2010 Vol. 34, No. 11

Particle and field theory
Kinematics of τ two-body decay near τ threshold at BESⅢ
MO Xiao-Hu
2010, 34(11): 1671-1679. doi: 10.1088/1674-1137/34/11/001

The kinematic properties of two-body decay near τ threshold are studied according to the special capacity of the BEPCⅡ accelerator and the BESⅢ detector. Explicitly presented are the transformations of energy and momentum of hadronic particles between different reference frames, and the corresponding distributions. A brand new method is proposed to obtain the energy spread of the accelerator by fitting the energy distribution of hadron from τ semi-leptonic decays.

Probing new physics in B→J/ψ π0 decay
LI Jing-Wu, WU Xiang-Yao
2010, 34(11): 1680-1686. doi: 10.1088/1674-1137/34/11/002

We calculate the branching ratio of B→J/ψ π0 with a mixed formalism that combines the QCD-improved factorization and the perturbative QCD approaches. The result is consistent with experimental data. The quite small penguin contribution in B→J/ψ π0 decay can be calculated with this method. We suggest two methods to extract the weak phase β. One is through the dependence of the mixing induced CP asymmetry SJ/ψπ0 on the weak phase β, the other is from the relation of the total asymmetry ACP with the weak phase β. Our results show that the deviation ΔSJ/ψ π0 of the mixing induced CP asymmetry from sin(-2β) is of O(10-3) and has much less uncertainty. The above O(10-3) deviation can provide a good reference for identifying new physics.

Supersymmetric contributions to Bs→Kπ+ decay
XU Yuan-Guo, WANG Ru-Min, YANG Ya-Dong
2010, 34(11): 1687-1692. doi: 10.1088/1674-1137/34/11/003

Recently, the CDF Collaboration has measured the branching fraction and time-integrated direct CP asymmetry of B_s→Kπ+ decay. The branching ratio is lower than the previous predictions based on QCD factorization. The experimental results favor a large CP asymmetry in Bs→Kπ+ decay while the standard model prediction is very small. We compute the supersymmetry contributions to Bs→Kπ+ decay using the mass insertion method, and find that the LR and RL mass insertions could suppress this branching ratio and increase this direct CP asymmetry well in line with the experimental data.

Entanglement in a two-qubit Heisenberg XXZ chain with different Dzyaloshinskii-Moriyacouplings and an inhomogeneous magnetic field
QIN Meng, LI Yan-Biao, BAI Zhong, LIN Shang-Jin, LIU Wei
2010, 34(11): 1693-1695. doi: 10.1088/1674-1137/34/11/004

Ground state entanglement and thermal entanglement of a two-qubit Heisenberg XXZ chain in the presence of the different Dzyaloshinski-Moriya interaction and inhomogeneous magnetic field are investigated. By the concept of concurrence, we find that the inhomogeneity of the magnetic field may make entanglement last for a long time and the critical temperature is dependent on Jz and b. The entanglement can be increased by increasing the temperature in some cases. We also find that the x-component parameter Dx has a higher critical temperature and more entanglement for a certain condition than the z-component parameter Dz.

particle and nuclear astrophysics and cosmology
Influence of medium effects on the rotating hybrid stars
KANG Miao, ZHOU Xia, WANG Xiao-Dong, HENG Yao-Fu
2010, 34(11): 1696-1699. doi: 10.1088/1674-1137/34/11/005

A hybrid star with a pure quark core, a hadron crust and a mixed phase between the two is considered. The relativistic mean field model for hadron matter and the effective mass bag model for quark matter are used to construct the equation of state for hybrid stars. The influences of medium effects that are parameterized by the strong coupling constant have been discussed on the configuration of rotating stars. The strong coupling constant is a prominent factor that influences the properties of rotating hybrid stars.

Beta decay of nuclide 56Fe, 56Co, 56Ni, 56Mn, 56Cr and 56V due to strong electron screening in stellar interiors
LIU Jing-Jing
2010, 34(11): 1700-1703. doi: 10.1088/1674-1137/34/11/006

According to a new electron screening theory, we discuss the beta decay rates of nuclide 56Fe, 56Co, 56Ni, 56Mn, 56Cr and 56V with and without strong electron screening (SES). The results show that SES has only a slight effect on the beta decay rates for ρ/μe<10^8 g/cm3. However the beta decay rates would be influenced greatly for ρ/μe≥10^8 g/cm3. Due to SES, the maximum values of the C-factor (in %) on beta decay rates of 56Fe, 56Co, 56Ni, 56Mn, 56Cr and 56V is of the order of 95.03%, 35.02%, 98.05%, 80.33%, 98.30% and 98.71% at T9 =4.0 and 98.83%, 98.89%, 99.65%, 10.32%, 4.10% and 40.21% at T9=7.0, respectively.

Effect of the mesons σ* and Φ and the variety of UΣ(N) on the transition density of hyperon stars
ZHAO Xian-Feng, ZHANG Hua
2010, 34(11): 1704-1708. doi: 10.1088/1674-1137/34/11/007

The effect of the mesons σ* and Φ and the variety of UΣ(N) on the transition density of hyperon stars is examined within the framework of relativistic mean field theory for the baryon octet {n, p, Λ, Σ, Σ0, Σ+, Ξ and Ξ0} system. It is found that, compared with that without considering the mesons σ* and Φ, the transition density of hyperon stars decreases, the critical baryon density that hyperons Σ, Σ0, Σ+, Ξ and Ξ0 appears to decrease too, but for Λ the effect is not obvious. As UΣ(N) goes up, the critical baryon density of Σ+, Σ0 and Σ increases, that of Ξ0 decreases and that of Λ and Ξ is fixed. In addition, it is found that the variety of UΣ(N) almost does not influence the transition density.

Effects of the density dependence of the symmetry energy on neutron stars
LIU Xiao-Jin, WU Chen, REN Zhong-Zhou
2010, 34(11): 1709-1713. doi: 10.1088/1674-1137/34/11/008

In this paper, we include the density dependence behavior of the symmetry energy in the improved quark mass density dependent (IQMDD) model. Under the mean field approximation, this model is applied to investigate neutron star matter and neutron stars successfully. Effects of the density dependence of the symmetry energy on neutron
stars are described.

Nuclear and ion Physics
Study of shape isomer yields of 240Am in the framework of a dynamical-statistical model
Hadi Eslamizadeh
2010, 34(11): 1714-1716. doi: 10.1088/1674-1137/34/11/009

A dynamical statistical model is used to analyze the experimental shape isomer yields data in the reaction d+240Pu at E=20—29 MeV. The possibility of determining the nuclear dissipation is discussed. Comparison of the experimental data with the calculations leads to a value of the reduced dissipation coefficient β=0.45×1021 s-1 for the Am isotopes.

Transverse mass distributions of protons produced in heavy-ion collisions at high energies
XIE Wen-Jie
2010, 34(11): 1717-1723. doi: 10.1088/1674-1137/34/11/010

The transverse mass distributions of protons produced in Au-Au collisions at 8 A GeV and Pb-Pb collisions at 158 A GeV are calculated by using the Monte Carlo method in the framework of the multisource ideal gas model. It is found that our calculated results are in agreement with the experimental data in nucleus-nucleus collisions at high energies.

Detection Technology and Methods
Study of absorption and re-emission processes in a ternary liquid scintillation system
XIAO Hua-Lin, LI Xiao-Bo, ZHENG Dong, CAO Jun, WEN Liang-Jian, WANG Nai-Yan
2010, 34(11): 1724-1728. doi: 10.1088/1674-1137/34/11/011
Liquid scintillators are widely used as the neutrino target in neutrino experiments. The absorption and emission of different components of a ternary liquid scintillator (Linear Alkyl Benzene (LAB) as the solvent, 2,5-diphenyloxazole (PPO) as the fluor and p-bis-(o-methylstyryl)-benzene (bis-MSB) as wavelength shifter) are studied. It is shown that the absorption of this liquid scintillator is dominant by LAB and PPO at wavelengths less than 349~nm, and the absorption by bis-MSB becomes prevalent at the wavelength larger than 349 nm. The fluorescence quantum yields, which are the key parameters to model the absorption and re-emission processes in large liquid scintillation detectors, are measured.
236U AMS measurement at CIRCE
GUAN Yong-Jing, de Cesare, WANG Hui-Juan
2010, 34(11): 1729-1732. doi: 10.1088/1674-1137/34/11/012

In order to measure the isotopic ratio of actinides, the upgrade of the accelerator mass spectrometry system at the Center for Isotopic Research on Cultural and Environmental heritage at the Second University of Naples, Italy, was performed. The beam emittance of 238U and the isotopic abundance sensitivity of 236U were measured on the present beam line. Utilizing a 16-strip silicon detector, the sensitivity of 236U/238U≈1×10-11 was obtained.

Multi-pulsed intense electron beam emission from velvet, carbon fibers, carbon nano-tubes and dispenser cathodes
XIA Lian-Sheng, YANG An-Min, CHEN Yi, ZHANG Huang, LIU Xing-Guang, LI Jin, JIANG Xiao-Guo, ZHANG Kai-Zhi, SHI Jin-Shui, DENG Jian-Jun, ZHANG Lin-Wen
2010, 34(11): 1733-1737. doi: 10.1088/1674-1137/34/11/013

The experimental results of studies of four kinds of cathode emitting intense electron beams are demonstrated under multi-pulsed mode based on an experimental setup including two multi-pulse high voltage sources. The tested cathodes include velvet, carbon fibers, carbon nano-tubes (CNTs) and dispenser cathodes. The results indicate that all four are able to emit multi-pulsed beams. For velvet, carbon fiber and CNTs, the electron induced cathode plasma emission may be the main process and this means that there are differences in beam parameters from pulse to pulse. For dispenser cathodes tested in the experiment, although there is a little difference from pulse to pulse for some reason, thermal-electric field emission may be the main process.

Theoretical analysis of a new extraction system for a DUHOCAMIS operating in a high magnetic field
WANG Jing-Hui, ZHU Kun, ZHAO Wei-Jiang, LIU Ke-Xin
2010, 34(11): 1738-1741. doi: 10.1088/1674-1137/34/11/014
A new extraction system is designed for a penning ion source DUHOCAMIS (dual hollow cathode ion source for metal ion beams) being installed at the Institute of Heavy Ion Physics, Peking University. We have analyzed theoretically the central particle trajectories in the extraction region for ions having different q/m ratios and then compared our results with the simulation results of CST (Computer Simulation Technology) software. The validity of the system is verified and some analytical formulas are obtained which will be used for the optimization of the extraction system as well as the experimental setup.
Application of movable collimators to the BEPCⅡ
LUO Tao, JIN Da-Peng, XING Jun, HUANG Nan, DONG Ming-Yi, LI Wei-Guo, LI Hai-Bo, WU Ying-Zhi, ZHANG Qing-Jiang, LIU Guan-Chuan
2010, 34(11): 1742-1748. doi: 10.1088/1674-1137/34/11/015

BEPCⅡ is a double ring e+e collider with high beam currents and luminosity, so the high beam-related backgrounds may disturb the detector. In order to have a good quality of data taking, backgrounds should be kept at a level as low as possible. A series of collimators are designed and installed in both the e+ and e rings. Two of the collimators are horizontally movable, each for one ring, about 8 m upstream from the interaction point. Experiments have been done to identify the effectiveness of the movable collimators with different apertures and beam currents. The results show that the movable collimators are very effective and can reduce as much as about 50% of beam-related backgrounds.

A Particle-in-cell scheme of the RFQ in the SSC-Linac
XIAO Chen, HE Yuan, LU Yuan-Rong, Yuri Batygin, YIN Ling, WANG Zhi-Jun, YUAN You-Jin, LIU Yong, CHANG Wei, DU Xiao-Nan, WANG Zhi, XIA Jia-Wen
2010, 34(11): 1749-1753. doi: 10.1088/1674-1137/34/11/016

A 52 MHz Radio Frequency Quadrupole (RFQ) linear accelerator (linac) is designed to serve as an initial structure for the SSC-Linac system (injector into Separated Sector Cyclotron). The designed injection and output energy are 3.5 keV/u and 143 keV/u, respectively. The beam dynamics in this RFQ have been studied using a three-dimensional Particle-In-Cell (PIC) code BEAMPATH. Simulation results show that this RFQ structure is characterized by stable values of beam transmission efficiency (at least 95%) for both zero-current mode and the space charge dominated regime. The beam accelerated in the RFQ has good quality in both transverse and longitudinal directions, and could easily be accepted by Drift Tube Linac (DTL). The effect of the vane error and that of the space charge on the beam parameters have been studied as well to define the engineering tolerance for RFQ vane machining and alignment.

A lattice scenario for a proton radiography accelerator
WEI Tao, YANG Guo-Jun, HE Xiao-Zhong, LONG Ji-Dong, ZHANG Zhuo, WANG Shao-Heng, YANG Zhen, LI Wei-Feng, LI Hong, YANG Xing-Lin, WANG Min-Hong, SHI Jin-Shui, ZHANG Kai-Zhi, DENG Jian-Jun, ZHANG Lin-Wen
2010, 34(11): 1754-1756. doi: 10.1088/1674-1137/34/11/017

A proton radiography system is an accelerator-based facility. Especially high-energy proton radiography is an advanced hydrodynamics diagnostic tool, and it is the trend of radiography technology development. In this paper, a 20 GeV accelerator complex scenario, including
a 35 MeV linac, a 1 GeV booster and a 20 GeV main ring, is introduced. The overall physics design of the proton radiography accelerator is described, including the design of each part of the accelerator and the choice of the main parameters.

Preliminary study of a niobium quarter-wave prototype cavity for a heavy-ion superconducting linac
ZHANG Cong, ZHAO Hong-Wei, HE Yuan, XU Zhe, ZHANG Zhou-Li, SUN Lie-Peng, MEI Li-Rong, CONG Yan
2010, 34(11): 1757-1761. doi: 10.1088/1674-1137/34/11/018

Superconducting quarter-wave resonators, due to their compactness and their convenient shape for tuning and coupling, are very attractive for low-β beam acceleration. In this paper, two types of cavities with different geometry have been numerically simulated:the first type with larger capacitive load in the beam line and the second type of lollipop-shape for 100 MHz, β=0.06 beams;then the relative electromagnetic parameters and geometric sizes have been compared. It is found that the second type, whose structural design is optimized with the conical stem and shaping drift-tube, can support the better accelerating performance. At the end of the paper, some structural deformation effects on frequency shifts and appropriate solutions have been discussed.

Study of lower emittance dedicated synchrotron radiation mode for the BEPCⅡ
WANG Dou, QIN Qing, GAO Jie
2010, 34(11): 1762-1767. doi: 10.1088/1674-1137/34/11/019

In this paper, a dedicated synchrotron radiation (SR) mode for the BEPCⅡ with an emittance of 85 nm has been designed, including the linear lattice, chromaticity correction and dynamic aperture optimization. The emittance of the new mode is about 60% of the previous mode used for routine operation of the BEPCⅡ. The effect of wigglers on the linear lattice was
compensated and the total dynamic aperture including the wigglers' nonlinear effect was estimated. The preliminary commissioning at the end of 2008 and the formal operation with the new mode confirmed its merits.

Synchrotron radiation,applications of nuclear techniquees,etc
Comparison of linac-based fractionated stereotactic radiotherapy and tomotherapy treatment plans for intra-cranial tumors
Jang Bo, Suk Lee, Sam Ju, Sang Hoon, Juree Kim, Kwang Hwan, Chul Kee, Hyun Do, Rena Lee, Dae Sik, Young Je, Won Seob, Chul Yong, Soo Il
2010, 34(11): 1768-1774. doi: 10.1088/1674-1137/34/11/020
This study compares and analyzes stereotactic radiotherapy using tomotherapy and linac-based fractionated stereotactic radiotherapy in the treatment of intra-cranial tumors, according to some cases. In this study, linac-based fractionated stereotactic radiotherapy and tomotherapy treatment were administered to five patients diagnosed with intra-cranial cancer in which the dose of 18—20 Gy was applied on 3—5 separate occasions. The tumor dosing was decided by evaluating the inhomogeneous index (II) and conformity index (CI). Also, the radiation-sensitive tissue was evaluated using low dose factors V1, V2, V3, V4, V5, and V10, as well as the non-irradiation ratio volume (NIV). The values of the II for each prescription dose in the linac-based non-coplanar radiotherapy plan and tomotherapy treatment plan were (0.125±0.113) and (0.090±0.180), respectively, and the values of the CI were (0.899±0.149) and (0.917±0.114), respectively. The low dose areas, V1, V2, V3, V4, V5, and V10, in radiation-sensitive tissues in the linac-based non-coplanar radiotherapy plan fell into the ranges 0.3%—95.6%, 0.1%—87.6%, 0.1%—78.8%, 38.8%—69.9%, 26.6%—65.2%, and 4.2%—39.7%, respectively, and the tomotherapy treatment plan had ranges of 13.6%—100%, 3.5%—100%, 0.4%—94.9%, 0.2%—82.2%, 0.1%—78.5%, and 0.3%—46.3%, respectively. Regarding the NIV for each organ, it is possible to obtain similar values except for the irradiation area of the brain stem. The percentages of NIV10%, NIV20%, and NIV30% for the brain stem in each patient were 15%—99.8%, 33.4%—100%, and 39.8%—100%, respectively, in the fractionated stereotactic treatment plan and 44.2%—96.5%, 77.7%—99.8%, and 87.8%—100%, respectively, in the tomotherapy treatment plan. In order to achieve higher-quality treatment of intra-cranial tumors, treatment plans should be tailored according to the isodose target volume, inhomogeneous index, conformity index, position of the tumor upon fractionated stereotactic radiosurgery, and radiation dosage for radiation-sensitive tissues.
Preliminary shielding analysis for the CSNS target station monolith
ZHANG Bin, CHEN Yi-Xue, YANG Shou-Hai, WU Jun, YIN Wen, LIANG Tian-Jiao, JIA Xue-Jun
2010, 34(11): 1775-1778. doi: 10.1088/1674-1137/34/11/021

The construction of the China Spallation Neutron Source (CSNS) has been initiated at Dongguan, Guangdong, China. In spallation neutron sources the target station monolith is contaminated by a large number of fast neutrons whose energies can be as large as those of the protons of the proton beam directed towards the tungsten target. A detailed radiation transport analysis of the target station monolith is important for the construction of the CSNS. The analysis is performed using the coupled Monte Carlo and multi-dimensional discrete ordinates method. Successful elimination of the primary ray effects via the two-dimensional uncollided flux and first collision source methodology is also illustrated. The dose at the edge of the monolith is calculated. The results demonstrate that the doses received by the hall staff members are below the required standard limit.