New, high-precision measurements of the 3He(e,e'p) reaction using the A1 collaboration spectrometers at the Mainz microtron MAMI are presented. These were performed in antiparallel kinematics at ...energy transfers below the quasi-elastic peak, and at a central momentum transfer of 685 MeV/c. Cross sections and distorted momentum distributions were extracted and compared to theoretical predictions and existing data. The longitudinal and transverse behavior of the cross section was also studied. Sizable differences in the cross-section behavior from theoretical predictions based on Plane Wave Impulse Approximation were observed in both the two- and three-body breakup channels. Full Faddeev-type calculations account for some of the observed excess cross section, but significant differences remain.
The reaction p(e,e′
π
+)n was measured at the Mainz Microtron MAMI at an invariant mass of
W=1125
MeV
and four-momentum transfers of
Q
2=0.117, 0.195 and
0.273
(
GeV/c)
2
. For each value of
Q
2, a ...Rosenbluth separation of the transverse and longitudinal cross sections was performed. An effective Lagrangian model was used to extract the `axial mass' from experimental data. We find a value of
M
A
=(1.077±0.039)
GeV
which is
(0.051±0.044)
GeV
larger than the axial mass known from neutrino scattering experiments. This is consistent with recent calculations in chiral perturbation theory.
Virtual Compton scattering, i.e. the exclusive reaction
γ
∗p → γ′p′
with
γ
∗
denoting a virtual photon, provides new insights on the internal structure of the proton. Below
π
0 production threshold, ...this experiment measures the generalized polarizabilities of the proton as defined by Guichon
et al 1, 2 and Drechsel
et al 3. These new electromagnetic observables, functions of
Q
2, enlarge the concept of electric (α0 and magnetic (β) polarizabilities in Real Compton Scattering (
Q
2=0) 4.
The first VCS experiment 5 of this kind was measured at the three spectrometer facility at the Mainz Microtron MAMI for
Q
2=0.33 GeV
2 and we present in this paper the preliminary results.
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