6,110 research outputs found
New structures in the proton-antiproton system
In the most recent measurements of the reaction
by the BABAR collaboration, new structures have been found with unknown origin.
We examine a possible relation of the most distinct peak to the recently
observed . Alternatively, we analyse possible explanations due to
the nucleon and thresholds. The latter
could explain a periodicity found in the data
Theoretical study of electronic damage in single particle imaging experiments at XFELs for pulse durations 0.1 - 10 fs
X-ray free-electron lasers (XFELs) may allow to employ the single particle
imaging (SPI) method to determine the structure of macromolecules that do not
form stable crystals. Ultrashort pulses of 10 fs and less allow to outrun
complete disintegration by Coulomb explosion and minimize radiation damage due
to nuclear motion, but electronic damage is still present. The major
contribution to the electronic damage comes from the plasma generated in the
sample that is strongly dependent on the amount of Auger ionization. Since the
Auger process has a characteristic time scale on the order of femtoseconds, one
may expect that its contribution will be significantly reduced for attosecond
pulses. Here, we study the effect of electronic damage on the SPI at pulse
durations from 0.1 fs to 10 fs and in a large range of XFEL fluences to
determine optimal conditions for imaging of biological samples. We analyzed the
contribution of different electronic excitation processes and found that at
fluences higher than - photons/m (depending on the
photon energy and pulse duration) the diffracted signal saturates and does not
increase further. A significant gain in the signal is obtained by reducing the
pulse duration from 10 fs to 1 fs. Pulses below 1 fs duration do not give a
significant gain in the scattering signal in comparison with 1 fs pulses. We
also study the limits imposed on SPI by Compton scattering.Comment: 35 pages, 9 figures, 1 table, 2 appendixes, 45 reference
Strong interference effects in the resonant Auger decay of atoms induced by intense X-Ray fields
The theory of resonant Auger decay of atoms in a high intensity coherent
X-ray pulse is presented. The theory includes the coupling between the ground
state and the resonance due to an intense X-ray pulse, taking into account the
decay of the resonance and the direct photoionization of the ground state, both
populating the final ionic states coherently. The theory also considers the
impact of the direct photoionization of the resonance state itself which
typically populates highly-excited ionic states. The combined action of the
resonant decay and of the direct ionization of the ground state in the field
induces a non-hermitian time-dependent coupling between the ground and the
'dressed' resonance stats. The impact of these competing processes on the total
electron yield and on the 2s2p3p P spectator and
2s2p S participator Auger decay spectra of the Ne 1s3p
resonance is investigated. The role of the direct photoionization of the ground
state and of the resonance increases dramatically with the field intensity.
This results in strong interference effects with distinct patterns in the
electron spectra, different for the participator and spectator final states.Comment: 31 pages, 6 figure
Breaking the resilience of a two-dimensional Bose-Einstein condensate to fragmentation
A two-dimensional Bose-Einstein condensate (BEC) split by a radial potential
barrier is investigated. We determine on an accurate many-body level the
system's ground-state phase diagram as well as a time-dependent phase diagram
of the splitting process. Whereas the ground state is condensed for a wide
range of parameters, the time-dependent splitting process leads to substantial
fragmentation. We demonstrate for the first time the dynamical fragmentation of
a BEC despite its ground state being condensed. The results are analyzed by a
mean-field model and suggest that a large manifold of low-lying fragmented
excited states can significantly impact the dynamics of trapped two-dimensional
BECs.Comment: 5+eps pages, 4 figure
The role of noise and initial conditions in the asymptotic solution of a bounded confidence, continuous-opinion model
We study a model for continuous-opinion dynamics under bounded confidence. In
particular, we analyze the importance of the initial distribution of opinions
in determining the asymptotic configuration. Thus, we sketch the structure of
attractors of the dynamical system, by means of the numerical computation of
the time evolution of the agents density. We show that, for a given bound of
confidence, a consensus can be encouraged or prevented by certain initial
conditions. Furthermore, a noisy perturbation is added to the system with the
purpose of modeling the free will of the agents. As a consequence, the
importance of the initial condition is partially replaced by that of the
statistical distribution of the noise. Nevertheless, we still find evidence of
the influence of the initial state upon the final configuration for a short
range of the bound of confidence parameter
Reduction of Guided Acoustic Wave Brillouin Scattering in Photonic Crystal Fibers
Guided Acoustic Wave Brillouin Scattering (GAWBS) generates phase and
polarization noise of light propagating in glass fibers. This excess noise
affects the performance of various experiments operating at the quantum noise
limit. We experimentally demonstrate the reduction of GAWBS noise in a photonic
crystal fiber in a broad frequency range using cavity sound dynamics. We
compare the noise spectrum to the one of a standard fiber and observe a 10-fold
noise reduction in the frequency range up to 200 MHz. Based on our measurement
results as well as on numerical simulations we establish a model for the
reduction of GAWBS noise in photonic crystal fibers.Comment: 4 pages, 7 figures; added numerical simulations, added reference
Off-resonance field enhancement by spherical nanoshells
We study light scattering by spherical nanoshells consistent of
metal/dielectric composites. We consider two geometries of metallic nanoshell
with dielectric core, and dielectric coated metallic nanoparticle. We
demonstrate that for both geometries the local field enhancement takes place
out of resonance regions ("dark states"), which, nevertheless, can be
understood in terms of the Fano resonance. At optimal conditions the light is
stronger enhanced inside the dielectric material. By using nonlinear dielectric
materials it will lead to a variety nonlinear phenomena applicable for
photonics applications
Reduction of the proton radius discrepancy by 3 sigma
We show that in previous analyses of electron-proton scattering, the
uncertainties in the statistical procedure to extract the proton charge radius
are underestimated. Using a fit function based on a conformal mapping, we can
describe the scattering data with high precision and extract a radius value in
agreement with the one obtained from muonic hydrogen.Comment: minor changes, matches the accepted versio
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