7,333 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 Constraints and Systematic Effects in the Determination of the Proton Form Factors
We calculate the two-photon exchange corrections to electron-proton
scattering with nucleon and intermediate states. The results show a
dependence on the elastic nucleon and nucleon--transition form factors
used as input which leads to significant changes compared to previous
calculations. We discuss the relevance of these corrections and apply them to
the most recent and precise data set and world data from electron-proton
scattering. Using this, we show how the form factor extraction from these data
is influenced by the subsequent inclusion of physical constraints. The
determination of the proton charge radius from scattering data is shown to be
dominated by the enforcement of a realistic spectral function. Additionally,
the third Zemach moment from the resulting form factors is calculated. The
obtained radius and Zemach moment are shown to be consistent with Lamb shift
measurements in muonic hydrogen.Comment: minor changes, added references, version to appear in PR
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
Structural and superconducting properties of MgBBe
We prepared MgBBe (, 0.2, 0.3, 0.4, and 0.6) samples where
B is substituted with Be. MgB structure is maintained up to .
In-plane and inter-plane lattice constants were found to decrease and increase,
respectively. Superconducting transition temperature decreases with
. We found that the decrease is correlated with in-plane contraction
but is insensitive to carrier doping, which is consistent with other
substitution studies such as MgAlB and MgBC.
Implication of this work is discussed in terms of the 2D nature of -band.Comment: 3 pages,4 figures, to be published in Phys. Rev.
Detection of Cherenkov light from air showers with Geiger-APDs
We have detected Cherenkov light from air showers with Geiger-mode APDs
(G-APDs). G-APDs are novel semiconductor photon-detectors, which offer several
advantages compared to conventional photomultiplier tubes in the field of
ground-based gamma-ray astronomy. In a field test with the MAGIC telescope we
have tested the efficiency of a G-APD / light catcher setup to detect Cherenkov
light from air showers. We estimate a detection efficiency, which is 60% higher
than the efficiency of a MAGIC camera pixel. Ambient temperature dark count
rates of the tested G-APDs are below the rates of the night sky light
background. According to these recent tests G-APDs promise a major progress in
ground-based gamma-ray astronomy.Comment: 4 pages, 5 figures, to appear in the proceedings of the 30th
International Cosmic Ray Conference, Merida, July 200
Ricci Collineations of the Bianchi Type II, VIII, and IX Space-times
Ricci and contracted Ricci collineations of the Bianchi type II, VIII, and IX
space-times, associated with the vector fields of the form (i) one component of
is different from zero and (ii) two components of are
different from zero, for , are presented. In subcase (i.b), which
is , some known solutions are found, and in subcase
(i.d), which is , choosing ,
the Bianchi type II, VIII, and IX space-times is reduced to the
Robertson-Walker metric.Comment: 12 Pages, LaTeX, 1 Table, no figure
Resistivity and Hall effect of LiFeAs: Evidence for electron-electron scattering
LiFeAs is unique among the broad family of FeAs-based superconductors,
because it is superconducting with a rather large K under
ambient conditions although it is a stoichiometric compound. We studied the
electrical transport on a high-quality single crystal. The resistivity shows
quadratic temperature dependence at low temperature giving evidence for strong
electron-electron scattering and a tendency towards saturation around room
temperature. The Hall constant is negative and changes with temperature, what
most probably arises from a van Hove singularity close to the Fermi energy in
one of the hole-like bands. Using band structure calculations based on angular
resolved photoemission spectra we are able to reproduce all the basic features
of both the resistivity as well as the Hall effect data.Comment: 6 pages, 3 figures included; V2 has been considerably revised and
contain a more detailed analysis of the Hall effect dat
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