106 research outputs found
Positron Beams and Two-Photon Exchange: The Key to Precision Form Factors
The proton elastic form factor ratio can be measured either via Rosenbluth
separation in an unpolarized beam and target experiment, or via the use of
polarization degrees of freedom. However, data produced by these two approaches
show a discrepancy, increasing with . The proposed explanation of this
discrepancy---two-photon exchange---has been tested recently by three
experiments. The results support the existence of a small two-photon exchange
effect but cannot establish that theoretical treatment at the measured momentum
transfers are valid. At larger momentum transfers, theory remains untested.
This paper investigates the possibilities of measurements at DESY and Jefferson
Lab to measure the effect at larger momentum transfers.Comment: 6 pages, 5 figures. Conference proceedings from JPOS17
(https://www.jlab.org/conferences/JPos2017/
Two-Photon Exchange: Future experimental prospects
The proton elastic form factor ratio is accessible in unpolarized
Rosenbluth-type experiments as well as experiments which make use of
polarization degrees of freedom. The extracted values show a distinct
discrepancy, growing with . Three recent experiments tested the proposed
explanation, two-photon exchange, by measuring the positron-proton to
electron-proton cross section ratio. In the results, a small two-photon
exchange effect is visible, significantly different from theoretical
calculation. Theory at larger momentum transfer remains untested. This paper
discusses the possibilities for future measurements at larger momentum
transfer.Comment: 7 pages, 4 figures. Contribution to the proceedings of the 11th
International Workshop on the Physics of Excited Nucleons (NSTAR 2017
The views of rich Europeans are more likely to be reflected by political parties than those of poorer citizens
How does income inequality affect political representation? Jan Rosset, Nathalie Giger and Julian Bernauer examine whether politicians represent the views of poorer and richer citizens equally. They find that in 43 out of the 49 elections included in their analysis, the preferences of low-income citizens are located further away from the policy positions of the closest political party than those with mid-range incomes. This suggests that income inequality may spill-over into political inequalities, although it is less clear whether this effect is likely to get better or worse as a result of the Eurozone crisis
The RMS Charge Radius of the Proton and Zemach Moments
On the basis of recent precise measurements of the electric form factor of
the proton, the Zemach moments, needed as input parameters for the
determination of the proton rms radius from the measurement of the Lamb shift
in muonic hydrogen, are calculated. It turns out that the new moments give an
uncertainty as large as the presently stated error of the recent Lamb shift
measurement of Pohl et al.. De Rujula's idea of a large Zemach moment in order
to reconcile the five standard deviation discrepancy between the muonic Lamb
shift determination and the result of electronic experiments is shown to be in
clear contradiction with experiment. Alternative explanations are touched upon.Comment: 6 pages, 4 figures, final version includes discussion of systematic
and numerical error
A helical-shape scintillating fiber trigger and tracker system for the DarkLight experiment and beyond
The search for new physics beyond the Standard Model has interesting
possibilities at low energies. For example, the recent 6.8 anomaly
reported in the invariant mass of pairs from nuclear
transitions and the discrepancy between predicted and measured values of muon
g-2 give strong motivations for a protophobic fifth-force model. At low
energies, the electromagnetic interaction is well understood and produces
straightforward final states, making it an excellent probe of such models.
However, to achieve the required precision, an experiment must address the
substantially higher rate of electromagnetic backgrounds. In this paper, we
present the results of simulation studies of a trigger system, motivated by the
DarkLight experiment, using helical-shape scintillating fibers in a solenoidal
magnetic field to veto electron-proton elastic scattering and the associated
radiative processes. We also assess the performance of a tracking detector for
lepton final states using scintillating fibers in the same setup
Successful aspiration thrombectomy in a patient with submassive, intermediate-risk pulmonary embolism following COVID-19 pneumonia
A 64-year-old female patient presented with severe dyspnea shortly after apparent recovery from COVID-19 disease. Chest computed tomography revealed central pulmonary embolism and ultrasonography showed a deep vein thrombosis of her right leg. The patient was tachycardiac with evidence of right ventricular strain on echocardiography. An interdisciplinary decision for interventional therapy was made.
Angiographic aspiration thrombectomy resulted in a significant reduction of thrombus material and improved flow in the pulmonary arteries and immediate marked clinical improvement and subsequent normalization of functional echocardiographic parameters.
This case adds to the emerging evidence for severe thromboembolic complications following COVID-19 and suggests aspiration thrombectomy can be considered in pulmonary embolism of intermediate risk
The electric and magnetic form factors of the proton
The paper describes a precise measurement of electron scattering off the
proton at momentum transfers of \ GeV. The
average point-to-point error of the cross sections in this experiment is
0.37%. These data are used for a coherent new analysis together with all world
data of unpolarized and polarized electron scattering from the very smallest to
the highest momentum transfers so far measured. The extracted electric and
magnetic form factors provide new insight into their exact shape, deviating
from the classical dipole form, and of structure on top of this gross shape.
The data reaching very low values are used for a new determination of the
electric and magnetic radii. An empirical determination of the
Two-Photon-Exchange (TPE) correction is presented. The implications of this
correction on the radii and the question of a directly visible signal of the
pion cloud are addressed.Comment: 38 pages, 20 figures. Updated data files. PRC versio
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