2012 Vol. 36, No. 6

Critical behavior of the XY spin chain with three-site interaction studied in terms of the Loschmidt echo
2012, 36(6): 479-484 . doi: 10.1088/1674-1137/36/6/001
The effect of the three-site interaction (α) on the critical behaviors of the XY spin chain is studied in terms of the Loschmidt echo (LE). The critical lines can be shifted by α, and the anisotropy parameter of the XY chain has no effect on the critical lines. The scaling behaviors of the LE reveal that the dynamical behaviors of the LE are reliable for characterizing quantum phase transition (QPT).
Particle and field theory
Production of a neutral scalar associatedwith a photon at the LHC in the topcolor-assisted technicolor model
LI Xu-Xin, YUE Chong-Xing, CHEN Jian-Xing, DAI Jie-Nian
2012, 36(6): 485-488 . doi: 10.1088/1674-1137/36/6/002
In the context of the topcolor-assisted technicolor (TC2) model, we consider the production of the neutral scalar S(πt0 or ht0) associated with a photon at the LHC and compare our results with those given by the minimal supersymmetric extension of the Standard Model (MSSM). We find that its production cross section is larger or smaller than that of the scalar particle predicted by the MSSM model, depending on the values of the relevant free parameters.
Lattice calculation of the κ meson
FU Zi-Wen
2012, 36(6): 489-497 . doi: 10.1088/1674-1137/36/6/003
We study the κ meson in 2+1 flavor QCD with sufficiently light u/d quarks. Using numerical simulations, we measure the point-to-point κ correlators in the "Asqtad" improved staggered fermion formulation. We then analyze these correlators using rooted staggered chiral perturbation theory (rSχPT), with particular attention paid to bubble contribution. After chiral extrapolation, we obtain the physical κ mass with 828±97 MeV, which is within the recent experimental value of 800-900 MeV. These numerical simulations are carried out with MILC 2+1 flavor gauge configurations at a lattice spacing of a ≈ 0.12 fm.
Analysis of (1/2)+ baryon states containing fourth-family quarks from QCD sum rules
YOU Fu-Yi, WANG Zhi-Gang, WAN Shao-Long
2012, 36(6): 498-504 . doi: 10.1088/1674-1137/36/6/004
When the fourth generation of quarks have sufficiently small mixing with ordinary standard-model quarks, the hadrons made up from these quarks can be long-lived enough. We analyze the (1/2)+ baryon states containing fourth-generation quarks and standard-model quarks, i.e. the charm or bottom quarks, in the QCD sum rules approach. Considering the perturbative and two gluon condensate contributions in the calculation, we give the numerical results of the masses and pole residues.
particle and nuclear astrophysics and cosmology
Effects of nuclear deformation on the form factorfor direct dark matter detection
CHEN Ya-Zheng, CHEN Jun-Mou, LUO Yan-An, SHEN Hong, LI Xue-Qian
2012, 36(6): 505-512 . doi: 10.1088/1674-1137/36/6/005
For the detection of direct dark matter, in order to extract useful information about the fundamental interactions from the data, it is crucial to properly determine the nuclear form factor. The form factor for the spin-independent cross section of collisions between dark matter particles and the nucleus has been thoroughly studied by many authors. When the analysis was carried out, the nuclei were always supposed to be spherically symmetric. In this work, we investigate the effects of the deformation of nuclei from a spherical shape to an elliptical one on the form factor. Our results indicate that as long as the ellipticity is not too large, such deformation will not cause any substantial effects. In particular, when the nuclei are randomly orientated in room-temperature circumstances, one can completely neglect them.
Nuclear and ion Physics
Nucleon effective mass in symmetric nuclearmatter from the extended Brueckner-Hartree-Fock approach
GAN Sheng-Xin, ZUO Wei
2012, 36(6): 513-518 . doi: 10.1088/1674-1137/36/6/006
We have calculated the nucleon effective mass in symmetric nuclear matter within the framework of the Brueckner-Bethe-Goldstone (BBG) theory, which has been extended to include both the contributions from the ground-state correlation effect and the three-body force (TBF) rearrangement effect. The effective mass is predicted by including the ground-state correlation effect and the TBF rearrangement effect, and we discuss the momentum dependence and the density dependence of the effective mass. It is shown that the effect of ground state correlations plays an important role at low densities, while the TBF-induced rearrangement effect becomes predominant at high densities.
Detection Technology and Methods
Delay line readout of a large dimension multi-wire proportional chamber
LI Xian-Li, ZHANG Yun-Long, QIAN Hao, XU Zi-Zong, WANG Xiao-Lian
2012, 36(6): 519-524 . doi: 10.1088/1674-1137/36/6/007
A two dimensional multi-wire proportional chamber with delay line readout was developed, which has a large sensitive area of 30 cm× 30 cm. Two cathode planes using printed circuit boards are orthogonally placed to give two coordinates of the impact point of the particle. Signals collected from the cathode strips are amplified and discriminated from two ends of the delay line at each cathode board. By recording the time difference between the two discrimination pulses and the common gate pulse from anode wires, a coordinate position was reconstructed, and a position resolution of better than 1 mm could be obtained in the whole sensitive area along the anode wires.
Developments of a 2D position sensitiveneutron detector
TIAN Li-Chao, TANG Bin, WANG Xiao-Hu, LIU Rong-Guang, ZHANG Jian, CHEN Yuan-Bo, SUN Zhi-Jia, XU Hong, YANG Gui-An, ZHANG Qiang
2012, 36(6): 525-530 . doi: 10.1088/1674-1137/36/6/008
China Spallation Neutron Source (CSNS), one project of the 12th Five-Year-Plan scheme of China, is under construction in Guangdong province. Three neutron spectrometers will be installed during the first phase of the project, and two-dimensional position sensitive thermal neutron detectors are required. Before the construction of the neutron detectors, a prototype of a two-dimensional 200 mm×200 mm Multi-wire Proportional Chamber (MWPC) with Ar/CO2 (90/10) flowing gas has been constructed. In 2009, the prototype was tested with the 55Fe X-ray using part of the electronics, and performed well.
Following the test in 2009, the neutron detector was constructed with the complete electronics and filled with the 6 atm. 3He+2.5 atm. C3H8 gas mixture in 2010. The neutron detector has been primarily tested with an Am-Be source. In this paper, new developments of the neutron detector including the design of the high pressure chamber, the optimization of the gas purifying system and the gas filling process will be reported. The results and discussion are also presented in this paper.
The QE numerical simulation of PEAsemiconductor photocathode
LI Xu-Dong, GU Qiang, ZHANG Meng, ZHAO Ming-Hua
2012, 36(6): 531-537 . doi: 10.1088/1674-1137/36/6/009
Several kinds of models have already been proposed to explain the photoemission process. The exact photoemission theory of the semiconductor photocathode was not well established after decades of research. In this paper an integral equation of quantum efficiency (QE) is constructed to describe the photoemission of positive electron affinity (PEA) of the semiconductor photocathode based on the three-step photoemission model. Various factors (e.g., forbidden band gap, electron affinity, photon energy, incident angle, degree of polarization, refractive index, extinction coefficient, initial and final electron energy, relaxation time, external electric field and so on) have an impact on the QE of the PEA semiconductor photocathode, which are entirely expressed in the QE equation. In addition, a simulation code is also programmed to calculate the QE of the K2CsSb photocathode theoretically at 532 nm wavelength. By and large, the result is in line with the expected experimental value. The reasons leading to the distinction between the experimental and theoretical QE are discussed.
Simulation study of neutrino nucleus crosssection measurement in a segmented detectorat a spallation neutron source
YANG Zhen-Wei, DING Ming-Ming, CHEN Shao-Min, WANG Zhe, ZHANG Feng, GAO Yuan-Ning
2012, 36(6): 538-543 . doi: 10.1088/1674-1137/36/6/010
Knowledge of νe-Fe/Pb differential cross sections for νe energy below several tens of MeV scale is believed to be crucial in understanding supernova physics. In a segmented detector at a spallation neutron source, νe energy reconstructed from the electron range measurement is strongly affected because both multiple scattering and electromagnetic showers occur along the electron passage in target materials. In order to estimate these effects, a simulation study has been performed with a cube block model assuming perfect tracking precision. The energy spectrum distortion is observed to be proportional to the atomic number of the target material. Feasibility of unfolding the distorted νe energy spectrum is studied for both Fe and Pb. An evaluation of the statistical accuracy attainable is therefore provided for a segmented detector.
Digital discrimination of neutrons and γ rays with organic scintillation detectors in an 8-bit sampling system using frequency gradient analysis
YANG Jun, LUO Xiao-Liang, LIU Guo-Fu, LIN Cun-Bao, WANG Yan-Ling, HU Qing-Qing, PENG Jin-Xian
2012, 36(6): 544-551 . doi: 10.1088/1674-1137/36/6/011
The feasibility of using frequency gradient analysis (FGA), a digital method based on Fourier transform, to discriminate neutrons and γ rays in the environment of an 8-bit sampling system has been investigated. The performances of most pulse shape discrimination methods in a scintillation detection system using the time-domain features of the photomultiplier tube anode signal will be lower or non-effective in this low resolution sampling system. However, the FGA method using the frequency-domain features of the anode signal exhibits a strong insensitivity to noise and can be used to discriminate neutrons and γ rays in the above sampling system. A detailed study of the quality of the FGA method in BC501A liquid scintillators is presented using a 5 G samples/s 8-bit oscilloscope and a 14.1 MeV neutron generator. A comparison of the discrimination results of the time-of-flight and conventional charge comparison (CC) methods proves the applicability of this technique. Moreover, FGA has the potential to be implemented in current embedded electronics systems to provide real-time discrimination in standalone instruments.
Bunch compression study using the envelope model in CSRm
YIN Da-Yu, LIU Yong, YUAN You-Jin, YANG Jian-Cheng, LI Peng, MEI Li-Rong, CHAI Wei-Ping, ZHANG Xiao-Hu
2012, 36(6): 552-554 . doi: 10.1088/1674-1137/36/6/012
The feasibility of attaining a short-pulse-duration heavy ion beam with a nanosecond pulse length is studied in the main ring of the Heavy Ion Research Facility in Lanzhou (HIRFL). Such a heavy ion beam can be produced by non-adiabatic compression, and it is implemented by fast rotation in the longitudinal phase space. In this paper, the possible beam parameters during longitudinal bunch compression are studied by using the envelope model. The result shows that a shortest heavy ion bunch 238U28+ of 29 ns with energy of 200 MeV/u can be obtained, which can satisfy high energy density physics research.
RF-thermal-structural-RF coupled analysis on a travelling wave disk-loaded accelerating structure
PEI Shi-Lun, CHI Yun-Long, ZHANG Jing-Ru, HOU Mi, LI Xiao-Ping
2012, 36(6): 555-560 . doi: 10.1088/1674-1137/36/6/013
The travelling wave (TW) disk-loaded accelerating structure is one of the key components in normal conducting (NC) linear accelerators, and has been studied for many years. In the design process, usually after the dimensions of each cell and the two couplers are finalized, the structure is fabricated and tuned, and then the whole structure RF characteristics are measured by using a vector network analyzer. Before fabrication, the whole structure characteristics (including RF, thermal and structural ones) are less simulated due to the limited capability of currently available computers. In this paper, we described a method for performing RF-thermal-structural-RF coupled analysis on a TW disk-loaded structure using only one PC. In order to validate our method, we first analyzed and compared our RF simulation results on the 3 m long BEPCⅡ structure with the corresponding experimental results, which shows very good consistency. Finally, the RF-thermal-structure-RF coupled analysis results on the 1.35 m long NSC KIPT linac accelerating structure are presented.
Synchrotron radiation,applications of nuclear techniquees,etc
Photoinjector beam quality improvement by shaping the wavefront of a drive laserwith oblique incidence
HE Zhi-Gang, WANG Xiao-Hui, JIA Qi-Ka
2012, 36(6): 561-565 . doi: 10.1088/1674-1137/36/6/014
To increase the quantum efficiency (QE) of a copper photocathode and reduce the thermal emittance of an electron beam, a drive laser with oblique incidence was adopted in a BNL type photocathode rf gun. The disadvantageous effects on the beam quality caused by oblique incidence were analyzed qualitatively. A simple way to solve the problems through wavefront shaping was introduced and the beam quality was improved.
Scatter correction for cone-beam computedtomography using self-adaptive scatterkernel superposition
XIE Shi-Peng, LUO Li-Min
2012, 36(6): 566-572. doi: 10.1088/1674-1137/36/6/015
The authors propose a combined scatter reduction and correction method to improve image quality in cone beam computed tomography (CBCT). The scatter kernel superposition (SKS) method has been used occasionally in previous studies. However, this method differs in that a scatter detecting blocker (SDB) was used between the X-ray source and the tested object to model the self-adaptive scatter kernel. This study first evaluates the scatter kernel parameters using the SDB, and then isolates the scatter distribution based on the SKS. The quality of image can be improved by removing the scatter distribution. The results show that the method can effectively reduce the scatter artifacts, and increase the image quality. Our approach increases the image contrast and reduces the magnitude of cupping. The accuracy of the SKS technique can be significantly improved in our method by using a self-adaptive scatter kernel. This method is computationally efficient, easy to implement, and provides scatter correction using a single scan acquisition.