Cross Section and Transverse Single-Spin Asymmetry of $\eta$ Mesons in $p^{\uparrow }+p$ Collisions at $\sqrt{s}=200$ GeV at Forward Rapidity

Abstract

We present a measurement of the cross section and transverse single-spin asymmetry ($A_N$) for $\eta$ mesons at large pseudorapidity from $\sqrt{s}=200$~GeV $p^{\uparrow }+p$ collisions. The measured cross section for $0.5<p_T<5.0$~GeV/$c$ and $3.0<|\eta |<3.8$ is well described by a next-to-leading-order perturbative-quantum-chromodynamics calculation. The asymmetries $A_N$ have been measured as a function of Feynman-$x$ ($x_F$) from $0.2<|x_F|<0.7$, as well as transverse momentum ($p_T$) from $1.0<p_T<4.5$~GeV/$c$. The asymmetry averaged over positive $x_F$ is $⟨A_N⟩=0.061\pm 0.014$. The results are consistent with prior transverse single-spin measurements of forward $\eta$ and ${\pi }^0$ mesons at various energies in overlapping $x_F$ ranges. Comparison of different particle species can help to determine the origin of the large observed asymmetries in $p^{\uparrow }+p$ collisions.

484 authors, 13 pages, 11 figures, 4 tables, 2008 data. v2 is version accepted by Phys. Rev. D. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be)publicly available at http://www.phenix.bnl.gov/papers.html