287 research outputs found
c-Axis tunneling in YBa2Cu3O7-\delta/PrBa2Cu3O7-\delta superlattices
In this work we report c-axis conductance measurements done on a superlattice
based on a stack of 2 layers YBa2Cu3O{7-\delta} and 7 layers
PrBa2Cu3O{7-\delta} (2:7). We find that these quasi-2D structures show no clear
superconducting coupling along the c-axis. Instead, we observe tunneling with a
gap of \Delta_c=5.0\pm 0.5 meV for the direction perpendicular to the
superconducting planes. The conductance spectrum show well defined
quasi-periodic structures which are attributed to the superlattice structure.
From this data we deduce a low temperature c-axis coherence length of
\xi_c=0.24\pm 0.03 nm.Comment: 15 pages, 5 figures. To appear in Phys.Rev.
The ARGO-YBJ Experiment Progresses and Future Extension
Gamma ray source detection above 30TeV is an encouraging approach for finding
galactic cosmic ray origins. All sky survey for gamma ray sources using wide
field of view detector is essential for population accumulation for various
types of sources above 100GeV. To target the goals, the ARGO-YBJ experiment has
been established. Significant progresses have been made in the experiment. A
large air shower detector array in an area of 1km2 is proposed to boost the
sensitivity. Hybrid detection with multi-techniques will allow a good
discrimination between different types of primary particles, including photons
and protons, thus enable an energy spectrum measurement for individual specie.
Fluorescence light detector array will extend the spectrum measurement above
100PeV where the second knee is located. An energy scale determined by balloon
experiments at 10TeV will be propagated to ultra high energy cosmic ray
experiments
High Altitude test of RPCs for the ARGO-YBJ experiment
A 50 m**2 RPC carpet was operated at the YangBaJing Cosmic Ray Laboratory
(Tibet) located 4300 m a.s.l. The performance of RPCs in detecting Extensive
Air Showers was studied. Efficiency and time resolution measurements at the
pressure and temperature conditions typical of high mountain laboratories, are
reported.Comment: 16 pages, 10 figures, submitted to Nucl. Instr. Met
Direct Measurements of the Branching Fractions for and and Determinations of the Form Factors and
The absolute branching fractions for the decays and
are determined using singly
tagged sample from the data collected around 3.773 GeV with the
BES-II detector at the BEPC. In the system recoiling against the singly tagged
meson, events for and events for decays are observed. Those yield
the absolute branching fractions to be and . The
vector form factors are determined to be
and . The ratio of the two form
factors is measured to be .Comment: 6 pages, 5 figure
The pole in
Using a sample of 58 million events recorded in the BESII detector,
the decay is studied. There are conspicuous
and signals. At low mass, a large
broad peak due to the is observed, and its pole position is determined
to be - MeV from the mean of six analyses.
The errors are dominated by the systematic errors.Comment: 15 pages, 6 figures, submitted to PL
Search for the Lepton Flavor Violation Processes and
The lepton flavor violation processes and are
searched for using a sample of 5.8 events collected with
the BESII detector. Zero and one candidate events, consistent with the
estimated background, are observed in and
decays, respectively. Upper limits on the branching ratios are determined to be
and at the 90% confidence level (C.L.).Comment: 9 pages, 2 figure
Observation of the decay \psip\rar\kstark
Using 14 million events collected with the BESII detector,
branching fractions of \psip\rar\kstarkpm and \kstarknn are determined to
be: \calB(\psip\rar\kstarkpm)=(2.9^{+1.3}_{-1.7}\pm0.4)\times 10^{-5} and
\calB(\psip\rar\kstarknn)=(13.3^{+2.4}_{-2.7}\pm1.9)\times 10^{-5}. The
results confirm the violation of the "12%" rule for these two decay channels
with higher precision. A large isospin violation between the charged and
neutral modes is observed.Comment: 5 pages, 3 figure
ARGO-YBJ constraints on very high energy emission from GRBs
The ARGO-YBJ (Astrophysical Radiation Ground-based Observatory at YangBaJing)
experiment is designed for very high energy -astronomy and cosmic ray
researches. Due to the full coverage of a large area () with
resistive plate chambers at a very high altitude (4300 m a.s.l.), the ARGO-YBJ
detector is used to search for transient phenomena, such as Gamma-ray bursts
(GRBs). Because the ARGO-YBJ detector has a large field of view (2 sr)
and is operated with a high duty cycle (90%), it is well suited for GRB
surveying and can be operated in searches for high energy GRBs following alarms
set by satellite-borne observations at lower energies. In this paper, the
sensitivity of the ARGO-YBJ detector for GRB detection is estimated. Upper
limits to fluence with 99% confidence level for 26 GRBs inside the field of
view from June 2006 to January 2009 are set in the two energy ranges 10100
GeV and 10 GeV1 TeV.Comment: accepted for publication in Astroparticle Physic
Measurement of Branching Ratios for Hadronic Decays
In a sample of 58 million events collected with the BES II detector,
the process J/ is observed in five decay channels: , , (with
), (with ) and . From
these signals, we determine ,
, ,
and .Comment: 8 pages, 1 figures and 4 table. Submitted to Phys. Lett.
Measurements of J/psi --> p \bar{p}
The process J/\psi --> p \bar{p} is studied using 57.7 X 10^6 J/\psi events
collected with the BESII detector at the Beijing Electron Positron Collider.
The branching ratio is determined to be Br(J/\psi --> p \bar{p})=(2.26 +- 0.01
+- 0.14) X 10^{-3}, and the angular distribution is well described by
\frac{dN}{d cos\theta_p}=1+\alpha\cos^2\theta_p with \alpha = 0.676 +- 0.036 +-
0.042, where \theta_p is the angle between the proton and beam directions. The
value of \alpha obtained is in good agreement with the predictions of
first-order QCD.Comment: 6 pages, 2 figures, RevTex4, Submitted to Phys.Lett.
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