Measurement of the Sigma^- Charge Radius at SELEX

Abstract

The charge radii of Sigma^- and pi^- have been determined by direct elastic scttering on shell electrons. The measurement was performed in the framework of the SELEX (E781) charm hadroproduction experiment at Fermilab which employs a 600 GeV/c high-intensity Sigma^-/pi^- beam and a 3-stage magnetic spectrometer covering 0.1 <= x_F <= 1.0. Scattering angles and momenta of both hadron and electron were measured with high precision using silicon microstrip detectors, thus allowing for a segmented solid target. Two TRDs provided full particle identification. A preliminary result for the Sigma^- charge radius for a four-momentum transfer squared of 0.03 GeV^2/c^2 <= Q^2 <= 0.16 GeV^2/c^2 will be reported. In a parallel analysis the pi^- charge radius has been determined for 0.03 GeV^2/c^2 <= Q^2 <= 0.2 GeV^2/c^2, and is found to be consistent with previous experiments.