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Deeply Virtual Compton scattering and its Beam Charge Asymmetry in ep collisions at HERA |
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| Abstract |
A measurement of elastic deeply virtual Compton scattering $\gamma^* p
ightarrow \gamma p$ using the complete set of $e^+ p$ and $e^- p$ collision
data recorded with the H1 detector at HERA since 2003 is presented.
The analysed data sample corresponds to an integrated luminosity of
$306$~pb$^{-1}$, almost equally shared between both beam charges. The cross
section is measured as a function of the virtuality $Q2$ of the exchanged
photon and the centre-of-mass energy $W$ of the $\gamma^*p$ system in the
kinematic domain $6.5 < Q2 < 80~GeV2$, $30 < W < 140~GeV$ and $|t| < 1~GeV2$,
where $t$ denotes the squared momentum transfer at the proton vertex. The cross
section is determined differentially in $t$ for different $Q2$ and $W$ values
and exponential $t$-slope parameters are derived. Using $e^+ p$ and $e^- p$
data samples, a beam charge asymmetry is extracted for the first time in the
low $x \simeq Q2/W2$ kinematic domain. The observed asymmetry is attributed to
the interference between Bethe-Heitler and deeply virtual Compton scattering
processes. This interference term is sensitive to the real part of the DVCS
amplitude. The ratio of real to imaginary parts of the DVCS amplitude is then
derived and is interpreted using dispersion relations. Experimental results
are discussed in the context of Generalised Parton Distributions and dipole
models. |
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