Search for Odderon-Induced Contributions to Exclusive pi^0 Photoproduction at HERA

TL;DR

This study searched for Odderon contributions in exclusive pi^0 photoproduction at HERA, finding no signal and setting an upper limit that challenges some theoretical predictions based on non-perturbative QCD models.

Contribution

It provides the first experimental upper limit on the photon-Odderon fusion cross section in exclusive pi^0 production at HERA energies.

Findings

No pi^0 signal observed in the data.

Upper limit on the cross section set at 49 nb.

Excludes certain non-perturbative QCD model predictions.

Abstract

A search for contributions to the reaction ep-> e pi^0 N^* from photon-Odderon fusion in the photoproduction regime at HERA is reported, at an average photon-proton centre-of-mass energy <W> = 215 GeV. The measurement proceeds via detection of the pi^0 decay photons, a leading neutron from the N^* decay, and the scattered electron. No pi^0 signal is observed and an upper limit on the cross section for the photon-Odderon fusion process of sigma(gamma p -> pi^0 N^*) < 49 nb at the 95% confidence level is derived, integrated over the experimentally accessible range of the squared four-momentum transfer at the nucleon vertex 0.02 < |t| < 0.3 Gev^2. This excludes a recent prediction from a calculation based on a non-perturbative QCD model of a photon-Odderon fusion cross section above 200 nb.