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 $45< W_{\gamma p}<100$ GeV, $\vert t\vert<1$ GeV$^2$ and $M_Y<1.6$ GeV. The $4\pi$ mass spectra indicate that the reaction proceeds predominatly via production and decay of $\rho(1450)$ and $\rho(1700)$ 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.
