2020 Impact factor 3.043
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

The electric form factor of the neutron GEn 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 GEn 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 GEn result is subject of calculations currently in progress elsewhere.

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

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