470 research outputs found
Relativistic Charge Form Factor of the Deuteron
Relativistic integral representation in terms of experimental neutron-proton
scattering phase shifts alone is used to compute the charge form factor of the
deuteron . The results of numerical calculations of
are presented in the interval of the four-momentum transfers
squared . Zero and the prominent secondary maximum
in are the direct consequences of the change of sign in the
experimental - phase shifts. Till the point the
total relativistic correction to is positive and reaches the
maximal value of 25% at .Comment: 9 pages, LaTeX, 2 postscript figures, uses wor-sci.sty, epsf.st
Large Logarithms in the Beam Normal Spin Asymmetry of Elastic Electron--Proton Scattering
We study a parity-conserving single-spin beam asymmetry of elastic
electron-proton scattering induced by an absorptive part of the two-photon
exchange amplitude. It is demonstrated that excitation of inelastic hadronic
intermediate states by the consecutive exchange of two photons leads to
logarithmic and double-logarithmic enhancement due to contributions of hard
collinear quasi-real photons. The asymmetry at small electron scattering angles
is expressed in terms of the total photoproduction cross section on the proton,
and is predicted to reach the magnitude of 20-30 parts per million. At these
conditions and fixed 4-momentum transfers, the asymmetry is rising
logarithmically with increasing electron beam energy, following the high-energy
diffractive behavior of total photoproduction cross section on the proton.Comment: 10 pages, 6 figures; typos fixed, a reference adde
Two-Photon Exchange in Electron-Proton Elastic Scattering: Theory Update
Recent theoretical developments in the studies of two-photon exchange effects
in elastic electron-proton scattering are reviewed. Two-photon exchange
mechanism is considered a likely source of discrepancy between polarized and
unpolarized experimental measurements of the proton electric form factor at
momentum transfers of several GeV. This mechanism predicts measurable
effects that are currently studied experimentally.Comment: 9 pages, 4 figures; To appear in Proceedings of International
Workshop on Exclusive Reactions at High Momentum Transfer, May 21-24, 2007,
Jefferson Lab, Newport News, V
Transverse target spin asymmetry in inclusive DIS with two-photon exchange
We study the transverse target spin dependence of the cross section for
inclusive electron-nucleon scattering with unpolarized beam. Such dependence is
absent in the one-photon exchange approximation (Christ-Lee theorem) and arises
only in higher orders of the QED expansion, from the interference of one-photon
and absorptive two-photon exchange amplitudes as well as from real photon
emission (bremsstrahlung). We demonstrate that the transverse spin-dependent
two-photon exchange cross section is free of QED infrared and collinear
divergences. We argue that in DIS kinematics the transverse spin dependence
should be governed by a "parton-like" mechanism in which the two-photon
exchange couples mainly to a single quark. We calculate the normal spin
asymmetry in an approximation where the dominant contribution arises from quark
helicity flip due to interactions with non-perturbative vacuum fields
(constituent quark picture) and is proportional to the quark transversity
distribution in the nucleon. Such helicity-flip processes are not significantly
Sudakov-suppressed if the infrared scale for gluon emission in the photon-quark
subprocess is of the order of the chiral symmetry breaking scale, mu_chiral^2
>> Lambda_QCD^2. We estimate the asymmetry in the kinematics of the planned
Jefferson Lab Hall A experiment to be of the order 10^{-4}, with different sign
for proton and neutron. We also comment on the spin dependence in the limit of
soft high-energy scattering.Comment: 22 pages, 14 figures; uses revtex
Collinear Photon Exchange in the Beam Normal Polarization Asymmetry of Elastic Electron-Proton Scattering
The parity-conserving single-spin beam asymmetry of elastic electron-proton
scattering is induced by an absorptive part of the two-photon exchange
amplitude. We demonstrate that this asymmetry has logarithmic and
double-logarithmic enhancement due to contributions of hard collinear
quasi-real photons. An optical theorem is used to evaluate the asymmetry in
terms of the total photoproduction cross section on the proton, predicting its
magnitude at a few parts per million for high electon beam energies and small
scattering angles. At fixed 4-momentum transfers, the asymmetry is rising
logarithmically with increasing electron beam energy, following the high-energy
diffractive behavior of total photoproduction cross section on the proton.Comment: 6 pages, 5 figures, Corrected an algebraic error in Eq.(17), other
formulas and plots changed accordingl
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