653 research outputs found
Dissociative recombination measurements of HCl+ using an ion storage ring
We have measured dissociative recombination of HCl+ with electrons using a
merged beams configuration at the heavy-ion storage ring TSR located at the Max
Planck Institute for Nuclear Physics in Heidelberg, Germany. We present the
measured absolute merged beams recombination rate coefficient for collision
energies from 0 to 4.5 eV. We have also developed a new method for deriving the
cross section from the measurements. Our approach does not suffer from
approximations made by previously used methods. The cross section was
transformed to a plasma rate coefficient for the electron temperature range
from T=10 to 5000 K. We show that the previously used HCl+ DR data
underestimate the plasma rate coefficient by a factor of 1.5 at T=10 K and
overestimate it by a factor of 3.0 at T=300 K. We also find that the new data
may partly explain existing discrepancies between observed abundances of
chlorine-bearing molecules and their astrochemical models.Comment: Accepted for publication in ApJ (July 7, 2013
Measurement of Length and Position with Frequency Combs
We show two different absolute distance measurement methods with micrometer accuracy based on frequency combs, and we discuss possible applications. Using a mode- locked laser and MEMS-based tracking optics, we measure the 3D position of a retroreflector within 10 ms and with a 24 μm volumetric accuracy. We also investigate modulator-based combs and show that they enable highly sensitive surface topography measurements with microsecond acquisition times and micrometer precision. Moreover, the potential for photonic integration of frequency comb sources is explored
Schr\"{o}dinger Fields on the Plane with Chern-Simons Interactions and Generalized Self-dual Solitons
A general non-relativistic field theory on the plane with couplings to an
arbitrary number of abelian Chern-Simons gauge fields is considered. Elementary
excitations of the system are shown to exhibit fractional and mutual
statistics. We identify the self-dual systems for which certain classical and
quantal aspects of the theory can be studied in a much simplified mathematical
setting. Then, specializing to the general self-dual system with two
Chern-Simons gauge fields (and non-vanishing mutual statistics parameter), we
present a systematic analysis for the static vortexlike classical solutions,
with or without uniform background magnetic field. Relativistic generalizations
are also discussed briefly.Comment: 49 pages including 4 figures, LATEX ( three LATEX figures and one
PICTEX figure), SNUTP 93-14, UMN-TH-113
Inclusive dielectron production in proton-proton collisions at 2.2 GeV beam energy
Data on inclusive dielectron production are presented for the reaction p+p at
2.2 GeV measured with the High Acceptance DiElectron Spectrometer (HADES). Our
results supplement data obtained earlier in this bombarding energy regime by
DLS and HADES. The comparison with the 2.09 GeV DLS data is discussed. The
reconstructed e+e- distributions are confronted with simulated pair cocktails,
revealing an excess yield at invariant masses around 0.5 GeV/c2. Inclusive
cross sections of neutral pion and eta production are obtained
Inclusive pion and eta production in p+Nb collisions at 3.5 GeV beam energy
Data on inclusive pion and eta production measured with the dielectron
spectrometer HADES in the reaction p+93Nb at a kinetic beam energy of 3.5 GeV
are presented. Our results, obtained with the photon conversion method,
supplement the rather sparse information on neutral meson production in
proton-nucleus reactions existing for this bombarding energy regime. The
reconstructed e+e-e+e- transverse-momentum and rapidity distributions are
confronted with transport model calculations, which account fairly well for
both pi0 and eta production.Comment: 12 pages, 9 figures, submitted to Physical Review
Searching a Dark Photon with HADES
We present a search for the e+e- decay of a hypothetical dark photon, also
names U vector boson, in inclusive dielectron spectra measured by HADES in the
p (3.5 GeV) + p, Nb reactions, as well as the Ar (1.756 GeV/u) + KCl reaction.
An upper limit on the kinetic mixing parameter squared epsilon^{2} at 90% CL
has been obtained for the mass range M(U) = 0.02 - 0.55 GeV/c2 and is compared
with the present world data set. For masses 0.03 - 0.1 GeV/c^2, the limit has
been lowered with respect to previous results, allowing now to exclude a large
part of the parameter region favoured by the muon g-2 anomaly. Furthermore, an
improved upper limit on the branching ratio of 2.3 * 10^{-6} has been set on
the helicity-suppressed direct decay of the eta meson, eta-> e+e-, at 90% CL
In-Medium Effects on K0 Mesons in Relativistic Heavy-Ion Collisions
We present the transverse momentum spectra and rapidity distributions of
and K in Ar+KCl reactions at a beam kinetic energy of 1.756 A
GeV measured with the spectrometer HADES. The reconstructed K sample is
characterized by good event statistics for a wide range in momentum and
rapidity. We compare the experimental and K distributions to
predictions by the IQMD model. The model calculations show that K at low
tranverse momenta constitute a particularly well suited tool to investigate the
kaon in-medium potential. Our K data suggest a strong repulsive in-medium
K potential of about 40 MeV strength.Comment: 10 pages, 10 figures, accepted by Phys. Rev.
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