2009 Vol. 33, No. 03

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Particle and field theory
J/ψ→μ+μ reconstruction in the CMS experiment
QIAN Si-Jin
2009, 33(03): 161-169. doi: 10.1088/1674-1137/33/3/001
Abstract:

In this paper the J/ψ→μ+μ reconstruction performance in the CMS experiment at the LHC is studied in detail by using Bs→J/ψ φ→μμKK events. The reconstruction efficiencies of J/ψ mesons and their decay muons are obtained as a function of the transverse momentum pT and the pseudo-rapidity η. We also study the muon trigger efficiency for this channel with the planned Level-1 trigger and High Level Trigger selection criteria. It was observed that the muon reconstruction efficiency decreases when the two decay muons have a small or large 3D angular separation, which further affects the overall J/ψ reconstruction efficiency.

Meson spectra governed by the Fermi-Breit potential
WANG Hai-Jun, ZHANG Wei-Ning, Cheuk-Yin Wong
2009, 33(03): 170-176. doi: 10.1088/1674-1137/33/3/002
Abstract:

We calculate the meson mass spectra in a quark potential model by using the complete Fermi-Breit potential including the terms of orbit-orbit interaction, spin-orbit coupling, and tensor force interaction. We find that these terms give nontrivial contributions to the calculated meson spectra. The orbit-orbit coupling term may lead to an instability of the solution of the Schrödinger equation
and should be regularized.

Topological approach to examine the singularity of the axial-vector current in an Abelian gauge field theory (QED)
YAO Hai-Bo, WU Shi-Shu
2009, 33(03): 177-180. doi: 10.1088/1674-1137/33/3/003
Abstract:

A topological way to distinguish divergences of the Abelian axial-vector current in quantum field theory is proposed. By using the properties of the Atiyah-Singer index theorem, the non-trivial Jacobian factor of the integration measure in the path-integral formulation of the theory is connected with the topological properties of the gauge field. The singularity of the fermion current related to the topological character can be correctly examined in a gauge background.

Nuclear and ion Physics
Simulation and analysis of 13N+p elastic resonance scattering
QIN Xing, WANG Bao-Xiang, LIU Wei-Ping, LI Zhi-Hong, BAI Xi-Xiang, LIAN Gang, ZENG Sheng, SU Jun, LI Yun-Ju, JIANG Chao
2009, 33(03): 181-186. doi: 10.1088/1674-1137/33/3/004
Abstract:

The 13N+p elastic resonance scattering has been studied at the secondary radioactive beam facility of CIAE in inverse kinematics via a thick-target method. The excitation function for the 13N(p,p) scattering was obtained in the energy interval of Ecm≈0.5—3.2 MeV with a 13N secondary beam of (47.8±1.5) MeV. Careful analysis of the secondary beam components and extensive Monte-Carlo simulations enable the resolution of the experimental proton spectra. The resonance parameters for five low-lying levels in 14O were deduced by R-matrix fitting calculations with MULTI7 and SAMMY-M6-BETA. The present results show general agreement with those from a recent similar work, and thus confirm the observation of a new 0 level at 5.7 MeV in 14O with an improved width of 400(45) keV.

Relativistic description of single-particle resonances via phase shift analysis
ZHANG Zi-Zhen
2009, 33(03): 187-190. doi: 10.1088/1674-1137/33/3/005
Abstract:

Single-particle resonant states in spherical nuclei are studied by the real stabilization method in coordinate space within the framework of self-consistent relativistic mean field theory. Taking 122Zr as an example, the resonant parameters, including the energies and widths are extracted by fitting energy and phase shift. Good agreement with the previous calculations has
been found. The details of single-particle resonant states are analysed.

An improved variational method
SHEN Peng-Nian, DING Yi-Bing
2009, 33(03): 191-196. doi: 10.1088/1674-1137/33/3/006
Abstract:

In order to improve the unitarity of the S-matrix, an improved variational formulism is derived by proposing new generating functionals and adopting proper asymptotic boundary conditions for trial relative wave functions. The formulas with the weighted line-column balance for the single-channel and multi-channel scatterings, where the non-central interaction is implicitly considered, are presented. A numerical check is performed with a soluble model in a four coupled channel scattering problem. The result shows that the high accuracy and the unitarity of the S-matrix are reached.

Scaling property in one-nucleon removal reactions induced by exotic nuclei
FU Yao, SUN Xiao-Yan, CAI Xiang-Zhou, GUO Wei, TIAN Wen-Dong, WANG Hong-Wei
2009, 33(03): 197-200. doi: 10.1088/1674-1137/33/3/007
Abstract:

Assuming a core plus valence nucleon structure, one-nucleon removal reaction
is investigated within the framework of few-body Glauber theory. Fermi-type distribution is used for the core density, while the wavefunction of the valence nucleon is calculated by solving the single particle eigenvalue problem of the Schrödinger equation with the Woods-Saxon potential. The parallel momentum distribution (P//) of the fragments is calculated for isotopes with 3R2v/R2c on the full width at half maximum of the parallel momentum distribution (FWHMP//). R2v/R2c is a measure of the exotic extent of the nuclear halo. Based on the obtained scaling law, FWHMP// can be used as an experimental observable to extract R2v/R2c and measure the exotic extent for the nuclear halo.

Jet-photon conversion with energy loss in heavy ion collisions
ZHANG Ben-Wei, ZHANG Han-Zhong, WANG En-Ke
2009, 33(03): 201-204. doi: 10.1088/1674-1137/33/3/008
Abstract:

The rate of high energy photons produced from energetic jets during their propagation through the QGP at RHIC and LHC is studied by taking into account the contribution of jet quenching in the medium. It is shown that the jet quenching effect reduces the rate of jet-photon conversion at large transverse momemtum by about 40% at RHIC with √s=200 AGeV, and by about 80% at LHC with √s=5500 AGeV.

Detection Technology and Methods
Heuristic approach for peak regions estimation in gamma-ray spectra measured by a NaI detector
LIU Liang-Gang, YOU Zhong, XU Ao-Ao
2009, 33(03): 205-209. doi: 10.1088/1674-1137/33/3/009
Abstract:

In this paper, a heuristic approach based on Slavic's peak searching method has been employed to estimate the width of peak regions for background removing. Synthetic and experimental data are used to test this method. With the estimated peak regions using the proposed method in the whole spectrum, we find it is simple and effective enough to be used together with the Statistics-sensitive Nonlinear Iterative Peak-Clipping method.

Software alignment of the BESⅢ main drift chamber using the Kalman Filter method
MAO Ze-Pu, BIAN Jian-Ming, CAO Guo-Fu, CAO Xue-Xiang, CHEN Shen-Jian, DENG Zi-Yan, GAO Yuan-Ning, HE Kang-Lin, HE Miao, HUA Chun-Fei, HUANG Bin, HUANG Xing-Tao0, JI Xiao-Bin, LI Fei, LI Hai-Bo, LI Wei-Dong, LIANG Yu-Tie, LIU Chun-Xiu, LIU Huai-Min, LIU Suo, LIU Ying-Jie, MA Qiu-Mei, MA Xiang, MAO Ya-Jun, MO Xiao-Hu, PAN Ming-Hua, PANG Cai-Ying, PING Rong-Gang, QIN Ya-Hong, QIU Jin-Fa, SUN Sheng-Sen, SUN Yong-Zhao, WANG Liang-Liang, WEN Shuo-Pin
2009, 33(03): 210-216. doi: 10.1088/1674-1137/33/3/010
Abstract:
Software alignment is quite important for a tracking detector to reach its ultimate position accuracy and momentum resolution. We developed a new alignment algorithm for the BESⅢ Main Drift Chamber using the Kalman Filter method. Two different types of data which are helix tracks and straight tracks are used to test this algorithm, and the results show that the design and implementation is successful.
An artificial neural network for proton identification in HERMES data
MAO Ya-Jun, YE Hong-Xue
2009, 33(03): 217-223. doi: 10.1088/1674-1137/33/3/011
Abstract:

The HERMES time-of-flight (TOF) system is used for proton identification, but must be carefully calibrated for systematic biases in the equipment. This paper presents an artificial neural network (ANN) trained to recognize protons from Λ0 decay using only raw event data such as time delay, momentum, and trajectory. To avoid the systematic errors associated with Monte Carlo models, we collect a sample of raw experimental data from the year 2000. We presume that when for a positive hadron (assigned one proton mass) and a negative hadron (assigned one π mass) the reconstructed invariant mass lies within the Λ0 resonance, the positive hadron is more likely to be a proton. Such events are assigned an output value of one during the training process; all others were assigned the output value zero.

The trained ANN is capable of identifying protons in independent experimental data, with an efficiency equivalent to the traditional TOF calibration. By modifying the threshold for proton identification, a researcher can trade off between selection efficiency and background rejection power. This simple and convenient method is applicable to similar detection problems in other experiments.

Accelerator
Tune optimization of the third generation light source storage ring based onFrequency Map Analysis
LIU Gui-Min, LI Hao-Hu, HOU Jie, ZHANG Wen-Zhi
2009, 33(03): 224-231. doi: 10.1088/1674-1137/33/3/012
Abstract:

Tune optimization is necessary to optimize the nonlinearity of the third generation light source storage ring. In this paper we summarize the common strategies for choosing a tune and discuss tune optimization. Frequency Map Analysis (FMA) is applied as a tune scanning tool to reveal information about nonlinear resonances and guide the tune optimization. The Shanghai Synchrotron Radiation Facility (SSRF) storage ring is taken as a test lattice, and the optimum solutions are presented in this paper. Moreover, the third order regular structural resonances excited by sextupoles are particularly investigated, and it is found that these resonances distort the tune shifts with amplitude and show a stop-band like the linear structural resonances.

Simulation of the relativistic backward wave oscillator with a sinusoidal guiding magnetic field
FAN Zhi-Kai, ZHOU Chuan-Ming
2009, 33(03): 232-235. doi: 10.1088/1674-1137/33/3/013
Abstract:

A simulation is carried out to investigate a relativistic backward wave oscillator (RBWO) with a sinusoidal guiding magnetic field. In the numerical simulation, a microwave output power of 1.33 GW at 9.57 GHz microwave frequency with 33% conversion efficiency is achieved. It is a significant attempt which is helpful for developing a practical high power microwave (HPM) source guided by a permanent magnetic field.

Thermal simulation and analysis of the STF cryomodule
Ohuchi Norihito, Kiyosumi Tsuchiya, Tsai Ming-Hsun, ZONG Zhan-Guo, ZHAI Ji-Yuan, GAO Jie
2009, 33(03): 236-239. doi: 10.1088/1674-1137/33/3/014
Abstract:

STF is a superconducting RF test facility constructed at the high energy accelerator research organization of Japan (KEK), as a main part of a R&D project for the proposed International Linear Collider (ILC) in Asia. Thermal study of the STF 1.3 GHz 9-cell cavity cryomodule was carried out within a collaboration between China and Japan. Static and dynamic thermal behaviors of the STF cryomodule were simulated and analyzed with the FEM method, and some simulation results were compared with the available experimental data. This paper presents the details.

Design and simulation of a beam position monitor for the high current proton linac
XU Tao-Guang, FU Shi-Nian
2009, 33(03): 240-244. doi: 10.1088/1674-1137/33/3/015
Abstract:

In this paper, the 2-D electrostatic field software, POISSON, is used to calculate the characteristic impedance of a BPM (beam position monitor) for a high current proton linac. Furthermore, the time-domain 3-D module of MAFIA with a beam microbunch at a varying offset from the axis is used to compute the induced voltage on the electrodes as a function of time. Finally, the effect of low β beams on the induced voltage, the sensitivity and the signal dynamic range of the BPM are discussed.