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Description
Exclusive photoproduction of $\rho^0(770)$ mesons is studied using the H1 detector at the $ep$ collider HERA. A sample of about 900000 events 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 $4$-momentum transfer $t$ at the proton vertex. The measurements are presented in various 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 proton-dissociative scattering. The observed cross section dependencies are described by analytic functions. Parametrising the $m_{\pi\pi}$ dependence with resonant and non-resonant contributions added at the amplitude level leads to a measurement of the $\rho^0(770)$ meson mass and width at $m_\rho=770.8^{+2.6}_{-2.7}$ (tot) MeV and $\Gamma_\rho=151.3^{+2.7}_{-3.6}$v (tot) MeV, respectively. The model is used to extract the $\rho^0(770)$ contribution to the $\pi^{+}\pi^{-}$ cross sections and measure it as a function of $t$ and $W_{\gamma{}p}$. In a Regge asymptotic limit in which one Regge trajectory $\alpha(t)$ dominates, the intercept $\alpha(t{=}0)=1.0654^{+0.0098}_{-0.0067}$ (tot) and the slope $\alpha^\prime(t{=}0)=0.233^{+0.067}_{-0.074}$ (tot) GeV$^{-2}$ of the $t$ dependence are extracted for the case $m_Y{=}m_p$.
Eur.Phys.J.C80 (2020), 1189
| Preferred track | Forward & Diffractive Physics |
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