First Measurement of the Neutral Current Excitation of the Delta Resonance on a Proton Target

AbstractThe parity-violating asymmetry arising from inelastic electron-nucleon scattering at backward angle (∼ 95 ◦ ) near the∆(1232) resonance has been measured using a hydrogen target. From this asymmetry, we extracted the axial transitionform factor G AN∆ , a function of the axial Adler form factors C Ai . Though G AN∆ has been previously studied using chargedcurrent reactions, this is the first measurement of the weak neutral current excitation of the ∆ using a proton target.For Q 2 = 0.34 (GeV/c) 2 and W = 1.18 GeV, the asymmetry was measured to be −33.4±(5.3) stat ±(5.1) sys ppm. Thevalue of G AN∆ determined from the hydrogen asymmetry was −0.05±(0.35) stat ±(0.34) sys ±(0.06) theory . These findingsagree within errors with theoretical predictions for both the total asymmetry and the form factor. In addition to thehydrogen measurement, the asymmetry was measured at the same kinematics using a deuterium target. The asymmetryfor deuterium was determined to be −43.6±(14.6) stat ±(6.2)