First Measurement of pi e -> pi e gamma Pion Virtual Compton Scattering

TL;DR

This paper reports the first experimental observation of pion virtual Compton scattering via the pi e -> pi e gamma reaction, comparing measured data with theoretical predictions from chiral perturbation theory.

Contribution

It provides the first measurement of pion virtual Compton scattering cross section and compares experimental results with theoretical models.

Findings

Reconstructed 9 events consistent with predictions

Measured cross section of 38.8+-13 nb agrees with theoretical 34.7 nb

Distribution of events matches theoretical expectations

Abstract

Pion Virtual Compton Scattering (VCS) via the reaction pi e --> pi e gamma was observed in the Fermilab E781 SELEX experiment. SELEX used a 600 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 sigma=38.8+-13 nb, in agreement with the theoretical expectation sigma=34.7 nb.