In a p((-->)e,e'p)pi(0) out-of-plane coincidence experiment at the three-spectrometer setup of the Mainz Microtron MAMI, the beam-helicity asymmetry has been precisely measured around the energy of ...the Delta(1232) resonance and Q(2) = 0.2(GeV/c)(2). The results are in disagreement with three up-to-date model calculations. This is interpreted as a lack of understanding of the nonresonant background, which in dynamical models is related to the pion cloud.
Eur.Phys.J.A24:101-109,2005 The electric form factor of the neutron, G_En, has been measured at the Mainz
Microtron by recoil polarimetry in the quasielastic D(e_pol,e'n_pol)p reaction.
Three data ...points have been extracted at squared four-momentum transfers Q^2 =
0.3, 0.6 and 0.8 (GeV/c)^2. Corrections for nuclear binding effects have been
applied.
Phys.Rev.Lett. 88 (2002) 142001 In a p(e_pol,e'p)pi_0 out-of-plane coincidence experiment at the
3-spectrometer setup of the Mainz Microtron MAMI, the beam-helicity asymmetry
has been precisely ...measured around the energy of the Delta(1232) resonance and
Q^2 = 0.2 (GeV/c)^2. The results are in disagreement with three up-to-date
model calculations. This is interpreted as lack of understanding of the
non-resonant background, which in dynamical models is related to the pion
cloud.
Phys.Rev.Lett.86:2959-2962,2001 The recoil proton polarization has been measured in the p (\vec e,e'\vec p)
pi^0 reaction in parallel kinematics around W = 1232 MeV, Q^2 = 0.121 (GeV/c)^2
and epsilon ...= 0.718 using the polarized c.w. electron beam of the Mainz
Microtron. Due to the spin precession in a magnetic spectrometer, all three
proton polarization components P_x/P_e = (-11.4 \pm 1.3 \pm 1.4) %, P_y =
(-43.1 \pm 1.3 \pm 2.2) %, and P_z/P_e = (56.2 \pm 1.5 \pm 2.6) % could be
measured simultaneously. The Coulomb quadrupole to magnetic dipole ratio CMR =
(-6.4\pm 0.7_{stat}\pm 0.8_{syst}) % was determined from P_x in the framework
of the Mainz Unitary Isobar Model. The consistency among the reduced
polarizations and the extraction of the ratio of longitudinal to transverse
response is discussed.
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