Speaker
Description
A significant sample of $pp\to p\pi^{0}X$ events has been observed at STAR in
$\sqrt{s}=200$ GeV transversely polarized $pp$ collisions, with an isolated
$\pi^0$ detected in the forward pseudorapidity range $2.65<\eta<3.9$, along with
the forward-going proton $p$, which scatters near the beamline into Roman Pot
detectors. The sum of the $\pi^{0}$ and the scattered proton energies is
consistent with the incident proton energy of 100 GeV, indicating that no
further particles are produced in this direction. It is postulated that the
forward incident proton may have fluctuated into a $p+\pi^{0}$ system, with the
$\pi^0$ angular momentum correlated with the initial proton spin. The
$p+\pi^{0}$ system scatters off the other beam proton and separates such that
the $\pi^{0}$ has a transverse momentum of ${\sim}2$ GeV/$c$ and the proton has
a transverse momentum of ${\sim}0.2$ GeV/$c$. The other beam proton shatters
into the remnant particles $X$, all in the backward direction. Correlations
between the $\pi^0$ and scattered proton will be presented, along with single
spin asymmetries which depend on the azimuthal angles of both the pion and the
proton. This is the first time that spin asymmetries have been explored for
this process, and a model to explain their azimuthal dependence is needed.
