1,191 research outputs found
The Structure of the Nucleon: Elastic Electromagnetic Form Factors
Precise proton and neutron form factor measurements at Jefferson Lab, using
spin observables, have recently made a significant contribution to the
unraveling of the internal structure of the nucleon. Accurate experimental
measurements of the nucleon form factors are a test-bed for understanding how
the nucleon's static properties and dynamical behavior emerge from QCD, the
theory of the strong interactions between quarks. There has been enormous
theoretical progress, since the publication of the Jefferson Lab proton form
factor ratio data, aiming at reevaluating the picture of the nucleon. We will
review the experimental and theoretical developments in this field and discuss
the outlook for the future.Comment: arXiv admin note: text overlap with arXiv:1301.0905,
arXiv:hep-ph/0609004, arXiv:1411.6908 by other author
The electric form factor of the neutron and its chiral content
Considering the nucleon as a system of confined valence quarks surrounded by
pions we derive a Galster-like parameterization of the neutron electric form
factor . Furthermore, we show that the proposed parameterization can be
linked to properties of the pion cloud. By this, the high quality data for the
pion form factor can be used in predictions of in the low region,
where the direct double polarization measurements are not available.Comment: 11 pages, 3 figure
Subdiffusion and weak ergodicity breaking in the presence of a reactive boundary
We derive the boundary condition for a subdiffusive particle interacting with
a reactive boundary with finite reaction rate. Molecular crowding conditions,
that are found to cause subdiffusion of larger molecules in biological cells,
are shown to effect long-tailed distributions with identical exponent for both
the unbinding times from the boundary to the bulk and the rebinding times from
the bulk. This causes a weak ergodicity breaking: typically, an individual
particle either stays bound or remains in the bulk for very long times. We
discuss why this may be beneficial for in vivo gene regulation by DNA-binding
proteins, whose typical concentrations are nanomolarComment: 4 pages, 1 figure, REVTeX4, accepted to Phys Rev Lett, some typos
correcte
Electroexcitation of the P33(1232), P11(1440), D13(1520), S11(1535) at Q^2=0.4 and 0.65(GeV/c)^2
Using two approaches: dispersion relations and isobar model, we have analyzed
recent high precision CLAS data on cross sections of \pi^0, \pi^+, and \eta
electroproduction on protons, and the longitudinally polarized electron beam
asymmetry for p(\vec{e},e'p)\pi^0 and p(\vec{e},e'n)\pi^+. The contributions of
the resonances P33(1232), P11(1440), D13(1520), S11(1535) to \pi
electroproduction and S11(1535) to \eta electroproduction are found. The
results obtained in the two approaches are in good agreement with each other.
There is also good agreement between amplitudes of the \gamma^* N \to S11(1535)
transition found in \pi and \eta electroproduction. For the first time accurate
results are obtained for the longitudinal amplitudes of the P11(1440),
D13(1520) and S11(1535) electroexcitation on protons.Comment: 9 pages, 9 figure
Beam normal spin asymmetry in elastic lepton-nucleon scattering
We discuss the two-photon exchange contribution to observables which involve
lepton helicity flip in elastic lepton-nucleon scattering. This contribution is
accessed through the spin asymmetry for a lepton beam polarized normal to the
scattering plane. We estimate this beam normal spin asymmetry at large momentum
transfer using a parton model and we express the corresponding amplitude in
terms of generalized parton distributions.Comment: 17 pages, 5 figure
Immobilization of the Erupting Molar in the Syrian Hamster
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67148/2/10.1177_00220345650440061901.pd
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