Figure 1

Drawing of the ${\mathrm{PbF}}_2$ calorimeter. The scintillators are placed between the scattering chamber and the lead fluoride crystals. The system is mounted on a rotatable platform.Reuse & Permissions

Figure 2

Left panel: The measured energy spectrum of coincidence events is shown by the dashed line. One can clearly identify the peak of the elastic scattered electrons. The contributions of the different processes are shown from bright to dark: (i) the elastically scattered electrons, (ii) the inelastically scattered electrons, (iii) the converted photons from ${\pi }^0$ decay, and (iv) empty target background. Upper right panel: The solid line shows a measured energy spectrum of noncoincidence events. Lower right panel: The dotted line shows the background contribution to the coincidence spectrum estimated from the noncoincidence events by applying the shifting and scaling method in comparison with the photon background obtained from the simulation (gray) together with the shifted and scaled noncoincidence events from an empty target measurement (dark).Reuse & Permissions

Figure 3

Measured asymmetries $A_{\mathrm{LR}}$ with respect to the position of the half-wave plate at the electron source (in or out). The reversal of the helicity can be easily observed in the sign flip of the extracted asymmetries. The two gray bands show fits to the data, $A_{\mathrm{out}}=(17.70\pm 1.27)\mathrm{ppm}$ and $A_{\mathrm{in}}=(-16.68\pm 1.37)\mathrm{ppm}$ (omitting systematic errors).Reuse & Permissions

Figure 4

The linear combination of $G_E^s+\zeta G_M^s$ from this work (solid band) together with the A4 forward angle measurement [19] (hatched band). The bands represent the possible values of $G_E^s+\zeta G_M^s$ within the one-$\sigma$ uncertainty with statistical and systematic error added in quadrature. The ellipses show the 68% and 95% C.L. constraints in the $G_E^s\mathrm{\text{−}}{G}_M^s$ plane. Also shown are theoretical predictions [3, 5, 6, 7, 8].Reuse & Permissions