302 research outputs found
Angular dependence of resistivity in the superconducting state of NdFeAsOF single crystals
We report the results of angle dependent resistivity of
NdFeAsOF single crystals in the superconducting state. By
doing the scaling of resistivity within the frame of the anisotropic
Ginzburg-Landau theory, it is found that the angle dependent resistivity
measured under different magnetic fields at a certain temperature can be
collapsed onto one curve. As a scaling parameter, the anisotropy can
be determined for different temperatures. It is found that
increases slowly with decreasing temperature, varying from 5.48
at T=50 K to 6.24 at T=44 K. This temperature dependence can be
understood within the picture of multi-band superconductivity.Comment: 7 pages, 4 figure
Thermally activated energy and critical magnetic fields of SmFeAsOF
Thermally activated flux flow and vortex glass transition of recently
discovered SmFeAsOF superconductor are studied in magnetic
fields up to 9.0 T. The thermally activated energy is analyzed in two analytic
methods, of which one is conventional and generally used, while the other is
closer to the theoretical description. The thermally activated energy values
determined from both methods are discussed and compared. In addition, several
critical magnetic fields determined from resistivity measurements are presented
and discussed.Comment: Accepted by Superconductor Science and Technolog. 5 page, 4 figure
Superconducting properties of SmO1-xFxFeAs wires with Tc = 52 K prepared by the powder-in-tube method
We demonstrate that Ta sheathed SmO1-xFxFeAs wires were successfully
fabricated by the powder-in-tube (PIT) method for the first time. Structural
analysis by mean of x-ray diffraction shows that the main phase of SmO1-xFxFeAs
was obtained by this synthesis method. The transition temperature of the
SmO0.65F0.35FeAs wires was confirmed to be as high as 52 K. Based on
magnetization measurements, it is found that a globe current can flow on
macroscopic sample dimensions with Jc of ~3.9x10^3 A/cm^2 at 5 K and self
field, while a high Jc about 2x10^5 A/cm^2 is observed within the grains,
suggesting that a significant improvement in the globle Jc is possible. It
should be noted that the Jc exhibits a very weak field dependence behavior.
Furthermore, the upper critical fields (Hc2) determined according to the
Werthamer-Helfand-Hohenberg formula are (T= 0 K) = 120 T, indicating a very
encouraging application of the new superconductors.Comment: 14 pages, 6 figure
Point contact Andreev reflection spectroscopy of NdFeAsO_0.85
The newly discovered oxypnictide family of superconductors show very high
critical temperatures of up to 55K. Whilst there is growing evidence that
suggests a nodal order parameter, point contact Andreev reflection spectroscopy
can provide crucial information such as the gap value and possibly the number
of energy gaps involved. For the oxygen deficient NdFeAsO0.85 with a Tc of
45.5K, we show that there is clearly a gap value at 4.2K that is of the order
of 7meV, consistent with previous studies on oxypnictides with lower Tc.
Additionally, taking the spectra as a function of gold tip contact pressure
reveals important changes in the spectra which may be indicative of more
complex physics underlying this structure.Comment: 11 pages, 3 figures. New references included, extra discussion. This
version is accepted in Superconductor Science and Technolog
Search for an axion-like particle in radiative decays
We search for an axion-like particle (ALP) through the process
, ,
in a data sample with
events collected by the BESIII detector. No significant ALP signal
is observed over the expected background, and the upper limits on the branching
fraction of the decay and the ALP-photon coupling
constant are set at the 95\% confidence level in the mass
range of 0.165\leq m_a\leq2.84\,\mbox{GeV}/c^2. The limits on
range from to
over the search region, and the constraints on the
ALP-photon coupling are the most stringent to date for 0.165\leq
m_a\leq1.468\,\mbox{GeV}/c^2.Comment: 10 pages, 5 figure
Measurements of the branching fractions of the inclusive decays D0(D+)→π+π+π−X
Using eþe− annihilation data corresponding to an integrated luminosity of 2.93 fb−1 taken at a center-of mass energy of 3.773 GeV with the BESIII detector, we report the first measurements of the branching
fractions of the inclusive decays D0 → πþπþπ−X and Dþ → πþπþπ−X, where pions from K0
S decays have
been excluded from the πþπþπ− system and X denotes any possible particle combination. The branching
fractions of D0ðDþÞ → πþπþπ−X are determined to be BðD0 → πþπþπ−XÞ¼ð17.60 0.11 0.22Þ%
and BðDþ → πþπþπ−XÞ¼ð15.25 0.09 0.18Þ%, where the first uncertainties are statistical and the
second systematic
Observation of decays to and
Using a data sample of events collected with
the BESIII detector, we report the first observation of the four-lepton-decays
and utilizing the process
. The branching fractions are determined to be
and
, respectively. The
results deviate from theoretical predictions, by 2.8 and 5.2 ,
respectively. No significant signal is observed for , and an upper limit on the branching fraction is set at
at the 90 confidence level. A CP asymmetry observable
is constructed for the first two channels, which is measured to be
and , respectively. No
evidence for CP violation is observed in this process.Comment: 9 pages, 1 figur
Observation of the and decays into
The decays and
are observed for the first time,
using and
events collected with the BESIII detector at the BEPCII collider.
We determine the branching fractions of these two decays to be and , where the first uncertainties are statistical
and the second are systematic. The ratio of these two branching fractions is
determined to be , which is in
agreement with the "12\% rule."Comment: 9 pages and 10 figure
Observation of
By analyzing events collected with the
BESIII detector operating at the BEPCII collider, the decays of (, 1 and 2) are observed for the first time with
statistical significances of , , and ,
respectively. The product branching fractions of
and are measured. Dividing by the world
averages of the branching fractions of , the
branching fractions of decays are
determined to be ,
, and
for , 1 and 2, respectively, where the first uncertainties are statistical
and the second systematic.Comment: 9 pages, 4 figure
Measurements of the electric and magnetic form factors of the neutron for time-like momentum transfer
We present the first measurements of the electric and magnetic form factors
of the neutron in the time-like (positive ) region as function of
four-momentum transfer. We explored the differential cross sections of the
reaction with data collected with the BESIII
detector at the BEPCII accelerator, corresponding to an integrated luminosity
of 354.6 pb in total at twelve center-of-mass energies between GeV. A relative uncertainty of 18% and 12% for the electric and
magnetic form factors, respectively, is achieved at GeV.
Our results are comparable in accuracy to those from electron scattering in the
comparable space-like (negative ) region of four-momentum transfer. The
electromagnetic form factor ratio is within the
uncertainties close to unity. We compare our result on and to
recent model predictions, and the measurements in the space-like region to test
the analyticity of electromagnetic form factors.Comment: main paper: 9 pages, 6 figures, 3 tables; supplement: 9 pages, 28
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