49221025
Mass dependence of pion production in heavy ion collisions near, but below threshold
Abstract We have measured the inclusive cross section for production of negative pions near mid-rapidity in 20 Ne + NaF , 139 La + 139 La and 197 Au + 197 Au collisions at E = 183 and 236 MeV/u. Au + Au is the heaviest system from which subthreshold pion production has been measured to date. The dependence of the pion cross section on pion energy, beam energy and associated charged particle multiplicity is consistent with previous results both above and below threshold. The dependence of the cross section on the mass of the colliding system varies only slightly as the beam energy is reduced below threshold, in contrast to some previous measurements. Comparison with theory suggests that at these energies the pion production process is still dominated by nucleon-nucleon collisions.
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.
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.
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.
117522082
First results on dilepton production at the Bevalac
We report on preliminary results of direct electron pair measurements in p+Be at 4.9 GeV and 2.1 GeV and Ca+Ca at 1.95 GeVA collisions at the Bevalac. The results are compared to existing data in p+Be at 12.1 GeV and ..pi../sup -/p at 15.9 and 16.9 GeV.
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.
31200728
Development of SNSPD System With Gifford-McMahon Cryocooler
A superconducting nanowire single photon detector (SNSPD) system for telecommunication wavelength using a GM cryocooler was developed and its performance was verified. The cryocooler based SNSPD system can operate continuously with a 100 V AC power supply without any cryogen. The packaged SNSPD device was cooled to 2.96 K within a thermal fluctuation range of 10 mK. An SNSPD with an area of 20 times 20 mum2 showed good system detection efficiency (DE) at 100 Hz dark count rate of 2.6% and 4.5% at wavelengths of 1550 and 1310 nm, respectively. An SNSPD with an area of 10 times 10 mum2 and kinetic inductance lower than that of the large area device showed good system DE of 2.6% at a wavelength of 1550 nm. The SNSPD system could be operated for over 10 h with constant system DE and dark count rate.
124633288
Beam dynamics simulation of HEBT for the SSC-linac injector
The SSC-linac (a new injector for the Separated Sector Cyclotron) is being designed in the HIRFL (Heavy Ion Research Facility in Lanzhou) system to accelerate 238U34+ from 3.72 keV/u to 1.008 MeV/u. As a part of the SSC-linac injector, the HEBT (high energy beam transport) has been designed by using the TRACE-3D code and simulated by the 3D PIC (particle-in-cell) Track code. The total length of the HEBT is about 12 meters and a beam line of about 6 meters are shared with the exiting beam line of the HIRFL system. The simulation results show that the particles can be delivered efficiently in the HEBT and the particles at the exit of the HEBT well match the acceptance of the SSC for further acceleration. The dispersion is eliminated absolutely in the HEBT. The space-charge effect calculated by the Track code is inconspicuous. According to the simulation, more than 60 percent of the particles from the ion source can be transported into the acceptance of the SSC.
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.
118845254
Analysis of the decay constants of the heavy pseudoscalar mesons with QCD sum rules
A bstractIn this article, we recalculate the contributions of all vacuum condensates up to dimension-6, in particular the one-loop corrections to the quark condensates $ {\alpha_s}\left\langle {\overline{q}q} \right\rangle $ and partial one-loop corrections to the four-quark condensates $ \alpha_s^2{{\left\langle {\overline{q}q} \right\rangle}^2} $, in the operator product expansion. Then we study the masses and decay constants of the heavy pseudoscalar mesons D, Ds, B and Bs using the QCD sum rules with two choices: I we choose the $ \overline{MS} $ masses by setting m = m(μ) and take perturbative corrections up to the order $ \mathcal{O}\left( {{\alpha_s}} \right) $; II we choose the pole masses m, take perturbative corrections up to the order $ \mathcal{O}\left( {\alpha_s^2} \right) $ and set the energy-scale to be the heavy quark pole mass μ = mQ. In the case of I, the predictions fD = (208 ± 11) MeV and fB = (189 ± 15) MeV are consistent with the experimental data within uncertainties, while the prediction $ {f_{{{D_s}}}}=\left( {241\pm 12} \right) $ MeV is below the lower bound of the experimental data $ {f_{{{D_s}}}}=\left( {260.0\pm 5.4} \right) $ MeV. In the case of II, the predictions fD = (211 ± 14) MeV, fB = (190 ± 17) MeV, $ {f_{{{D_s}}}}=\left( {258\pm 13} \right) $ MeV and $ {{{{f_{{{D_s}}}}}} \left/ {{{f_D}}} \right.}=1.22\pm 0.08 $ are all in excellent agreements with the experimental data within uncertainties.
18351437
Search for the Optical Counterparts of Southern Anomalous X-Ray Pulsars and Radio-Quiet Neutron Stars in Young Supernova Remnants
We report on our search for the optical counterparts of the Southern Hemisphere anomalous X-ray pulsar 1E1048.1-5937 and the radio-quiet neutron stars in supernova remnants Puppis A, RCW 103, and PKS 1209-52. The observations were carried out with the new MIT/CfA MagIC camera on the Magellan-I 6.5 m telescope in Chile. We present deep multiband optical images of the X-ray error circles for each of these targets and discuss the resulting candidates and limits.