2010 Vol. 34, No. 05

Particle and field theory
ηb decay into charmonium in association with cc pair
LI Bai-Qing, LI Rong, HE Zhi-Guo
2010, 34(05): 521-527. doi: 10.1088/1674-1137/34/5/001
Abstract:

We calculate the inclusive decay rates of ηb into charmonium via double cc pairs for S- and P-wave states ηc, J/ψ and χcJ within the framework of non-relativistic QCD (NRQCD) factorization at leading order in αs. Besides calculating the contributions of the color-singlet channels ηb→cc[2S+1SL(1)]+cc, the effects of cc pair in the color-octet configurations are also considered. We find that ηb→cc[3S1(8)]+cc make a small contribution to Brb→J/ψ(ηc)+cc). While in the ηb→χcJ+cc case, the color octet contributions are significant, for they are of the same αs4 vc5 order as the color-singlet processes. We predict Brb→J/ψ(ηc)+cc)=2.99(2.75)×10-5 for S-wave states J/ψ and ηc, and Brb→χcJ+cc)=(4.37,3.40,2.83)×10-5 (for J=0,1,2) for P-wave states χcJ. In the end, we also find Brb→cccc) is almost saturated by ηb decay into charmonium in association with cc pair from the point of view of duality.

Study of scalar meson a0(980) from B→a0(980)π decays
ZHANG Zhi-Qing, XIAO Zhen-Jun
2010, 34(05): 528-534. doi: 10.1088/1674-1137/34/5/002
Abstract:

In this paper, we calculate the branching ratios and the direct CP-violating asymmetries for decays B0→a00(980)π0, a+0(980)π, a0(980)π+ and B-→ a00(980)π, a0(980)π0 by employing the perturbative QCD (pQCD) factorization approach at the leading order. We found that (a) the pQCD predictions for the branching ratios are around (0.4-2.8)×10-6, consistent with currently available experimental upper limits; (b) the CP asymmetries of B0→a00(980)π0 and B→a0(980)π0 decays can be large, about (70—80)% for α=100°.

Quantal symmetries in the non-linear σ model with Maxwell and non-Abelian Chern-Simons terms
WANG Ke, JIANG Yun-Guo, HUO Qiu-Hong
2010, 34(05): 535-538. doi: 10.1088/1674-1137/34/5/003
Abstract:

The quantal symmetry property of the CP1 nonlinear σ model with Maxwell non-Abelian Chern-Simons terms in (2+1) dimension is studied. In the Coulomb gauge, the system is quantized by using the Faddeev-Senjanovic (FS) path-integral formalism. Based on the quantaum Noether theorem, the quantal conserved angular momentum is derived and the fractional spin at the quantum level in this system is presented.

Bs,d→μ+μ decays in a flavor changing Z′ model
WANG Shuai-Wei, YANG Xing-Qiang, LI Gen-Quan, HUANG Jin-Shu
2010, 34(05): 539-542. doi: 10.1088/1674-1137/34/5/004
Abstract:

We study the pure leptonic decays Bs,d→μ+μ in a Flavor Changing Z′ Model. From the recent measurements of the branching ratios B(Bs,d→μ+μ), we have derived the bounds on the effective μ-μ-Z′ lepton coupling BμμL. We find that, (i) if neglecting the contribution from the right-handed lepton coupling BμμR, we obtain 1.32< BμμL <3.32; (ii) if considering the contribution from the right-handed lepton coupling BμμR and setting BμμL=BμμR, we obtain 0.99< BμμL<2.19. Our results could be useful for researching Z′ effects.

Spin-1/2 relativistic particle in a magnetic field in NC phase space
YUAN Yi, LI Kang, WANG Jian-Hua, CHEN Chi-Yi
2010, 34(05): 543-547. doi: 10.1088/1674-1137/34/5/005
Abstract:

This work provides an accurate study of the spin-1/2 relativistic particle in a magnetic field in NC phase space. By detailed calculation we find that the Dirac equation of the relativistic particle in a magnetic field in noncommutative space
has similar behaviour to what happens in the Landau problem in commutative space even if an exact map does not exist. By solving the Dirac equation in NC phase space, we not only obtain the energy level of the spin-1/2 relativistic particle in a magnetic field in NC phase space but also explicitly offer some additional terms related to the momentum-momentum non-commutativity.

Nuclear and ion Physics
Neutron dose measurement in carbon ion radiation therapy at HIRFL (IMP)
SU You-Wu, LI Zong-Qiang, LI Wu-Yuan, WANG Gui-Ling
2010, 34(05): 548-550. doi: 10.1088/1674-1137/34/5/006
Abstract:

For radiation protection purposes, the neutron dose in carbon ion radiation therapy at the HIRFL (Heavy Ion Research Facility in Lanzhou) was investigated. The neutron dose from primary 12C ions with a specific energy of 100 MeV/u delivered from SSC was roughly measured with a standard Anderson-Broun rem-meter using a polyethylene target at various distances. The result shows that a maximum neutron dose contribution of 19 mSv in a typically surface tumor treatment was obtained, which is less than 1% of the planed heavy ion dose and is in reasonable agreement with other reports. Also the γ-ray dose was measured in this experiment using a thermo luminescent detector.

System size effects on probing nuclear dissipation with neutrons
WU Feng, YE Wei
2010, 34(05): 551-554. doi: 10.1088/1674-1137/34/5/007
Abstract:

Using a dynamical Langevin equation coupled with a statistical decay model, we calculate the excess of the pre-scission neutron multiplicities over its standard statistical-model values as a function of the nuclear dissipation strength for the three nuclei 190Os, 200Hg, and 210Po which have the same neutron-to-proton ratio N/Z. We find that by decreasing the size of the fissioning nuclei, the effects of nuclear dissipation on the excess of the pre-scission neutron multiplicity are substantially amplified, and that the sensitivity of this excess to the nuclear friction strength is considerably increased as well. We suggest that for those fissioning systems with the same N/Z that are populated in fusion reactions, to obtain a more accurate information of the nuclear dissipation strength by measuring the pre-scission neutron multiplicity, it is best to choose a system with a small size.

Detection Technology and Methods
ARGO-YBJ detector simulation using GEANT4
GUO Yi-Qing, ZHANG Xue-Yao, ZHANG Jian-Li, HU Hong-Bo, ZHA Min, HE Hui-Hai, FENG Zhao-Yang, WU Chao-Yong, WANG Bo, ZHANG Yi, LU Hong
2010, 34(05): 555-559. doi: 10.1088/1674-1137/34/5/008
Abstract:

'G4argo', a GEANT4-based simulation package for the ARGO-YBJ detector, is described in this paper. G4argo incorporates in the simulation the true RPC time resolution and another 0.5 ns time uncertainty which is introduced from the offline calibration of TDC. In addition, the correct RPC geometry and the true materials for the ARGO-YBJ experimental hall are implemented. As a result, G4argo simulation shows a very good agreement with real data.

Optimum condition of efficiency functions for HPGe γ-ray detectors in the 121-1408 keV energy range
CHEN Zhi-Lin, SONG Guo-Yang, MU Long, WANG He-Yi, XING Shi-Xiong, GUO Hong-Bo, LIAO Zhen-Xing, CHEN Ping, HUA Sheng
2010, 34(05): 560-564. doi: 10.1088/1674-1137/34/5/009
Abstract:

The optimum condition of three commonly used functions in the Genie 2000 γ spectra analysis software have been studied in the 121—1408 keV energy range. The three functions are applied for fitting the full-energy peak efficiency of the HPGe gamma-ray detector. A detailed procedure to obtain the optimum condition is described. The HPGe detector is calibrated at 11 cm by three radioactive sources of point form (152Eu, 137Cs, 60Co) providing 11 energy peaks. After data processing, results shows that the three functions used in the Genie 2000 gamma spectra analysis software fit best at orders 3—5. Lastly the standard radioactive source 133Ba is chosen to validate the results. Differences between the standard activity of 133Ba and the result obtained from the fitting functions are below 1.5%. Therefore the optimum orders of the three functions used in the Genie 2000 γ spectra analysis software are 3—5 with the 11 energy peaks.

Measurement of avalanche size and position resolution of RPCs with different surface resistivities of the high voltage provider
YUE Qian, LI Yuan-Jing, YE Jin, CHENG Jian-Ping, WANG Yi, LI Jin, WU Yu-Cheng
2010, 34(05): 565-570. doi: 10.1088/1674-1137/34/5/010
Abstract:

The effects of surface resistivity of the high voltage provider on the space dispersion of the induced charge of a prototype Resistive Plate Chamber (RPC) have been studied experimentally and theoretically. The results of both experiment and theory agree and confirm that a two-Gaussian function can be used to fit the dispersion of the induced charge of the RPC. It is shown that the Gaussian function with the narrower width is mainly due to the expansion of the avalanche charge in the gas gap of the RPC, and the Gaussian function with the larger width is due to the charge dispersion when it passes through the resistive carbon film. This will be useful in the RPC design when one wants to make an RPC with high position resolution.

Oxygen quenching in a LAB based liquid scintillator and the nitrogen bubbling model
XIAO Hua-Lin, DENG Jing-Shan, WANG Nai-Yan
2010, 34(05): 571-575. doi: 10.1088/1674-1137/34/5/011
Abstract:

The oxygen quenching effect in a Linear Alkl Benzene (LAB) based liquid scintillator (LAB as the solvent, 3 g/L 2, 5 diphe-nyloxazole (PPO) as the fluor and 15 mg/L p-bis-(o-methylstyryl)-benzene (bis-MSB) as the λ-shifter) is studied by measuring the light yield as a function of the nitrogen bubbling time. It is shown that the light yield of the fully purged liquid scintillator is increased by 11% at room temperature and the room atmospheric pressure. A simple nitrogen bubbling model is proposed to describe the relationship between the relative light yield (oxygen quenching factor) and the bubbling time.

Accelerator
Analysis of the impacts of mechanical errors on the RF performance of a single spoke cavity
YAO Zhong-Yuan, LU Xiang-Yang, ZHANG Bao-Cheng, QUAN Sheng-Wen, HE Fei-Si, ZHAO Kui
2010, 34(05): 576-579. doi: 10.1088/1674-1137/34/5/012
Abstract:

Mechanical errors can not be avoided in fabrication. They will cause geometry errors and have impacts on the cavity performance. This paper systematically analyzes the impacts of mechanical errors on the RF performance of Peking University single spoke cavity. The various kinds of shape and size errors are considered, the influences on the resonation frequency and field flatness are studied by numerical simulation and the theoretical models are analyzed. The results show that the single spoke cavity is robust with respect to the mechanical tolerance. It also indicates the most essential factors for fabrication.

Thermal analysis of the CSNS H ion source
WU Xiao-Bing, OUYANG Hua-Fu
2010, 34(05): 580-583. doi: 10.1088/1674-1137/34/5/013
Abstract:

There are two cooling systems to maintain the thermal stability of the CSNS H ion source during its operation: Air-cooling in the source body of the discharging chamber and water-cooling in the flange on which the discharging chamber is installed. The optimal cooling parameters to ensure the operation of the H ion source are determined through a thermal analysis. In addition, a transient analysis is also performed to know exactly the transient temperature variation during the whole 40 ms period of the pulsed mode operation of the ion source.

Emittance measurement & optimization for the photocathode RF gun with laser profile shaping
LIU Sheng-Guang, Masafumi Fukuda, Sakae Araki, Nobuhiro Terunuma, Junji Urakawa
2010, 34(05): 584-588. doi: 10.1088/1674-1137/34/5/014
Abstract:

The Laser Undulator Compact X-ray source (LUCX) is a test bench for a compact high brightness X-ray generator, based on inverse Compton Scattering at KEK, which requires high intensity multi-bunch trains with low transverse emittance. A photocathode RF gun with emittance compensation solenoid is used as an electron source. Much endeavor has been made to increase the beam intensity in the multi-bunch trains. The cavity of the RF gun is tuned into an unbalanced field in order to reduce space charge effects, so that the field gradient on the cathode surface is relatively higher when the forward RF power into gun cavity is not high enough. A laser profile shaper is employed to convert the driving laser profile from Gaussian into uniform. In this research we seek to find the optimized operational conditions for the decrease of the transverse emittance. With the uniform driving laser and the unbalanced RF gun, the RMS transverse emittance of a 1 nC bunch has been improved effectively from 5.46 πmm&#12539;mrad to 3.66 πmm&#12539;mrad.

Excitation curve calibration for the SSRF magnet system
ZHOU Xue-Mei, LIU Gui-Min, HOU Jie, ZHANG Wen-Zhi, TIAN Shun-Qiang
2010, 34(05): 589-592. doi: 10.1088/1674-1137/34/5/015
Abstract:

The needed electrical current for the magnet working under different energy loads can be easily calculated once the right relation between the magnet and the electrical current has been found. Therefore the excitation curve calibration for the magnet system is important to the SSRF. The measuring method on the magnet and the result of the excitation curve calibration are presented. The application of the excitation curve calibration for the bending magnet is given, and it is proved that the COD (Closed Orbit Distortion) and the working point of the storage ring are greatly affected by the current of the bending magnet.

Design of a PXR experiment based on the NCEL
XIANG Xin-Lei, LUO Xiao-Wei, XIE Jia-Lin, PEI Guo-Xi, XIE Ya-Ning
2010, 34(05): 593-597. doi: 10.1088/1674-1137/34/5/016
Abstract:

Parametric X-ray Radiation (PXR) can be used as a novel, quasi-monochromatic energy-tunable and high-yield X-ray source. It is produced at the Bragg angle by a relativistic electron beam passing through the periodic structure of crystal materials. This article concerns the PXR experiment using low energy electrons (10 MeV) from NCEL (Novel Compact Electron-Linac). The difficulty of the experiment is to distinguish the PXR photons form the background. The design of the experiment relies mainly on the yield of PXR, the Bremsstrahlung background of the X-rays and the capability of the detector.

Mode control in a high-gain relativistic klystron amplifier
LI Zheng-Hong, ZHANG Hong, JU Bing-Quan, SU Chang, WU Yang
2010, 34(05): 598-602. doi: 10.1088/1674-1137/34/5/017
Abstract:

Middle cavities between the input and output cavity can be used to decrease the required input RF power for the relativistic klystron amplifier. Meanwhile higher modes, which affect the working mode, are also easy to excite in a device with more middle cavities. In order for the positive feedback process for higher modes to be excited, a special measure is taken to increase the threshold current for such modes. Higher modes' excitation will be avoided when the threshold current is significantly larger than the beam current. So a high-gain S-band relativistic klystron amplifier is designed for the beam of current 5 kA and beam voltage 600 kV. Particle in cell simulations show that the gain is 1.6×105 with the input RF power of 6.8 kW, and that the output RF power reaches 1.1 GW.

Design and study of a high-current 5-cell superconducting rf cavity
LIU Zhen-Chao
2010, 34(05): 603-605. doi: 10.1088/1674-1137/34/5/018
Abstract:

The Advanced Photon Source (APS) at Argonne National Laboratory is considering the development of a superconducting linac-based fourth-generation hard X-ray source to meet future scientific needs of the hard X-ray user community. This work specifically focuses on the design of an optimized 5-cell superconducting radio-frequency structure well suited for a high-energy, high-beam-current energy recovery linac. The cavity design parameters are based on the APS storage ring nominal 7 GeV and 100 mA beam operation. A high-current 5-cell cw superconducting cavity operating at 1.4 GHz has been designed. In order to achieve a high current, the accelerating cavity shape has been optimized and large end-cell beam pipes have been adopted. The beam break-up threshold of the cavity has been estimated using the code TDBBU, which predicts a high threshold beam current for a 7 GeV energy recovery linac model. A copper prototype cavity has been fabricated that uses half-cell modules, initially assembled by clamping the cells together.

Synchrotron radiation,applications of nuclear techniquees,etc
Improvement of the determination of hydrogen content in a multicomponent sample by D—T generator
CHENG Dao-Wen, GU De-Shan, LIU Lin-Mao, JIA Fu-Quan, LI Xiang-Long
2010, 34(05): 606-609. doi: 10.1088/1674-1137/34/5/019
Abstract:

If a D—T generator is used as a neutron source to simultaneously measure the content of carbon, hydrogen and oxygen in a multicomponent sample by NIPGA (Neutron Induced Prompt Gamma-ray Analysis), the 14 MeV neutron flux can be regarded as a constant value. The relationship between the production of the hydrogen characteristic gamma-rays and its content is nonlinear. In this paper, we use MCNP (Monte Carlo N-Particle Transport code) to simulate the relationship and analyze it. In practical measurement of the characteristic gamma-ray, it's impossible to get the net count. Therefore, we use the experiment to obtain the relationship between the hydrogen content and the total count of its characteristic gamma-rays. If we use the relationship combined
with the simulation result to calculate the hydrogen content, the metrical precision can be much increased. The deviation of hydrogen content between NIPGA and chemical analysis is less than 0.25%, which meets the requirement of coal industry.

Muon radiography technology for detecting high-Z materials
MA Ling-Ling, WANG Wen-Xin, ZHOU Jian-Rong, SUN Shao-Hua, LIU Zuo-Ye, LI Lu, DU Hong-Chuan, ZHANG Xiao-Dong, HU Bi-Tao
2010, 34(05): 610-614. doi: 10.1088/1674-1137/34/5/020
Abstract:

This paper studies the possibility of using the scattering of cosmic muons to identify threatening high-Z materials. Various scenarios of threat material detection are simulated with the Geant4 toolkit. PoCA (Point of Closest Approach) algorithm reconstructing muon track gives 3D radiography images of the target material. Z-discrimination capability, effects of the placement of high-Z materials, shielding materials inside the cargo, and spatial resolution of position sensitive detector for muon radiography are carefully studied. Our results show that a detector position resolution of 50 μm is good enough for shielded materials detection.