14 research outputs found
Two-Boson Exchange Physics: A Brief Review
Current status of the two-boson exchange contributions to elastic
electron-proton scattering, both for parity conserving and parity-violating, is
briefly reviewed. How the discrepancy in the extraction of elastic nucleon form
factors between unpolarized Rosenbluth and polarization transfer experiments
can be understood, in large part, by the two-photon exchange corrections is
discussed. We also illustrate how the measurement of the ratio between
positron-proton and electron-proton scattering can be used to differentiate
different models of two-photon exchange. For the parity-violating
electron-proton scattering, the interest is on how the two-boson exchange
(TBE), \gamma Z-exchange in particular, could affect the extraction of the
long-sought strangeness form factors. Various calculations all indicate that
the magnitudes of effect of TBE on the extraction of strangeness form factors
is small, though can be large percentage-wise in certain kinematics.Comment: 6 pages, 5 figures, prepared for Proceedings of the fifth
Asia-Pacific Conference on Few-Body Problems in Physics (APFB2011), Seoul,
Korea, August 22-26, 2011, to appear in Few-Body Systems, November 201
QED Radiative Corrections in Processes of Exclusive Pion Electroproduction
Formalism for radiative correction (RC) calculation in exclusive pion
electroproduction on the proton is presented. A FORTRAN code EXCLURAD is
developed for the RC procedure. The numerical analysis is done in the
kinematics of current Jefferson Lab experiments.Comment: 13 pages, 9 figures; requires RevTeX
Nucleon Spin-Polarisabilities from Polarisation Observables in Low-Energy Deuteron Compton Scattering
We investigate the dependence of polarisation observables in elastic deuteron
Compton scattering below the pion production threshold on the spin-independent
and spin-dependent iso-scalar dipole polarisabilities of the nucleon. The
calculation uses Chiral Effective Field Theory with dynamical Delta(1232)
degrees of freedom in the Small Scale Expansion at next-to-leading order.
Resummation of the NN intermediate rescattering states and including the Delta
induces sizeable effects. The analysis considers cross-sections and the
analysing power of linearly polarised photons on an unpolarised target, and
cross-section differences and asymmetries of linearly and circularly polarised
beams on a vector-polarised deuteron. An intuitive argument helps one to
identify kinematics in which one or several polarisabilities do not contribute.
Some double-polarised observables are only sensitive to linear combinations of
two of the spin-polarisabilities, simplifying a multipole-analysis of the data.
Spin-polarisabilities can be extracted at photon energies \gtrsim 100 MeV,
after measurements at lower energies of \lesssim 70 MeV provide high-accuracy
determinations of the spin-independent ones. An interactive Mathematica 7.0
notebook of our findings is available from [email protected]: 30 pages LaTeX2e, including 22 figures as 66 .eps file embedded with
includegraphicx; three errors in initial submission corrected. This
submission includes ot the erratum to be published in EPJA (2012) and the
corrections in the tex
Spin Correlations in Pair Creation by Two-Photons and Entanglement in QED
Spin correlations of pair productions of two colliding photons
are investigated and explicit expressions for their corresponding probabilities
are derived and found to be \textit{energy} (speed) dependent, for initially
\textit{linearly} and \textit{circularly polarized} photons, different from
those obtained by simply combining the spins of the relevant particles, for
initially \textit{polarized} photons. These expressions also depend on the
angles of spin of (and/or of ), for initially {\it linearly
polarized} photons, but not for {\it circularly polarized} photons, as a
function of the energy. It is remarkable that these explicit results obtained
from quantum field theory show a clear violation of Bell's inequality of Local
Hidden Variables theories at all {\it energies} beyond that of the threshold
one for particle production, in support of quantum field theory in the
relativistic regime. We hope that our explicit expression will lead to
experiments, of the type described in the bulk of this paper, which can monitor
energy (and speed) in polarization correlation experiments.Comment: 12 pages, 4 figure
Observation of exclusive DVCS in polarized electron beam asymmetry measurements
We report the first results of the beam spin asymmetry measured in the
reaction e + p -> e + p + gamma at a beam energy of 4.25 GeV. A large asymmetry
with a sin(phi) modulation is observed, as predicted for the interference term
of Deeply Virtual Compton Scattering and the Bethe-Heitler process. The
amplitude of this modulation is alpha = 0.202 +/- 0.028. In leading-order and
leading-twist pQCD, the alpha is directly proportional to the imaginary part of
the DVCS amplitude.Comment: 6 pages, 5 figure
eta-prime photoproduction on the proton for photon energies from 1.527 to 2.227 GeV
Differential cross sections for the reaction gamma p -> eta-prime p have been
measured with the CLAS spectrometer and a tagged photon beam with energies from
1.527 to 2.227 GeV. The results reported here possess much greater accuracy
than previous measurements. Analyses of these data indicate for the first time
the coupling of the etaprime N channel to both the S_11(1535) and P_11(1710)
resonances, known to couple strongly to the eta N channel in photoproduction on
the proton, and the importance of j=3/2 resonances in the process.Comment: 6 pages, 3 figure
Model independent radiative corrections in processes of polarized electron-nucleon elastic scattering
Polarized tagged photons
SIGLEAvailable from CEN Saclay, Service de Documentation, 91191 Gif-sur-Yvette Cedex (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc