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

Abstract
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.

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


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