121208627
Subthreshold production of strange hadrons in relativistic heavy ion collisions
We report on preliminary measurements of subthreshold antikaons produced in relativistic heavy ion collisions. Comparison with hadrochemical and transport models show that while the total level of antikaon production may be accounted for, important difficulties remain in describing their momentum and angular distributions.
44598663
Measurement of dielectron production in niobium-niobium collisions at 1.05 GeV/nucleon.
A dielectron signal for pair masses greater than [ital M][sub [pi]] is observed in Nb+Nb collisions at 1.05 GeV/nucleon beam kinetic energy. The invariant mass spectrum and the associated multiplicity distribution are presented. Comparisons are made with previous cross section measurements in [ital p]+Be and Ca+Ca.
120239957
Threshold behavior of direct electron production in proton‐beryllium collisions
We report measurements of direct electron pair production in p‐Be interactions at 1.0, 2.1 and 4.9 GeV kinetic beam energies. The invariant mass and pt spectra along with the total cross sections are presented. A rapid decrease in the total cross section is observed at the lowest energy.
119395992
Dilepton production from p-p to CaCa at the Bevalac
Abstract The DLS collaboration has recently completed a high statistics study of dilepton production at the Bevalac. In particular, we have measured dielectrons (e + e − ) from p - p and p - d collisions to understand the basic dilepton production mechanisms in the energy range from 1.05 – 4.9 GeV. These data can be used to determine the basic processes which contribute to nucleon-nucleon dilepton production such as hadronic bremsstrahlung, vector meson processes, and hadronic Dalitz decay. The data show that a simple elastic bremsstrahlung calculation is insufficient to explain the data. Theoretical models are compared with the data. A new high statistics study of Ca  Ca at 1.05 A·GeV has been made to study the collectivity of A - A collisions.
6986761
Threshold behavior of electron pair production in p-Be collisions.
We report on the measurements of electron pair production in /ital p/-Becollisions at 1.0, 2.1, and 4.9 GeV beam kinetic energies. The invariant-massand transverse-momentum spectra are presented, along with the total crosssections. A rapid decrease in the integrated cross section is observed as thebeam energy is reduced. Comparison of the excitation function for dielectron(/ital e//sup +/e/sup /minus//) and dipion (..pi../sup +/..pi../sup /minus//)production suggests that the dominant production mechanism at beam kineticenergies 2.1 and 4.9 GeV may be ..pi../sup +/..pi../sup /minus// annihilation.
121663887
Mass and transverse momentum dependence of the dielectron yield in p-Be collisions at 4.9 GeV
We present the invariant mass and transverse momentum dependence of direct electron-positron pair production in {ital p}-Be collisions at a beam kinetic energy of 4.9 GeV. The acceptance of our apparatus is shown to have no significant effect for masses above 0.15 GeV. After a correction is made for the available phase space, the transverse momentum dependence of the data is found to be comparable to hadron-hadron observations. A phenomenological calculation involving {pi}{sup +}{pi}{sup {minus}} annihilation into {ital e}{sup +}e{sup {minus}} is shown to be in good agreement with our measurements.
118630803
Particle-in-cell mode beam dynamics simulation of the low energy beam transport for the SSC-linac injector
A new SSC-linac system (injector into separated sector cyclotron) is being designed in the HIRFL (heavy ion research facility of Lanzhou). As part of SSC-Linac, the LEBT (low energy beam transport) consists of seven solenoids, four quadrupoles, a bending magnet and an extra multi-harmonic buncher. The total length of this segment is about 7 meters. The beam dynamics in this LEBT has been studied using three-dimensional PIC (particle-in-cell) code BEAMPATH. The simulation results show that the continuous beam from the ion source is first well analyzed by a charge-to-mass selection system, and the beam of the selected charge-to-mass ratio is then efficiently pre-bunched by a multi-harmonic buncher and optimally matched into the RFQ (radio frequency quadrupole) for further acceleration. The principles and effects of the solenoid collimation channel are discussed, and it could limit the beam emittance by changing the aperture size.
123937746
INTRINSIC LOOP REGULARIZATION AND RENORMALIZATION IN QED
We show how to regularize and renormalize the QED at the one-loop order by means of the intrinsic loop regularization method proposed by the authors. All the results are the same as those derived by means of other regularization methods.
22580845
Dynamical mass generation of composite Dirac fermions and fractional quantum Hall effects near charge neutrality in graphene.
We develop a composite Dirac fermion theory for the fractional quantum Hall effects (QHE) near charge neutrality in graphene. We show that the interactions between the composite Dirac fermions lead to a dynamical mass generation through exciton condensation. The four-fold spin-valley degeneracy is fully lifted due to the mass generation and exchange effects such that the odd-denominator fractional QHE observed in the vicinity of charge neutrality can be understood in terms of the integer QHE of composite Dirac fermions. At a filling factor ν = 1/2, we show that the massive composite Dirac fermion liquid is unstable against chiral p-wave pairing for weak Coulomb interactions and the ground state is a paired non-Abelian quantum Hall state described by the Moore-Read Pfaffian in the long wavelength limit.
16893295
ASCA observations of two SNRs and NEI analysis
Based on the data from the ASCA observation of SNRs Kes79 and W49B, we present here the analysis of their X-ray spectra and morphologies. The Kes79 spectrum can be well fitted by a single NEI component, and the narrow-band images of that source show an inhomogeneous distribution of heavy elements. The heavy elements are richest in the positions S, SE and SW of Kes79, where there may exist interaction between shocks and molecular clouds implied by radio observations. For W49B we present here the non-equilibrium ionization (NEI) analysis based on its emission line diagnostics, and the spectral fit using two NEI components. The reverse shock in W49B may be still hot and we don't find evidence for a hotter blast wave in ASCA spectra.
119791200
Zero-Point Time of Quantum Fields
Based on the first principles and without resorting to any additional assumption, a new physical quantity describing the space-time position of particle-number center of quantum fields is introduced, which can be regarded as a generalized Noether charge related to the symmetry under a local gauge transformation. As an interesting result, one can show that quantum fields have a zero-point time, which is related to the zero-point energy of quantum fields via the Heisenberg uncertainty principle.