Utilizing the 2012 transversely polarized proton data from the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, the forward $η$-meson transverse single-spin asymmetry ($A_N$) was measured for $p^{\uparrow}+p$ collisions at $\sqrt{s}=200$ GeV as a function of Feynman-x ($x_F$) for $0.2<|x_F|<0.8$ and transverse momentum ($p_T$) for $1.0<p_T<5.0$ GeV/$c$. Large asymmetries at positive $x_F$ are observed ($\left<A_N\right>=0.086 \pm 0.019$), agreeing well with previous measurements of $π^{0}$ and $η$$A_N$, but with reach to higher $x_F$ and $p_T$. The contribution of initial-state spin-momentum correlations to the asymmetry, as calculated in the collinear twist-3 framework, appears insufficient to describe the data and suggests a significant impact on the asymmetry from fragmentation.
The $\eta$ meson transverse single-spin asymmetry vs. Feynman-x at forward rapidity in pp collisions at center-of-mass energy 200 GeV.
The $\eta$ meson transverse single-spin asymmetry vs. $\eta$ meson $p_T$ at forward rapidity in pp collisions at center-of-mass energy 200 GeV.
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