Evidence for strange-quark contributions to the nucleon's form factors at Q2=0.108 (GeV/c)2.
We report on a measurement of the parity violating asymmetry in the elastic scattering of polarized electrons off unpolarized protons with the A4 apparatus at MAMI in Mainz at a four momentum transfer value of Q(2)=0.108 (GeV/c)(2) and at a forward electron scattering angle of 30 degrees <theta(e)<40 degrees . The measured asymmetry is A(LR)(e-->p)=[-1.36+/-0.29(stat)+/-0.13(syst)]x10(-6). The expectation from the standard model assuming no strangeness contribution to the vector current is A(0)=(-2.06+/-0.14)x10(-6). We have improved the statistical accuracy by a factor of 3 as compared to our previous measurements at a higher Q2. We have extracted the strangeness contribution to the electromagnetic form factors from our data to be G(s)(E)+0.106G(s)(M)=0.071+/-0.036 at Q(2)=0.108 (GeV/c)(2). We again find the value for G(s)(E)+0.106G(s)(M) to be positive, this time at an improved significance level of two sigma.
Maas
F E
FE
Institut für Kernphysik, Johannes Gutenberg-Universität Mainz, JJ Becherweg 45, D-55099 Mainz, Germany.
Aulenbacher
K
K
Baunack
S
S
Capozza
L
L
Diefenbach
J
J
Gläser
B
B
Hammel
T
T
von Harrach
D
D
Imai
Y
Y
Kabuss
E-M
EM
Kothe
R
R
Lee
J H
JH
Lorente
A
A
Schilling
E
E
Schwaab
D
D
Sikora
M
M
Stephan
G
G
Weber
G
G
Weinrich
C
C
Altarev
I
I
Arvieux
J
J
El-Yakoubi
M
M
Frascaria
R
R
Kunne
R
R
Morlet
M
M
Ong
S
S
van de Wiele
J
J
Kowalski
S
S
Plaster
B
B
Suleiman
R
R
Taylor
S
S