956 research outputs found
Neutron scattering study of the effects of dopant disorder on the superconductivity and magnetic order in stage-4 La_2CuO_{4+y}
We report neutron scattering measurements of the structure and magnetism of
stage-4 La_2CuO_{4+y} with T_c ~42 K. Our diffraction results on a single
crystal sample demonstrate that the excess oxygen dopants form a
three-dimensional ordered superlattice within the interstitial regions of the
crystal. The oxygen superlattice becomes disordered above T ~ 330 K, and a fast
rate of cooling can freeze-in the disordered-oxygen state. Hence, by
controlling the cooling rate, the degree of dopant disorder in our
La_2CuO_{4+y} crystal can be varied. We find that a higher degree of quenched
disorder reduces T_c by ~ 5 K relative to the ordered-oxygen state. At the same
time, the quenched disorder enhances the spin density wave order in a manner
analogous to the effects of an applied magnetic field.Comment: 4 figures included in text; submitted to PR
Exact soliton solution and inelastic two-soliton collision in spin chain driven by a time-dependent magnetic field
We investigate dynamics of exact N-soliton trains in spin chain driven by a
time-dependent magnetic field by means of an inverse scattering transformation.
The one-soliton solution indicates obviously the spin precession around the
magnetic field and periodic shape-variation induced by the time varying field
as well. In terms of the general soliton solutions N-soliton interaction and
particularly various two-soliton collisions are analyzed. The inelastic
collision by which we mean the soliton shape change before and after collision
appears generally due to the time varying field. We, moreover, show that
complete inelastic collisions can be achieved by adjusting spectrum and field
parameters. This may lead a potential technique of shape control of soliton.Comment: 5 pages, 5 figure
Angular momenta creation in relativistic electron-positron plasma
Creation of angular momentum in a relativistic electron-positron plasma is
explored. It is shown that a chain of angular momentum carrying vortices is a
robust asymptotic state sustained by the generalized nonlinear Schrodinger
equation characteristic to the system. The results may suggest a possible
electromagnetic origin of angular momenta when it is applied to the MeV epoch
of the early Universe.Comment: 20 pages, 6 figure
Measurements of the observed cross sections for exclusive light hadrons containing at , 3.650 and 3.6648 GeV
By analyzing the data sets of 17.3, 6.5 and 1.0 pb taken,
respectively, at , 3.650 and 3.6648 GeV with the BES-II
detector at the BEPC collider, we measure the observed cross sections for
, , ,
and at the three energy
points. Based on these cross sections we set the upper limits on the observed
cross sections and the branching fractions for decay into these
final states at 90% C.L..Comment: 7 pages, 2 figure
Partial wave analysis of J/\psi \to \gamma \phi \phi
Using events collected in the BESII detector, the
radiative decay is
studied. The invariant mass distribution exhibits a near-threshold
enhancement that peaks around 2.24 GeV/.
A partial wave analysis shows that the structure is dominated by a
state () with a mass of
GeV/ and a width of GeV/. The
product branching fraction is: .Comment: 11 pages, 4 figures. corrected proof for journa
Measurements of the observed cross sections for exclusive light hadron production in e^+e^- annihilation at \sqrt{s}= 3.773 and 3.650 GeV
By analyzing the data sets of 17.3 pb taken at GeV
and 6.5 pb taken at GeV with the BESII detector at the
BEPC collider, we have measured the observed cross sections for 12 exclusive
light hadron final states produced in annihilation at the two energy
points. We have also set the upper limits on the observed cross sections and
the branching fractions for decay to these final states at 90%
C.L.Comment: 8 pages, 5 figur
Direct Measurements of Absolute Branching Fractions for D0 and D+ Inclusive Semimuonic Decays
By analyzing about 33 data sample collected at and around 3.773
GeV with the BES-II detector at the BEPC collider, we directly measure the
branching fractions for the neutral and charged inclusive semimuonic decays
to be and , and determine the ratio of the two branching
fractions to be
BESII Detector Simulation
A Monte Carlo program based on Geant3 has been developed for BESII detector
simulation. The organization of the program is outlined, and the digitization
procedure for simulating the response of various sub-detectors is described.
Comparisons with data show that the performance of the program is generally
satisfactory.Comment: 17 pages, 14 figures, uses elsart.cls, to be submitted to NIM
Search for the Rare Decays J/Psi --> Ds- e+ nu_e, J/Psi --> D- e+ nu_e, and J/Psi --> D0bar e+ e-
We report on a search for the decays J/Psi --> Ds- e+ nu_e + c.c., J/Psi -->
D- e+ nu_e + c.c., and J/Psi --> D0bar e+ e- + c.c. in a sample of 5.8 * 10^7
J/Psi events collected with the BESII detector at the BEPC. No excess of signal
above background is observed, and 90% confidence level upper limits on the
branching fractions are set: B(J/Psi --> Ds- e+ nu_e + c.c.)<4.8*10^-5, B(J/Psi
--> D- e+ nu_e + c.c.) D0bar e+ e- + c.c.)<1.1*10^-5Comment: 10 pages, 4 figure
A study of charged kappa in
Based on events collected by BESII, the decay
is studied. In the invariant mass
spectrum recoiling against the charged , the charged
particle is found as a low mass enhancement. If a Breit-Wigner function of
constant width is used to parameterize the kappa, its pole locates at MeV/. Also in this channel,
the decay is observed for the first time.
Its branching ratio is .Comment: 14 pages, 4 figure
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