## 2013 Vol. 37, No. 6

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2013, 37(6): 063001. doi: 10.1088/1674-1137/37/6/063001

**Abstract:**

The number of ψ' events accumulated by the BESIII experiment from March 3 through April 14, 2009, is determined by counting inclusive hadronic events. The result is 106.41×(1.00± 0.81%)×10

^{6}. The error is systematic dominant; the statistical error is negligible.

2013, 37(6): 063101. doi: 10.1088/1674-1137/37/6/063101

**Abstract:**

By applying an appropriate Pekeris approximation to deal with the centrifugal term, we present an approximate systematic solution of the two-body spinless Salpeter (SS) equation with the Woods-Saxon interaction potential for an arbitrary

*l*-state. The analytical semi-relativistic bound-state energy eigenvalues and the corresponding wave functions are calculated. Two special cases from our solution are studied: the approximated Schrödinger-Woods-Saxon problem for an arbitrary

*l*-state and the exact

*s*-wave (

*l*=0).

2013, 37(6): 063102. doi: 10.1088/1674-1137/37/6/063102

**Abstract:**

We analyze the theoretical prediction on the branching ratio of B→X

_{s}γ to order

*Λ*

_{EW}

^{2}/

*Λ*

_{KK}

^{2}in extension of the standard model with a warped extra dimension and the custodial symmetry

*SU*(3)

_{c}×

*SU*(2)

_{L}×

*SU*(2)

_{R}×

*U*(1)

_{X}×

*P*

_{LR}, where

*Λ*

_{KK}denotes the energy scale of low-lying Kaluze-Klein excitations and

*Λ*

_{EW}denotes the electroweak energy scale. Contributions from the in nite series of Kaluze-Klein excitations are summed over through the residue theorem. The numerical result indicates that the present experimental data constrain the parameter space of the concerned model strongly.

2013, 37(6): 063103. doi: 10.1088/1674-1137/37/6/063103

**Abstract:**

In this paper, we calculate the branching ratios of Λ

_{b}→pK

^{-}and pπ

^{-}decays in the avor changing Z' model. We nd that the branching ratios for these two decay modes are sensitive to the contributions of the Z' boson. For Λ

_{b}→pK

^{-}decay, if the left-handed couplings are equal to the right-handed couplings, the branching ratio of this decay could match up to the currently experimental data for

*ξ*

_{s}=0.01 and -52°<

*φ*

_{s}

^{L}<132°, or

*ξ*

_{s}=0.004 and 0°<

*φ*

_{s}

^{L}<84°; if only the left-handed couplings are considered, it could match up to the experimental data for

*ξ*

_{s}=0.01 and -10°

*φ*

_{s}

^{L}<138°. And for Λ

_{b}→pK

^{-}decay, if the left-handed and right-handed couplings are equal, the branching ratio of Λ

_{b}→pK

^{-}decay may be consistent with the currently experimental data with

*ξ*

_{d}=0.05 and -135°

*φ*

_{d}

^{L}<43°, if only the left-handed couplings are considered, it may be consistent with

*ξ*

_{d}=0.05 and -114°

*φ*

_{d}

^{L}<8°.

2013, 37(6): 063104. doi: 10.1088/1674-1137/37/6/063104

**Abstract:**

Motivated by the rst measurement on

*B*(B

_{s}→φμ

^{+}μ

^{-}) by the CDF Collaboration, we study the supersymmetric e ects in semi-leptonic B

_{s}→φμ

^{+}μ

^{-}decay. In our evaluations, we analyze the dependences of the dimuon invariant mass spectrum and the forward-backward asymmetry on relevant supersymmetric couplings in the MSSM with and without

*R*-parity. The analyses show that the new experimental upper limits of

*B*(B

_{s}→φμ

^{+}μ

^{-})from the LHCb Collaboration could further improve the bounds on sneutrino exchange couplings and (

*δ*

_{LL}

^{u})

_{23}as well as (

*δ*

_{LL,RR}

^{u})

_{23}mass insertion couplings. In addition, within the allowed ranges of relevant couplings under the constraints from

*B*(B

_{s}→φμ

^{+}μ

^{-}),

*B*(B→K

^{(*)}μ

^{+}μ

^{-}) and (B

_{s}→φμ

^{+}μ

^{-}), the dimuon forward-backward asymmetry and the di erential dimuon forward-backward asymmetry of B

_{s}→φμ

^{+}μ

^{-}are highly sensitive to the squark exchange contribution and the (

*δ*

_{LL}

^{u})

_{23}mass insertion contribution. The results obtained in this work will be very useful in searching for supersymmetric signals at the LHC.

2013, 37(6): 063105. doi: 10.1088/1674-1137/37/6/063105

**Abstract:**

We perform an analysis of all existing experimental data on the pion-photon transition form factor (TFF). In the calculation, we include the next-to-leading order correction to the valence-quark contribution and estimate the non-valence-quark contribution by a phenomenological model based on the TFF's limiting behavior at both

*Q*

^{2}→0 and

*Q*

^{2}→∞. At present, the pion distribution amplitude (DA) is not de nitely determined, it is helpful to have a pion DA model that can mimic all the behaviors suggested in the literature. For the purpose, we adopt the conventional model for pion wavefunction/DA whose broadness is dominantly controlled by a single parameter

*B*. We fix the DA parameters by using the CELLO, CLEO, BABAR and Belle data within small

*Q*

^{2}region (

*Q*

^{2}≤15 GeV

^{2}), where all the data are consistent with each other. The pion-photon TFF is then extrapolated into a larger

*Q*

^{2}region. It is found that we still need more data at a large

*Q*

^{2}region in order to determine the precise value of

*B*, and we hope that the de nite behavior of pion DA can be concluded nally by the consistent data in the coming future.

2013, 37(6): 063106. doi: 10.1088/1674-1137/37/6/063106

**Abstract:**

For a spin-1/2 particle moving in a background magnetic field in noncommutative phase space, the Dirac equation is solved when the particle is allowed to move off the plane that the magnetic field is perpendicular to. It is shown that the motion of the charged particle along the magnetic field has the effect of increasing the magnetic field. In the classical limit, matrix elements of the velocity operator related to the probability give a clear physical picture. Along an effective magnetic field, the mechanical momentum is conserved and the motion perpendicular to the effective magnetic field follows a round orbit. If using the velocity operator defined by the coordinate operators, the motion becomes complicated.

2013, 37(6): 064101. doi: 10.1088/1674-1137/37/6/064101

**Abstract:**

An appropriate density dependence of hyperon potentials is important for the stiffening of the equation of state and massive neutron stars. To persist in covariance and thermodynamic consistency, the rearrangement term is indispensable. In this work, we derive the rearrangement term for hyperon potentials with arbitrary density-dependence. The importance of the rearrangement term is also exhibited in numerical instances.

2013, 37(6): 066001. doi: 10.1088/1674-1137/37/6/066001

**Abstract:**

Geant4 tools were used to model the single event upset (SEU) of static random access memory cells induced by heavy ion irradiation. Simulated results obtained in two different regions of incident ion energies have been compared in order to observe the SEU occurrence by energetic ions and their effects on the radial ionization profile of deposited energy density. The disagreement of SEU cross sections of device response and radial distribution of deposited energy density have been observed in both low energy and high energy regions with equal linear energy transfer (LET) which correspond to the both sides of the Bragg peak. In the low energy region, SEUs induced by heavy ions are more dependent upon the incident ion species and radial distribution of deposited energy density, as compared with the high energy region. In addition, the velocity effect of the incident ion in silicon in the high energy region provides valuable feedback for gaining insight into the occurrence of SEU.

2013, 37(6): 066002. doi: 10.1088/1674-1137/37/6/066002

**Abstract:**

A normal pressure MWPC for beam diagnostics at RIBLL2 has been developed, which has a sensitive area of 80 mm×80 mm and consists of three-layer wire planes. The anode plane is designed with a wider frame to reduce the discharge and without using protection wires. The detector has been tested with a

^{55}Fe X-ray source and a 200 MeV/u

^{12}C beam from CSRm. A position resolution better than 250 μm along the anode wires and a detection efficiency higher than 90% have been achieved.

2013, 37(6): 066201. doi: 10.1088/1674-1137/37/6/066201

**Abstract:**

Frequency gradient analysis (FGA) effectively discriminates neutrons and γ rays by examining the frequency-domain features of the photomultiplier tube anode signal. This approach is insensitive to noise but is inevitably affected by the baseline drift similar to other pulse shape discrimination methods. The baseline drift effect is attributed to factors such as power line fluctuation, dark current, noise disturbances, hum, and pulse tail in front-end electronics. This effect needs to be elucidated and quantified before the baseline shift can be estimated and removed from the captured signal. Therefore, the effect of baseline shift on the discrimination performance of neutrons and γ rays with organic scintillation detectors using FGA is investigated in this paper. The relationship between the baseline shift and discrimination parameters of FGA is derived and verified by an experimental system consisting of an americium-beryllium source, a BC501A liquid scintillator detector, and a 5 GSample/s 8-bit oscilloscope. The theoretical and experimental results both show that the estimation of the baseline shift is necessary, and the removal of baseline drift from the pulse shapes can improve the discrimination performance of FGA.

2013, 37(6): 066202. doi: 10.1088/1674-1137/37/6/066202

**Abstract:**

A pattern matching based tracking algorithm, named MdcPatRec, is used for the reconstruction of charged tracks in the drift chamber of the BESⅢ detector. This paper addresses the shortage of segment finding in the MdcPatRec algorithm. An extended segment construction scheme and the corresponding pattern dictionary are presented. Evaluation with Monte-Carlo and experimental data show that the new method can achieve higher efficiency for low transverse momentum tracks.

2013, 37(6): 067001. doi: 10.1088/1674-1137/37/6/067001

**Abstract:**

The China Spallation Neutron Source (CSNS) uses H

^{-}stripping and phase space painting method to fill a large ring acceptance with a small emittance linac beam. The dependence of the painting beam on the injection beam parameters was studied for the Rapid Cycling Synchrotron (RCS). The simulation study was done for injection with different momentum spreads, different rms emittances of the injection beam, and different matching conditions. Then, the beam loss, 99% and rms emittances were obtained, and the optimized injection beam parameters were given. The interaction between H

^{-}beam and stripping foil was studied, and the effect of foil scattering was simulated. The stripping efficiency was calculated and the suitable thickness of stripping foil was obtained. In addition, the energy deposition on the foil and the beam loss due to the foil scattering were also studied.

2013, 37(6): 067002. doi: 10.1088/1674-1137/37/6/067002

**Abstract:**

'Ultimate" storage rings (USRs), with electron emittance smaller than 100 pm·rad and on the scale of the diffraction limit for hard X-rays in both transverse planes, have the potential to deliver photons with much higher brightness and higher transverse coherence than that projected for the rings currently operational or under construction. Worldwide efforts have been made to design and to build light sources based on USRs. How to obtain a round beam, i.e., a beam with equivalent transverse emittances, is an important topic in USR studies. In this paper, we show that a locally-round beam can be achieved by using a pair of solenoid and anti-solenoid with a circularly polarized undulator located in between. Theoretical analysis and application of this novel method, particularly to one of the Beijing Advanced Photon Source storage ring design having natural emittance of 75 pm·rad, are presented.

2013, 37(6): 068001. doi: 10.1088/1674-1137/37/6/068001

**Abstract:**

The propagation of a hard X-ray beam from a partially coherent synchrotron source is simulated by using the novel method based on the coherent mode decomposition of Gaussian Schell model and wave-front propagation. We investigate how the coherency properties and intensity distributions of the beam are changed by propagation through optical elements. Here, we simulate and analyze the propagation of the partially coherent radiation transmitted through an ideal slit. We present the first simulations for focusing partially coherent synchrotron hard X-ray beams using this novel method. And when compared with the traditional method which assumes the source is a totally coherent point source or completely incoherent, this method is proved to be more reasonable and can also demonstrate the coherence properties of the focusing beam. We also simulate the Young's double slit experiment and the simulated results validate the academic analysis.

2013, 37(6): 068101. doi: 10.1088/1674-1137/37/6/068101

**Abstract:**

In this paper, the harmonics suppression effect of quasi-periodic undulators (QPUs) in self-amplified spontaneous emission free-electron laser (SASE FEL) is investigated. The numerical results show that the harmonics power is reduced by using QPUs, but the fundamental radiation power also has a pronounced decrease as the saturation length gets very long. The cases of employing QPUs as parts of undulators are studied. The calculations show that if the fraction of QPUs and their offgap are appropriate in an undulator system, the harmonics radiation could be suppressed remarkably, meanwhile the fundamental saturation length does not increase too much.

2013, 37(6): 068201. doi: 10.1088/1674-1137/37/6/068201

**Abstract:**

Proton radiography has provided a potential development direction for advanced hydrotesting, and its image blur is a crucial point that needs to be deeply studied. In this article, numerical simulation by using the Monte Carlo code Geant4 has been implemented to investigate the entire physics mechanism of high energy proton beam travelling through the object and beamline and arriving at the image plane. This article will mainly discuss the various factors which cause the image blur, including the chromatic aberration of the imaging beamline, the insufficient modulation of an incident particle's transverse displacement and angle deviation, the longitudinal length of an object, the influence of containment vessel and otherwise.

**ISSN** 1674-1137 **CN** 11-5641/O4

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