Transverse electrodisintegration of the deuteron in the threshold region at high Q2.

Cross sections for 180’ deuteron electrodisintegration have been measured near threshold for the Q2-range 1.21 to 2.77 (GeV/c)2. The new data, together with previous data (Ref. 2) at lower Q2, show a change in slope near Q2 = 1 ( GeV/c)2. Nonrelativistic calculations based on both meson-nucleon and hybrid quark-hadron models are not in quantitative agreement with the data over the entire Q2-range. The ratio WI/W2 of inelastic structure functions has been extracted using previous forward angle data and is found to decrease strongly near threshold. Submitted to Physical Review Letters *This work was supported in part by Department of Energy contracts DE-ACO3-76SFOO515 (SLAC), W-7405-ENG-48 (LLNL), and DE-AC02-76ER-02853 (U. Mass.); National Science Foundation Grant PHY85-10549 (A.U.); and the U.S.-Israel Binational Science Foundation. The deuteron is the most important nucleus for the study of the nucleon-nucleon interaction and the effects of meson exchange currents (MEC). Of particular interest is the transverse electrodisintegration of the deuteron, where a single magnetic transition to an unbound isospin triplet ‘SO state dominates the cross section near threshold. Existing data1j2 are inconsistent with the diffraction minimum predicted in the impulse approximation (IA) at squared four-momentum transfer Q2 FZ 0.5 (GeV/c)2. The discrepancy is removed by MEC3-’ and is the firmest evidence to date for their existence. The previous data extend to Q 2 = 1.1 (GeV/c)2. At higher Q2, theoretical predictions have been made within the meson-nucleon framework,4-6 and using hybrid quark-hadron models. 7-g In the latter, the deuteron is represented as a sixquark cluster when the n-p separation is comparable to or less than the nucleon size. These various approaches have resulted in orderrof-magnitude differences in the crosg sections predicted for Q2 > 1 ( GeV/c)2. In this Letter we present new measurements of threshold ineIastic scattering from deuterium which more than double the Q2 range of previous data. The new data were obtained as a series of single-arm spectra of electron scattering near 180’. Doublearm measurements of elastic electron-deuteron scattering” were taken simultaneously with the single-arm data. The expected small cross sections made it necessary to use long liquid deuterium targets and a large acceptance spectrometer. The experiment used electron beams of energy E = 0.734, 0.843, 0.885, 0.934, 1.020, 1.102, 1.201, and 1.279 GeV, produced by the Nuclear Physics Injector a.nd the Stanford Linear Accelerator with a maximum intensity of 5 x 10” electrons per 1.6 psec pulse at a rate of 150 Hz. Energy-defining slits limited the uncertainty in E to f0.35%. The beams were transported to a 180’ spectrometer systemr’