Speaker
Description
Exclusive photoproduction of $\rho(770)$ mesons is studied using the H1 detector at HERA. The analysis is based on a sample of about 900000 events that were collected in the years 2006-2007. It is used to measure single- and double-differential cross sections for the reaction $\gamma p \to \pi^{+}\pi^{-}Y$. Reactions where the proton stays intact ($M_Y=M_p$) are statistically separated from those where the proton dissociates to a low-mass hadronic system ($M_p< M_Y< 10$ GeV). The double differential cross sections are measured as a function of the invariant mass $m_{\pi\pi}$ of the decay pions and the squared momentum transfer at the proton vertex $t$. These measurements are repeated in bins of the photon-proton collision energy $W_{\gamma p}$. The phase-space restrictions are $0.5 < m_{\pi\pi} < 2.2$ GeV, $\vert t\vert < 1.5$ GeV$^2$ and $20 < W_{\gamma p} < 80$ GeV. Cross-section measurements are presented for both elastic and dissociative scattering. The observed kinematic dependencies are described by analytic functions. In particular, a Soding model is used to extract the $\rho(770)$ contribution to the $\pi^{+}\pi^{-}$ cross-sections. From the resulting single-differential $\rho(770)$ cross-section as a function of $t$, measured in bins of $W_{\gamma p}$, the leading effective Regge trajectory is extracted.
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