Searching for Diffractive Contributions to the Forward $\pi^0$ Transverse Single-Spin Asymmetry in $\sqrt{s}=200$ GeV Polarized $pp$ Collisions

The observation of large transverse single-spin asymmetries, $A_N$, has been around since 1976, but their
origin is not yet fully understood. Recent measurements of $\pi^0$ $A_N$ at STAR carried out with the
Forward Meson Spectrometer (FMS), an electromagnetic calorimeter covering a forward pseudorapidity range
of $2.6<\eta<4$, have shown that more-isolated $\pi^0$s have larger asymmetries than those which are
less-isolated. In 2015, Roman Pot (RP) detectors were installed which allow for the identification of
outgoing protons at near-beam rapidities. These RP protons can be used to select for $\pi^0$s in the FMS
which could have originated from diffractive-type processes. In particular, a sample of highly-isolated
$\pi^0$s is observed in the FMS, in coincidence with the forward-going proton deflecting into a RP,
and nothing more in the forward direction. This presentation will focus on this
class of events and its properties, along with other FMS and RP correlations, venturing into these
unexplored possible contributions to the large $\pi^0$ $A_N$.