2013 Vol. 37, No. 3
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The light scalar mesons below 1 GeV configured as tetraquark systems are studied in the framework of the flux-tube model. Comparative studies indicate that a multi-body confinement, instead of the additive two-body confinement, should be used in a multiquark system. The σ and κ mesons could be well accommodated in the diquark-antidiquark tetraquark picture, and could be colour-confinement resonances. The m a0(980) and m f0(980) mesons are not described as m KK molecular states and nsns diquark-antidiquark states. However, the mass of the first radial excited state of the diquark-antidiquark state, nnnn is 1019 MeV, is close to the experimental data of the m f0(980).
We propose an extended Nambu-Jona-Lasinio model to include heavy mesons with heavy quark symmetry. The quark current-current interaction is generalized to include the heavy quark currents. In order to comply with the heavy quark spin symmetry at the heavy quark limit, the dependence of the quark mass on the interaction strength is introduced. The light and heavy pseudo-scalar and vector mesons, their masses and the weak decay constants are calculated in the unified frame.
In the littlest Higgs model with T-parity, the heavy photon (AH) is supposed to be a possible dark matter (DM) candidate. The direct proof of the validity of this model is to produce the heavy photon at an accelerator. In this paper, we study the production rate of e+e-→AHAH at the international e+e- linear collider (ILC) in the littlest Higgs model with T-parity, and show the distributions of the transverse momenta of AH. The numerical results indicate that the heavy photon production rate could reach the 10-1fb level at some parameter space, so this could be a good chance to observe the heavy photon via the pair production process with high luminosity at the ILC (500 fb-1). We know that DM is composed of weakly interacting massive particles, so the interactions with standard model particles are weak. How to detect heavy photons at a collider and distinguish them from other DM candidates are discussed in the nal section of the paper.
We study possible exotic JPC = 0+- states using tetraquark interpolating currents with the QCD sum rule approach. The extracted masses are around 4.85 GeV for the charmonium-like states and 11.25 GeV for the bottomonium-like states. There is no working region for the light tetraquark currents, which implies that the light 0+- state may not exist below 2 GeV.
We study the m J/ψ pair production issue at the Fermilab Tevatron Run II with a center-of-mass energy of √s=1.96 TeV. Both the color-singlet and color-octet production mechanisms are considered. Our results show that the transverse momentum (pT) scaling behaviors of the double m J/ψ differential cross-sections in the color-singlets and color-octets deviate distinctively from each other while pT is larger than 8 GeV, and with a luminosity of 5 fb-1, the m J/ψ pair events from the color-singlet scheme are substantially measurable in the Tevatron experiments, even with a certain lower transverse momentum cut. Hence the Tevatron is still a possible platform to check the heavy quarkonium production mechanism.
The energy levels, transition energy, B(E2) values, intrinsic quadrupole moment Q0 and potential energy surface for even-even 184W and 184Os nuclei were calculated using IBM-1. The predicted energy levels, transition energy, B(E2) values and intrinsic quadrupole moment Q0 results are reasonably consistent with the experimental data. A contour plot of the potential energy surfaces shows that two interesting nuclei are deformed and have rotational characters.
In the framework of the projected shell model, we investigate the competition between the two-quasineutron and two-quasiproton Kπ=6+ states in the ytterbium isotopes and N=104 isotones adjacent to 174Yb. The 174Yb results are compared with the experimental data. The Kπ=6+ isomer observed in 174Yb is assigned as an admixture of the ν7/2-×ν5/2- and π7/2+×π5/2+ intrinsic structure, which explains the experimental |gK-gR| value. Similar mixing would appear in 172Yb, 176Hf, and 178W. The low-lying Kπ=6+ states are also predicted in 170-178Yb.
Elastic proton scattering from Be, C, and O isotopes has been investigated in the relativistic impulse approximation (RIA). In the calculations, the nucleon-nucleus optical potentials are obtained using ground state nuclear matter densities, which are computed using the relativistic mean field model with the FSU parameter set. The scattering observables, including differential cross section, analyzing power, and spin-rotation function, are analyzed. It is found that the scattering observables for O isotopic chains display a clear mass dependence, for instance, the minimum analyzing power shifts to a low scattering angle with increasing mass number. While for the Be isotopic chain, the emergence of a neutron halo in 14Be breaks this trend, i.e., the minimum analyzing powers for 12Be and 14Be are almost the same as each other.
We study the sidereal and solar time modulation of multi-TeV cosmic rays using the east-west method with Tibet Ⅲ air shower array data taken from November 1999 to December 2008. The statistics are twice the amount used in our previous paper. In this analysis, the amplitude of the observed sidereal time modulation is about 0.1%, and the modulation shows an excess from about 4 to 7 hours and a deficit around 12 hours in local sidereal time. The sidereal time modulation has a weak dependence on the primary energy of the cosmic rays. However, the solar time modulation shows a large energy dependence. We find that the solar time modulation is fairly consistent with the prediction of the Compton-Getting effect for high-energy samples (6.2 TeV and 12.0 TeV), but exceeds the prediction for the low-energy sample (4.0 TeV). Such a discrepancy may be due to the solar modulation or the characteristics of the experimental device in the near threshold energy.
This paper studies the thermodynamic properties of the 5D black hole in Einstein-Gauss-Bonnet gravity from the viewpoint of geometrothermodynamics. It is found that the Legendre invariant metrics of the 5D black holes in Einstein-Yang-Mills-Gauss-Bonnet theory and Einstein-Maxwell-Gauss-Bonnet theory reproduce the behavior of the thermodynamic interaction and phase transition structure of the corresponding black hole configurations correctly. It is shown that they are both curved and that the curvature scalar provides information about the phase transition point.
The photomultiplier tube (PMT) used in the water Cherenkov detector array (WCDA) of the Large High Altitude Air Shower Observatory (LHAASO) requires a good single photoelectron (SPE) spectrum and a charge dynamic range from 1 to 4000 photoelectrons. In this paper, the bases design and improvement of the photomultiplier tube R5912 are presented. The results show that at the gain of 2.6×106, the anode output has a good single photoelectron spectrum, and its charge non-linearity is within 5% when the number of photoelectrons (nPE) is 3500. The charge non-linearity of the 8th dynode output is within 2% when the number of nPE is 4000, which satisfies the dynamic range requirement.
Sensitive X-ray polarimetry in the keV energy range can be achieved by measuring the azimuthal angle distribution of emitted electrons after the photoelectric absorption of X-rays in a micropattern gas detector. However, the initial direction of the electron is not readily measurable due to the randomization of its motion during energy loss. By using the Geant4, Maxwell and Garfield packages, we simulated the detected electron tracks following photoelectric absorption, electron drift and diffusion in the gas, and proposed a technique capable of reconstructing the initial direction of the emitted photoelectron. The technique allows us to measure the angular modulation of flux predicted for a polarized X-ray beam. We calculated the modulation factors in 2-10 keV with a gas mixture of neon and CO2, and discussed how electron diffusion along the drift will dilute the track and suppress the modulation. These results are useful for the design of the X-ray polarimeter.
In this paper we address the problem of the low beam transmission efficiency of the HIRFL-SSC. The influence of the SFC-SSC energy match, the SSC RF voltage, and harmonic field in the injection area of the SSC, and the SSC central trajectory on the beam transmission efficiency have been analyzed both from the theoretical side and from the actual operating data. The main reason is that the soft-edge approximation of the magnet field (the so-called theoretical field) and the simplified calculation programs were adopted when calculating the beam center trajectory and designing the injection and extraction system, and the measured magnetic field was not used to correct the calculation results. These led to large deviations of the calculated center trajectory, and then resulted in low efficiency of the SSC beam transmission. Therefore, the re-calculation of SSC beam center trajectory and injection and extraction system, as well as the measured magnet field correction are the key points required to solve the problem.
Space-charge forces acting in mismatched beams have been identified as a major cause of beam halo. In this paper, we describe the beam halo experimental results in a FODO beam line at IHEP. With this beam transport line, experiments are carried out to compare the measured data with the multi-particle simulations and to study the formation of a beam halo. The maximum measured amplitudes of the matched and mismatched beam profiles agree well with simulations. Details of the experiment are presented.
In the Hefei Light Source (HLS) storage ring, multibunch operation is used to obtain a high luminosity. Multibunch instabilities can severely limit light source performance with a variety of negative impacts, including beam loss, low injection efficiency, and overall degradation of the beam quality. Instabilities of a multibunch beam can be mitigated using certain techniques including increasing natural damping (operating at a higher energy), lowering the beam current, and increasing Landau damping. However, these methods are not adequate to stabilize a multibunch electron beam at a low energy and with a high current. In order to combat beam instabilities in the HLS storage ring, active feedback systems including a longitudinal feedback system (LFB) and a transverse feedback system (TFB) will be developed as part of the HLS upgrade project, the HLS-Ⅱ storage ring project. As a key component of the longitudinal bunch-by-bunch feedback system, an LFB kicker cavity with a wide bandwidth and high shunt impedance is required. In this paper we report our work on the design of the LFB kicker cavity for the HLS-Ⅱ storage ring and present the new tuning and optimization techniques developed in designing this high performance LFB kicker.
Precise and fast 3D space-charge calculations have become important for high intensity hadron accelerator design. The PIC method is most frequently used due to its efficiency. This paper introduces a 3D-PIC code that computes the potential of the bunch in the rest frame by means of Poisson's equation. FFT is applied as Poisson solvers. The details and the results are presented as well as error analysis.
The period length is usually much larger than the cavity effective length in a low energy superconducting linac.The long drifts between cavities will not only decrease the acceptance of the linac, but also lead to possible instability. The linac will be more sensitive to mismatch and other perturbations. From the longitudinal motion equation, the function which describes the parametric resonance is deduced and the relation between the instability region and the cavity filling factor is discussed. It indicates that if the zero current phase advance per period is kept below 90°, instability driven by parametric resonance will never occur. The space charge effect will enhance the instability, so that a stricter limitation on the phase advance per cell is required. From the numerical simulation results for two different schemes of Injector-I of the C-ADS driver linac, one can find that even with just three cells in the unstable region, significant emittance growth can be observed. Further investigations show that it is apt to produce halo particles under resonance, and the machine becomes more sensitive to errors and mismatches. Therefore, it is important to keep all cells in the stable region throughout the linac of very high beam power to minimize beam losses.
The China Spallation Neutron Source (CSNS) accelerators consist of a low energy H- linac and a high energy proton Rapid Cycling Synchrotron (RCS). The proton beam is accumulated in the RCS and accelerated from 80 MeV to 1.6 GeV with a repetition of 25 Hz. Independent component analysis (ICA) is a robust method for processing the collected data (samples) recorded by the turn-by-turn beam position monitor (BPM), which was recently applied to the accelerator. The samples are decomposed to source signals, or the so-called independent components, which correspond to the inherent motion of samples, such as betatron motion and synchrotron motion. A study on the application of the ICA method to CSNS/RCS has been made. It shows that the beta function, phase advance, and dispersion can be well reconstructed by using ICA in CSNS/RCS. The effects of BPM errors on the ICA results are also studied. By comparing the different solving methods in ICA, the so-called SOBI has more advantages for isolating the independent components on the application of ICA to CSNS/RCS. Beam emittance dilution in the process of exciting the turn-by-turn samples is considered, and thus an RF kicker is adopted to avoid such emittance growth.
The pressure-induced phase transitions of PbCO3 are studied using synchrotron radiation in a diamond anvil cell at room temperature. The XRD measurement indicates that PbCO3 with an initial phase of aragonite-type structure undergoes two phase transitions at ～ 7.8 GPa and ～ 15.7 GPa，respectively. The higher-pressure phase appearing at ～ 15.7 GPa is stable up to 51.8 GPa. The two phase transitions are further confirmed by Raman scattering up to 23.3 GPa. During the decompression process, the high-pressure phases of PbCO3 are gradually recovered to the starting aragonite-type structure, but exhibit some hysteresis. The bulk modulus B0 of the aragonite-type structure is obtained to be 63± (3) GPa by fitting the volume-pressure data to the Birch-Murnaghan equation of states with B0' fixed to 4.
Conventionally, the polarization of a synchrotron soft X-ray beam is measured through a polarimeter based on multilayer optical elements. The major drawback of the traditional approach is the difficulty in comparing different configurations due to the misalignment of each incident angle. In this paper, a new analytical model, based on the variation of reflectivity for different incident angles, is established to facilitate the extraction of important polarization-related information, i.e. angular distribution of polarization components, a tiny change of the direction of azimuth rotation axis of polarizer, etc.
The hydrated shell of both Fe2+ and Fe3+ aqueous solutions are investigated by using the molecular dynamics (MD) and X-ray absorption structure (XAS) methods. The MD simulations show that the first hydrated shells of both Fe2+ and Fe3+ are characterized by a regular octahedron with an Fe-O distance of 2.08Å for Fe2+ and 1.96Å for Fe3+, and rule out the occurrence of a Jahn-Teller distortion in the hydrated shell of an Fe2+ aqueous solution. The corresponding X-ray absorption near edge fine structure (XANES) calculation successfully reproduces all features in the XANES spectra in Fe2+ and Fe3+ aqueous solution. A feature that is located at energy 1 eV higher than the white line (WL) in an Fe3+ aqueous solution may be assigned to the contribution of the charge transfer.
The latent ion track in α -quartz is studied by molecular dynamics simulations. The latent track is created by depositing electron energies into a cylindrical region with a radius of 3 nm. In this study, the electron stopping power varies from 3.0 keV/nm to 12.0 keV/nm, and a continuous latent track is observed for all the simulated values of electron stopping power except 3.0 keV/nm. The simulation results indicate that the threshold electron stopping power for a continous latent track lies between 3.0 keV/nm and 3.7 keV/nm. In addition, the coordination defects produced in the latent track are analyzed for all the simulation conditions, and the results show that the latent track in α -quartz consists of an O-rich amorphous phase and Si-rich point defects. At the end of this paper, the influence of the energy deposition model on the latent track in α -quartz is investigated. The results indicate that different energy deposition models reveal similar latent track properties. However, the values of the threshold electron stopping power and the ion track radius are dependent on the choice of energy deposition model.
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