Figure 2
The azimuthal SSA
in Drell-Yan lepton pair production,
, as function of y for the kinematics of the RHIC experiment with
. The left plots show
, and the right plots
. The upper plots show the effects of varying the Sivers antiquark distributions within the range of model I—see Eqs. (
10,
11). The lower plots show instead the results of model II. In all cases, the central estimates are based on our fit (
4) for the Sivers quark distribution functions from the HERMES data [
16]. The inner error band (solid lines) shows the 1-
uncertainty of the fit. The outer error bands (dashed lines) show the error from varying the Sivers antiquark distribution functions within the ranges specified in Eqs. (
10,
11), model I for the upper plots, and model II for the lower plots. The
-region explored in the HERMES kinematics is indicated. For
we show the estimated statistical error for STAR and PHENIX. For
the statistical error at STAR and PHENIX is comparable to the asymmetry. See text and Table for a discussion of the planned RHIC II.
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