as plastic scintillator size, readout mode and angle effects, are discussed. T0 detector timing resolutions of ~41-62 ps are achieved, which means that the T0 detector can be used in the MRPC beam test.
Thermal analysis of DTL in the SSC-LINAC
WU Xi, YUAN Ping, HE Yuan, MA Li-Zhen, ZHANG Xiao-Qi, WU Wei, YANG Ya-Qing
2011, 35(10): 952-954. doi: 10.1088/1674-1137/35/10/012
A linear accelerator as a new injector for the Separated Sector Cyclotron at the Heavy Ion Research Facility of LAN Zhou is being designed. The Drift-Tube-Linac (DTL) has been designed to accelerate 238U34+ from 0.140 MeV/u to 0.97 MeV/u [1]. The 3D finite element analysis of thermal behavior is presented in this paper. During operation, the cavity will produce Joule heat. The cavity will not work normally due to the high temperature and thermal deformation will lead to frequency drift. So it is necessary to perform thermal analysis to ensure the correct working temperature is used. The result of the analysis shows that after the water cooling system is put into the cavity the temperature rise is about 20 degrees and the frequency drift is about 0.15%.
Design of a low level radio frequency control system for the direct current-superconductive photocathode injector at Peking University
ZHANG He, WANG Fang, ZHANG Bao-Cheng, LIN Lin, HAO Jian-Kui, LIU Ke-Xin
2011, 35(10): 955-958. doi: 10.1088/1674-1137/35/10/013
A digital low level radio frequency (LLRF) control system based on a high precision field-programmable gate array (FPGA) is being developed for the stable operation of the upgraded direct current-superconductive (DC-SC) photocathode injector at Peking University. The design of this LLRF control system is described, including both the hardware and the internal algorithm. Analysis of disturbances shows that the system can achieve the requirement of ±0.1% for amplitude stability and ±0.1° for phase stability. Through experiments, preliminary results are presented in the paper.
Application of the transfer matrix for tuning the CSNS-DTL
LI A-Hong, YIN Xue-Jun, FU Shi-Nian, SUN Zhi-Rui
2011, 35(10): 959-963. doi: 10.1088/1674-1137/35/10/014
In the construction of a drift tube LINAC (DTL), many factors caused during the fabrication and assembly of the structure cells cause the electric field distribution not as the same as the design curve. To solve this problem, the traditional way is to solve the equation of Slater's perturbation theorem to obtain the electrical field variation due to local frequency shift. However, that is very difficult under complicated conditions. Since the field perturbation equation is similar to the particle's transverse motion equation, which can be simply solved by using the transfer matrix method, we thus propose to apply a transfer matrix method in tuning the DTL. We demonstrate the availability and advantages of this method with 3D microwave code simulation and the LabVIEW calculation program. After two iterations, the initial error of the electric field of 19.5% has been improved greatly down to 1.3%- -4.5%. This indicates that the transfer matrix method is very useful and convenient for the simplification of tuning procedures.
Numerical optimization and multi-particle dynamics simulation of the radial matching section of the RFQ
XIAO Chen, HE Yuan, YUAN You-Jin, WANG Zhi-Jun, LIU Yong, HE Shou-Bo, XU Meng-Xin, CHANG Wei, LI Chao, YUE Wei-Ming, ZHAO Hong-Wei, XIA Jia-Wen
2011, 35(10): 964-968. doi: 10.1088/1674-1137/35/10/015
The ABC code is an optimization program for the development of matching channels and dynamical matchers in radio frequency quadrupole (RFQ) structures, and a new approach to this code to define the geometry of the radial matching section of the RFQ has been developed. This approach is based on the application of the numerical optimization step by step. This optimization is intended to search for the initial matching condition of a beam, the optimization of parameters of a cell of the channel on given characteristic parameters and traces of a beam in linear channels in both forward and backward directions. To further verify the results of the optimization, multi-particle beam dynamics simulations have been carried out using the BEAMPATH and TRACK codes. The result of the beam dynamics simulation shows that the optimization result of the ABC code is reasonable and this approach provides an opportunity to redesign the structure of the radial matching section of the RFQ.
Synchrotron radiation,applications of nuclear techniquees,etc
Fluorescence lifetime measurement from a designated single-bunch in the BEPCⅡ colliding mode
SUN Shuai-Shuai, XU Guang-Lei, LEI Ge, HUANG Yan, GAO Zhen-Hua, ZHANG Zhi-Yin, TAO Ye
2011, 35(10): 969-973. doi: 10.1088/1674-1137/35/10/016
Fluorescence lifetime measurement in the time domain requires excitation from a well separated single bunch using synchrotron light sources. In the colliding mode of the Beijing Electron Positron Collider Ⅱ (BEPCⅡ), a hybrid filling pattern was realized such that a single bunch was placed in the middle of a large gap between two multi-bunch groups. Detection of fluorescence lifetime, based on the excitation of the light pulse from this designated single-bunch, was established at Beamline 4B8 of the Beijing Synchrotron Radiation Facility (BSRF). The timing signal of the BEPCII was utilized as a trigger to gate this fluorescence event. L-Tryptophan amino acid, a known lifetime standard, was selected to assess the lifetime measurement performance. The measured lifetime was consistent in both colliding and single-bunch mode with the time resolution down to 450 ps. Moreover, both the bunch purity and the fine structure of the hybrid filling pattern were characterized.
Solution conformation of the response regulator proteins from Deinococcus radiodurans studied by SAXS
LI Li-Qin, LIU Ying, LIU Peng, DONG Yu-Hui
2011, 35(10): 974-977. doi: 10.1088/1674-1137/35/10/017
In this paper the solution conformation of the response regulator proteins from Deinococcus radiodurans was studied by small-angle X-ray scattering (SAXS). The SAXS curves of Dr-rrA in solutions were obtained at Beamline 1W2A of Beijing Synchrotron Radiation Facility (BSRF). Two possible conformations of the response regulator proteins, compact and incompact conformations, have been represented by the known crystallographic structures. And theoretical solution scattering curves of the two possible conformations were calculated and fitted to the experimental scattering curve of Dr-rrA, respectively. The result indicates that the solution conformation of the response regulator proteins is inclined to the compact one, which is in agreement with the result of biochemical experiments.
Beam hardening correction for a cone-beam CT system and its effect on spatial resolution
ZHAO Wei, FU Guo-Tao, SUN Cui-Li, WANG Yan-Fang, WEI Cun-Feng, CAO Da-Quan, QUE Jie-Min, TANG Xiao, SHI Rong-Jian, WEI Long, YU Zhong-Qiang
2011, 35(10): 978-985. doi: 10.1088/1674-1137/35/10/018
In this paper, we present a beam hardening correction (BHC) method in three-dimension space for a cone-beam computed tomography (CBCT) system in a mono-material case and investigate its effect on the spatial resolution. Due to the polychromatic character of the X-ray spectrum used, cupping and streak artifacts called beam hardening artifacts arise in the reconstructed CT images, causing reduced image quality. In addition, enhanced edges are introduced in the reconstructed CT images because of the beam hardening effect. The spatial resolution of the CBCT system is calculated from the edge response function (ERF) on different planes in space. Thus, in the CT images with beam hardening artifacts, enhanced ERFs will be extracted to calculate the modulation transfer function (MTF), obtaining a better spatial resolution that deviates from the real value. Reasonable spatial resolution can be obtained after reducing the artifacts. The 10% MTF value and the full width at half maximum (FWHM) of the point spread function with and without BHC are presented.