Evidence for strange-quark contributions to the nucleon's form factors at Q2=0.108 (GeV/c)2.
/ Authors
F. Maas, K. Aulenbacher, S. Baunack, L. Capozza, J. Diefenbach, B. Gläser, T. Hammel, D. Harrach, Y. Imai, E. Kabuß
and 21 more authors
R. Kothe, J. Lee, A. Lorente, E. Schilling, D. Schwaab, M. Sikora, G. Stephan, G. Weber, C. Weinrich, I. Altarev, J. Arvieux, M. El-Yakoubi, R. Frascaria, R. Kunne, M. Morlet, S. Ong, J. Wiele, S. Kowalski, B. Plaster, R. Suleiman, S. Taylor
/ Abstract
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 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.
Journal: Physical review letters