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Description
Exclusive production of four charged pions at the ep collider HERA is studied at small photon virtualities $Q^2<2$ GeV${}^2$. The data were taken with the H1 detector in the years 2006 and 2007 at a centre-of-mass energy of $\sqrt{s}=319$ GeV and correspond to an integrated luminosity of 7.6 pb$^{-1}$. The cross section of the reaction $\gamma p \to 2(\pi^+\pi^-)Y$ is determined in the phase space of $45\lt W_gp\lt 100$ GeV, $\vert t\vert\lt 1$ GeV${}^2$ and $M_Y\lt 1.6$ GeV. The $4\pi$ mass spectra indicate that the reaction proceeds predominatly via production and decay of $\rho^{\prime}(1450)$ and $\rho^{\prime\prime}(1700)$ resonances. Parameters of these resonances as well as production cross sections times branching ratio into four charged pions are estimated from the mass fit, which includes contributions from non-resonant $4\pi$ channel and interference terms.
