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{\bf EPS-HEP99} \\
{\bf Abstract \# 000} \\
{\bf Parallel sessions: 3} \\
{\bf Plenary sessions: 3}
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\abstractheader{ {\bf
\boldmath Proton Dissociative and Elastic Electroproduction of
$\rho$ Mesons at HERA } \\ \\
H1 Collaboration, \\
DESY, Notkestr.85, D-22607 Hamburg, Germany
}
\abstractbody{
The proton dissociative and elastic production of $\rho$ mesons is studied
with the H1 detector at HERA for a photon virtuality in the range $1 <
Q^2 < 60 {\rm\ GeV}^2$ and for a hadronic centre of mass energy in the
range $20 < W < 150 {\rm\ GeV}$.
The shape of the ($\pi\pi$) mass distribution in the $\rho$ resonance
region is measured as a function of $Q^2$.
The cross section is presented as a function of $Q^2$, $W$ and $t$ (the
four-momentum transfer squared to the proton) and the parameters of the
pomeron trajectory are extracted.
Angular distributions are studied as a function of $t$ and $Q^2$ and the
full set of $\rho$ spin density matrix elements is determined. Evidence is
found for a helicity flip amplitude at the level of $8 \pm 3\%$ of the
non-flip amplitudes indicating a significant deviation from the prediction
of $s$-channel helicity conservation.
}
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{\bf Reference} for elastic $\rho$ production \\
1. H1 Collaboration, C.~Adloff {\it et al},
DESY-99-010 / submitted to Eur.Phys.J. C
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