2009 Vol. 33, No. 8

Particle and field theory
Result of search for low velocity exotic particles
MA Xin-Hua, DING Lin-Kai, GUO Ya-Nan, HE Zuo-Xiu, HUO An-Xiang, JING Cai-Liu, KUANG Hao-Huai, MA Yu-Qian, QING Cheng-Rui, SHEN Chang-Quan, YU Zhong-Qiang, ZHANG Chao, ZHU Qing-Qi
2009, 33(8): 603-608. doi: 10.1088/1674-1137/33/8/001
The L3+C experiment, taking advantage of the L3 muon magnetic spectrometer, measured the spatial tracks of charged cosmic ray particles to obtain rigidity as well as velocity. One possible low velocity exotic particle is observed. The existing uncertainties are discussed, and the flux upper limit of the low velocity exotic particles from this observation is deduced based on the assumption of a null observation. The result is 6.2×10-10 cm-2﹒s-1﹒sr-1 at 90% confidence level in the velocity range from 0.04c to 0.5c.
Feasibility study of a J/ψ cross section measurement with early CMS data
YANG Zong-Chang, QIAN Si-Jin
2009, 33(8): 609-616. doi: 10.1088/1674-1137/33/8/002

We report the methods and plans for measuring the differential cross section of J/ψ→μ+μ production, using data to be collected in the first LHC run by the CMS detector. Making use of the large B-hadron lifetime, we show how to separate the promptly produced J/ψ's from those coming from B-hadron decays. Since the J/ψ production cross section is expected to be large, the analysis should be viable with relatively small data sets, that will become available early in the startup of the LHC. We also address effects of a non-perfect detector alignment, as well as systematic uncertainties.
About 70 thousand J/ψ decays are reconstructed from Monte Carlo data, which corresponds to an integrated luminosity of 3 pb-1 in 14 TeV collisions, in the range of ptJ/ψ between 5 and 40 GeV/c. The precision of the result is limited by systematic uncertainties, and is at the 15% level.

On ηc line shape in charmonium transitions
PING Rong-Gang
2009, 33(8): 617-621. doi: 10.1088/1674-1137/33/8/003

The line shapes to observe ηc in charmonium transitions, i.e., ψ(2S), J/ψ→γηc, are investigated. The ηc line shapes in exclusive decays or by observing the inclusive photon spectrum are given. The sensitivities to measure the ηc resonance parameters are also evaluated. With more than two thousand ηc events observed, the precision of the ηc decay width measurement will be improved by better than 3%. However, the uncertainties associated with the ηc modified line shapes will dominate the systematic errors and this will prohibit precision mass and width measurements.

Photon higher-order squeezing effects of the q analogue of a single-mode field interacting with a Ξ-type three-level atom
ZHANG Hui-Hui, SHEN Hua-Jun, ZHOU Jing-Tao, LIU Xin-Yu
2009, 33(8): 622-625. doi: 10.1088/1674-1137/33/8/004

The nonlinear theory of interaction between the q analogue of a single-mode field and a Ξ-type three-level atom has been established. And the formal solution of the Schrödinger equation in the representation and its average number are obtained. Then, the photon squeezing effects are studied through numerical calculation. The results show that the q deformation nonlinear action has a lot of influence on the quantum coherence and quantum properties. When $q$ approaches 1, the theory reduces to the common linear theory.

particle and nuclear astrophysics and cosmology
Ultra-high energy cosmic rays threshold in Randers-Finsler space
2009, 33(8): 626-628. doi: 10.1088/1674-1137/33/8/005

Kinematics in Finsler space is used to study the propagation of ultra high energy cosmic rays particles through the cosmic microwave background radiation. We find that the GZK threshold is lifted dramatically in Randers-Finsler space. A tiny deformation of spacetime from Minkowskian to Finslerian allows more ultra-high
energy cosmic rays particles to arrive at the earth. It is suggested that the lower bound of particle mass is related with the negative second invariant speed in Randers-Finsler space.

Nuclear and ion Physics
Electric-dipole transitions in 165Er
WANG Shi-Tao, ZHOU Xiao-Hong, ZHANG Yu-Hu, ZHENG Yong, LIU Min-Liang, MA Fei, HU Jun, CHEN Liang, ZHANG Xin, ZHANG Ning-Tao, ZHU Li-Hua, WU Xiao-Guang, LI Guang-Sheng
2009, 33(8): 629-632. doi: 10.1088/1674-1137/33/8/006
High-spin states of 165Er were studied using the 160Gd(9Be, 4n)reaction at beam energies of 42 and 45 MeV. The previously known bands based on the ν5/2[523] and ν5/2+[642] configurations have been extended to high-spin states. Electric-dipole transitions linking these two opposite parity bands were observed. Relatively large B(E1) values have been extracted experimentally and were attributed to octupole softness.
α-decay half-lives of superheavy nuclei and general predictions
DONG Jian-Min, ZHANG Hong-Fei, WANG Yan-Zhao, ZUO Wei, SU Xin-Ning, LI Jun-Qing
2009, 33(8): 633-638. doi: 10.1088/1674-1137/33/8/007

The generalized liquid drop model (GLDM) and the cluster model have been employed to calculate the α-decay half-lives of superheavy nuclei (SHN) using the experimental α-decay Q values. The results of the cluster model are slightly poorer than those from the GLDM if experimental $Q$ values are used. The prediction powers of these two models with theoretical $Q$ values
from Audi et al. (QAudi) and Muntian et al. (QM) have been tested to find that the cluster model with QAudi and QM could provide reliable results for Z>112 but the GLDM with QAudi for Z≤112. The half-lives of some still unknown nuclei are predicted by these two models and these results may be useful for future experimental assignment and identification.

Density-dependent potential for multi-neutron halo nuclei
CHEN Shuang, CHU Yan-Yun, REN Zhong-Zhou
2009, 33(8): 639-644. doi: 10.1088/1674-1137/33/8/008

We apply a simple density-dependent potential model to the three-body calculation of the ground-state structure of drip-line nuclei with a weakly bound core. The hyperspherical harmonics method is used to solve the Faddeev equations. There are no undetermined potential parameters in this calculation. We find that for the halo nuclei with a weakly-bound core, the calculated properties of the ground-state structure are in better agreement with experimental data than the results calculated from the standard Woods-Saxon and Gauss type potentials. We also successfully reproduce the experimental cross sections by using the density calculated from this method. This may be explained by the fact that the simple Fermi or Gaussian function can not exactly describe the density distribution of the drip-line nuclei.

Strange K nuclear systems (S=-1)
LI Yi-He, WU Shi-Shu
2009, 33(8): 645-647. doi: 10.1088/1674-1137/33/8/009

Λ(1405) is considered as a superposition of two resonances instead of a simple bound state of the kaon and proton. Within the framework of the Brueckner-Hartree-Fock(BHF) theory, we have investigated the K nuclear systems (S=-1), especially Kpp and Kpnn}(T=1). The binding energy BK- is 23 MeV (3 MeV) and the width Γ is 62 MeV (56 MeV) for Kpp(Kpnn(T=1)).

Stable solutions for qq bound states with a regularized Breit potential
ZHANG Wei-Ning
2009, 33(8): 648-654. doi: 10.1088/1674-1137/33/8/010

The Breit interaction contains singular terms which may lead to an instability in quark-antiquark bound state calculations. We regularize the Breit interaction by multiplying the singular terms in momentum space by the form factor μ2/(q22) such that the interaction is not singular at the origin and the intermediate- and long-range parts of the interaction remain unchanged. The singular terms in the Breit potential find their stable contributions in the calculations after being multiplied by the form factor with different powers. Such a regularized Breit potential with a linear and a relativistically corrected confining potential are applied to the study of qq bound states. The spectra for most familiar mesons are consistently obtained and agree well with the experimental data.

Characterizing variable for the critical point in momentum space
DU Jia-Xin, KE Hong-Wei, XU Ming-Mei, LIU Lian-Shou
2009, 33(8): 655-660. doi: 10.1088/1674-1137/33/8/011

The possible experimentally observable signal in momentum space for the critical point, which is free from the contamination of statistical fluctuations, is discussed. It is shown that the higher order scaled moment of transverse momentum can serve as an appropriate signal for the critical point, provided the transverse momentum distribution has a sudden change when energy increases passing through this point. A 2-D percolation model with a linear temperature gradient is constructed to check this suggestion. A sudden change of third order scaled moment of transverse momentum is observed.

Imaging source with Gaussian proper time distribution
CHEN Li-Zhu, KE Hong-Wei, WU Yuan-Fang
2009, 33(8): 661-665. doi: 10.1088/1674-1137/33/8/012
Making use of the maximum entropy method, we study the most probable
source function in heavy ion collisions. An anisotropic Gaussian source is deduced by simply assuming that the particles are emitted within a finite proper-time. The general relations between the most probable source function and the minimal assumptions are discussed, which are instructive in constructing a self-consistent source function from observed Hanbury-Brown/Twiss(HBT) correlations.
Detection Technology and Methods
Track reconstruction in the BESⅢ muon counter
LIANG Yu-Tie, LIU Kun, YOU Zheng-Yun, MAO Ya-Jun, LI Wei-Dong
2009, 33(8): 666-672. doi: 10.1088/1674-1137/33/8/013

The reconstruction algorithm for BESⅢ Muon Counter, MucRecAlg, is developed with the object-oriented language C++ in BESⅢ offline software environment. MucRecAlg consists of the following functions: to find track seeds either from extrapolation of tracks in the main drift chamber or from the fired strips in muon counter, to select fired strips associated to the candidate tracks, to fit the
candidate tracks with a linear or quadratic function and to calculate other parameters of the tracks for muon identification. Monte Carlo samples are generated to check the performance of the reconstruction package, such as reconstruction efficiency, muon remaining rate and pion rejection rate, etc. The preliminary results show that the pion rejection rate is around 3%—4% while the muon remaining rate is better than 90% in 0.4—1.6 GeV/c momentum
region, which meets the requirement as shown in the design report.

Effect of the integrated time of the induced current signal on the position resolution of the RPC detector
YE Jin, YUE Qian, LI Yuan-Jing, CHENG Jian-Ping, LI Jin, WANG Yi
2009, 33(8): 673-676. doi: 10.1088/1674-1137/33/8/014

A prototype RPC with position resolution less than 1 mm has been produced and studied. Based on this RPC detector, the effect of the width of the integrated FADC time window on the position resolution of a RPC has been studied experimentally and theoretically. The results of theoretical calculation and experimental measurement have shown good agreement.

Measurement of the response function and the detection efficiency of an organic liquid scintillator for neutrons between 1 and 30 MeV
HUANG Han-Xiong, RUAN Xi-Chao, CHEN Guo-Chang, ZHOU Zu-Ying, LI Xia, BAO Jie, NIE Yang-Bo, ZHONG Qi-Ping
2009, 33(8): 677-681. doi: 10.1088/1674-1137/33/8/015

The light output function of a φ50.8 mm×50.8 mm BC501A scintillation detector was measured in the neutron energy region of 1 to 30 MeV by fitting the pulse height (PH) spectra for neutrons with the simulations from the NRESP code at the edge range. Using the new light output function, the neutron detection efficiency was determined with two Monte-Carlo codes, NEFF and SCINFUL. The calculated efficiency was corrected by comparing the simulated PH spectra with the measured ones. The determined efficiency was verified at the near threshold region and normalized with a Proton-Recoil-Telescope (PRT) at the 8—14 MeV energy region.

Central region design for a 10 MeV internal ion source cyclotron
QIN Bin, LIU Kai-Feng, FENG Yi-Zhang, FAN Ming-Wu
2009, 33(8): 682-686. doi: 10.1088/1674-1137/33/8/016

Internal ion sources are widely adopted in commercial cyclotrons used for short-life isotopes production. Without beam manipulation provided by the external beam injection line, the central region of this type of cyclotron is more sensitive and should be carefully designed. A design study and beam dynamics simulation for the central region of a 10 MeV compact cyclotron is presented. The OPERA3D/TOSCA code was used to calculate the electric field from a parameterized three dimensional (3D) central region model. With iterative structure optimizations of the central region, the beam centering and vertical focusing is well controlled, and the RF phase acceptance is around 25°. A c++ code for beam simulation in the central region was developed and tested.

Design optimization of a tapered mirror for microfocusing optics
MAO Cheng-Wen, XI Zai-Jun, YU Xiao-Han, XIAO Ti-Qiao
2009, 33(8): 687-690. doi: 10.1088/1674-1137/33/8/017

A facile microfocusing optical design is presented which is optimized for less slope error against the traditional tapered mirror. The essential idea of the innovation is based on the characteristics of the slope-error curve for the prototype. The relationship between the mirror shape of the improved model and the driving moments is established. Analytical results have been compared with the results of the prototype. The design demonstrates theoretically that
smaller slope error is obtained with longer active length.

Experiment studies on the polarized gamma-rays generation at KEK-ATF
LI Xiao-Ping, PEI Guo-Xi
2009, 33(8): 691-695. doi: 10.1088/1674-1137/33/8/018

Polarized positrons can be created through electron-positron pair creation from circularly polarized gamma-rays. Laser-Compton scattering is an efficient method to generate circularly polarized gamma-rays. A high finesse 2-mirror optical stacking cavity had been installed on the straight section of the electron storage ring at KEK-ATF. A 1064~nm circularly polarized pulsed laser beam was stacked in the cavity. Polarized gamma-rays with a maximum energy of 28.3 MeV were produced via inverse Compton scattering of the enhanced laser pulse off an electron beam of 1.28 GeV. The number of generated gamma photons per collision was estimated by a photon detector. It was found that the experimental result was in agreement with the simulated value.

Design study on the merger for BXERL-FEL
ZHU Xiong-Wei, WANG Shu-Hong, CHEN Sen-Yu
2009, 33(8): 696-700. doi: 10.1088/1674-1137/33/8/019

In North China, there is a preliminary proposal for ERL-FEL light source (BXERL-FEL) with its aim at ``one machine, two purposes'' (the XFEL and ERL work simultaneously). One of the key technologies is the merger section. In this paper, we give the physical design of the merger section for BXERL-FEL which merges three kinds of electron beam.

Synchrotron radiation,applications of nuclear techniquees,etc
A new cell for X-ray absorption spectroscopy study under high pressure
ZHENG Li-Rong, CHE Rong-Zheng, LIU Jing, DU Yong-Hua, ZHOU Ying-Li, HU Tian-Dou
2009, 33(8): 701-705. doi: 10.1088/1674-1137/33/8/020

X-ray absorption fine structure (XAFS) spectroscopy is a powerful technique for the investigation of the local environment around selected atoms in condensed matter. XAFS under pressure is an important method for the synchrotron source. We design a cell for a high pressure XAFS experiment. Sintered boron carbide is used as the anvils of this high pressure cell in order to obtain a full XAFS spectrum free from diffraction peaks. In addition, a hydraulic pump was adopted to make in-suit pressure modulation. High quality XAFS spectra of ZrH2 under high pressure (up to 13 GPa) were obtained by this cell.

Operating the SDUV-FEL with the echo-enabled harmonic generation scheme
CHEN Jian-Hui, DENG Hai-Xiao, GU Qiang, LI Dong-Guo, WANG Dong, ZHANG Meng, ZHAO Zhen-Tang
2009, 33(8): 706-710. doi: 10.1088/1674-1137/33/8/021

Using the recently proposed echo-enabled harmonic generation (EEHG) free-electron laser (FEL) scheme, it is shown that operating the Shanghai deep ultraviolet FEL (SDUV-FEL) with single-stage to higher harmonics is very promising, with higher frequency up-conversion efficiency, higher harmonic selectivity and lower power requirement of the seed laser. The considerations on a proof-of-principle experiment and expected performance in SDUV-FEL are given.