Search for Odderon induced contributions to exclusive Meson Photoproduction at HERA

Abstract

Odderon induced contributions to exclusive photoproduction of $\pi^{\circ}$, $f_2(1270)$ and $a_2(1320)$ have been searched for at HERA, using the multiphoton decays of these mesons. No indication for such contributions was found, in a kinematic region defined by the average photon-proton centre-of-mass energy $<W> = 200 - 215$ GeV, photon virtualities $Q^2 < 0.01 $GeV$^2$ and $0.02 $GeV$^2 < |t| < 0.3 $GeV$^2$, where t is the squared momentum transfer at the proton vertex. The measured upper limits for the cross sections, $\sigma(\gamma p\to^{\hspace*{-2ex}\mathbb{O}}\pi^{\circ}N^{\ast}) < 39$ nb, $\sigma(\gamma p\to^{\hspace*{-2ex}\mathbb{O}} f_2(1270)X) < 16$ nb and $\sigma(\gamma p\to^{\hspace*{-2ex}\mathbb{O}} a_2(1320)X) < 96$ nb, all at 95% CL, are lower than the predictions by a theoretical model. Exclusive photoproduction of $\omega$ and $\omega\pi^{\circ}$, in the $3\gamma$ and $5\gamma$ decay modes, is observed with the expected cross sections.