Measurement of strange-quark contributions to the nucleon's form factors at Q(2) = 0.230 (GeV/c)(2).
We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a Q2 of 0.230 (GeV/c)(2) and a scattering angle of theta (e) = 30 degrees - 40 degrees. Using a large acceptance fast PbF2 calorimeter with a solid angle of delta omega = 0.62 sr, the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is A(phys)=(-5.44+/-0.54(stat)+/-0.26(sys))x10(-6). The standard model expectation assuming no strangeness contributions to the vector form factors is A(0) = (-6.30+/-0.43) x 10(-6). The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is G(s)(E) + 0.225G(s)(M) = 0.039+/-0.034 or F(s)(1) + 0.130F(s)(2) = 0.032+/-0.028.
Maas
F E
FE
Institut für Kernphysik, Johannes Gutenberg Universität Mainz, J. J. Becherweg 45, D-55099 Mainz, Germany.
Achenbach
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P
Aulenbacher
K
K
Baunack
S
S
Capozza
L
L
Diefenbach
J
J
Grimm
K
K
Imai
Y
Y
Hammel
T
T
von Harrach
D
D
Kabuss
E M
EM
Kothe
R
R
Lee
J H
JH
Lorente
A
A
Lopes Ginja
A
A
Nungesser
L
L
Schilling
E
E
Stephan
G
G
Weinrich
C
C
Altarev
I
I
Arvieux
J
J
Collin
B
B
Frascaria
R
R
Guidal
M
M
Kunne
R
R
Marchand
D
D
Morlet
M
M
Ong
S
S
van de Wiele
J
J
Kowalski
S
S
Plaster
B
B
Suleiman
R
R
Taylor
S
S