740 research outputs found
A Start-Timing Detector for the Collider Experiment PHENIX at RHIC-BNL
We describe a start-timing detector for the PHENIX experiment at the
relativistic heavy-ion collider RHIC. The role of the detector is to detect a
nuclear collision, provide precise time information with an accuracy of 50ps,
and determine the collision point along the beam direction with a resolution of
a few cm. Technical challenges are that the detector must be operational in a
wide particle-multiplicity range in a high radiation environment and a strong
magnetic field. We present the performance of the prototype and discuss the
final design of the detector.Comment: 12 pages, LaTeX, 9 gif and 4 ps figures. Submitted to NIM
Magnetic soft modes in the locally distorted triangular antiferromagnet alpha-CaCr2O4
In this paper we explore the phase diagram and excitations of a distorted
triangular lattice antiferromagnet. The unique two-dimensional distortion
considered here is very different from the 'isosceles'-type distortion that has
been extensively investigated. We show that it is able to stabilize a 120{\deg}
spin structure for a large range of exchange interaction values, while new
structures are found for extreme distortions. A physical realization of this
model is \alpha-CaCr2O4 which has 120{\deg} structure but lies very close to
the phase boundary. This is verified by inelastic neutron scattering which
reveals unusual roton-like minima at reciprocal space points different from
those corresponding to the magnetic order.Comment: 5 pages, 3 figures and lots of spin-wave
Fermi-Bose mapping for one-dimensional Bose gases
One-dimensional Bose gases are considered, interacting either through the
hard-core potentials or through the contact delta potentials. Interest in these
gases gained momentum because of the recent experimental realization of
quasi-one-dimensional Bose gases in traps with tightly confined radial motion,
achieving the Tonks-Girardeau (TG) regime of strongly interacting atoms. For
such gases the Fermi-Bose mapping of wavefunctions is applicable. The aim of
the present communication is to give a brief survey of the problem and to
demonstrate the generality of this mapping by emphasizing that: (i) It is valid
for nonequilibrium wavefunctions, described by the time-dependent Schr\"odinger
equation, not merely for stationary wavefunctions. (ii) It gives the whole
spectrum of all excited states, not merely the ground state. (iii) It applies
to the Lieb-Liniger gas with the contact interaction, not merely to the TG gas
of impenetrable bosons.Comment: Brief review, Latex file, 15 page
Hyperfine Structure Constants for Eu Isotopes: Is The Empirical Formula of HFS Anomaly Universal ?
We calculate the hyperfine structure constant for the Eu isotopes with shell
model wave functions. The calculated results are compared with those predicted
by the Moskowitz-Lombardi (M-L) empirical formula. It turns out that the two
approaches give the very different behaviors of the hfs constants in the
isotope dependence. This should be easily measured by experiment, which may
lead to the universality check of the M-L formula.Comment: 18 pages, Latex, two figure
On Phase Transition of -Type Crystals by Cluster Variation Method
The Cluster Variation Method (CVM) is applied to the Ishibashi model for
ammonium dihydrogen phosphate () of a typical hydrogen
bonded anti-ferroelectric crystal. The staggered and the uniform susceptibility
without hysteresis are calculated at equilibrium. On the other hand, by making
use of the natural iteration method (NIM) for the CVM, hysteresis phenomena of
uniform susceptibility versus temperature observed in experiments is well
explained on the basis of local minimum in Landau type variational free energy.
The polarization curves against the uniform field is also calculated.Comment: 14 pages, 10 figure
Heavy resonance production in high energy nuclear collisions
We estimate freezeout conditions for , , and quarks in high energy
nuclear collisions. Freezeout is due either to loss of thermal contact, or to
particles ``wandering'' out of the region of hot matter. We then develop a
thermal recombination model in which both single-particle (quark and antiquark)
and two-particle (quark-antiquark) densities are conserved. Conservation of
two-particle densities is necessary because quarks and antiquarks are always
produced in coincidence, so that the local two-particle density can be much
larger than the product of the single-particle densities. We use the freezeout
conditions and recombination model to discuss heavy resonance production at
zero baryon density in high energy nuclear collisions.Comment: revtex, 15 pages, no figures, KSUCNR-009-9
Spin current and magneto-electric effect in non-collinear magnets
A new microscopic mechanism of the magneto-electric (ME) effect based on the
spin supercurrent is theoretically presented for non-collinear magnets. The
close analogy between the superconductors (charge current) and magnets (spin
current) is drawn to derive the distribution of the spin supercurrent and the
resultant electric polarization. Application to the spiral spin structure is
discussed.Comment: 5 pages, 2 figure
Resonance model study of strangeness production in pp collisions
Results for the energy dependence of the elementary kaon production cross
sections in proton-proton collisions are reported. Calculations are performed
within an extended version of the resonance model which was used for the
previous studies of elementary kaon production in pion-nucleon and
pion- collisions. Although the model treatment is within the {\it
empirical} tree level (observed widths for the resonances are used), it is
fully relativistic, and includes all relevant baryon resonances up to 2 GeV.
One of the purposes of this study is to provide the results for the simulation
codes of subthreshold kaon production in heavy ion collisions. This is the
first, consistent study of the elementary kaon production reactions including
both and () collisions on the same footing.
Comparisons are made between the calculated results and the existing
semi-empirical parametrizations which are widely used for the simulation codes,
as well as the experimental data.Comment: 10 pages with 5 postscript figures, Latex, revised version for
publication in Phys. Lett.
Paramaterizations of inclusive cross sections for pion production in proton-proton collisions. II. Comparison to new data
A set of new, precise data have recently been made available by the NA49
collaboration for charged pion production in proton-proton and proton-Carbon
reactions at 158 GeV. The current paper compares this new data to five
currently available arithmetic parameterizations. Although a precise fit is not
expected, two of the parameterizations do not work very well but the other
three are able to provide a moderately good, but not precise fit to the
proton-proton data. The best two of these three parameterizations are scaled to
the proton-Carbon data and again provide a moderately good, but not precise
fit.Comment: 11 pages, 13 figures, Accepted for publication in Physical Review
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