학술논문
Evidence for Strange Quark Contributions to the Nucleon's Form Factors at $Q^2$ = 0.108 (GeV/c)$^2$
Document Type
Working Paper
Author
Maas, F. E.; Aulenbacher, K.; Baunack, S.; Capozza, L.; Diefenbach, J.; Gläser, B.; Hammel, T.; von Harrach, D.; Imai, Y.; Kabuß, E. -M.; Kothe, R.; Lee, J. H.; Lorente, A.; Schilling, E.; Schwaab, D.; Sikora, M.; Stephan, G.; Weber, G.; Weinrich, C.; Altarev, I.; Arvieux, J.; El-Yakoubi, M.; Frascaria, R.; Kunne, R.; Morlet, M.; Ong, S.; van de Wiele, J.; Kowalski, S.; Plaster, B.; Suleiman, R.; Taylor, S.
Source
Phys.Rev.Lett.94:152001,2005
Subject
Language
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 $Q^2$ = \Qsquare (GeV/c)$^2$ and at a forward electron scattering angle of 30$^\circ < \theta_e < 40^\circ$. The measured asymmetry is $A_{LR}(\vec{e}p)$ = (\Aphys $\pm$ \Deltastat$_{stat}$ $\pm$ \Deltasyst$_{syst}$) $\times$ 10$^{-6}$. The expectation from the Standard Model assuming no strangeness contribution to the vector current is A$_0$ = (\Azero $\pm$ \DeltaAzero) $\times$ 10$^{-6}$. We have improved the statistical accuracy by a factor of 3 as compared to our previous measurements at a higher $Q^2$. We have extracted the strangeness contribution to the electromagnetic form factors from our data to be $G_E^s$ + \FakGMs $G_M^s$ = \GEsGMs $\pm $ \DeltaGEsGMs at $Q^2$ = \Qsquare (GeV/c)$^2$. As in our previous measurement at higher momentum transfer for $G_E^s$ + 0.230 $G_M^s$, we again find the value for $G_E^s$ + \FakGMs $G_M^s$ to be positive, this time at an improved significance level of 2 $\sigma$.
Comment: 4 pages, 3 figures
Comment: 4 pages, 3 figures