Search for Odderon induced contributions to exclusive Meson Photoproduction at HERA

TL;DR

This study searched for Odderon contributions in exclusive meson photoproduction at HERA but found no evidence, setting upper limits below theoretical predictions, while confirming expected cross sections for other processes.

Contribution

First experimental search for Odderon effects in exclusive meson photoproduction at HERA, establishing upper limits below theoretical expectations.

Findings

No Odderon signals observed within the studied kinematic region.

Upper limits on cross sections are below theoretical model predictions.

Confirmed expected cross sections for $ ext{ω}$ and $ ext{ωπ}^0$ photoproduction.

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.