Determination of the neutron electric form factor from the reaction $^3\vec{He}(\vec{e},e'n)$ at medium momentum transfer

J. Becker - et al.

doi:doi:10.1007/s100500050351

2021 Impact factor 3.131

Hadrons and Nuclei

Eur. Phys. J. A 6, 329-344

Determination of the neutron electric form factor from the reaction $^3\vec{He}(\vec{e},e'n)$ at medium momentum transfer

J. Becker¹ - H.G. Andresen² - J.R.M. Annand³ - K. Aulenbacher² - K. Beuchel¹ - J. Blume-Werry² - Th. Dombo² - P. Drescher¹ - M. Ebert¹ - D. Eyl² - A. Frey² - P. Grabmayr⁴ - T. Großmann¹ - P. Hartmann¹ - T. Hehl⁴ - W. Heil¹ - C. Herberg² - J. Hoffmann¹ - J.D. Kellie³ - F. Klein⁵ - K. Livingston³ - M. Leduc⁶ - M. Meyerhoff¹ - H. Möller² - Ch. Nachtigall¹ - A. Natter⁴ - M. Ostrick² - E.W. Otten¹ - R.O. Owens³ - S. Plützer¹ - E. Reichert¹ - D. Rohe¹ - M. Schäfer¹ - H. Schmieden² - R. Sprengard² - M. Steigerwald¹ - K.-H. Steffens² - R. Surkau¹ - Th. Walcher² - R. Watson³ - E. Wilms¹

¹ Institut für Physik, Universität Mainz, 55099 Mainz, Germany
² Institut für Kernphysik, Universität Mainz, 55099 Mainz, Germany
³ Department of Physics and Astronomy, University of Glasgow, Glasgow, UK
⁴ Physikalisches Institut, Universität Tübingen, 72076 Tübingen, Germany
⁵ Physikalisches Institut, Universität Bonn, 53115 Bonn, Germany
⁶ École Normale Superiéure, Paris, France

Received: 29 April 1999 Communicated by B. Povh

Abstract
The electric form factor of the neutron G_En has been determined in double polarized exclusive $^3\vec{He}(\vec{e},e'n)$ scattering in quasi-elastic kinematics by measuring asymmetries $A_{\perp}, A_{\Vert}$ of the cross section with respect to helicity reversal of the electron, with the nuclear spin being oriented perpendicular to the momentum transfer $\vec{q}$ in case of $A_{\perp}$ and parallel in case of $A_{\Vert}$ . The experiment was performed at the 855 MeV c. w. microtron MAMI at Mainz. The degree of polarization of the electron beam and of the gaseous $^3\vec{He}$ target were each about 50 %. Scattered electrons and neutrons were detected in coincidence by detector arrays covering large solid angles. Quasi-elastic scattering events were reconstructed from the measured electron scattering angles $\vartheta_e, \varphi_e$ and the neutron momentum vector $\vec{p}_n'$ in the plane wave impulse approximation. We obtain the result $\left<G_{En} \right>$ ${(\rm0.27 \le Q^2c^2/GeV^2 \le 0.5)}$ $= 0.0334 \pm 0.0033_{\rm stat} \pm 0.0028_{\rm syst}$ which is averaged over the indicated range of Q², the squared momentum transfer. This G_En value is significantly smaller than measured from the $D(\vec{e}, e' \vec{n})$ reaction under similar kinematical conditions. To what extent final state interactions in ³He quench the G_En result is subject of calculations currently in progress elsewhere.

PACS
14.20.Dh Properties of specific particles: Protons and neutrons - 24.70.+s Nuclear reactions: Polarization phenomena in reactions - 13.40.Gp Specific reactions and phenomenology: Electromagnetic form factors - 25.10.+s Nuclear reactions involving few-nucleon systems - 25.30.Fj Nuclear reactions: Inelastic electron scattering to continuum