2011 Vol. 35, No. 2

Large transverse momentum dilepton production in heavy ion collisions with two-photon processes
FU Yong-Ping, LI Yun-De
2011, 35(2): 109-112. doi: 10.1088/1674-1137/35/2/001
The cold component of large transverse momentum dilepton production via semi-coherent two-photon interaction is calculated. The cold contribution is essential to the dilepton spectra in the soft region for different mass bins. The results are compared with the PHENIX experimental data at RHIC, and we find that the modification of semi-coherent two-photon processes is more evident with the rising dilepton mass bins.
Particle and field theory
Possible heavy molecular states composed of a pair of excited charm-strange mesons
HU Bin, CHEN Xiao-Lin, LUO Zhi-Gang, HUANG Peng-Zhi, ZHU Shi-Lin, YU Peng-Fei, LIU Xiang
2011, 35(2): 113-125. doi: 10.1088/1674-1137/35/2/002
The P-wave charm-strange mesons Ds0(2317) and Ds1(2460) lie below the DK and D* K threshold respectively. They are extremely narrow because their strong decays violate the isospin symmetry. We study the possible heavy molecular states composed of a pair of excited charm strange mesons. As a byproduct, we also present the numerical results for the bottonium-like analogue.
One-loop QCD contribution to the potential of QQ
LIU Li-Quan, ZHAO Shu-Min, ZHANG Jian-Jun, YANG Bao-Zhu, HUANG De-Bao
2011, 35(2): 126-129. doi: 10.1088/1674-1137/35/2/003
Without the non-relativistic approximation in one-loop function, the dominating one-loop contribution to the quark-antiquark potential is studied numerically in terms of perturbative Quantum Chromo Dynamics (QCD). For Coulomb-like potential, the ratio of the one-loop correction to the tree diagram contribution is presented, whose absolute value is about 20%. Our result is consistent with the analysis that the one-loop contribution should be suppressed by a factor αs/π to the leading order contribution. This work can deepen the comprehension of αs in Cornel potential.
Dynamical CP violation of the generalized Yang-Mills model
WANG Dian-Fu, SUN Xiao-Yu, CHANG Xiao-Jing
2011, 35(2): 130-134. doi: 10.1088/1674-1137/35/2/004
Starting from the generalized Yang-Mills model which contains, besides the vector part Vμ, also a scalar part S and a pseudoscalar part P. It is shown, in terms of the Nambu-Jona-Lasinio (NJL) mechanism, that CP violation can be realized dynamically. The combination of the generalized Yang-Mills model and the NJL mechanism provides a new way to explain CP violation.
Controllable entanglement sudden birth of Heisenberg spins
ZHENG Qiang, ZHI Qi-Jun, ZHANG Xiao-Ping, REN Zhong-Zhou
2011, 35(2): 135-138. doi: 10.1088/1674-1137/35/2/005
We investigate the Entanglement Sudden Birth (ESB) of two Heisenberg spins A and B. The third controller, qutrit C is introduced, which only has the Dzyaloshinskii-Moriya (DM) spin-orbit interaction with qubit B. We find that the DM interaction is necessary to induce the Entanglement Sudden Birth of the system qubits A and B, and the initial states of the system qubits and the qurit C are also important to control its Entanglement Sudden Birth.
Spin path integral and quantum mechanics in the rotating frame of reference
CHEN Tong, WU Ning, YU Yue
2011, 35(2): 139-143. doi: 10.1088/1674-1137/35/2/006
We have developed a path integral formalism of the quantum mechanics in the rotating frame of reference, and proposed a path integral description of spin degrees of freedom, which is connected to the Schwinger bosons realization of the angular momenta. We have also given several important examples for the applications in the rotating frames.
Quantum phase transitions about parity breaking in matrix product systems
ZHU Jing-Min
2011, 35(2): 144-148. doi: 10.1088/1674-1137/35/2/007
According to our scheme to construct quantum phase transitions (QPTs) in spin chain systems with matrix product ground states, we first successfully combine matrix product state (MPS) QPTs with spontaneous symmetry breaking. For a concrete model, we take into account a kind of MPS QPTs accompanied by spontaneous parity breaking, though for either side of the critical point the GS is typically unique, and show that the kind of MPS QPTs occur only in the thermodynamic limit and are accompanied by the appearance of singularities, diverging correlation length, vanishing energy gap and the entanglement entropy of a half-infinite chain not only staying finite but also whose first derivative discontinuous.
A result on certain coset subalgebras of the βγ-system
CHU Yan-Jun, HUANG Fang, ZHENG Zhu-Jun
2011, 35(2): 149-152. doi: 10.1088/1674-1137/35/2/008
In this paper, for the highest weight module V4 of sl(2,C) with the highest weight 4, we describe subalgebras Sβ(V4)θ+ and Sγ(V4)θ+ of the βγ-system coset S(V4)θ+ by giving their generators. These coset subalgebras are interesting, new examples of strongly finitely generated vertex algebra.
particle and nuclear astrophysics and cosmology
Study on the separation of 100 TeV γ-rays from cosmic rays for the Tibet ASγ experiment
FENG Zhao-Yang, ZHANG Yi, LIU Cheng, FAN Chao, LI Hong-Chao, WANG Bo, WU Han-Rong, HU Hong-Bo, LU Hong, TAN You-Heng
2011, 35(2): 153-157. doi: 10.1088/1674-1137/35/2/009
A γ/hadron separation analysis is described for the observed air shower events with primary energy above 100 TeV based on the Tibet ASγ detector configuration. The shower age and size parameters are fitted from the measured lateral density distribution and used as discrimination variables. According to the MC simulation while taking into account the systematic uncertainty estimated from data and MC comparison, it is found that 70% of the cosmic ray (CR) background can be rejected while more than 78% of the γ-rays can be retained. Sensitivity for 100 TeV γ-rays observation can thus be improved by at least 40%.
Nuclear and ion Physics
Quantitative conditions for the formation of p-wave neutron halos
GUO Yan-Qing, SONG Jie
2011, 35(2): 158-162. doi: 10.1088/1674-1137/35/2/010
With the experimental binding energies and configurations, the root-mean-square radii of p-wave valence neutron distributions for nuclei up to the second p-shell have been calculated in the framework of the single-particle potential model. By analyzing the relations between the radii and the binding energies, the scaling laws of p-wave valence neutron distributions are obtained. The quantitative conditions for the formation of p-wave neutron halos are deduced from these scaling laws. Based on the investigation on the probability of finding the valence nucleon outside the range of the interaction potential, a 2p3/2 halo state in 47S is anticipated for the first time. These obtained results might provide reference for searching for p-wave neutron halos in nuclei up to the second p-shell.
Detection Technology and Methods
Micromegas prototypes with thermo-bond film separators
GUAN Liang, TANG Hao-Hui, GUO Jun-Jun, WANG Xiao-Lian, XU Zi-Zong, ZHAO Tian-Chi
2011, 35(2): 163-168. doi: 10.1088/1674-1137/35/2/011
In this paper we report the results of Micromegas prototypes constructed by attaching micromesh to an anode using thermo-bond films. The excellent metal attaching ability and good dielectical property of this kind of film make it a promising material to be used as avalanche gap spacers. Several prototypes are successfully made. The electron transmission properties are first studied and then the gas gain is measured in argon-isobutane mixtures. The maximum gain of more than 104 is easily obtained. The energy resolutions for 55Fe 5.9 keV Kα ray can be better than 20% over one magnitude in gain for different operational gas mixtures and the best energy resolution of 13.7% (FWHM) can be achieved with the gas mixture of 94% argon concentration. The preliminary test results of the prototypes with sensitive area of 45 mm×45 mm without internal support show good uniformity across the sensitive area.
Effects of orientation of substrate on the enhanced low-dose-rate sensitivity (ELDRS) in NPN transistors
LU Wu, ZHENG Yu-Zhan, WANG Yi-Yuan, REN Di-Yuan, GUO Qi, WANG Zhi-Kuan, WANG Jian-An
2011, 35(2): 169-173. doi: 10.1088/1674-1137/35/2/012
The radiation effects and annealing characteristics of two types of domestic NPN bipolar junction transistors, fabricated with different orientations, were investigated under different dose-rate irradiation. The experimental results show that both types of the NPN transistors exhibit remarkable Enhanced Low-Dose-Rate Sensitivity (ELDRS). After irradiation at high or low dose rate, the excess base current of NPN transistors obviously increased, and the current gain would degrade rapidly. Moreover, the decrease of collector current was also observed. The NPN transistor with <111> orientation was more sensitive to ionizing radiation than that with <100> orientation. The underlying mechanisms of various experimental phenomena are discussed in detail in this paper.
Experimental studies of micromegas detectors with different micro-meshes
YANG He-Run, HU Bi-Tao, ZHANG Xiao-Dong, ZOU Chun-Yan
2011, 35(2): 174-178. doi: 10.1088/1674-1137/35/2/013
The structure of micromegas (micro-mesh gaseous structure) detectors with different micro-meshes of stainless steel wire woven netting and Ni foil has been presented. The counting rates, energy resolution, gain, discharge probability and time resolution have been measured. Wider counter plateaus and gain for the developed detector were obtained. Excellent energy resolution of the micromegas detector, 17% (FWHM) based on Ni foil micro-mesh and 25% (FWHM) based on stainless steel wire woven netting micro-mesh, has been obtained for the 5.9 keV photon peak of the 55Fe X-ray source in an Ar/CO2(10%) gas mixture. The best time resolution at -620 V micro-mesh voltage and -870 V drift voltage is 14.8 ns for cosmic rays in an Ar/CO2(10%) gas mixture. These results satisfy the basic demand of the micromegas detector preliminary design.
Analysis of superconducting cavity quench events at SSRF
HOU Hong-Tao, LIU Jian-Fei, ZHAO Yu-Bin, ZHAO Shen-Jie, ZHANG Zhi-Gang, LUO Chen, FENG Zi-Qiang, MAO Dong-Qing, ZHENG Xiang, LI Zheng
2011, 35(2): 179-182. doi: 10.1088/1674-1137/35/2/014
Quench is important and dangerous to superconducting RF cavities. This paper illustrates the mechanism of quench and how a quench detector works, and analyzes the quench events happening during beam operations and cavity conditioning. We find that the quench protection is mostly triggered by some reasons such as fluctuation of cavity voltage, multipacting or arc, rather than a real cavity thermal breakdown. The results will be beneficial to optimize the operation parameters of superconducting cavities, to discover the real reasons for beam trip by quench interlock, and to improve the operation stability of superconducting RF systems.
Simulation and analysis of the transverse spectrum in HIRFL-CSR
LI Peng, YUAN You-Jin, MAO Li-Jun, YANG Jian-Cheng, LI Guo-Hong, YIN Da-Yu, LI Jie, LI Xiao-Ni, CHAI Wei-Ping, SHI Jian
2011, 35(2): 183-187. doi: 10.1088/1674-1137/35/2/015
Particles in a storage ring oscillate in the longitudinal and transverse dimensions. Therefore, the signal that beam has generated can be analyzed in the frequency domain to extract many beam parameters, such as tune, momentum spread, emittance and their evolution with time and so on. In this paper, the transverse spectrum in HIRFL-CSR was simulated and analyzed under different conditions, including electron cooling, hollow electron beam, solenoid effect, the tune shift caused by power supply ripple and the misalignment between ion and electron beams. The result of the simulation shows that the longitudinal magnetic field of the electron cooling device should be compensated by a “compensation solenoid”, and the power supply ripple must be controlled, otherwise the accumulation would be affected and the beam would be lost.
Study on the HOMs coupler design of spoke cavity
XIAO Yong-Chuan, YIN Xue-Jun, MU Zhen-Cheng, FU Shi-Nian
2011, 35(2): 188-192. doi: 10.1088/1674-1137/35/2/016
The superconducting spoke cavity has been proposed to accelerate the proton in the low energy section of high power proton linac for an Accelerator Driven Sub-critical System (ADS). Considering that the High Order Modes (HOMs) in the superconducting cavity have far reaching influence on power dissipation and beam stability, the analysis of HOMs of the spoke cavity is needed. In this paper, we put emphasis on the analysis of HOMs of the spoke cavity and the HOMs coupler design.
Design of triode extraction system for a dual hollow cathode ion source
WANG Jing-Hui, ZHU Kun, ZHAO Wei-Jiang, LIU Ke-Xin
2011, 35(2): 193-198. doi: 10.1088/1674-1137/35/2/017
A triode extraction system is designed for a dual hollow cathode ion source being developed at the Institute of Heavy Ion Physics, Peking University. Basic parameters of the plasma are selected after examining the operation principle of the ion source, then the triode extraction system is designed and optimized by using software PBGUNS (for Particle Beam GUN Simulations). The physical design of the system is given in this paper.
Synchrotron radiation,applications of nuclear techniquees,etc
Total electron yield mode for XANES measurements in the energy region of 2.1--6.0 keV
ZHENG Lei, ZHAO Yi-Dong, TANG Kun, MA Chen-Yan, HAN Yong, CUI Ming-Qi
2011, 35(2): 199-202. doi: 10.1088/1674-1137/35/2/018
The total electron yield (TEY) mode has been developed successfully for XANES measurements at Beamline 4B7A of BSRF (Beijing Synchrotron Radiation Facility). Its performance was studied by measuring sulphur K-edge XANES of three CdS samples (mixed with graphite powder as an electric conductor) with different concentration: 75%, 50% and 25%. The data are collected in TEY mode and fluorescence yield (FY) mode respectively for comparison. The results demonstrate that the TEY spectra of three samples agree well with each other after the background is subtracted and normalized. The measured XANES spectra by TEY mode without bias and with 100V bias are almost identical to one another, but the signal-to-noise ratio of spectra measured without bias is better than that with 100V bias. The consistency of the self-absorption corrected FY spectra and TEY spectra are within 10% for the three samples.
Spectral distributions of the scattered photons within an acceptance angle in Thomson scattering
2011, 35(2): 203-208. doi: 10.1088/1674-1137/35/2/019
In this paper, we present the analysis of the spectral distributions of the scattered photons within a certain acceptance angle in Thomson scattering, in which the beam divergence, energy spread and spatial distribution are all considered. The analytical results are compared with the simulation results, and good agreement between the two approaches is obtained.