2011 Vol. 35, No. 9

Particle and field theory
Fine splitting in the charmonium spectrum with a channel coupling effect
YANG Chun, LI Bao-Fei, CHEN Xiao-Lin, DENG Wei-Zhen
2011, 35(9): 797-803. doi: 10.1088/1674-1137/35/9/001
We study the fine splitting in the charmomium spectrum in the quark model with the channel coupling effect, including DD, DD*, D*D* and DsDs, DsDs*, Ds*Ds* channels. The interaction for channel coupling is constructed from the current-current Lagrangian related to the color confinement and the one-gluon exchange potentials. By adopting the massive gluon propagator from the lattice calculation in the nonperturbative region, the coupling interaction is further simplified to four-fermion interaction. The numerical calculation still prefers the assignment 1++ of X(3872).
The dependence of J/ψ-nucleon inelastic cross section on the Feynman variable
DUAN Chun-Gui, LIU Na, MIAO Wen-Dan
2011, 35(9): 804-807. doi: 10.1088/1674-1137/35/9/002
By means of two typical sets of nuclear parton distribution functions, meanwhile taking account of the energy loss of the beam proton and the nuclear absorption of the charmonium states traversing the nuclear matter in the uniform framework of the Glauber model, a leading order phenomenological analysis is given in the color evaporation model of the E866 experimental data on J/ψ production differential cross section ratios RFe/Be(xF). It is shown that the energy loss effect of beam proton on RFe/Be(xF) is more important than the nuclear effects on parton distribution functions in the high Feynman variable xF region. It is found that the J/ψ-nucleon inelastic cross section depends on the Feynman variable xF and increases linearly with xF in the region xF>0.2.
Fourth generation effects in Bs → π-K+ decay
WANG Shuai-Wei, CHANG Qin, HUANG Jin-Shu
2011, 35(9): 808-811. doi: 10.1088/1674-1137/35/9/003
We study the effects of the fourth quark generation model in Bs → π-K+ decay. Combining with the up-to-date experimental measurement for B(Bs → π-K+) and Acpdir(Bs → π-K+) by the CDF Collaboration, we derive the new bound of weak phase øbd, which are 0°< øbd <44°, 321°< øbd < 360° and 0°< øbd < 26°, 342°< øbd < 360° for mt'=400 and 600 GeV respectively. In these regions, B(Bs → π-K+) and Acpdir(Bs → π-K+) consist with the current experimental data within errors.
particle and nuclear astrophysics and cosmology
Effects of the δ meson on the direct Urca processes in neutron stars
YU Zi, DING Wen-Bo
2011, 35(9): 812-816. doi: 10.1088/1674-1137/35/9/004
In the framework of the relativistic mean field theory, the effects of the δ meson on the direct Urca (DURCA) processes are investigated. In a neutron star, the DURCA processes involving nucleons, Λ and Ξ- can take place while the process involving the Ξ0 can not. With the inclusion of the δ meson, the threshold densities for the DURCA processes become lower. With the δ included, the threshold neutron star mass for the DURCA process among nucleons and electrons becomes smaller while the threshold masses for the processes involving hyperons become larger. When the δ meson is included, the total neutrino emissivity remarkably increases in the density range of 0.32--0.41 fm-3. The total neutrino luminosity increases with the neutron star mass first and then decreases. The neutrino luminosity gets larger with the inclusion of the δ meson. The cooling of the EXO0748-676 is sensitive to the isovector scalar interaction.
Nuclear and ion Physics
Isospin and mixed symmetry structure in 26Mg
DONG Hong-Fei, BAI Hong-Bo
2011, 35(9): 817-820. doi: 10.1088/1674-1137/35/9/005
The isospin excitation states and electromagnetic transitions of the 26Mg nucleus are studied with the isospin-dependent interacting boson model (IBM-3). The mixed symmetry states at low spin and the main components of the wave function for some states are also analyzed. The results show good agreement with the available experimental data. From the IBM-3 Hamiltonian expressed in Casimir operator form, the 26Mg is also proved to be a transition nuclei from U(5) to SU(3).
A relativistic continuum Hartree-Bogoliubov theory description of N=3 isotones
HAN Rui, JI Juan-Xia, LI Jia-Xing
2011, 35(9): 821-824. doi: 10.1088/1674-1137/35/9/006
The ground-state properties of N=3 isotones and mirror nuclei have been investigated in the Rrelativistic Continuum Hartree-Bogoliubov theory with the NLSH effective interaction. Pairing correlations are taken into account by a density-dependent δ-force. The calculations show that the proton density distributions of 8B and 9C have a long tail, the core has an increasing tendency of 9C and the paired off valence protons make the halo distribution shrink. The cross sections for the 8B(9C)+12C reaction which are consistent with the experimental data are calculated using the Glauber model. On the whole, we think that 8B is a one-proton halo nucleus and 9C is a two-proton halo nucleus.
Perturbative pseudospin symmetry limit with linear spin-orbit potential
LI Fang-Qiong, ZHAO Peng-Wei, LIANG Hao-Zhao
2011, 35(9): 825-828. doi: 10.1088/1674-1137/35/9/007
The pseudospin symmetry (PSS) limits which conserve substantial spin-orbit splitting are investigated. It is found that while the strength of the spin-orbit potential as well as the spin-orbit splitting increase, the pseudospin doublets, e.g., 2p3/2 and 1f5/2 states, are always degenerate. Furthermore, by examining the perturbation corrections to the single-particle energies, the perturbative nature of the proposed PSS limits is also discussed.
Drell-Yan dilepton production in relativistic heavy-ion collisions at RHIC
FENG Xiu-Mei, ZHANG Ben-Wei
2011, 35(9): 829-832. doi: 10.1088/1674-1137/35/9/008
We investigate the lepton pair production with the Drell-Yan process in relativistic heavy ion collisions by computing the double differential cross section dσ/dM2dy and dσ/dM2dxF at the next-to-leading order in p+Au and Au+Au collisions with √sNN =200 GeV at RHIC. The resulting nuclear modification factors RpAu and RAuAu show strong sensitivity to the cold nuclear matter (CNM) effects and could probe the CNM effects at a very wide region of the longitudinal momentum fraction x. The variation of R with the invariant mass M, the rapidity y and the Feynman variable xF is shown and we find that the nuclear modification factor for the double differential cross section could be smaller than 0.4 in some kinematic regions of high-energy nucleus-nucleus reactions at RHIC.
Study on the method of mini-jet identification in relativistic heavy ion collisions
LI De-Sheng, TIAN Feng-Ge, CHEN Gang
2011, 35(9): 833-837. doi: 10.1088/1674-1137/35/9/009
In this paper a set of methods identifying minijet from final state particles in the relativistic heavy ion collision events is established and the parameter dependence has been investigated in Au+Au collisions at √s= 200 GeV using a multiphase transport model (AMPT). It is found that the number of minijets reduces with the increasing of collision parameter and raises with the increasing of c.m energy. Furthermore, we analyze the rapidity and momentum distribution inside minijets identified using this method.
Detection Technology and Methods
Beam test of signal cross-talk and transmission for LMPRC
SUN Yong-Jie, LI Cheng, TANG Ze-Bo, XU Lai-Lin, CHEN Tian-Xiang, SHAO Ming
2011, 35(9): 838-843. doi: 10.1088/1674-1137/35/9/010
A new prototype of large area Multi-gap Resistive Plate Chamber (MRPC) with long readout strips was built. This Long-strip Multi-gap Resistive Plate Chamber (LMRPC) is double stacked and has ten 250 μm-thick gas gaps. Signals are read out from the two ends of each strip with an active area of 50 cm×2.5 cm in each. The detector was tested at FOPI in GSI, using the secondary particles of proton beams (E=3.5 GeV) colliding with a Pb target. The results show that the LMRPC prototype has a time resolution of about 60-70 ps; the detecting efficiency is over 98% and the ratio of cross-talk is lower than 2%. The detector also has a good spatial resolution of 0.36 cm along the strip direction.
Design and preliminary test results of Daya Bay RPC modules
XU Ji-Lei, GUAN Meng-Yun, YANG Chang-Gen, WANG Yi-Fang, ZHANG Jia-Wen, LU Chang-Guo, Kirk McDonald, Robert Hackenburg, Kwong Lau, Logan Lebanowski, Cullen Newsom, Lin Shih-Kai, Jonathan Link, MA Lie-Hua, Viktor Pec, Vit Vorobel, CHEN Jin, LIU Jin-Chang, ZHOU Yong-Zhao, LIANG Hao
2011, 35(9): 844-850. doi: 10.1088/1674-1137/35/9/011
Resistive Plate Chamber (RPC) modules will be used as one part of the cosmic muon veto system in the Daya Bay reactor neutrino experiment. A total of 189 RPC modules will cover the three water pools in the experiment. To achieve track reconstruction and high efficiency, each module consists of 4 layers, each of which contains two sizes of bare chambers. The placement of bare chambers is reversed in different layers to reduce the overlapping dead areas. The module efficiency and patch efficiency were studied both in simulation and test of the data analysis. 143 modules have been constructed and tested. The preliminary study shows that the module and patch 3 out of 4 layers efficiency reaches about 98%.
RF phase jitter in a klystron amplifier
LI Zheng-Hong, XIE Hong-Quan
2011, 35(9): 851-854. doi: 10.1088/1674-1137/35/9/012
RF phase jitter is a very important parameter for a relativistic klystron amplifier. This parameter is closely linked with the physics processes in the klystron. RF phase jitter is theoretically studied together with Particle in Cell (PIC) simulations in the paper. The main factor is deduced and verified in the PIC simulation. RF phase jitter is significantly affected by the fluctuation of the beam voltage. The relation between the phase jitter and the voltage fluctuation is linear in certain ranges.
Amplitude and phase stability studies in a DC superconducting injector
WANG Fang, LIN Lin, ZHANG He, HAO Jian-Kui, ZHANG Bao-Cheng, LIU Ke-Xin
2011, 35(9): 855-858. doi: 10.1088/1674-1137/35/9/013
The DC superconducting injector will be used in the PKU-THz facility which consists of a DC-gun and a 3+1/2-cell superconducting cavity. The cavity must accelerate the electron beam to 5.82 MeV which is susceptible to perturbations because of its narrow bandwidth. In this paper, the sources and influences of the perturbations in the 3+1/2-cell cavity are discussed. It is shown that the control system is essential for the cavity. The design of a feedback based digital RF low level control system for the 3+1/2-cell cavity is accomplished.
Low emittance lattice optimization using a multi-objective evolutionary algorithm
GAO Wei-Wei, WANG Lin, LI Wei-Min, HE Duo-Hui
2011, 35(9): 859-864. doi: 10.1088/1674-1137/35/9/014
A low emittance lattice design and optimization procedure are systematically studied with a non-dominated sorting-based multi-objective evolutionary algorithm which not only globally searches the low emittance lattice, but also optimizes some beam quantities such as betatron tunes, momentum compaction factor and dispersion function simultaneously. In this paper the detailed algorithm and lattice design procedure are presented. The Hefei light source upgrade project storage ring lattice, with fixed magnet layout, is designed to illustrate this optimization procedure.
BXERL photo-injector based on a 217 MHz normal conducting RF gun
LIU Sheng-Guang, HUANG Tong-Ming, XU Jin-Qiang
2011, 35(9): 865-869. doi: 10.1088/1674-1137/35/9/015
The Beijing X-ray Energy Recovery Linac (BXERL) test facility is proposed in Institute of High Physics (IHEP). In this proposal, the main linac requires the injector to provide an electron beam with 5 MeV energy and 10 mA average current. An injector based on DC gun technology is the first candidate electron source for BXERL. However, the field emission in the DC gun cavity makes it much more difficult to increase the high voltage to more than 500 kV. Another technology based on a 217 MHz normal conducting RF gun is proposed as the backup injector for this test facility. We have designed this RF gun with 2D SUPERFISH code and 3D MICROWAVE STUDIO code. In this paper, we present the optimized design of the gun cavity, the gun RF parameters and the set-up of the whole injector system. The detailed beam dynamics have been done and the simulation results show that the injector can generate electron bunches with RMS normalized emittance 1.0 uppi mmcdotmrad, bunch length 0.77 mm, beam energy 5.0 MeV and energy spread 0.60%.
Synchrotron radiation,applications of nuclear techniquees,etc
Characterization of the nanopore structures of PAN-based carbon fiber precursors by small angle X-ray scattering
WANG De-Hong, HAO Jun-Jie, XING Xue-Qing, MO Guang, GONG Yu, WU Zhong-Hua
2011, 35(9): 870-874. doi: 10.1088/1674-1137/35/9/016
The nanopore structures in precursors are crucial to the performance of PAN-based carbon fibers. Four carbon-fiber precursors are prepared. They are bath-fed filaments (A), water-washing filaments (B), hot-stretching filaments (C) and drying-densification filaments (D). Synchrotron radiation small angle X-ray scattering is used to probe and compare the nanopore structures of the four fibers. The nanopore size, discrete volume distribution, nanopore orientation degree along the fiber axis and the porosity are obtained. The results demonstrate that the nanopores are mainly formed in the water-washing stage. During the processes of the subsequent production technologies, the slenderness ratio of nanopores and their orientation degree along the fiber axis increase further and simultaneously, the porosity decreases. These results are helpful for improving the performance of the final carbon fibers.
GISAXS and SAXS studies on the spatial structures of Co nanowire arrays
CHENG Wei-Dong, MO Guang, XING Xue-Qing, WANG De-Hong, GONG Yu, CAI Quan, CHEN Zhong-Jun, WU Zhong-Hua
2011, 35(9): 875-879. doi: 10.1088/1674-1137/35/9/017
The spatial structures of magnetic Co nanowire array embedded in anodic aluminium membranes were investigated by grazing incidence small angle X-ray scattering (GISAXS) and conventional small angle X-ray scattering (SAXS) techniques. Compared with SEM observation, the GISAXS and SAXS measurements can get more overall structural information in a large-area scale. In this study, the two-dimensional GISAXS pattern was well reconstructed by using the IsGISAXS program. The results demonstrate that the hexagonal lattice formed by the Co nanowires is distorted (a ≈ 105 nm, b ≈ 95 nm). These Co nanowires are isolated into many structure domains with different orientations with a size of about 2 μm. The SAXS results have also confirmed that the nanopore structures in the AAM can be retained after depositing Co nanowires although the Co nanowires can not completely but only just fill up the nanopores. These results are helpful for understanding the global structure of the Co nanowire array.
Parameter study for enhanced high gain harmonic generation scheme
JIA Qi-Ka, LI He-Ting
2011, 35(9): 880-884. doi: 10.1088/1674-1137/35/9/018
An easy-to-implement scheme called Enhanced High Gain Harmonic Generation is expected to be able to significantly enhance the performance of HG-FEL. In this paper we investigate the effects of the system parameters in the new scheme, including the electron energy detuning, initial electron-beam energy spread, seeding laser power, dispersive field strength and amount of the phase shift, etc. The numerical results from GENESIS (3D-code) are presented and show that the new scheme has acceptable parameters tolerance requirements and is no more or even less sensitive to the system parameters than that of the existing scheme; With the electron energy above the resonance, the efficiency is enhanced for both the new scheme and the existing scheme compared with the resonant energy case.
Raman scattering investigation of C-doped a-SiO2 after high energy heavy ion irradiations
LIU Chun-Bao, WANG Zhi-Guang
2011, 35(9): 885-889. doi: 10.1088/1674-1137/35/9/019
Thermally grown amorphous SiO2 films were implanted at room temperature with 100 keV C-ions to 5.0×1017 or 1.2×1018 ions/cm2. These samples were irradiated at room temperature with 853 MeV Pb-ions to 5.0×1011, 1.0×1012, 5.0×1012 ions/cm2, or with 308 MeV Xe-ions to 1.0×1012, 1.0×1013, 1.0×1014 ions/cm2, respectively. Then the samples were investigated using micro-Raman spectroscopy. From the obtained Raman spectra, we deduced that Si--C bonds and sp2 carbon sites were created and nano-inclusions may also be produced in the heavy ion irradiated C-doped SiO2. Furthermore, some results show that Pb ion irradiations could produce larger size inclusions than Xe ions and the inclusion size decreased with increasing the irradiation fluence. The possible modification process of C-doped a-SiO2 under swift heavy ion irradiations was briefly discussed.