Measurement of transverse single-spin asymmetries for dijet production in polarized proton-proton collisions at s = 200     GeV

This is the authors' abstract. We don't add key points for this paper.

We report a new measurement of transverse single-spin asymmetries for dijet production in collisions of polarized protons at <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:msqrt> <a:mi>s</a:mi> </a:msqrt> <a:mo>=</a:mo> <a:mrow> <a:mn>200</a:mn> <a:mtext> </a:mtext> <a:mtext> </a:mtext> <a:mi>GeV</a:mi> </a:mrow> </a:math> . Correlations between the proton spin and the transverse momenta of its partons, each perpendicular to the proton momentum direction, are probed at high <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:msup> <c:mi>Q</c:mi> <c:mn>2</c:mn> </c:msup> <c:mo>≈</c:mo> <c:mn>160</c:mn> <c:mtext> </c:mtext> <c:mtext> </c:mtext> <c:msup> <c:mi>GeV</c:mi> <c:mn>2</c:mn> </c:msup> </c:math> . 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 <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mi>u</e:mi> </e:math> - or <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mi>d</g:mi> </g:math> -quark contributions to separate data samples. The resulting asymmetries are compared to recent theoretical calculations. Separately, the associated Sivers observable <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mo stretchy="false">⟨</i:mo> <i:msub> <i:mi>k</i:mi> <i:mi>T</i:mi> </i:msub> <i:mo stretchy="false">⟩</i:mo> </i:math> , 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.