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Exclusive photoproduction of    $${{\rho ^0}} (770)$$  ρ 0 ( 770 ) mesons is studied using the H1 detector at the  ep  collider HERA. A sample of about 900,000 events is used to measure single- and double-differential cross sections for the reaction    $$\gamma p \rightarrow \pi ^{+}\pi ^{-}Y$$  γ p → π + π - Y . Reactions where the proton stays intact (   $${{{m_Y}} {=}m_p}$$  m Y = m p ) are statistically separated from those where the proton dissociates to a low-mass hadronic system (   $$m_p{&lt;}{{m_Y}} {&lt;}10~{{\text {GeV}}} $$  m p &lt; m Y &lt; 10 GeV ). The double-differential cross sections are measured as a function of the invariant mass    $$m_{\pi \pi }$$  m π π 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    $${{W_{\gamma p}}} $$  W γ p . The phase space restrictions are    $$0.5\le m_{\pi \pi } \le 2.2~{{\text {GeV}}} $$  0.5 ≤ m π π ≤ 2.2 GeV ,    $$\vert t\vert \le 1.5~{{\text {GeV}^2}} $$  | t | ≤ 1.5 GeV 2 , and    $$20 \le W_{\gamma p} \le 80~{{\text {GeV}}} $$  20 ≤ W γ 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    $${m_{\pi \pi }}$$  m π π dependence with resonant and non-resonant contributions added at the amplitude level leads to a measurement of the    $${{\rho ^0}} (770)$$  ρ 0 ( 770 ) meson mass and width at    $$m_\rho = 770.8{}^{+2.6}_{-2.7}~({\text {tot.}})~{{\text {MeV}}} $$  m ρ = 770.8 - 2.7 + 2.6 ( tot. ) MeV and    $$\Gamma _\rho = 151.3 {}^{+2.7}_{-3.6}~({\text {tot.}})~{{\text {MeV}}} $$  Γ ρ = 151.3 - 3.6 + 2.7 ( tot. ) MeV , respectively. The model is used to extract the    $${{\rho ^0}} (770)$$  ρ 0 ( 770 ) contribution to the    $$\pi ^{+}\pi ^{-}$$  π + π - cross sections and measure it as a function of  t  and    $${W_{\gamma p}}$$  W γ p . In a Regge asymptotic limit in which one Regge trajectory    $$\alpha (t)$$  α ( t ) dominates, the intercept    $$\alpha (t{=}0) = 1.0654\ {}^{+0.0098}_{-0.0067}~({\text {tot.}})$$  α ( t = 0 ) = 1.0654 - 0.0067 + 0.0098 ( tot. ) and the slope    $$\alpha ^\prime (t{=}0) = 0.233 {}^{+0.067 }_{-0.074 }~({\text {tot.}}) ~{{\text {GeV}^{-2}}} $$  α ′ ( t = 0 ) = 0.233 - 0.074 + 0.067 ( tot. ) GeV - 2 of the  t  dependence are extracted for the case    $$m_Y{=}m_p$$  m Y = m p .

Measurement of exclusive $${\varvec{{{{\pi ^+\pi ^-}}}}}$$ and $${\varvec{{{{\rho ^0}}}}}$$ meson photoproduction at HERA