Measurement of the beam-helicity asymmetry in the p((-->)e,e'p)pi(0) reaction at the energy of the Delta(1232) resonance.
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.
Bartsch
P
P
Institut für Kernphysik, Universität Mainz, D-55099 Mainz, Germany.
Baumann
D
D
Bermuth
J
J
Böhm
R
R
Bohinc
K
K
Bosnar
D
D
Ding
M
M
Distler
M
M
Drechsel
D
D
Elsner
D
D
Ewald
I
I
Friedrich
J
J
Friedrich
J M
JM
Grözinger
S
S
Hedicke
S
S
Jennewein
P
P
Kahrau
M
M
Kamalov
S S
SS
Klein
F
F
Krygier
K W
KW
Liesenfeld
A
A
Merkel
H
H
Merle
P
P
Müller
U
U
Neuhausen
R
R
Pospischil
Th
T
Potokar
M
M
Rosner
G
G
Schmieden
H
H
Seimetz
M
M
Süle
A
A
Tiator
L
L
Wagner
A
A
Walcher
Th
T
Weis
M
M