## 2015 Vol. 39, No. 10

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2015, 39(10): 103001. doi: 10.1088/1674-1137/39/10/103001

**Abstract:**

A maximum likelihood method is used to deal with the combined estimation of multi-measurements of a branching ratio, where each result can be presented as an upper limit. The joint likelihood function is constructed using observed spectra of all measurements and the combined estimate of the branching ratio is obtained by maximizing the joint likelihood function. The Bayesian credible interval or upper limit of the combined branching ratio, is given in cases both with and without inclusion of systematic error.

2015, 39(10): 103101. doi: 10.1088/1674-1137/39/10/103101

**Abstract:**

We calculate the next-to-leading order (NLO) quantum chromodynamics (QCD) corrections to double charmonium production processes e

^{+}e

^{-}→ γ

^{*}→η

_{c}+h

_{c}(1

*P*)=ψ

_{1,2}(1

*D*) within the non-relativistic QCD (NRQCD) factorization framework. We find that the corrections to η

_{c}+h

_{c}(1

*P*) production are positive, while those to η

_{c}+ψ

_{1,2}(1

*D*) are negative. Unlike the J/ψ+η

_{c}case, all the corrections here are not large. Uncertainties in the renormalization scale, quark mass and running energy of center-of-mass are discussed, and the scale dependence of these processes is found to be greatly reduced with the NLO QCD corrections.

2015, 39(10): 103102. doi: 10.1088/1674-1137/39/10/103102

**Abstract:**

In this paper, a minimal surface in

*q*-deformed

*AdS*

_{5}×

*S*

^{5}with a cusp boundary is studied in detail. This minimal surface is dual to a cusped Wilson loop in dual field theory. We find that the area of the minimal surface has both logarithmic squared divergence and logarithmic divergence. The logarithmic squared divergence cannot be removed by either Legendre transformation or the usual geometric subtraction. We further make an analytic continuation to the Minkowski signature, taking the limit such that the two edges of the cusp become light-like, and extract the anomalous dimension from the coefficient of the logarithmic divergence. This anomalous dimension goes back smoothly to the results in the undeformed case when we take the limit that the deformation parameter goes to zero.

2015, 39(10): 104001. doi: 10.1088/1674-1137/39/10/104001

**Abstract:**

In this paper, we present direct mass measurements of neutron-rich

^{86}Kr projectile fragments conducted at the HIRFL-CSR facility in Lanzhou by employing the Isochronous Mass Spectrometry (IMS) method. The new mass excesses of

^{52-54}Sc nuclides are determined to be -40492(82), -38928(114), -34654(540) keV, which show a significant increase of binding energy compared to the reported ones in the Atomic Mass Evaluation 2012 (AME12). In particular,

^{53}Sc and

^{54}Sc are more bound by 0.8 MeV and 1.0 MeV, respectively. The behavior of the two neutron separation energy with neutron numbers indicates a strong sub-shell closure at neutron number

*N*=32 in Sc isotopes.

2015, 39(10): 104002. doi: 10.1088/1674-1137/39/10/104002

**Abstract:**

The multiplicity distribution, multiplicity moment, scaled variance, entropy and reduced entropy of target evaporated fragments emitted in forward and backward hemispheres in 12 A GeV

^{4}He, 3.7 A GeV

^{16}O, 60 A GeV

^{16}O, 1.7 A GeV

^{84}Kr and 10.7 A GeV

^{197}Au-induced emulsion heavy target (AgBr) interactions are investigated. It is found that the multiplicity distribution of target evaporated fragments emitted in both forward and backward hemispheres can be fitted by a Gaussian distribution. The multiplicity moments of target evaporated particles emitted in the forward and backward hemispheres increase with the order of the moment

*q*, and the second-order multiplicity moment is energy independent over the entire energy range for all the interactions in the forward and backward hemisphere. The scaled variance, a direct measure of multiplicity fluctuations, is close to one for all the interactions, which indicate a correlation among the produced particles. The entropy of target evaporated fragments emitted in both forward and backward hemispheres are the same within experimental errors.

2015, 39(10): 104101. doi: 10.1088/1674-1137/39/10/104101

**Abstract:**

We present a new idea to understand the structure of nuclei and compare it to the liquid drop model. After discussing the probability that the nuclear system may be a fractal object with the characteristic of self-similarity, the irregular nuclear structure properties and the self-similarity characteristic are considered to be an intrinsic aspect of the nuclear structure properties. For the description of nuclear geometric properties, the nuclear fractal dimension is an irreplaceable variable similar to the nuclear radius. In order to determine these two variables, a new nuclear potential energy formula which is related to the fractal dimension is put forward and the phenomenological semi-empirical Bethe-Weizsäcker binding energy formula is modified using the fractal geometric theory. One important equation set with two equations is obtained, which is related to the concept that the fractal dimension should be a dynamic parameter in the process of nuclear synthesis. The fractal dimensions of the light nuclei are calculated and their physical meanings are discussed. We compare the nuclear fractal mean density radii with the radii calculated by the liquid drop model for the light stable and unstable nuclei using rational nuclear fractal structure types. In the present model of fractal nuclear structure there is an obvious additional feature compared to the liquid drop model, since the present model can reflect the geometric information of the nuclear structure, especially for nuclei with clusters, such as the α-cluster nuclei and halo nuclei.

2015, 39(10): 104102. doi: 10.1088/1674-1137/39/10/104102

**Abstract:**

Within the relativistic mean field (RMF) theory, the ground state properties of dysprosium isotopes are studied using the shell-model-like approach (SLAP), in which pairing correlations are treated with particle-number conservation, and the Pauli blocking effects are taken into account exactly. For comparison, calculations of the Bardeen-Cooper-Schrieffer (BCS) model with the RMF are also performed. It is found that the RMF+SLAP calculation results, as well as the RMF+BCS ones, reproduce the experimental binding energies and one- and two-neutron separation energies quite well. However, the RMF+BCS calculations give larger pairing energies than those obtained by the RMF+SLAP calculations, in particular for nuclei near the proton and neutron drip lines. This deviation is discussed in terms of the BCS particle-number fluctuation, which leads to the sizable deviation of pairing energies between the RMF+BCS and RMF+SLAP models, where the fluctuation of the particle number is eliminated automatically.

2015, 39(10): 104103. doi: 10.1088/1674-1137/39/10/104103

**Abstract:**

Some binding energy related quantities serving as effective order parameters have been used to analyze the shape phase transition in the odd Sm nuclei. It is found that the signals of phase transition in the odd Sm nuclei are greatly enhanced in contrast to the even Sm nuclei. A further analysis shows that the transitional behaviors related to pairing in the Sm nuclei can be well described by the mean field plus pairing interaction model, with a monotonic decrease in the pairing strength

*G*.

2015, 39(10): 104104. doi: 10.1088/1674-1137/39/10/104104

**Abstract:**

The electromagnetic form factors of the deuteron, particularly its quadrupole form factor, are studied with the help of a phenomenological Lagrangian approach where the vertex of the deuteron-proton-neutron with

*D*-state contribution is explicitly taken into account. The results show the importance of this contribution to the deuteron quadrupole form factor in the approach.

2015, 39(10): 104105. doi: 10.1088/1674-1137/39/10/104105

**Abstract:**

Relativistic heavy-ion collisions can produce extremely strong magnetic fields in the collision regions. The spatial variation features of the magnetic fields are analyzed in detail for non-central Pb-Pb collisions at LHC at √

*s*

_{NN}=900, 2760 and 7000 GeV and Au-Au collisions at RHIC at √

*s*

_{NN}=62.4, 130 and 200 GeV. The dependencies of magnetic field on proper time, collision energies and impact parameters are investigated in this paper. It is shown that an enormous and highly inhomogeneous spatial distribution magnetic field can indeed be created in off-centre relativistic heavy-ion collisions in RHIC and LHC energy regions. The enormous magnetic field is produced just after the collision, and the magnitude of magnetic field of the LHC energy region is larger than that of the RHIC energy region at small proper time. It is found that the magnetic field in the LHC energy region decreases more quickly with the increase of proper time than that of the RHIC energy region.

2015, 39(10): 105101. doi: 10.1088/1674-1137/39/10/105101

**Abstract:**

A unified model is based on a generalized gauge symmetry with groups [

*SU*

_{3c}]

_{color}× (

*SU*

_{2}×

*U*

_{1}) × [

*U*

_{1b}×

*U*

_{1l}]. It implies that all interactions should preserve conservation laws of baryon number, lepton number, and electric charge, etc. The baryonic

*U*

_{1b}, leptonic

*U*

_{1l}and color

*SU*

_{3c}gauge transformations are generalized to involve non-integrable phase factors. One has gauge invariant fourth-order equations for massless gauge fields, which leads to linear potentials in the [

*U*

_{1b}×

*U*

_{1l}] and color [

*SU*

_{3c}] sectors. We discuss possible cosmological implications of the new baryonic gauge field. It can produce a very small constant repulsive force between two baryon galaxies (or between two anti-baryon galaxies), where the baryon force can overcome the gravitational force at very large distances and leads to an accelerated cosmic expansion. Based on conservation laws in the unified model, we discuss a simple rotating dumbbell universe with equal amounts of matter and anti-matter, which may be pictured as two gigantic rotating clusters of galaxies. Within the gigantic baryonic cluster, a galaxy will have an approximately linearly accelerated expansion due to the effective force of constant density of all baryonic matter. The same expansion happens in the gigantic anti-baryonic cluster. Physical implications of the generalized gauge symmetry on charmonium confining potentials due to new

*SU*

_{3c}field equations, frequency shift of distant supernovae Ia and their experimental tests are discussed.

2015, 39(10): 105102. doi: 10.1088/1674-1137/39/10/105102

**Abstract:**

This study investigates the relativistic neutrino emissivity of the nucleonic and hyperonic direct Urca processes in the degenerate baryon matter of neutron stars, within the framework of relativistic mean field theory. In particular, we study the influence of the isovector scalar interaction on the nucleonic and hyperonic direct Urca processes by exchanging δ mesons. The results indicate that δ mesons lead to obvious enhancement of the total neutrino emissivity, which must result in a more rapid cooling rate of neutron star matter.

2015, 39(10): 106001. doi: 10.1088/1674-1137/39/10/106001

**Abstract:**

For MWPCs used for X-ray position detection, simulation studies of the anode wire modulation effect of the detector were carried out using the Garfield program. Different gas mixtures were used as the working gas in the simulation, so as to obtain the influence of the X-ray cross section and electron diffusion coefficient of the working gases on the anode wire modulation effect of {an} MWPC with anode wire spacing of 2 mm. Results show that, though a working gas with higher X-ray cross section implies a larger average drift distance for the ionized electrons, such gas mixtures are of little use in improving the anode wire modulation effect of MWPCs. It is found that the transverse electron diffusion coefficient is the determining factor for the extent of the anode wire modulation effect in the detector.

2015, 39(10): 106002. doi: 10.1088/1674-1137/39/10/106002

**Abstract:**

The X-ray spectrometer is one of the satellite payloads on the Chang'E-2 satellite. The soft X-ray detector is one of the devices on the X-ray spectrometer, designed to detect the major rock-forming elements within the 0.5-10 keV range on the lunar surface. In this paper, energy linearity and energy resolution calibration is done using a weak

^{55}Fe source. Temperature and time effects are found not to give a large error. The total uncertainty of calibration is estimated to be within 5% after correction.

2015, 39(10): 106003. doi: 10.1088/1674-1137/39/10/106003

**Abstract:**

The resistance to neutron irradiation of LaBr

_{3}scintillator was studied in this work. The change of background counting rate, light output and energy resolution of the LaBr

_{3}scintillator were analyzed to determine whether the scintillator was damaged under different neutron flux rates induced by

^{241}Am-Be, D-T neutron generator, and reactor neutron source. The results show that the neutron radiation damage in LaBr

_{3}scintillator is mainly affected by neutron flux rate. Under low flux rate, the properties of the scintillator were hardly changing, while under high flux rate, there is obvious deterioration in the background spectra and in the energy resolution because of the neutron activation. After a period, the neutron radiation damage will spontaneously recover.

2015, 39(10): 106101. doi: 10.1088/1674-1137/39/10/106101

**Abstract:**

We first clarify timing issues of non-uniform sampling intervals regarding a 5 GS/s fast pulse sampling module with DRS4. A calibration strategy is proposed, and as a result, the waveform timing performance is improved to below 10 ps RMS. We then further evaluate waveform-timing performance of the module by comparing with a 10 GS/s oscilloscope in a setup with plastic scintillators and fast PMTs. Different waveform timing algorithms are employed for analysis, and the module shows comparable timing performance with that of the oscilloscope.

2015, 39(10): 106201. doi: 10.1088/1674-1137/39/10/106201

**Abstract:**

The concept of isochronous mass spectrometry (IMS) applying two time-of-flight (TOF) detectors originated many years ago at GSI. However, the corresponding method for data analysis has never been discussed in detail. Recently, two TOF detectors have been installed at CSRe and the new working mode of the ring is under test. In this paper, a data analysis method for this mode is introduced and tested with a series of simulations. The results show that the new IMS method can significantly improve mass resolving power via the additional velocity information of stored ions. This improvement is especially important for nuclides with Lorentz factor γ-value far away from the transition point γ

_{t}of the storage ring CSRe.

2015, 39(10): 107001. doi: 10.1088/1674-1137/39/10/107001

**Abstract:**

For the application of high intensity continuous wave (CW) proton beam acceleration, a new superconducting accelerating structure for extremely low

*β*protons working in TE210 mode has been proposed at Peking University. The cavity consists of eight electrodes and eight accelerating gaps. The cavity's longitudinal length is 368.5 mm, and its transverse dimension is 416 mm. The RF frequency is 162.5 MHz, and the designed proton input energy is 200 keV. A peak field optimization has been performed for the lower surface field. The accelerating gaps are adjusted by phase sweeping based on KONUS beam dynamics. The first four gaps are operated at negative synchronous RF phase to provide longitudinal focusing. The subsequent gaps are 0° sections which can minimize the transverse defocusing effect. Solenoids are placed outside the cavity to provide transverse focusing. Numerical calculation shows that the transverse defocusing of the KONUS phase is about three times smaller than that of the conventional negative synchronous RF phase. The beam dynamics of a 10 mA CW proton beam is simulated by the TraceWin code. The simulation results show that the beam's transverse size is under effective control, while the increase in the longitudinal direction is slightly large. Both the TraceWin simulation and the numerical calculation show that the cavity has a relatively high effective accelerating gradient of 2.6 MV/m. On the whole, our results show that this new accelerating structure may be a possible candidate for superconducting operation at such a low energy range.

2015, 39(10): 107002. doi: 10.1088/1674-1137/39/10/107002

**Abstract:**

Electron cloud interaction with high energy positive beams are believed responsible for various undesirable effects such as vacuum degradation, collective beam instability and even beam loss in high power proton circular accelerators. An important uncertainty in predicting electron cloud instability lies in the detailed processes of the generation and accumulation of the electron cloud. The simulation on the build-up of electron cloud is necessary to further studies on beam instability caused by electron clouds. The China Spallation Neutron Source (CSNS) is an intense proton accelerator facility now being built, whose accelerator complex includes two main parts: an H-linac and a rapid cycling synchrotron (RCS). The RCS accumulates the 80 MeV proton beam and accelerates it to 1.6 GeV with a repetition rate of 25 Hz. During beam injection with lower energy, the emerging electron cloud may cause serious instability and beam loss on the vacuum pipe. A simulation code has been developed to simulate the build-up, distribution and density of electron cloud in CSNS/RCS.

2015, 39(10): 107003. doi: 10.1088/1674-1137/39/10/107003

**Abstract:**

A Medium Energy Beam Transport line 1 (MEBT1) has been designed for Injector Scheme II of the China ADS project. To match the beam from RFQ to Superconducting (SC) Half Wave Resonator (HWR) sections with emittance preservation, the MEBT1 has been designed to be mechanically compact. Working at 162.5 MHz, the MEBT1 transports a 10 mA, 2.1 MeV proton beam using seven quadrupoles and two bunching cavities within 2.7 meters. Three collimators are placed between every two adjacent quadrupoles to collimate the beam halo. Design and construction of the MEBT1 are presented in this paper.

2015, 39(10): 108201. doi: 10.1088/1674-1137/39/10/108201

**Abstract:**

An empirical numerical model that includes nuclear absorption, multiple Coulomb scattering and energy loss is presented for the calculation of transmission through thick objects in high energy proton radiography. In this numerical model the angular distributions are treated as Gaussians in the laboratory frame. A Monte Carlo program based on the Geant4 toolkit was developed and used for high energy proton radiography experiment simulations and verification of the empirical numerical model. The two models are used to calculate the transmission fraction of carbon and lead step-wedges in proton radiography at 24 GeV/

*c*, and to calculate radial transmission of the French Test Object in proton radiography at 24 GeV/

*c*with different angular cuts. It is shown that the results of the two models agree with each other, and an analysis of the slight differences is given.

2015, 39(10): 108202. doi: 10.1088/1674-1137/39/10/108202

**Abstract:**

The Positron Emission Mammography imaging system (PEMi) provides a novel nuclear diagnosis method dedicated for breast imaging. With a better resolution than whole body PET, PEMi can detect millimeter-sized breast tumors. To address the requirement of semi-quantitative analysis with a radiotracer concentration map of the breast, a new attenuation correction method based on a three-dimensional seeded region growing image segmentation (3DSRG-AC) method has been developed. The method gives a 3D connected region as the segmentation result instead of image slices. The continuity property of the segmentation result makes this new method free of activity variation of breast tissues. The threshold value chosen is the key process for the segmentation method. The first valley in the grey level histogram of the reconstruction image is set as the lower threshold, which works well in clinical application. Results show that attenuation correction for PEMi improves the image quality and the quantitative accuracy of radioactivity distribution determination. Attenuation correction also improves the probability of detecting small and early breast tumors.

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

Original research articles, Ietters and reviews Covering theory and experiments in the fieids of

- Particle physics
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- Particle and nuclear astrophysics
- Cosmology

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