2010 Vol. 34, No. 04
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The decay channel ψ′→π+π－J/ψ(J/ψ→γpp) is studied using a sample of 1.06×108 ψ′ events collected by the BESIII experiment at BEPCII. A strong enhancement at threshold is observed in the pp invariant mass spectrum. The enhancement can be fitted with an S-wave Breit-Wigner resonance function with a resulting peak mass of M=1861+6－13 (stat)+7－26 (syst) MeV/c2 and a narrow width that is Γ<38 MeV/c2 at the 90% confidence level. These results are consistent with published BESII results. These mass and width values do not match with well established mesons.
The Minimal Higgsless Model predicts the existence of new vector gauge boson W±1. By the process PP→W±1qq→W±Z0qq, Z0→l+l－, W±→qq (l=e, μ; q is hadronized to be jets), we study the sensitivity of searching for this possible vector gauge boson in the level of generator events of signal and backgrounds, then give integrated luminosity required to discover 5σ signal as a function of W±1 mass. The generator for the signal PP→W±1qq→W±Z0qq at tree level is developed with the Minimal Higgsless Model and then interfaced with PYTHIA for the parton showers and hadronization. The backgrounds are produced with
MadGraph and PYTHIA.
The lepton-number-violating decays of singly-charged Higgs bosons H± are investigated in the minimal type-(Ⅰ+Ⅱ) seesaw model with one SU(2)L Higgs triplet Δ and one heavy Majorana neutrino N1 at the TeV scale. We find that the branching ratios B (H+→l+αν) (for α=e, μ, τ) depend not only on the mass and mixing parameters of three light neutrinos νi (for i=1,2,3) but also on those of N1. Assuming that the mass of N1 lies in the range of 200 GeV to 1 TeV, we figure out the generous interference bands for the contributions of νi and N1 to B(H+→l+αν). We illustrate some salient features of such interference effects by considering three typical mass patterns of νi, and show that the relevant Majorana CP-violating phases can affect the magnitudes of B (H+→l+αν) in this parameter region.
In the paper we discuss the role of the axial U(1)A symmetry in the chiral phase transition using the U(Nf)R×U(Nf)L linear sigma model with two massless quark flavors. It is expected that above a certain temperature the axial U(1)A symmetry will be restored. A string-like static solution, the η string can be formed and detected in the ultrarelativistic heavy-ion collision process.
We investigate the properties of spin-orbit interaction in the ground state and thermal entanglement of a two-qutrit Heisenberg XYZ system in the presence of an inhomogeneous magnetic field. Using negativity as entanglement measure, we give the dependence of entanglement on each parameter in detail. The result shows that one can get appropriate entanglement by adjusting the magnetic field, Dzyaloshinskii-Moriya interaction and anisotropy parameter simultaneously.
The mirror nuclei 12N and 12B are separated by the Radioactive Ion Beam Line in Lanzhou (RIBLL) at HIRFL from the breakup of 78.6 MeV/u 14N on a Be target. The total reaction cross-sections of 12N at 34.9 MeV/u and 12B at 54.4 MeV/u on a Si target have been measured by using the transmission method. Assuming 12N consists of a 11C core plus one halo proton, the excitation function of 12N and 12B on a Si target and a C target were calculated with the Glauber model. It can fit the experimental data very well. The characteristic halo structure for 12N was found with a large diffusion of the protons density distribution.
High-spin states in nucleus 139Pm have been studied using the reaction 116Cd(27Al, 4n) 139Pm. Two dipole cascades have been found. Spin and parity assignments were based on the Directional Correlation of Oriented Nuclei (DCO) ratios and systematic behavior in neighboring odd-proton nuclei. The level structures of 139Pm are compared with those of the N=78 isotone 141Eu in which two dipole bands have been confirmed as magnetic rotational bands. The close similarity between them suggests that the dipole bands in 139Pm may be magnetic rotational bands.
The binding energies εη and widths Γη of η-mesic nuclei are calculated. We parameterize the η self-energy in the nuclear medium as a function of energy and density. We find that the single-particle energies are sensitive to the scattering length, and increase monotonically with the nucleus. The key point for the study of η-nucleus bound states is the η-nuclear optical potential. We study the s-wave interactions of η mesons in a nuclear medium and obtain the optical potential Uη≈－72 MeV. Comparing our results with the previous results, we find that the ηN scattering length aηN is indeed important to the calculations. With increasing nuclear density the effective mass of the η meson decreases.
We study the vector meson electro-production off the proton in a QCD inspired model. A calculation of the differential cross section is performed for the J/ψ, φ meson off the proton. The theoretical results are consistent with the experimental data, and remind us to consider the contribution from the tensor glueball and Odderon to the differential cross section. Since gluons interact among themselves via self-interaction, the gluons can form a glueball with quantum numbers IG, JPC=0+, 2++, with a decay width Γt=100 MeV and mass of mG=2.23 GeV. The three gluons can form a three gluon color bound state with charge conjugation quantum number C=－1. This study is quite important to verify the validity of QCD and to search for new particles (tensor glueball and Odderon) as well as quest for new physics.
We examine the space-time structure of particle-emitting source and two-pion interferometry in a smoothed hydrodynamic model with fluctuating initial conditions. An equation of state with a crossover transition between quark-gluon plasma and hadronic gas is adopted in the description of the system evolution. We find that the fluctuating initial conditions lead to inhomogeneous particle-emitting sources. The interferometry results of Rs and Ro indicate that both the source size and the duration of pion emission decrease when the freeze-out temperature increases. The values of Ro/Rs obtained by our simulated two-pion interferometry are consistent with the previous results of smoothed particle hydrodynamics, and smaller than those calculated in usual hydrodynamic models.
A novel Micro-pattern gaseous detector (MPGD), thick GEM with electrodes made of a resistive material (RETGEM) is presented. In this paper we mainly investigate the energy resolution of a RETGEM in Ar+CO2 with different gas mixtures. The results indicate that an energy resolution 30% in single and double mode can be obtained. The existence of an optimum energy resolution is discussed.
Micromegas (MICRO MEsh GAseous Structure) is a position-sensitive gaseous
detector. It is widely used in particle physics. We present the results of full 3D Monte Carlo simulations of Micromegas performance, taking into account all the processes from the primary ionization, the elctron collection efficiency, and the gain to the signal formation. The simulation results are in good agreement with experimental data.
The fast luminosity monitor counting the γ photons above a given energy threshold emitted from radiative Bhabha scattering has been operated in the BEPCⅡ to measure the relative luminosity bunch by bunch for the first time and used successfully in beam tuning of BEPCⅡ. In the relative mode the monitor is able to deliver the relative luminosities with an accuracy of 0.8%. By steering the electron beam while observing the counting rate changes of the monitor the horizontal and vertical sizes of the bunch spots can be estimated as: sxe+ =sxe－=0.356 mm, sye+ =sye－=0.011 mm.
A NbTi 7 T superconducting magnet with a 338 mm bore system was rebuilt and the first experiment was carried out in Jan. 2009. The balancing-bridge method used for the quench detection system is analyzed and an improvement of the principle of balancing-bridge conformation is given. The inductances of the coils are calculated to estimate the proportion of the bridge arms. The appropriate parameters are selected for the balancing-bridge.
A method based on circuit model is used to tune the first home-made 9-cell TESLA type superconducting niobium cavity at Peking University. After tuning, a flat field profile with a final π-mode frequency within 3 kHz of target frequency is achieved. The field flatness is measured by a bead-pull method, and the relative electric field is calculated from the frequency shift perturbed by the bead stepping along the axis of the cavity.
Experiment is carried out on the accelerator Sinus-700 to investigate the Relativistic Backward Wave Oscillator (RBWO) with a periodic guiding magnetic field. When the strength of the guiding magnetic field, whose period is 4.6 cm, is 0.54 T, a microwave output power of 0.95 GW at 9.1 GHz microwave frequency is achieved. It is shown that the RBWO with a periodic guiding magnetic field is feasible.
SFRFQ (Separated Function Radio Frequency Quadrupoles) accelerator is a new post accelerator of RFQ (Radio Frequency Quadrupoles) type, which has been developed since the beginning of the 1990s at Peking University. In order to demonstrate the possibility of the SFRFQ, a prototype cavity has been designed. A special dynamics design method has been proposed to avoid the sparking problem and decrease the energy spread at the exit of SFRFQ. It consists of two aspects: the asymmetry structure design for transverse focusing and the inner buncher design for longitudinal bunching. This allows the improvement of the beam properties without increasing the cavity length. The simulation results show that the energy spread can be substantially reduced by using the inner buncher in the SFRFQ structure.
The current design of the CSNS/RCS beam collimation system consists of a two-stage betatron collimation and a single momentum collimator. This paper summarizes various aspects of collimator design, including collimation principle and layout, material choice and collimator mechanical structure, etc. At last, radiation and thermal analysis are carried out to illustrate the feasibility of the current beam collimation scheme.
We present a design study of a free electron laser (FEL) oscillator for high power THz source experiments on the basis of the Shanghai femtosecond accelerator device. A circular groove guide is used as a new interaction structure. Plane metal meshes are used as upstream and downstream mirrors of the resonator. The general design parameters are presented. We analyzed the spontaneous emission and stimulated emission in the oscillator using these parameters.
A conception design of the Advanced Proton Therapy Facility (APTF) has been carried out. The system intentionally employs a slow-cycling synchrotron with a maximum energy of 250 MeV, two rotating gantries and two fixed beam nozzles for the treatment. In this paper, we try to compare the strength and weaknesses between the two treatment methods: the beam spreading and the pencil beam scanning. The application of the pencil beam scanning method and the double-scattering method together with the related nozzle design at APTF is also given. The simulation results of employing the double-scattering method have been given during the preliminary design.
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