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27 April 2024

» arxiv » nucl-ex/0412030

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Evidence for Strange Quark Contributions to the Nucleon's Form Factors at $Q^2$ = 0.108 (GeV/c)$^2$
F. E. Maas ; K. Aulenbacher ; S. Baunack ; L. Capozza ; J. Diefenbach ; B. Gläser ; T. Hammel ; D. von Harrach ; Y. Imai ; E.-M. Kabuss ; R. Kothe ; J. H. 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. van de Wiele ; S. Kowalski ; B. Plaster ; R. Suleiman ; S. Taylor ;
Date:	14 Dec 2004
Journal:	Phys.Rev.Lett. 94 (2005) 152001
Subject:	nucl-ex
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$^circ < heta_e < 40^circ$. The measured asymmetry is $A_{LR}(vec{e}p)$ = (Aphys $pm$ Deltastat$_{stat}$ $pm$ Deltasyst$_{syst}$) $ imes$ 10$^{-6}$. The expectation from the Standard Model assuming no strangeness contribution to the vector current is A$_0$ = (Azero $pm$ DeltaAzero) $ imes$ 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 $sigma$.
Source:	arXiv, nucl-ex/0412030
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