Diffractive mechanisms in $pp\to pp{\pi }^0$ reaction at high energies

Abstract

We present a study of exclusive production of ${\pi }^0$ meson in proton-proton collisions at high energies. Both diffractive bremsstrahlung (Drell-Hiida-Deck type model), photon-photon, photon-omega and photon-odderon exchange mechanisms are included in the calculation. The ${\pi }^0$-bremsstrahlung contribution dominates at large (forward, backward) pion rapidities and contributes at small ${\pi }^{0}p$ invariant mass and could be therefore misinterpreted as the Roper resonance $N^{\ast }(1440)$. Large cross sections of the order of mb are predicted. We predict strong dependence of the slope in $t$ (squared four-momentum transfer between ingoing and outgoing proton) on the mass of the supplementary excited ${\pi }^{0}p$ system. At high energy and midrapidity, the photon-photon contribution dominates over the diffractive components, however, the corresponding cross section is rather small. The photon-odderon and odderon-photon contributions are included in addition and first estimates (upper limits) of their contributions are presented. We suggest a search for the odderon contribution at midrapidity and at $p_{\perp ,{\pi }^0}\sim$ 0.5 GeV. Our predictions are ready for verification at LHC. The bremsstrahlung mechanisms discussed here contribute also to the $pp\to p(n{\pi }^{+})$ reaction. Both channels give a sizable contribution to the low-mass single diffractive cross section and must be included in extrapolating the measured experimental single diffractive cross section.

Comments: 7 pages, 5 figures, presented by P. Lebiedowicz at DIS2013, Marseille, 22-26.04.2013