2015 Vol. 39, No. 2
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We propose to understand the mixing angles and CP-violating phases from the Δ(48) family symmetry combined with the generalized CP symmetry. A model-independent analysis is performed by scanning all the possible symmetry breaking chains. We find a new mixing pattern with only one free parameter, excellent agreement with the observed mixing angles can be achieved and all the CP-violating phases are predicted to take nontrivial values. This mixing pattern is testable in the near future neutrino oscillation and neutrinoless double-beta decay experiments. Finally, a flavor model is constructed to realize this mixing pattern.
The confirmation of charged charmonium-like states indicates that heavy quark molecules should exist. Here we discuss the possibility of a molecule state with JPC=3-+. In a one-boson-exchange model investigation for the S wave C=+D* 2* states, one finds that the strongest attraction is in the case J=3 and I=0 for both π and σ exchanges. Numerical analysis indicates that this hadronic bound state might exist if a phenomenological cutoff parameter around 2.3 GeV (1.5 GeV) is reasonable with a dipole (monopole) type form factor in the one-pion-exchange model. The cutoff for binding solutions may be reduced to a smaller value once the σ exchange contribution is included. If a state around the D* 2* threshold (≈4472 MeV) in the channel J/ψω (P wave) is observed, the heavy quark spin symmetry implies that it is not a c meson and the JPC are likely to be 3-+.
Within the hidden local symmetry framework, the Dalitz decay η'→Ve+e- is studied with the vector meson dominance model. It is found that the partial width Γ(η'→ωe+e-)≈40 eV and branching ratio B(η'→ω+e-)≈2×10-4, and Γ(η'→ρe+e-)≈10Γ(η'→ωe+e-) and B(η'→ρe+e-)≈10B(η'→ωe+e-). The maximum position of the dilepton distribution is me+e-≈1:33 MeV. These decays are measurable with the advent of high statistic η' experiments.
The Standard Model (SM) prediction on the forward-backward asymmetry for m b production (AFBb) is well consistent with the data of LEP Ⅰ at the Z-pole, but deviates from the data at √ =89.55 and 92.95 GeV which are slightly away from the pole. This deviation implies that there is still room for new physics. We calculate the AFBb at the vicinity of the Z-pole in the little Higgs model as well as other measurable parameters such as Rb and Rc, by which we may constrain the parameter space of the little Higgs model. This can be further tested in the newly proposed tera-Z factory. With the fitted parameters we further make predictions on AFBb and AFBt for m t production at the International Linear Collider (ILC).
The properties of γ instability in rapidly rotating even-even 132-138Nd isotopes have been investigated using the pairing-deformation self-consistent total-Routhian-surface calculations in a deformation space of (β2, γ, β4). It is found that even-even 134-138Nd nuclei exhibit triaxiality in both ground and excited states, even up to high-spin states. The lightest isotope possesses a well-deformed prolate shape without a γ deformation component. The current numerical results are compared with previous calculations and available observables such as quadrupole deformation β2 and the feature of γ-band levels, showing basically a general agreement with the observed trend of γ correlations (e.g. the pattern of the odd-even energy staggering of the γ band). The existing differences between theory and experiment are analyzed and discussed briefly.
Proton radioactivity has been investigated using the effective liquid drop model with varying mass asymmetry shapes and effective inertial coefficients. An effective nuclear radius constant formula replaces the old empirical one in the calculations. The theoretical half-lives are in good agreement with the available experimental data. All the deviations between the calculated logarithmic half-lives and the experimental values are less than 0.8. The root-mean-square (rms) deviation is 0.523. Predictions for the half-lives of proton radioactivity are made for elements across the periodic table. From the theoretical results, there are 11 candidate nuclei for proton radioactivity in the region Z<51. In the region Z>83, no nuclei are suggested as probable candidate nuclei for proton radioactivity within the selected range of half-lives studied.
A high-efficiency fast neutron detector prototype based on a triple Gas Electron Multiplier (GEM) detector, which, coupled with a novel multi-layered high-density polyethylene (HDPE) as a neutron-to-proton converter for improving the neutron detection efficiency, is introduced and tested with the Am-Be neutron source in the Institute of Modern Physics (IMP) at Lanzhou in the present work. First, the developed triple GEM detector is tested by measuring its effective gain and energy resolution with 55Fe X-ray source to ensure that it has a good performance. The effective gain and obtained energy resolution is 5.0×104 and around 19.2%, respectively. Secondly, the novel multi-layered HDPE converter is coupled with the cathode of the triple GEM detector making it a high-efficiency fast neutron detector. Its effective neutron response is four times higher than that of the traditional single-layered conversion technique when the converter layer number is 38.
Offline calibration plays an important role in BESⅢ offline data processing. In order to achieve good spatial and momentum resolution, it is necessary to implement high precision offline calibration for the BESⅢ drift chamber. This paper studies the time-to-distance relations, which are important calibration constants for track reconstruction. The parameterization of the time-to-distance relation, studies of left-right asymmetry and studies of variation with entrance angle are performed. The impact of dead channels on the time-to-distance relation is given special attention in order to reduce the shift in measured momentum for tracks passing near dead cells. Finally we present the resolutions for barrel Bhabha events (|cosθ|<0.8) from a J/ψ data set taken in 2012. The average spatial resolution is 123 μ and the momentum resolution for 1.548 GeV/c Bhabha tracks is 11.9 MeV/c.
A single width NIM module that includes eight channels of the time-to-amplitude converter (TAC) and the charge-to-amplitude converter (QAC) is introduced in the paper, which is designed for the large neutron wall detector to measure charge (energy) and time interval simultaneously. The module adopts a high precision gated integration circuit to realize TAC and QAC. The input range of TAC is from 30 ns to 1 μs, and the input range of QAC is from 40 pC to 600 pC. The linearity error of TAC is lower than 1.28%, and the time resolution of TAC is less than 0.871%. The linearity error of QAC is lower than 0.81%, and the resolution of QAC is better than 0.936%.
In order to further obtain the information of three-body force (TBF) from 200-400 MeV/u 12C+12C elastic scattering, we plan to perform this experiment on a SHARAQ spectrometer. Based on the experimental condition of the Radioactive Ion Beam Factory (RIBF)-SHARAQ facility, a simulation is given to find a compromise between the better energy and angular resolutions, and higher yield by optimizing the target thickness, beam transport mode, beam intensity and angular step. From the simulation, we found that the beam quality mainly limits the improvements of energy and angular resolutions. A beam tracking system as well as a lateral and angular dispersion-matching technique are adopted to reduce the influence of beam quality. According to the two angular settings of SHARAQ as well as the expected cross sections on the basis of the theoretical model, the energy and angular resolutions, and statistical accuracy are estimated.
For the injector Scheme-Ⅰ test stand of the China-ADS (Accelerator Driven subcritical System), a beam with the maximum power of 100 kW will be produced and transported to the beam dump. To solve the very high thermal load problem at the dump, two measures are taken to deal with the huge power density at the target. One is to enlarge the contact area between the beam and the target, and this is to be accomplished by expanding the beam profile at the target and using slanted target plates. The other is to produce a more homogenous beam profile at the target to minimize the maximum power density. Here the beam dump line is designed to meet the requirement of beam expansion and homogenization at 3 different energies (3.2 MeV, 5 MeV and 10 MeV), and the step-like field magnets are employed for the beam spot homogenization. Taking into account the fact that the space charge effects are very strong at such low beam energies, the simulations have included space charge effects and errors which show that the beam line can meet the requirements very well. In the meantime, the alternative beam design using standard multipole magnets is also presented.
The rapid cycling synchrotron (RCS) is part of the China Spallation Neutron Source (CSNS). The RCS provides 1.6 GeV protons with a repetition rate of 25 Hz. The RF system in RCS is mainly composed of a ferrite loaded RF cavity, a high power tetrode amplifier, a bias supply of 3300 A and a digital low level RF (LLRF) system based on FPGA. The major challenge of the LLRF system is to solve problems caused by rapid frequency sweeping and the heavy beam loading effect. A total of eight control loops are applied to ensure the normal operation. An effective feedforward scheme is widely used to improve the dynamic performance of the system. The design of the LLRF system and high power integration test results with the prototype RF system are presented.
A novel parallel plate model is proposed that divides the electron cloud into three parts at saturation, and it is studied in detail using both an analytical approach and particle-in-cell (PIC) code simulations. As one part of the electron cloud, ribbons modes are suggested by tracking the trajectory of individual particles, and the aim of this mode form is to simplify the progress of the multipacting effect in the parallel plate so as to be eliminated by optimizing RF parameters. The micro-pulse electron gun (MPG) has demonstrated the potential to address the need for high peak and average current electron beams, hence studying the multipacting in MPG is essential. On the basis of studying multipacting in the parallel plate, it is clear that increasing the cavity voltage is of interest in yielding high quality beams in the gun.
In conventional research on beam gas coulomb scattering (BGCS), only the related beam lifetime using the analytical method is studied. In this paper, using the particle-in-cell Monte Carlo collisions (PIC-MCC) method, we not only simulated the beam lifetime but also explored the effect of BGCS on the beam distribution. In order to better estimate the effect on particle distribution, we study the ultra-low emittance electron beam. Here we choose the HeFei Advanced Light Source. By counting the lost particles in a certain time, the corresponding beam lifetime we simulated is 4.8482 h/13.8492 h in x/y, which is very close to the theoretic value (5.0555 h /13.7024 h in x/y). By counting the lost particles relative to the collided particles, the simulated value of the loss probability of collided particles is 1.3431e-04, which is also very close to the theoretical value (1.3824e-04). Besides, the simulation shows there is a tail in the transverse distribution due to the BGCS. The close match of the simulation with the theoretic value in beam lifetime and loss probability indicates our simulation is reliable.
In this paper, we present the RF simulation, the fabrication and the normal RF test of a six-cell copper model cross bar H mode (CH) cavity. The CH cavity was researched and developed at the Institute of Modern Physics for Injector II of the superconducting linac of the accelerator driven system of China, operating at a frequency 162.5 MHz, β=0.065. The deep drawing and electron beam welding were employed to fabricate this cavity, which would be used to develop the superconducting CH cavity in the future. The results of the normal RF test agree with the simulation of the electromagnetic properties, such as the electric field distribution on the cavity axis, frequency and Q factor.
The local structures and optical absorption characteristics of Fe doped TiO2 nanoparticles synthesized by the sol-gel method were characterized by X-ray diffraction (XRD), X-ray absorption fine structure spectroscopy (XAFS) and ultraviolet-visible absorption spectroscopy (UV-Vis). XRD patterns show that all Fe-doped TiO2 samples have the characteristic anatase structure. Accurate Fe and Ti K-edge EXAFS analysis further reveal that all Fe atoms replace Ti atoms in the anatase lattice. The analysis of UV-Vis data shows a red shift to the visible range. According to the above results, we claim that substitutional Fe atoms lead to the formation of structural defects and new intermediate energy levels appear, narrowing the band gap and extending the optical absorption edge towards the visible region.
In this paper, a division-of-amplitude photopolarimeter (DOAP) for measuring the polarization state of a free-electron laser (FEL) pulse is described. The incident FEL beam is divided into four separate beams, and four Stokes parameters can be measured in a single-shot. In the crossed-planar undulators experiment at the Shanghai deep ultraviolet FEL test facility, this DOAP instrument constructed in house responsed accurately and timely while the polarization-state of fully coherent FEL pulses were switched, which is helpful for confirming the crossed-planar undulators technique for short-wavelength FELs.
Peking University is developing a 1.3 GHz superconducting accelerating section highpower THz free-electron laser for the China Academy of Engineering Physics (CAEP). A compact fast/slow tuner has been developed by the Institute of High Energy Physics (IHEP) for the accelerating section to control Lorentz detuning, compensate for beam loading effect, microphonics and liquid helium pressure fluctuations. The tuner design, warm test and cold test of the first prototype are presented, which has a guiding significance for the manufacture of the formal tuner and cryomodule assembly.
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