2017 Vol. 41, No. 4
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We first construct the effective chiral Lagrangians for the 1-+ exotic mesons. With the infrared regularization scheme, we derive the one-loop infrared singular chiral corrections to the π1(1600) mass explicitly. We investigate the variation of the different chiral corrections with the pion mass under two schemes. Hopefully, the explicit non-analytical chiral structures will be helpful for the chiral extrapolation of lattice data from the dynamical lattice QCD simulation of either the exotic light hybrid meson or the tetraquark state.
We investigate flavor phenomenology and dark matter in the context of the scotogenic model. In this model, the neutrino masses are generated through radiative corrections at the one-loop level. Considering the neutrino mixing matrix to be of tri-bimaximal form with additional perturbations to accommodate the recently observed non-zero value of the reactor mixing angle θ13, we obtain the relation between various neutrino oscillation parameters and the model parameters. Working in a degenerate heavy neutrino mass spectrum, we obtain light neutrino masses obeying the normal hierarchy and also study the relic abundance of fermionic dark matter candidates, including coannihilation effects. A viable parameter space is thus obtained, consistent with neutrino oscillation data, relic abundance and various lepton flavor violating decays such as lα→lβγ and lα→3lβ.
Motivated by the search for flavor-changing neutral current (FCNC) top quark decays at the LHC, we calculate the rare Higgs three body decay H→Wbc induced by top-Higgs FCNC coupling in the littlest Higgs model with T-parity (LHT). We find that the branching ratio of H→Wbc in the LHT model can reach O(10-7) in the allowed parameter space.
The masses of the three generations of charged leptons are known to completely satisfy Koide's mass relation, but the question remains of whether such a relation exists for neutrinos. In this paper, by considering the seesaw mechanism as the mechanism generating tiny neutrino masses, we show how neutrinos satisfy Koide's mass relation, on the basis of which we systematically give exact values of both left- and right-handed neutrino masses.
We study the sound perturbation of a rotating acoustic black hole in the presence of a disclination. The radial part of the massless Klein-Gordon equation is written into a Heun form, and its analytical solution is obtained. These solutions have an explicit dependence on the parameter of the disclination. We obtain the exact Hawking-Unruh radiation spectrum.
Recently, the CMS and ATLAS collaborations have reported direct searches for the 125 GeV Higgs decay with lepton flavor violation, h→μτ. In this work, we analyze the signal of the lepton flavour violating (LFV) Higgs decay h→μτ in the μ from ν Supersymmetric Standard Model (μνSSM) with slepton flavor mixing. Simultaneously, we consider the constraints from the LFV decay τ →μ γ, the muon anomalous magnetic dipole moment and the lightest Higgs mass around 125 GeV.
An attempt is made to study the symmetry energy at the time of primary fragment formation from the experimentally observed cold fragments for a neutron-rich system of 64Ni+9Be at 140 MeV/nucleon, utilizing the recent finding that the excitation energy becomes lower for more neutron-rich isotopes with a given Z value. The extracted asym/T values from the cold fragments, based on the Modified Fisher Model (MFM), are compared to those from the primary fragments of the antisymmetrized molecular dynamics (AMD) simulation and become consistent with the simulation when the I=N-Z value becomes larger, indicating that the excitation energy of these neutron-rich isotopes is indeed lower.
The 232Th(n,γ)233Th neutron capture reaction cross sections were measured at average neutron energies of 14.1 MeV and 14.8 MeV using the activation method. The neutron flux was determined using the monitor reaction 27Al(n,α)24Na. The induced gamma-ray activities were measured using a low background gamma ray spectrometer equipped with a high resolution HPGe detector. The experimentally determined cross sections were compared with the data in the literature, and the evaluated data of ENDF/B-VⅡ.1, JENDL-4.0u+, and CENDL-3.1. The excitation functions of the 232Th(n,γ)233Th reaction were also calculated theoretically using the TALYS1.6 computer code.
High-spin states in 126Te have been investigated by using in-beam γ ray spectroscopy with the 124Sn(7Li, 1p4n)126Te reaction at a beam energy of 48 MeV. The previously known level scheme has been enriched, and a new negative-parity sequence has been established. The yrast positive-parity band shows a shape change between triaxial shape and collective oblate shape as a function of spin. In particular, three competitive minima appear in the potential energy surface for the Iπ=8+ states, with one aligned state at γ=-120° and two triaxial states at γ~30° and -45°, respectively. The signature splitting behavior of the negative-parity band is discussed. The shape change with increasing angular momentum and the signature splitting can be interpreted well in terms of the Cranked Nilsson-Strutinsky-Bogoliubov and Cranked Nilsson-Strutinsky model calculations.
A two-dimensional dynamical model based on the Langevin equation was used to study the fission dynamics of the compound nuclei 206Po and 168Yb produced in the reactions 12C+194Pt and 18O+150Sm, respectively. The fission cross section and average pre-scission neutron multiplicity were calculated for the compound nuclei206Po and 168Yb, and results of the calculations compared with the experimental data. The elongation coordinate was used as the first dimension and the projection of the total spin of the compound nucleus onto the symmetry axis, K, considered as the second dimension in the Langevin dynamical calculations. In the two-dimensional calculations, a constant dissipation coefficient of K and a non-constant dissipation coefficient have been used to reproduce the above-mentioned experimental data. It is shown that the two-dimensional Langevin equation can satisfactorily reproduce the fission cross section and average pre-scission neutron multiplicity for the compound nuclei 206Po and 168Yb by using constant values of the dissipation coefficient of K equal to γK=0.18(MeV zs)-1/2 and γK=0.20(MeV zs)-1/2 for the compound nuclei 206Po and 168Yb, respectively.
The yield ratios of neutron/proton and 3H/3He and the directed flow per nucleon for these projectile-like fragments at large impact parameters are studied for 50Ca+40Ca and 50Cr+40Ca for comparison at 50 MeV/u using the isospin-dependent quantum molecular dynamics (IQMD) model. It is found that the yield ratios and the directed flows per nucleon are different for reactions induced by the neutron-rich nucleus 50Ca and the stable isobaric nucleus 50Cr, and depend on the hardness of the EOS. The ratios of neutron/proton and 3H/3He and the difference of directed flow per nucleon of neutron-proton are suggested to be possible observables to investigate the isospin effects.
The correlation between quarter-point angle of elastic scattering and nuclear matter radius is studied systematically. Various phenomenological formulae with parameters for nuclear radius are adopted and compared by fitting the experimental data of quarter point angle extracted from nuclear elastic scattering reaction systems. A parameterized formula related to binding energy is recommended, which gives a good reproduction of nuclear matter radii of halo nuclei. It indicates that the quarter-point angle of elastic scattering is quite sensitive to the nuclear matter radius and can be used to extract the nuclear matter radius.
Resonance research is a hot topic in nuclear physics, and many methods have been developed for resonances. In this paper, we explore resonances by solving the Schrödinger equation in complex momentum representation, in which the bound states and resonant states are separated completely from the continuum and exposed clearly in the complex momentum plane. We have checked the convergence of the calculations on the grid numbers of the Gauss-Hermite quadrature and the Gauss-Legendre quadrature, and the dependence on the contour of momentum integration. Satisfactory results are obtained. 17O is chosen as an example, and we have calculated the bound and resonant states to be in excellent agreement with those calculated in the coordinate representation.
A new empirical formula has been developed that describes the (γ, n) nuclear reaction cross sections for isotopes with Z≥60. The results were supported by calculations using TALYS—1.6 and EMPIRE—3.2.2 nuclear modular codes. The energy region for incident photon energy has been selected near the giant dipole resonance (GDR) peak energy. The evaluated empirical data were compared with available data in the experimental data library EXFOR. The data produced using TALYS—1.6 and EMPIRE—3.2.2 are in good agreement with experimental data. We have tested and presented the reproducibility of the present new empirical formula. We observe the reproducibility of the new empirical formula near the GDR peak energy is in good agreement with the experimental data and shows a remarkable dependency on key nuclei properties: the neutron, proton and atomic number of the nuclei. The behavior of nuclei near the GDR peak energy and the dependency of the GDR peak on the isotopic nature are predicted. An effort has been made to explain the deformation of the GDR peak in (γ, n) nuclear reaction cross sections for some isotopes, which could not be reproduced with TALYS—1.6 and EMPIRE—3.2.2. The evaluated data have been presented for the isotopes 180W, 183W, 202Pb, 203Pb, 204Pb, 205Pb, 231Pa, 232U, 237U and 239Pu, for which there are no previous measurements.
Linear polarization has been observed in both the prompt phase and afterglow of some bright gamma-ray bursts (GRBs). Polarization in the prompt phase spans a wide range, and may be as high as ≳50%. In the afterglow phase, however, it is usually below 10%. According to the standard fireball model, GRBs are produced by synchrotron radiation and Compton scattering process in a highly relativistic jet ejected from the central engine. It is widely accepted that prompt emissions occur in the internal shock when shells with different velocities collide with each other, and the magnetic field advected by the jet from the central engine can be ordered on a large scale. On the other hand, afterglows are often assumed to occur in the external shock when the jet collides with interstellar medium, and the magnetic field produced by the shock through, for example, Weibel instability, is possibly random. In this paper, we calculate the polarization properties of the synchrotron self-Compton process from a highly relativistic jet, in which the magnetic field is randomly distributed in the shock plane. We also consider the generalized situation where a uniform magnetic component perpendicular to the shock plane is superposed on the random magnetic component. We show that it is difficult for the polarization to be larger than 10% if the seed electrons are isotropic in the jet frame. This may account for the observed upper limit of polarization in the afterglow phase of GRBs. In addition, if the random and uniform magnetic components decay with time at different speeds, then the polarization angle may change 90° during the temporal evolution.
The relativistic mean field (RMF) FSUGold model extended to include hyperons is employed to study the properties of neutron stars with strong magnetic fields. The chaotic magnetic field approximation is utilized. The effect of anomalous magnetic moments (AMMs) is also investigated. It is shown that the equation of state (EOS) of neutron star matter is stiffened by the presence of the magnetic field, which increases the maximum mass of a neutron star by around 6%. The AMMs only have a small influence on the EOS of neutron star matter, and increase the maximum mass of a neutron star by 0.02Msun. Neutral particles are spin polarized due to the presence of the AMMs.
The tunneling radiation of particles from black holes in Lovelock-Born-Infeld (LBI) gravity is studied by using the Parikh-Wilczek (PW) method, and the emission rate of a particle is calculated. It is shown that the emission spectrum deviates from the purely thermal spectrum but is consistent with an underlying unitary theory. Compared to the conventional tunneling rate related to the increment of black hole entropy, the entropy of the black hole in LBI gravity is obtained. The entropy does not obey the area law unless all the Lovelock coefficients equal zero, but it satisfies the first law of thermodynamics and is in accordance with earlier results. It is distinctly shown that the PW tunneling framework is related to the thermodynamic laws of the black hole.
We study the constraints on dark matter (DM) annihilation/decay from the Fermi-LAT Isotropic Gamma-Ray Background (IGRB) observation. We consider the contributions from both extragalactic and galactic DM components. For DM annihilation, the evolution of extragalactic DM halos is taken into account. We find that the IGRB annihilation constraints under some DM subhalo models can be comparable to those derived from the observations of dwarf spheroidal galaxies and CMB. We also use the IGRB results to constrain the parameter regions accounting for the latest AMS-02 electron-positron anomaly. We find that the majority of DM annihilation/decay channels are strongly disfavored by the latest Fermi-LAT IGRB observation; only DM decays to μ+μ- and 4μ channels may be valid.
The scintillation properties of a CdMoO4 crystal have been investigated experimentally. The fluorescence yields and decay times measured from 22 K to 300 K demonstrate that CdMoO4 crystal is a good candidate for an absorber for a bolometer readout, for both heat and scintillation signals. The results from Monte Carlo studies, taking the backgrounds from 2ν2β of 42100Mo (48116Cd) and internal trace nuclides 214Bi and 208Tl into account, show that the expected sensitivity of a CdMoO4 bolometer for neutrinoless double beta decay experiments with an exposure of 100 kg·years is one order of magnitude higher than those of the current sets of the T1/20νββ of 42100Mo and 48116Cd.
Topmetal-Ⅱ- is a low noise CMOS pixel direct charge sensor with a pitch of 83 μm. CdZnTe is an excellent semiconductor material for radiation detection. The combination of CdZnTe and the sensor makes it possible to build a detector with high spatial resolution. In our experiments, an epoxy adhesive is used as the conductive medium to connect the sensor and cadmium zinc telluride (CdZnTe). The diffusion coefficient and charge efficiency of electrons are measured at a low bias voltage of -2 V, and the image of a single alpha particle is clear with a reasonable spatial resolution. A detector with such a structure has the potential to be applied in X-ray imaging systems with further improvements of the sensor.
The spoke cavities mounted in the China Accelerator Driven sub-critical System (C-ADS) have high quality factor (Q) and very small bandwidth, making them very sensitive to mechanical perturbations, whether external or self-induced. The transfer function is used to characterize the response of the cavity eigenfrequency to the perturbations. This paper describes a method to measure the transfer function of a spoke cavity. The measured Lorentz transfer function shows there are 206 Hz and 311 Hz mechanical eigenmodes excited by Lorentz force in the cavity of C-ADS, and the measured piezo fast tuner transfer function shows there are 12 mechanical eigenmodes from 0 to 500 Hz. According to these results, some effective measures have been taken to weaken the influence of helium pressure fluctuation, avoid mechanical resonances and improve the reliability of the RF system.
Higher-order mode (HOM) based intra-cavity beam diagnostics has been proved effective and convenient in superconducting radio-frequency (SRF) accelerators. Our recent research shows that the beam harmonics in the bunch train excited HOM spectrum, which have much higher signal-to-noise ratio than the intrinsic HOM peaks, may also be useful for beam diagnostics. In this paper, we will present our study on bunch train excited HOMs, including a theoretical model and recent experiments carried out based on the DC-SRF photoinjector and SRF linac at Peking University.
This work investigates the positional single photon incidence response (P-SPIR) to provide an accurate point spread function (PSF)-contained system matrix and its incorporation within the image reconstruction framework. Based on the Geant4 Application for Emission Tomography (GATE) simulation, P-SPIR theory takes both incidence angle and incidence position of the gamma photon into account during crystal subdivision, instead of only taking the former into account, as in single photon incidence response (SPIR). The response distribution obtained in this fashion was validated using Monte Carlo simulations. In addition, two-block penetration and normalization of the response probability are introduced to improve the accuracy of the PSF. With the incorporation of the PSF, the homogenization model is then analyzed to calculate the spread distribution of each line-of-response (LOR). A primate PET scanner, Eplus-260, developed by the Institute of High Energy Physics, Chinese Academy of Sciences (IHEP), was employed to evaluate the proposed method. The reconstructed images indicate that the P-SPIR method can effectively mitigate the depth-of-interaction (DOI) effect, especially at the peripheral area of field-of-view (FOV). Furthermore, the method can be applied to PET scanners with any other structures and list-mode data format with high flexibility and efficiency.
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