187 research outputs found
A topological insulator surface under strong Coulomb, magnetic and disorder perturbations
Three dimensional topological insulators embody a newly discovered state of
matter characterized by conducting spin-momentum locked surface states that
span the bulk band gap as demonstrated via spin-resolved ARPES measurements .
This highly unusual surface environment provides a rich ground for the
discovery of novel physical phenomena. Here we present the first controlled
study of the topological insulator surfaces under strong Coulomb, magnetic and
disorder perturbations. We have used interaction of iron, with a large Coulomb
state and significant magnetic moment as a probe to \textit{systematically test
the robustness} of the topological surface states of the model topological
insulator BiSe. We observe that strong perturbation leads to the
creation of odd multiples of Dirac fermions and that magnetic interactions
break time reversal symmetry in the presence of band hybridization. We also
present a theoretical model to account for the altered surface of BiSe.
Taken collectively, these results are a critical guide in manipulating
topological surfaces for probing fundamental physics or developing device
applications.Comment: 14 pages, 4 Figures. arXiv admin note: substantial text overlap with
arXiv:1009.621
Measurements of absolute hadronic branching fractions of baryon
Using of collisions recorded at
with the BESIII detector, we report first measurements
of absolute hadronic branching fractions of Cabibbo-favored decays of the
baryon with a double-tag technique. A global least-square
fitter is utilized to improve the measured precision. Among the measurements
for twelve decay modes, the branching fraction for
is determined to be
, where the first uncertainty is statistical and the
second is systematic. In addition, the measurements of the branching fractions
of the other eleven Cabbibo-favored hadronic decay modes are significantly
improved
Observation of an anomalous line shape of the mass spectrum near the mass threshold in
Using events collected by the BESIII experiment
in 2012, we study the
process and observe a significant abrupt change in the slope of the
invariant mass distribution at the
proton-antiproton () mass threshold. We use two models to
characterize the line shape around
: one which explicitly incorporates the opening of a
decay threshold in the mass spectrum (Flatt\'{e} formula), and another which is
the coherent sum of two resonant amplitudes. Both fits show almost equally good
agreement with data, and suggest the existence of either a broad state around
with strong couplings to final states or a
narrow state just below the mass threshold. Although we cannot
distinguish between the fits, either one supports the existence of a
molecule-like state or bound state with greater than significance
Improved measurement of the absolute branching fraction of
By analyzing 2.93 fb of data collected at GeV with the
BESIII detector, we measure the absolute branching fraction , which is consistent with previous measurements within
uncertainties but with significantly improved precision. Combining the Particle
Data Group values of , , and the lifetimes of the and
mesons with the value of measured in this work, we determine the following ratios of
partial widths: and .Comment: 9 pages; 8 figure
Determination of the number of events with inclusive decays
A measurement of the number of events collected with the BESIII
detector in 2009 and 2012 is performed using inclusive decays of the .
The number of events taken in 2009 is recalculated to be
, which is in good agreement with the previous
measurement, but with significantly improved precision due to improvements in
the BESIII software. The number of events taken in 2012 is determined
to be . In total, the number of events
collected with the BESIII detector is measured to be , where the uncertainty is dominated by systematic effects and the
statistical uncertainty is negligible.Comment: 10 pages, 6 figure
Observation of near = 4.42 and 4.6 GeV
Based on data samples collected with the BESIII detector operating at the
BEPCII storage ring at center-of-mass energies 4.4 GeV, the
processes are observed for the first
time. With an integrated luminosity of near 4.42
GeV, a significant signal is found, and the cross section is
measured to be (20.9 \pm 3.2 \pm 2.5)\pb. With near 4.6 GeV, a clear signal is seen, and the cross section is
measured to be (9.5 \pm 2.1 \pm 1.3) \pb, while evidence is found for an
signal. The first errors are statistical and the second are
systematic. Due to low luminosity or low cross section at other energies, no
significant signals are observed. In the cross section, an
enhancement is seen around 4.42 GeV. Fitting the cross section
with a coherent sum of the Breit-Wigner function and a phase space
term, the branching fraction is
obtained to be of the order of .Comment: 7 pages, 3 figure
Observation of radiative decay and evidence for
A search for radiative decays of the -wave spin singlet charmonium
resonance is performed based on events
collected with the BESIII detector operating at the BEPCII storage ring. Events
of the reaction channels and are
observed with a statistical significance of and ,
respectively, for the first time. The branching fractions of and are measured to be
and , respectively, where the first errors are
statistical and the second are systematic uncertainties.Comment: 7 pages, 2 figure
Study of decays to the and final states
We study the decays of the charmonium resonances and to
the final states ,
based on a single baryon tag method
using data samples of and events collected with the BESIII detector at
the BEPCII collider. The decay
is observed for
the first time, and the measurements of the other processes, including the
branching fractions and angular distributions, are in good agreement with and
much more precise than the previously published results. Additionally, the
ratios
,
and
are determined.Comment: 10 pages, 9 figures, 5 tables. This version is consistent with paper
published in Phys. Rev. D on 04 Apr 201
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