Search for Quadrupole Strength in the Electro-excitation of the Delta(1232)
nucl-ex
/ Authors
C. Mertz, C. Vellidis, R. Alarcon, D. H. Barkhuff, A. M. Bernstein, W. Bertozzi, V. Burkert, J. Chen, J. R. Comfort, G. Dodson
and 33 more authors
S. Dolfini, K. Dow, M. Farkhondeh, J. M. Finn, S. Gilad, R. W. Gothe, X. Jiang, K. Joo, N. I. Kaloskamis, A. Karabarbounis, J. J. Kelly, S. Kowalski, C. Kunz, R. W. Lourie, J. I. McIntyre, B. D. Milbrath, R. Miskimen, J. H. Mitchell, C. N. Papanicolas, C. F. Perdrisat, A. J. Sarty, J. Shaw, S. -B. Soong, D. Tieger
/ Abstract
High-precision H(e,e'p)pi0 measurements at Q2=0.126 (GeV/c)2 are reported, which allow the determination of quadrupole amplitudes in the gamma* N->Delta transition; they simultaneously test the reliability of electroproduction models. The derived quadrupole-to-dipole amplitude ratios, Rsm=(-6.5 +- 0.2{stat+sys} +- 2.5{mod}) % and Rem=(-2.1 +- 0.2{stat+sys} +- 2.0{mod}) %, are dominated by model error. Previous Rsm and Rem results should be reconsidered after the model uncertainties associated with the method of their extraction are taken into account.