References - Bogoliubov Laboratory of Theoretical Physics - JINR

4 Results of GEp-III Experiment
In Fig. 5 we show the preliminary results for the GEp-III experiment. Because GEp-III
is the first recoil polarization experiment to use a completely different apparatus in a
Q 2 range where direct comparison with the Hall A recoil polarization results is possible,
it provides an important test of the reproducibility of the recoil polarization technique.
Figure 5 shows the results of GEp-III experiment (filled triangles) together with the results
of the Hall A experiments [2,3] (filled circles) and [4] (filled squares). The error bars shown
are statistical only. The overlap point at 5.2 GeV 2 is in reasonably good agreement with
the two surrounding points from [4], and confirms the continuing decrease of G p
E /Gp
M with
Q 2 . The two new data points extend the knowledge of G p
E /Gp
M to yet higher Q2 .
Additionally, the preliminary results of the high-statistics survey of the ɛ-dependence
of G p
E /Gp
M at Q2 =2.5 GeV 2 ,GEp-2γ experiment, also shown as black triangle in Fig. 5
is in excellent agreement with the Hall A results [3] at Q 2 =2.47 GeV 2 .SincetheGEp-2γ
experiment was performed with identical apparatus and the data were analyzed in exactly
the same way as in the GEp-III experiment, a systematic error in the analysis is all but
ruled out.
The interesting feature of the results is that the linearly decreasing trend observed
in the previous data appears to be slowing in the Hall C data. Although the ratios still
decreases with Q 2 , all of the new data points come in higher than the linear fit to the
Hall A data.
Figure 5: Results of GEp-III experiment (filled triangles) shown as μpG p
E /Gp M . The results of experiments
GEp-I (filled circles) and GEp-II (filled squares) and the Rosenbluth separation data (empty
triangles) are shown for comparison. The error bars on the data points are statistical only.
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