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"Two-photon exchange corrections in elastic lepton-proton scattering"

Oleksandr Tomalak, Johannes Gutenberg-Universität Mainz (JGU Mainz)
Monday, October 17, 2016 - 2:00pm to 3:00pm
PAT C-421

INT/NTG

In
recent years,
elastic
electron-proton
scattering
experiments,
with and
without
polarized
protons, gave
strikingly
different
results for
the electric
over magnetic
proton form
factor ratio.
A mysterious
discrepancy
("the proton
radius
puzzle") has
been observed
in the
measurement of
the proton
charge radius
in muon
spectroscopy
experiments
versus
electron
spectroscopy
and electron
scattering.
Two-photon
exchange (TPE)
contributions
are the
largest source
of the
hadronic
uncertainty in
these
experiments. We
estimate the
forward
Compton
scattering
subtraction
function and
corresponding
correction to
the Lamb shift
of 2S level in
muonic
hydrogen from
the proton
structure
function data
in high-energy
and resonance
regions. We
also compare
the existing
models of the
elastic
contribution
to TPE
correction in
lepton-proton
scattering. An
alternative
dispersive
evaluation of
the TPE
correction to
the hydrogen
hyperfine
splitting was
found and
applied
. A
subtracted
dispersion
relation
formalism for
the TPE in
electron-proton
scattering has
been developed
and tested.
Its relative
effect on
cross section
is in the
1-2% range for
a low value of
the momentum
transfer. For
the inelastic
TPE
contribution,
the low
momentum
transfer
expansion was
studied, and a
good agreement
with the
experimental
TPE fit to
electron data
was found. We
compare the
resulting TPE
with VEPP-3
and CLAS data
and give
predictions in
OLYMPUS
kinematics and
for a
forthcoming
muon-proton
scattering
experiment
(MUSE).​

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