2009 Vol. 33, No. 9

Particle and field theory
Systematic impact of spent nuclear fuel on θ13 sensitivity at reactor neutrino experiment
AN Feng-Peng, TIAN Xin-Chun, ZHAN Liang, CAO Jun
2009, 33(9): 711-716. doi: 10.1088/1674-1137/33/9/001

Reactor neutrino oscillation experiments, such as Daya Bay, Double Chooz and RENO are designed to determine the neutrino mixing angle θ13 with a sensitivity of 0.01—0.03 in sin213 at 90% confidence level, an improvement over the current limit by more than one order of magnitude. The control of systematic uncertainties is critical to achieving the sin213 sensitivity goal of these experiments. Antineutrinos emitted from spent nuclear fuel (SNF) would distort the soft part of energy spectrum and may introduce a non-negligible systematic uncertainty. In this article, a detailed calculation of SNF neutrinos is performed taking account of the operation of a typical reactor and the event rate in the detector is obtained. A further estimation shows that the event rate contribution of SNF neutrinos is less than 0.2% relative to the reactor neutrino signals. A global χ2 analysis shows that this uncertainty will degrade the θ13 sensitivity at a negligible level.

Production of the neutral top-pion πt0 in association with a high-pT jet at the LHC
ZHU Shi-Hai, YUE Chong-Xing, LIU Wei, DING Li
2009, 33(9): 717-721. doi: 10.1088/1674-1137/33/9/002

In the framework of the topcolor-assisted technicolor (TC2) model, we study the production of the neutral top-pion πt0 in association with a high-pT jet at the LHC, which proceeds via the partonic processes gg→πt0g, gq→πt0q, qq→πt0g, gb(b)→πt0b(b), and bb→πt0g. We find that it is very challenging to detect the neutral top-pion πt0 via the process pp→πt0+jet+X→tt+jet+X, while the possible signatures of πt0 might be detected via the process pp→πt0+jet+X→(tc+tc)+jet+X at the LHC.

B→πη(′)(′)η(′)decays and NLO contributions in the pQCD approach
ZHANG Zhi-Qing, LIU Xin, XIAO Zhen-Jun
2009, 33(9): 722-728. doi: 10.1088/1674-1137/33/9/003

By employing the perturbative QCD (pQCD) factorization approach, we calculate the full leading and the partial next-to-leading order (NLO) contributions to the seven B→πη(′)and η(′)η(′) decays. For B+→π+η(′) decays, the pQCD predictions for their decay rates agree very well with the data after the inclusion of the small NLO contributions. For neutral decays, the pQCD predictions are also consistent with the experimental upper limits and can be tested by the LHC experiments. The measured value of ACPdir(π±η)=-19±7% can also be accommodated by the pQCD approach.

particle and nuclear astrophysics and cosmology
Search for exotic events from the L3+C data
DING Lin-Kai, HE Zuo-Xiu, HUO An-Xiang, JING Cai-Liu, KUANG Hao-Huai, LEI Yu, LI Li, MA Xin-Hua, MA Yu-Qian, QING Cheng-Rui, WANG Rui-Guang, YAO Zhi-Guo, YU Zhong-Qiang, ZHANG Chao, ZHANG Feng, ZHANG Jing, ZHU Qing-Qi
2009, 33(9): 729-736. doi: 10.1088/1674-1137/33/9/004
An effort to search for Kolar-like events within the data set of the L3+C
experiment is reported. From a total of 0.89×1010 triggered events there are no reliable two-prong Kolar-like events observed. The corresponding event flux upper limit 7.1×10-13 cm-2﹒s-1﹒sr-1 at 90% confidence level is deduced based on some reasonable assumptions.
Microscopic calculation of the magnetic field of neutron stars
LIU Jun, JIA Wen-Zhi, WANG Shun-Jin
2009, 33(9): 737-742. doi: 10.1088/1674-1137/33/9/005

Based on the Dirac equation describing an electron moving in a uniform and cylindrically symmetric magnetic field which may be the result of the self-consistent mean field of the electrons themselves in a neutron star, we have obtained the eigen solutions and the orbital magnetic moments of electrons in which each eigen orbital can be calculated. From the eigen energy spectrum we find that the lowest energy level is the highly degenerate orbitals with the quantum numbers pz=0, n=0, and m≥0. At the ground state, the electrons fill the lowest eigen states to form many Landau magnetic cells and each cell is a circular disk with the radius λfree and the thickness λe, where λfree is the electron mean free path determined by Coulomb cross section and electron density and λe is the electron Compton wavelength. The magnetic moment of each cell and the number of cells in the neutron star are calculated, from which the total magnetic moment and magnetic field of the neutron star can be calculated. The results are compared with the observational data and the agreement is reasonable.

Nuclear and ion Physics
Study of the νi13/21 band in 189Pt
HUA Wei, ZHOU Xiao-Hong, ZHANG Yu-Hu, GUO Ying-Xiang, Oshima M, Toh Y, Koizumi M, Osa A, Hatsukawa Y, QI Bin, ZHANG Shuang-Quan, MENG Jie, Sugawara M
2009, 33(9): 743-747. doi: 10.1088/1674-1137/33/9/006

High-spin levels of 189Pt have been studied with the in-beam γ-spectroscopy method via the 176Yb(18O,5n) reaction at the beam energies of 88 and 95 MeV. The previously known νi13/21 band has been confirmed, and its unfavored signature branch extended up to the 31/2+ state. Within the framework of the triaxial particle-rotor model, the νi13/21 band is suggested to be associated with the 11/2[615] configuration, and to have triaxial deformation.

Free quarks and antiquarks versus hadronic matter
XU Xiao-Ming, PENG Ru
2009, 33(9): 748-752. doi: 10.1088/1674-1137/33/9/007

Meson-meson reactions A(q1q1)+B(q2q2)→q1+q1+q2+q2 in high-temperature hadronic matter are found to produce an appreciable amount of quarks and antiquarks freely moving in hadronic matter and to establish a new mechanism for deconfinement of quarks and antiquarks in hadronic matter.

An Abelian Ward identity and the vertex corrections to the color superconducting gap
XU Hao-Jie, WANG Qun
2009, 33(9): 753-758. doi: 10.1088/1674-1137/33/9/008

We derive an Abelian-like Ward identity in the color superconducting phase and calculate vertex corrections to the color superconducting gap. Making use of the Ward identity, we show that subleading order contributions to the gap from vertices are absent for gapped excitations.

Influence of angular momentum in axially symmetric potentials with octupole deformation
JIN Hua, SUN Zhen-Wu, ZHENG Ren-Rong
2009, 33(9): 759-763. doi: 10.1088/1674-1137/33/9/009

The chaotic classical single-particle motion in an oblate octupole deformed potential with a non-zero z-component of angular momentum Lz is investigated. The stability analysis of the trajectories shows that with increasing rotation of the system, the unstable negative curvature regions of the effective potential surface decrease, which converts the chaotic motion of the system into a regular one.

Alpha-decay branching ratios to high-lying excited-states of the 242Cm→238Pu→234U→230Th→226Rn decay chain
ZHANG Jin-Juan, XU Chang, REN Zhong-Zhou
2009, 33(9): 764-768. doi: 10.1088/1674-1137/33/9/010

We present a systematic calculation on the α-decay branching ratios to excited-states of an even-even α-decay chain 242Cm→238Pu→234U→230Th→226Rn by the improved barrier penetration approach. The changes of the parities between the parent nuclei and the daughter nuclei are properly taken into account. The theoretical values are compared with the available experimental data and the deviation between them is within a factor of 5 in most cases.

Detection Technology and Methods
Study of the RPC-Gd as thermal neutron detector
QIAN Sen, WANG Yi-Fang, ZHANG Jia-Wen, LI Jin, CHEN Yuan-Bo, CHEN Jin, WANG Zhi-Gang, MA Lie-Hua
2009, 33(9): 769-773. doi: 10.1088/1674-1137/33/9/011

The BESⅢ RPC with Gd coating as thermal neutron detector was designed and constructed. Three prototypes were built with different techniques of producing the gadolinium converter. The performance of the cosmic ray test, the signal and the radiation spectrum were discussed in this paper. Lastly, the efficiency of one prototype with the best performance for detecting the thermal neutron was tested as 8.7%.

Online measurement of the BEPCⅡ background using RadFET dosimeters
GONG Hui, LI Jin, GONG Guang-Hua, LI Yu-Xiong, HOU Lei, SHAO Bei-Bei
2009, 33(9): 774-776. doi: 10.1088/1674-1137/33/9/012

To monitor the integral dose deposited in the BESⅢ electromagnetic calorimeter whose performance degrades due to exposure to the BEPCⅡ background, a 400 nm IMPL RadFET dosimeter-based integral dose online monitor system is built. After calibration with the 60Co source and verification with TLD in the pulse radiation fields, an experiment was arranged to measure the BEPCⅡ background online. The results are presented.

A new gaseous detector — micro mesh gaseous structure
TANG Hao-Hui, GUO Jun-Jun, WANG Xiao-Lian, XU Zi-Zong
2009, 33(9): 777-780. doi: 10.1088/1674-1137/33/9/013

The structure and working principle of Micromegas (MICRO Mesh Gaseous
Structure) is discussed. Some radiation sources of α and X rays are used to test this detector. The optimized electric-field intensity of the conversion gap is obtained. The transmission of electrons and the uniformity of the amplification gap are also presented. The energy resolution of the 5.9 keV peak is better than 27%.

Studies of timing properties for a TOF counter at an external target facility
YU Yu-Hong, XU Hua-Gen, XU Hu-Shan, ZHAN Wen-Long, SUN Zhi-Yu, GUO Zhong-Yan, HU Zheng-Guo, CHEN Jun-Ling, TANG Shu-Wen
2009, 33(9): 781-784. doi: 10.1088/1674-1137/33/9/014

Timing and amplitude properties of a prototype scintillator TOF counter at an external target facility are studied with a cosmic rays test. The dependence of signal pulse height and time resolution on the coordinate along the scintillator TOF counter is investigated with two different discriminators. A time resolution of 165 ps can be achieved at the center of the counter with a constant fraction discriminator. Time resolution better than 150 ps is obtained at the center with a leading edge discriminator after time walk correction is applied for off-line analysis.

Orbit response matrix analysis and lattice periodicity restoration of the SSRF storage ring
CHEN Jian-Hui, ZHANG Man-Zhou, ZHAO Zhen-Tang
2009, 33(9): 785-788. doi: 10.1088/1674-1137/33/9/015

In this paper, we present numerically and experimentally the linear beam-optics distortion in the SSRF storage ring and the correction of optics by using a number of quadrupole magnets installed in the storage ring. The measured orbit-response matrices were fitted to the model-response matrices to obtain the β and the dispersion functions in the storage ring. By readjusting the currents of quadrupole-magnet power supplies, we were able to successfully restore the optics parameters to values very close to the design ones, with rms deviations around 1%. This periodicity restoration is verified with the β function measurement.

Alignment techniques for DRAGON-Ⅰ LIA
DAI Zhi-Yong, XIE Yu-Tong, LI Hong, ZHANG Wen-Wei, LIU Yun-Long, PAN Hai-Feng, ZHANG Lin-Wen, DENG Jian-Jun
2009, 33(9): 789-791. doi: 10.1088/1674-1137/33/9/016

DRAGON-Ⅰdesigned and manufactured by CAEP is a linear induction accelerator which can produce a 20 MeV-3 kA-60 ns electron beam. The high performance required for the machine is determined by the beam quality and thus is greatly dependent on the accelerator alignment. In order to reduce the chromatic effect of the beam, the stretched wire technique has been developed to measure magnetic axes of the cells precisely, and the dipole steering magnets have been equipped into each cell to correct its magnetic axis misalignment. Finally, the laser tracker has been used to examine the installation error of the accelerator. In this paper, different alignment techniques and the primary results are presented and discussed.

Investigation on the fabrication of the 3rd harmonic superconducting cavity for the SSRF storage ring
MA Zhen-Yu, MA Guang-Ming, YU Hai-Bo, MAO Dong-Qing, FENG Zi-Qiang, HOU Hong-Tao, LIU Jian-Fei
2009, 33(9): 792-797. doi: 10.1088/1674-1137/33/9/017

A third harmonic superconducting niobium cavity has been proposed for installation in the Shanghai Synchrotron Radiation Facility (SSRF) storage ring to improve the Touschek lifetime. In order to investigate the feasibility of the superconducting cavity fabrication indigenously and the possibility to master the fabrication techniques, cavities were fabricated from copper and niobium sheets by deep drawing and electron-beam welding, and a series of measurements, such as resonant frequency, shape dimensions and wall thickness, were carried out during this process. After analysis of various problems existing in the fabrication process, technique improvements were proposed, and finally the precise shape as designed and resonant frequency within 1.2 MHz were achieved for the new completed cavities. In addition, full annealing was finally proved to be a good cure for niobium sheets' tearing up during deep drawing. By fabricating niobium cavities successfully, some problems to the next step were cleared. This paper introduces the process of cavity fabrication and its technique improvements towards forming, and the initial vertical test result of niobium cavity is also presented.

Matrix method for the solution of RF field perturbations due to local frequency shifts
SUN Zhi-Rui, PENG Jun, FU Shi-Nian
2009, 33(9): 798-803. doi: 10.1088/1674-1137/33/9/018

To tune the accelerating field to the design value in a periodical radio frequency accelerating structure, Slater's perturbation theorem is commonly used. This theorem solves a second-order differential equation to obtain the electrical field variation due to a local frequency shift. The solution becomes very difficult for a complex distribution of the local frequency shifts. Noticing the similarity between the field perturbation equation and the equation describing the transverse motion of a particle in a quadrupole channel, we propose in this paper a new method in which the transfer matrix method is applied to the field calculation instead of directly solving the differential equation. The advantage of the matrix method is illustrated in examples.

HIRFL-CSR complex
XIA Jia-Wen, ZHAN Wen-Long, WEI Bao-Wen, YUAN You-Jin, YUAN Ping, QIAO Wei-Min
2009, 33(9): 804-810. doi: 10.1088/1674-1137/33/9/019

The construction and commissioning of HIRFL-CSR were finished in 2007. From 2000 to 2005 the subsystem and key devices of CSR were successfully fabricated, such as magnet, power supply, UHV system, e-cooler, electric-static deflector with the septum of 0.1 mm, and the fast-pulse kicker with the rise time of 150 ns. After that the CSR commissioning activities were performed in 2006 and 2007, including the accumulation of those heavy ions of C, Ar, Kr and Xe by the combination of stripping injection (STI) or multiple multi-turn injection (MMI) and e-cooling with a hollow e-beam, wide energy-range synchrotron ramping by changing the RF harmonic-number at mid-energy, the beam stacking in the experimental ring CSRe, the RIBs mass-measurement with the isochronous-mode in CSRe by using the time-of-flight method, and the ion beam slow-extraction from CSRm.

Emittance coupling driven by space charge in the CSNS linac
YIN Xue-Jun, FU Shi-Nian, PENG Jun
2009, 33(9): 811-814. doi: 10.1088/1674-1137/33/9/020

In the conventional design of RF linacs, the bunched beams are not in thermal equilibrium. The space charge forces couple the particle motions between the transverse and the longitudinal directions. Furthermore it will cause the equipartitioning process which leads to emittance growth and halo formation. In the design of the China Spallation Neutron Source (CSNS) linac, three cases are investigated using the Hofmann stability charts. In this paper, we present the equipartitioning beam study of the CSNS Alvarez DTL linac.

Study on the Lorentz detuning and tuning of β=0.3, 352 MHz spoke cavity
XIAO Yong-Chuan, FU Shi-Nian
2009, 33(9): 815-818. doi: 10.1088/1674-1137/33/9/021

The superconducting spoke cavity has been proposed to accelerate the proton in the low energy section of the high power proton linac for the Accelerator Driven Sub-critical System in China. In this paper, the basic geometric and RF parameters of a β=0.3, 352 MHz spoke cavity are given, and the Lorenz detuning and tuning are presented.