2012 Vol. 36, No. 10

Particle and field theory
Determination of the number of J/ψ events with J/ψ → inclusive decays
M. Ablikim et al (BESⅢ collaboration)
2012, 36(10): 915-925. doi: 10.1088/1674-1137/36/10/001
The number of J/ψ events collected with the BES0 detector at the BEPC/ from June 12 to July 28, 2009 is determined to be (225:3±2:8)×106 using J/ψ → inclusive events, where the uncertainty is the systematic error and the statistical one is negligible.
Event generators for η/η' rare decays into π+π-l+l- and e+e-μ+μ-
ZHANG Zhen-Yu, QIN Li-Qing
2012, 36(10): 926-931. doi: 10.1088/1674-1137/36/10/002
Study of the rare and forbidden decays of η/η' offers a sensitive probe to test fundamental symmetries of quantum chromodynamics and search for new physics beyond the Standard Model. To study the rare decays of η/η' to π+π-e+e-, π+π-μ+μ- and e+e-μ+μ- at the BESⅢ detector, we developed several event generators based on the vector meson dominant model with finite-width corrections and the pseudoscalar mesons mixing theory. The various distributions from event generators are in good agreement with the theoretical predictions, which indicates that the event generators work very well after implemention in the BESⅢ Monte Carlo simulation package. In the BESⅢ physics analysis, the performance of the event generators will be improved in accordance with the distributions of different variables of η/η' from data and the improvement on the theoretical calculations.
Mini-review of rare charmonium decays at BESⅢ
LI Hai-Bo, ZHU Shi-Hai
2012, 36(10): 932-940. doi: 10.1088/1674-1137/36/10/003
Recently, the LHCb experiment announced 3.5σ evidence for direct CP violation in D0 decay by looking at the difference between ACP(D0→K+K-) and ACP(D0→π+π-). This is the rst evidence of CP violation in a charm system, which may indicate new physics beyond the Standard Model. Motivated by this measurement, we review rare processes in charmonium decay, especially, the weak decay, C or P violated decay, and lepton avor violated decays. In case the new physics appears in charm sector, these rare decays of charmonium states will provide an opportunity to search for signi cant contributions from physics beyond the Standard Model. With huge J/ψ and ψ(2S) samples in BES0 experiment, the rare decays may be feasible.
Space- and time-like kaon electromagnetic form factors in perturbative QCD
JIN Dan, YANG Ya-Dong
2012, 36(10): 941-946. doi: 10.1088/1674-1137/36/10/004
We present a phenomenological analysis of the space- and time-like charged kaon electromagnetic form factors in factorized perturbative QCD (pQCD) by employing an analytic model for αs(Q2) and an infrared (IR) finite gluon propagator. In the space-like region, due to the lack of available experimental data above Q2~0.2 GeV2, we only give our results for intermediate energies and make no comparison. In the time-like region, our results agree reasonably well with the available experimental data at moderate energies, including the CLEO data and the m J/ψ result.
particle and nuclear astrophysics and cosmology
One-gluon-exchange effect on the properties of quark matter and strange stars
CHEN Shi-Wu, GAO Li, PENG Guang-Xiong
2012, 36(10): 947-953. doi: 10.1088/1674-1137/36/10/005
We present a modified version of quark mass scaling via considering the important one-gluon-exchange interaction between quarks in the quark mass density-dependent model. The properties of strange quark matter and the structure of strange stars are then studied with the new scaling and a self-consistent thermodynamic treatment. It is found that the one-gluon-exchange effect lowers the system energy considerably, makes the equation of state stiffer, and the sound velocity tends to the ultra-relativistic value faster, which make the biggest value of the maximum mass of strange stars become as big as approximately 2 times the solar mass, in accordance with the latest astronomical observations.
Nuclear and ion Physics
Experimental measurement of the correlation between CT number and heavy ion range
HE Peng-Bo, LI Qiang, LIU Xin-Guo
2012, 36(10): 954-957. doi: 10.1088/1674-1137/36/10/006
For precision delivery of the Bragg peak of a heavy-ion beam to a target volume in ion beam therapy, it is necessary to know the tissue stopping power. A general approach to solve this problem in ion beam therapy is to convert X-ray CT (computed tomography) numbers into water-equivalent path length (WEPL) coefficients using a CT-WEPL calibration curve for all voxels traversed by the beam. This work aims at establishing a CT-WEPL coefficient calibration curve for the heavy ion therapy project at IMP, so as to compute the range of carbon ion beams in tissues easily according to the patient CT data. Several tissue-equivalent materials were applied to measure their WEPL coefficients using a high-energy carbon ion beam in this work. A CT-WEPL calibration curve was obtained through fitting the measured data, which can be used directly for dose optimization and facilitates the design of patient treatment plans significantly at IMP.
Description of the candidate chiral doublet bands in 98Tc
QI Bin, ZHANG Pan, ZHANG Jing, FU Jie, LI Yu-Qi, SONG He-He, WANG Shou-Yu
2012, 36(10): 958-963. doi: 10.1088/1674-1137/36/10/007
The candidate chiral doublet bands in 98Tc with configuration πg9/2 × νh11/2 are studied theoretically for the first time via the triaxial particle rotor model. The main properties of the doublet bands including the energy spectra and electromagnetic transitions are calculated for different triaxiality parameter γ, and the data in 98Tc can be well described by the calculations with γ=38°. Based on the analysis of angular momentum components, it is found that the chiral rotational geometry in 98Tc deviates from the ideal chiral picture.
Half-life of bismuth isotopes predicted by the Coulomb and proximity potential model; a proposition for the spherical nuclei
H. Hassanabadi, A. A. Rajabi, H. Rahimov, S. Zarrinkamar
2012, 36(10): 964-966. doi: 10.1088/1674-1137/36/10/008
We know that the ground state energy, half-life, spin and parity of the heavy nuclei can be determined via the study of alpha decay. Bearing this in mind, we have calculated the penetration probability in the barrier, the decay constant and thereby the half-lives of 21 isotopes of Bi by using the proximity potential model. The comparison with the existing data is motivating.
Single particle potentials of asymmetric nuclear matter in different spin-isospin channels
ZUO Wei, GAN Sheng-Xin
2012, 36(10): 967-972. doi: 10.1088/1674-1137/36/10/009
We investigate the neutron and proton single particle (s.p.) potentials of asymmetric nuclear matter and their isospin dependence in various spin-isospin ST channels within the framework of the Brueckner-Hartree-Fock approach. It is shown that in symmetric nuclear matter, the s.p. potentials in both the isospin-singlet T=0 channel and isospin-triplet T=1 channel are essentially attractive, and the magnitudes in the two different channels are roughly the same. In neutron-rich nuclear matter, the isospin-splitting of the proton and neutron s.p. potentials turns out to be mainly determined by the isospin-singlet T=0 channel contribution which becomes more attractive for the proton and more repulsive for the neutron at higher asymmetries.
Detection Technology and Methods
Design and development of compact readou telectronics with silicon photomultiplier array for a compact imaging detector
ZHANG Xiao-Hui, QI Yu-Jin, ZHAO Cui-Lan
2012, 36(10): 973-978. doi: 10.1088/1674-1137/36/10/010
This work aims at developing compact readout electronics for a compact imaging detector module with silicon photomultiplier (SPM) array. The detector module consists of a LYSO crystal array coupling with a SensL's 4×4 SPM array. A compact multiplexed readout based on a discretized positioning circuit (DPC) was developed to reduce the readout channels from 16 to 4 outputs. Different LYSO crystal arrays of 4×4, 8×8 and 12×12 with pixel sizes of 3.2, 1.6 and 1.0 mm respectively, have been tested with the compact readout board using a 137Cs source. The initial results show that the compact imaging detector module with the compact multiplexed readout could clearly resolve 1 mm× 1 mm× 10 mm LYSO scintillation crystal array except those at the edges. The detector's intrinsic spatial resolution up to 1 mm can be achieved with the 3 mm×3 mm size SPMArray4 through light sharing and compact multiplexed readout. Our results indicate that this detector module is feasible for the development of high-resolution compact PET.
Discrimination of converted photons and neutral pions at high energies
XIAO Hong, CHEN Guo-Ming, TAO Jun-Quan, BIAN Jian-Guo, FAN Jia-Wei, LIANG Song, MENG Xiang-Wei, SHEN Yu-Qiao, TANG Zhi-Cheng, WANG Jian, WANG Xian-You, WANG Zheng, XU Ming, XU Wei-Wei, YANG Min, YAN Qi
2012, 36(10): 979-984. doi: 10.1088/1674-1137/36/10/011
In the LHC experiment, the H→γγ channel provides a clean nal state with an effective mass peak that is reconstructed with great precision, despite the small branching ratio. As a consequence, the H→γγ channel is one of the most promising channels for the Higgs discovery in the very low mass region. In order to increase the sensitivity of the Higgs search, background rejection rate is very important, so γ/π0 discrimination is one of the key points in the analysis. At least 40% of photons will convert with the experience of ATLAS and CMS. We constructed electromagnetic calorimeter (ECAL) in GEANT4 simulation, using 6 variables which have different shapes between converted γ and π0, with the TMVA (Toolkit for Multivariate Data Analysis) to do the separation. With this method we can get 30% to 60% π0 rejection efficiency when keeping 90% converted γ efficiency, in the region of transverse momentum 15 GeV to 75 GeV, not only in MC sumulation but also in real data.
Performance study of a micro-pattern gas detector: leak microstructure
ZHANG Ai-Wu, XIE Yu-Guang, YU Bo-Xiang, AN Zheng-Hua, WANG Zhi-Gang, CAI Xiao, SUN Xi-Lei, SHI Feng, FANG Jian, XUE Zhen, U Qi-Wen, SUN Li-Jun, GE Yong-Shuai, LIU Ying-Biao, LIU Hong-Bang, ZHENG Yang-Heng, XIE Yi-Gang, HU Tao, ZHOU Li, U Jun-Guang
2012, 36(10): 985-990. doi: 10.1088/1674-1137/36/10/012
A micro-pattern gas detector named leak microstructure (LM) has been studied. A new chemical electrolytic technique is introduced to make perfect shaped LM needles with very sharp tips, and this method may be developed to make LM array detectors in batches. The experimental results are presented for both a single needle LM detector and a small LM array detector. The gas gain is up to 105 by calculation from the waveform. Good gain stability and uniformity are achieved. The light emission from the needle tip is also measured in Ar/CF4(95/5) gas mixture. The result shows a promising application for imaging.
Low temperature testing and neutron irradiation of a swept charge device on board the HXMT satellite
WANG Yu-Sa, CHEN Yong, XU Yu-Peng, YANG Yan-Ji, CUI Wei-Wei, LI Mao-Shun, LIU Xiao-Yan, WANG Juan, HAN Da-Wei, CHEN Tian-Xiang, LI Cheng-Kui, HUO Jia, LI Zheng-Wei, LI Wei, HU Wei, ZHANG Yi, LU Bo, ZHU Yue, LIU Yan, WU Di, SUN Qing-Rong, ZHANG Zi-Liang
2012, 36(10): 991-995. doi: 10.1088/1674-1137/36/10/013
We present the low temperature testing of an SCD detector, investigating its performance such as readout noise, energy resolution at 5.9 keV and dark current. The SCD's performance is closely related to temperature, and the temperature range of -80 ℃ to -50 ℃ is the best choice, where the FWHM at 5.9 keV is about 130 eV. The influence of the neutron irradiation from an electrostatic accelerator with fluence up to 1×109 cm-2 has been examined. We find the SCD is not vulnerable to neutron irradiation. The detailed operations of the SCD and the test results of low temperature are reported, and the results of neutron irradiation are discussed.
Horizontal test for BEPCⅡ 500 MHz spare cavity
MI Zheng-Hui, SUN Yi, WANG Guang-Wei, PAN Wei-Min, LI Zhong-Quan, DAI Jian-Ping, MA Qiang, LIN Hai-Ying, LIU Ya-Ping, XU Bo, HUANG Hong, WANG Qun-Yao, XU Yu-Fen, ZHAO Guang-Yuan, HUANG Tong-Ming, SHA Peng, MENG Fan-Bo, QIU Feng, LI Han, CHEN Xu, ZHAO Dan-Yang, ZHANG Juan
2012, 36(10): 996-999. doi: 10.1088/1674-1137/36/10/014
The horizontal test for the BEPCⅡ 500 MHz spare cavity has been completed at IHEP. The maximum voltage of the cavity reached 2.17 MV, while Q0 was 5.78× 108. The process and results of the high power horizontal test are presented and discussed in this paper.
A preliminary study of a negative hydrogen PIG-type ion source for the compact cyclotron
YANG Zhen, LONG Ji-Dong, DONG Pan, WANG Tao, WEI Tao, HE Xiao-Zhong, ZHANG Kai-Zhi, SHI Jin-Shui
2012, 36(10): 1000-1003. doi: 10.1088/1674-1137/36/10/015
A Penning ion gauge (PIG)-type ion source has been used for the generation of negative hydrogen ions (H-) as the internal ion source of the compact cyclotron. The discharge characteristics of the ion source are systematically studied for hydrogen operation at different discharge currents and gas flow rates on the prototype cyclotron. The preliminary study results for the low DC voltage H- extraction measurements are presented in this paper. The H- beam current is measured by the order of magnitude from several tens to hundreds of microamperes at different parameter conditions. The discussion and analysis for the experimental results are good for improving the design and working stability of the ion source.
RF knock-out extraction in HITFiL
SHI Jian, YANG Jian-Cheng, XIA Jia-Wen, YUAN You-Jin, LI Jie, CHAI Wei-Ping, SONG Ming-Tao, ZHANG Xiao-Hu
2012, 36(10): 1004-1008. doi: 10.1088/1674-1137/36/10/016
A compact facility for cancer therapy has been designed and is presently under construction. A slow beam extraction system using the RF-Knock Out method and 3rd-order resonance is adopted in the synchrotron of this facility. Eight sextupoles are used, four of them are for correcting the chromaticity and the rest for driving the 3rd-order resonance. In order to save the aperture of vacuum chamber, a 3-magnet bump is adopted during the extraction process. The extraction phase space map and the last 3 turns' particle trajectory before extraction are given. The matching betatron functions with HEBT (high energy beam transport) are also presented.
Simulation studies on the polarized positron generation from circularly polarized gamma-rays
LI Xiao-Ping, PEI Guo-Xi, PEI Shi-Lun
2012, 36(10): 1009-1012. doi: 10.1088/1674-1137/36/10/017
Polarized positrons can be generated through the electron-positron pair creation from circularly polarized gamma-rays hitting a conversion target. Laser-Compton scattering is an efficient method to generate circularly polarized gamma-rays. Simulation studies on these two processes have been done with the Monte Carlo codes, CAIN and GEANT4. Using CAIN to simulate the Laser-Compton scattering process, the energy spectrum of the generated polarized photons could be obtained. GEANT4 was used to study the yield, energy spectrum and the mean polarization of the positrons emanating from the conversion target. To increase the yield of the generated positrons, an optimization study on the thickness of conversion target was also performed.
Three-dimensional particle-in-cell with Monte Carlo collision simulation of the electron energy distribution function in the multi-cusp ion source for proton therapy
YANG Chao, WU Xiao-Bing, LIU Da-Gang
2012, 36(10): 1013-1018. doi: 10.1088/1674-1137/36/10/018
For optimization and accurate prediction of the amount of proton production in the multi-cusp ion source, analysis of the electron energy distribution function (EEDF) is necessary. A three dimensional particle-in-cell with Monte Carlo collision (PIC-MCC) code based on the CHIPIC software platform are developed. The code is applied to the multi-cusp proton source. The results show that there are two energy distributions in the discharge chamber, and a spatial non-uniformity of electron density due to the B×▽B drift of the top permanent magnets is observed.
Synchrotron radiation,applications of nuclear techniquees,etc
Geometric calibration for a SPECT systemdedicated to breast imaging
WU Li-Wei, CAO Xue-Xiang, WANG Lu, HUANG Xian-Chao, CHAI Pei, YUN Ming-Kai, ZHANG Yu-Bao, ZHANG Long, SHAN Bao-Ci, WEI Long
2012, 36(10): 1019-1024. doi: 10.1088/1674-1137/36/10/019
Geometric calibration is critical to the accurate SPECT reconstruction. In this paper, a geometric calibration method was developed for a dedicated breast SPECT system with a tilted parallel beam (TPB) orbit. The acquisition geometry of the breast SPECT was firstly characterized. And then its projection model was established based on the acquisition geometry. Finally, the calibration results were obtained using a nonlinear optimization method that fitted the measured projections to the model. Monte Carlo data of the breast SPECT were used to verify the calibration method. Simulation results showed that the geometric parameters with reasonable accuracy could be obtained by the proposed method.
Respiratory motion correction with an improved demons algorithm for PET images
GAO Juan, CHAI Pei, YUN Ming-Kai, LIU Shuang-Quan, SHAN Bao-Ci, WEI Long
2012, 36(10): 1025-1030. doi: 10.1088/1674-1137/36/10/020
Respiratory motion is a major factor that affects the quality of PET images of the thoracic area. The diaphragm moves about 15-20 mm due to respiratory motion, which substantially degrades the effective spatial resolution of PET. In this paper, a gated acquisition method is used to correct the motion effects. In this method, an improved demons algorithm is proposed to align the gated images. The experimental results show that the quality of PET images is significantly improved when using our improved method and the proposed method has a faster convergence rate than the original demons algorithm.