First Measurement of the $Q^2$ Dependence of the Beam-Normal Single Spin Asymmetry for Elastic Scattering off Carbon

A. Esser , M. Thiel , P. Achenbach , K. Aulenbacher , S. Baunack , J. Beričič , D. Bosnar , L. Correa (1) , M. Dehn , M.O. Distler , H. Fonvieille (1) , I. Friščić , M. Gorchtein , S. Heidrich , P. Herrmann , M. Hoek , S. Kegel , Y. Kohl , T. Kolar , H.J. Kreidel , F.E. Maas , H. Merkel , M. Mihovilovič , J. Müller , U. Müller , F. Nillius , C. Palatchi , K.D. Paschke , J. Pochodzalla , B.S. Schlimme , M. Schoth , F. Schulz , S. Širca , B. Spruck , S. Štajner , V. Tioukine , A. Tyukin , A. Weber , C. Sfienti

1 LPC - Laboratoire de Physique de Clermont

We report on the first Q2-dependent measurement of the beam-normal single spin asymmetry An in the elastic scattering of 570 MeV vertically polarized electrons off C12. We cover the Q2 range between 0.02 and 0.05  GeV2/c2 and determine An at four different Q2 values. The experimental results are compared to a theoretical calculation that relates An to the imaginary part of the two-photon exchange amplitude. The result emphasizes that the Q2 behavior of An given by the ratio of the Compton to charge form factors cannot be treated independently of the target nucleus.

Mots clés: spin: asymmetry: measured; exchange: two-photon; form factor: charge; form factor: ratio; nucleus: target; electron nucleus: elastic scattering; experimental results; electron: polarized beam; polarization: transverse; carbon: target; momentum transfer dependence; amplitude analysis; gallium: arsenic; photoelectron; radiation: laser; Mainz Linac

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

A. Esser, M. Thiel, P. Achenbach, K. Aulenbacher, S. Baunack, et al.. First Measurement of the $Q^2$ Dependence of the Beam-Normal Single Spin Asymmetry for Elastic Scattering off Carbon. Physical Review Letters, 2018, 121 (2), pp.022503. ⟨10.1103/PhysRevLett.121.022503⟩. ⟨hal-01851161⟩