Pion virtual compton scattering (VCS) via the reaction ${\pi }^{-}\overrightarrow{e}{\pi }^{-}e\gamma$ was observed in the Fermilab E781 SELEX experiment. SELEX used a $600\mathrm{GeV}/c$ ${\pi }^{-}$ beam incident on target atomic electrons, detecting the incident ${\pi }^{-}$ and the final state ${\pi }^{-},$ electron and $\gamma .$ Theoretical predictions based on chiral perturbation theory are incorporated into a Monte Carlo simulation of the experiment and are compared to the data. The number of reconstructed events (=9) and their distribution with respect to the kinematic variables (for the kinematic region studied) are in reasonable accord with the predictions. The corresponding ${\pi }^{-}$ VCS experimental cross section is σ=38.8±13 nb, in agreement with the theoretical expectation of σ=34.7 nb.

• Received 9 September 2001

DOI:https://doi.org/10.1103/PhysRevC.66.034613