2015 Vol. 39, No. 6
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In this work, we tentatively assign the charmed mesons DJ(2580), DJ*(2650), DJ(2740), DJ*(2760), DJ(3000) and DJ*(3000) observed by the LHCb collaboration according to their spin, parity and masses, then systematically study their strong decays to ground state charmed mesons plus pseudoscalar mesons with the 3P0 decay model. Based on these studies, we assign the DJ*(2760) as the 1D(5/2)3- state, the DJ*(3000) as the 1F(5/2)2+ or 1F(7/2)4+ state, the DJ(3000) as the 1F(7/2)3+ or 2P(1/2)1+ state in the D meson family. As a byproduct, we also study the strong decays of the states 2P(1/2)0+, 2P(3/2)2+, 3S(1/2)1-, 3S(1/2)0- etc, which will be valuable in searching for the partners of these D mesons.
Apart from the charmful decay channels of Y(4260), the charmless decay channels of Y(4260) also provide us a good platform to study the nature and the decay mechanism of Y(4260). In this paper, we propose to probe the structure of Y(4260) through the charmless decays Y(4260)→VP via intermediate D1 +c.c. meson loops, where V and P stand for light vector and pseudoscalar mesons, respectively. Under the molecule ansatz of Y(4260), the predicted total branching ratio BRVP for all Y(4260)→VP processes are about (0.34-0.23+0.23)% to (0.75-0.52+0.72)% with the cutoff parameter α=2-3. Numerical results show that the intermediate m D1 +c.c. meson loops may be a possible transition mechanism in the Y(4260)→VP decays. These predicted branching ratios are the same order to that of Y(4260)→Zc+(3900)π-, which may be an evidence of D1D molecule and can be examined by the forthcoming BESⅢ data in the near future.
We investigate the behavior of the chiral condensate in lattice QCD at finite temperature and finite chemical potential. The study was done using two flavors of light quarks and with a series of β and ma at the lattice size 24×122×6. The calculation was done in the Taylor expansion formalism. We are able to calculate the first and second order derivatives of < ψ> in both isoscalar and isovector channels. With the first derivatives being small, we find that the second derivatives are sizable close to the phase transition and that the magnitude of ψ decreases under the influence of finite chemical potential in both channels.
The rotational invariants constructed by the products of three spherical harmonic polynomials are expressed generally as homogeneous polynomials with respect to the three coordinate vectors in the compact form, where the coefficients are calculated explicitly in this paper.
In this paper, the one-loop self energy of λφ3 theory is calculated by using Krein regularization in four and six dimensions and the result, which is finite, is compared with the conventional result of λφ3 theory in Hilbert space. The self energy is calculated in the one-loop approximation and the result is automatically regularized as a result of "Krein Regularization".
In this paper, the Schrödinger equation for a 6-body system is studied. We solve this equation for the lithium nucleus by using a supersymmetry method with several specific potentials. These potentials are the Yukawa potential, the generalized Yukawa potential and the Hellmann potential. The results of our model for all calculations show that the ground state binding energy of the lithium nucleus with these potentials is very close to that obtained experimentally.
The low-lying spectra of 7Li and 9Li are investigated within an ab initio Monte Carlo Shell Model (MCSM) employing a realistic potential obtained via the Unitary Correlation Operator Method (UCOM). The MCSM calculations in a 4-major-shells model space for the binding energy and mass quadrupole moment of 7,9Li show good convergence when the MCSM dimension reaches 20. The excitation energy of the Jπ=1/2- state for 7Li and the magnetic moments for 7,9Li ground states in the MCSM with a treatment of spurious center-of-mass motion are close to the experimental data. Correct level ordering of Jπ=3/2- and 1/2- states for 7,9Li can be reproduced due to the inclusion of three-body correlations in the MCSM+UCOM. However, the excitation energy of Jπ=1/2- state for 9Li is not reproduced in the MCSM mainly due to the lack of larger model space.
We study the structural properties of some light mass nuclei using two different formalisms (i) a recently developed simple effective interaction in the frame work of microscopic non-relativistic Hartree-Fock method and (ii) the well-known relativistic mean field approach with NL3 parameter set. The bulk properties like binding energy, root mean square radii and quadrupole deformation parameter are estimated and compared with the available experimental data. The predicted results of both the formalisms are well comparable with the experimental observations. The analysis of density profiles of these light mass nuclei suggest that 22O, 23F, 34Si and 46Ar have bubble like structure.
We study properties of hadrons in the O(4) linear σ model, where we take into account fluctuations of mesons around their mean field values using the Gaussian functional (GF) method. In the GF method we calculate dressed σ and π masses, where we include the effect of fluctuations of mesons to find a better ground state wave function than the mean field approximation. Then we solve the Bethe-Salpeter equations and calculate physical σ and π masses. We recover the Nambu-Goldstone theorem for the physical pion mass to be zero in the chiral limit. The σ meson is a strongly correlated meson-meson state, and seems to have a two meson composite structure. We calculate σ and π masses as functions of temperature for both the chiral limit and explicit chiral symmetry breaking case. We get similar behaviors for the physical σ and π masses as the case of the mean field approximation, but the coupling constants are much larger than the values of the case of the mean field approximation.
THGEMs based on a ceramic substrate have been successfully developed for neutron and single photon detection. The influences on thermal neutron scattering and internal radioactivity of both ceramic and FR-4 substrates were studied and compared. The ceramic THGEMs are homemade, of 200 μm hole diameter, 600 μm pitch, 200 μm thickness, 80 μm rim, and 50 mm×50 mm sensitive area. FR-4 THGEMs with the same geometry were used as a reference. The gas gain, energy resolution and gain stability were measured in different gas mixtures using 5.9 keV X-rays. The maximum gain of a single layer ceramic THGEM reaches 6×104 and 1.5×104 at Ne+CH4=95:5 and Ar+i-C4H10=97:3, respectively. The energy resolution is better than 24%. Good gain stability was obtained during a more than 100 hour continuous test in Ar+CO2=80:20. By using a 239Pu source, the alpha deposited energy spectrum and gain curve of the ceramic THGEM were measured.
Types 316 and 304 stainless steel are two candidates for the storage vessels and piping systems of LAB-based liquid scintillator (LS) in the JUNO experiment. LS aging experiments are carried out at temperatures of 40℃ and 25℃. After 192 days aging at 40℃, the attenuation length of LS was reduced by 6% in a glass container, 12% in a type 304 stainless steel tank, and 10% in a type 316 stainless steel tank. At 25℃ in 304 and 316 stainless steel tanks, the attenuation length was reduced by 6% after 307 days. The light yield and the absorption spectrum were practically the same as that of the unaged sample. The concentration of element Fe in the LAB-based LS did not show a clear change. Type 316 and 304 stainless steel can be used as vessels and transportation pipeline material for LAB-based LS.
The water Cherenkov detector array (WCDA) for the Large High Altitude Air Shower Observatory (LHAASO) will employ more than 3600 hemisphere 8-inch photomultiplier tubes (PMTs). Good time performance of the PMT, especially the transit time spread (TTS), is required for the WCDA. In order to meet the demand of the WCDA experiment, an accurate measurement of PMT TTS based on the photoelectron spectrum is studied. The method is appropriate for multi-photoelectrons and makes it possible to measure the TTS of different photoelectrons simultaneously. The TTS of different photoelectrons for a Hamamatsu R5912 PMT is tested with a specially designed divider circuit. The relationship between TTS and number of photoelectrons is also presented in this paper.
Nonionizing energy loss (NIEL) has been applied to a number of studies concerning displacement damage effects in materials and devices. However, most studies consider only the contribution of displacement damage effects, neglecting the contribution from phonons. In this paper, a NIEL model, which considers the contribution of phonons, has been established using the Monte Carlo code SRIM. The maximum endurable fluence for silicon detectors has been estimated using the equivalent irradiation fluence compared with experimental data for the incident particles. NIEL is proportional to the equivalent irradiation fluence that the detector has received.
In the fabrication of a 48 mm×48 mm silicon micro-strip nuclear radiation detector with 96 strips on each side, a perfect P-N junction cannot be formed consistently by the one-step implantation process, and thus over 50% of strips produced do not meet application requirements. However, the method of stratified implantation not only avoids the P region between the surface of wafers and the P+ region, but also overcomes the shadow effect. With the help of the stratified implantation process, a perfect functional P-N junction can be formed, and over 95% of strips meet application requirements.
The target parameters of modern ultra-low emittance storage ring light sources are entering into a regime where intra-beam scattering (IBS) becomes important and, in the case of the Beijing Advanced Photon Source (BAPS), which is being designed at the Institute of High Energy Physics (IHEP), even a limitation for achieving the desired emittances in both transverse planes at the diffraction limit for X-ray wavelengths (≈10 pm). Due to the low emittance, the IBS effect will be very strong. Accurate calculations are needed to check if the design goal (εh+εv=20 pm) can be reached. In this paper, we present the results of numerical simulation studies of the IBS effect on a BAPS temporary design lattice.
The TAC (Turkish Accelerator Center) project aims to build an accelerator center in Turkey. The first stage of the project is to construct an Infra-Red Free Electron Laser (IR-FEL) facility. The second stage is to build a synchrotron radiation facility named TURKAY, which is a third generation synchrotron radiation light source that aims to achieve a high brilliance photon beam from a low emittance electron beam at 3 GeV. The electron beam parameters are highly dependent on the magnetic lattice of the storage ring. In this paper a low emittance storage ring for TURKAY is proposed and the beam dynamic properties of the magnetic lattice are investigated.
At Shanghai Jiao Tong University (SJTU) we have established a research laboratory for advanced acceleration research based on high-power lasers and plasma technologies. In a primary experiment based on the laser wakefield acceleration (LWFA) scheme, multi-hundred MeV electron beams of reasonable quality are generated using 20-40 TW, 30 femtosecond laser pulses interacting independently with helium, neon, nitrogen and argon gas jet targets. The laser-plasma interaction conditions are optimized for stabilizing the electron beam generation from each type of gas. The electron beam pointing angle stability and divergence angle as well as the energy spectra from each gas jet are measured and compared.
A new generation of storage ring-based light sources, called diffraction-limited storage rings (DLSR), with emittance approaching the diffraction limit for multi-keV photons by using multi-bend achromat lattice, has attracted worldwide and extensive studies of several laboratories, and been seriously considered as a means of upgrading existing facilities in the imminent future. Among various DLSR proposals, the PEPX design demonstrated that it is feasible to achieve sufficient ring acceptance for off-axis injection in a DLSR, by designing the lattice based on the ‘third-order achromat’ concept and with a special high-beta injection section. For the High Energy Photon Source (HEPS) planned to be built in Beijing, a PEPX-type lattice has been designed and continuously improved. In this paper, we report the evolution of the PEPX-type design for HEPS, and discuss the main issues relevant to the linear optics design and nonlinear optimization.
Energy resolution is affected by the intrinsic energy resolution of the detector, ballistic deficit, pile-up pulses and noise. Pile-up pulses become the dominant factor that degrades energy resolution after the system is established, so pile-up rejection is often applied to obtain good energy resolution by discarding pulses that are expected to be contaminated by pile-up. However, pile-up rejection can reduce count rates and thus lower the measurement precision. In order to improve count rates and maintain energy resolution, a new method of pile-up pulse identification based on trapezoidal pulse shaping is presented. Combined with pulse width discrimination, this method is implemented by recording pulses that are not seriously piled up. Some experimental tests with a Cu-Pb alloy sample are carried out to verify the performance of this method in X-ray spectrometry. The results show that the method can significantly improve count rates without degrading energy resolution.
A geometric matrix model of nuclear waste drums is proposed for transmission image reconstruction from tomographic gamma scans (TGS). The model assumes that rays are conical, with intensity uniformly distributed within the cone. The attenuation coefficients are centered on the voxel (cube) of the geometric center. The proposed model is verified using the EM algorithm and compared to previously reported models. The calculated results show that the model can obtain good reconstruction results even when the sample models are highly heterogeneous.
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