Measurement of transverse single-spin asymmetries for dijet production in polarized proton-proton collisions at $\sqrt{\mathbf{s}}$ = 200 $\mathrm{GeV}$

Abstract

We report a new measurement of transverse single-spin asymmetries for dijet production in collisions of polarized protons at $\sqrt{s}$ = 200 $\mathrm{GeV}$. Correlations between the proton spin and the transverse momenta of its partons, each perpendicular to the proton momentum direction, are probed at high $Q^2$ $\approx$160 ${\mathrm{GeV}}^2$. Evidence for nonzero Sivers effects is measured for the first time in dijets from proton-proton collisions, but only when the jets are sorted by their net charge, which enhances the otherwise canceling opposite-sign $u$- or $d$-quark contributions to separate data samples. The resulting asymmetries are compared to recent theoretical calculations. Separately, the associated Sivers observable $⟨k_T⟩$, the average parton transverse momentum, is extracted using a simple kinematics approach which further enables a determination of the individual partonic contributions to the observed asymmetries.

main text: 8 pages with 5 figures; supplement text: 2 figures, 4 tables; now updated following PRD-L publication. For this update: some main and supplement text changes are made to clarify and reduce length. Note previously, had added information and references in response to PRL referee comments with minor changes to former Figs. 2-4 and new figure (comparing to theory) added

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