# Exclusive $\rho^0$ Meson Photoproduction with a Leading Neutron at HERA

Abstract : A first measurement is presented of exclusive photoproduction of $\rho^0$ mesons associated with leading neutrons at HERA. 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 $1.16$ pb$^{-1}$. The $\rho^0$ mesons with transverse momenta $p_T<1$ GeV are reconstructed from their decays to charged pions, while leading neutrons carrying a large fraction of the incoming proton momentum, $x_L>0.35$, are detected in the Forward Neutron Calorimeter. The phase space of the measurement is defined by the photon virtuality $Q^2 < 2$ GeV$^2$, the total energy of the photon-proton system $20 < W_{\gamma p} < 100$ GeV and the polar angle of the leading neutron $\theta_n < 0.75$ mrad. The cross section of the reaction $\gamma p \to \rho^0 n \pi^+$ is measured as a function of several variables. The data are interpreted in terms of a double peripheral process, involving pion exchange at the proton vertex followed by elastic photoproduction of a $\rho^0$ meson on the virtual pion. In the framework of one-pion-exchange dominance the elastic cross section of photon-pion scattering, $\sigma^{\rm el}(\gamma\pi^+ \to \rho^0\pi^+)$, is extracted. The value of this cross section indicates significant absorptive corrections for the exclusive reaction $\gamma p\to\rho^0 n \pi^+$.
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Submitted on : Friday, September 4, 2015 - 3:41:15 PM
Last modification on : Wednesday, October 30, 2019 - 1:38:43 AM

### Citation

V. Andreev, J. Feltesse, L. Schoeffel, C. Diaconu, D. Hoffmann, et al.. Exclusive $\rho^0$ Meson Photoproduction with a Leading Neutron at HERA. European Physical Journal C: Particles and Fields, Springer Verlag (Germany), 2016, 76, pp.41. ⟨10.1140/epjc/s10052-015-3863-1⟩. ⟨in2p3-01193145⟩

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