SCHOLARS@TAMU

The STAR Collaboration reports a measurement of the transverse single-spin asymmetries, $A_{N}$, for neutral pions produced in polarized proton collisions with protons ($pp$), with aluminum nuclei ($p
m{Al}$) and with gold nuclei ($p
m{Au}$) at a nucleon-nucleon center-of-mass energy of 200 GeV. Neutral pions are observed in the forward direction relative to the transversely polarized proton beam, in the pseudo-rapidity region $2.7angle} = -0.027 pm 0.005$. No significant difference in $P$ is observed between the low-$p_T$ region, $p_T<2.5$ GeV/$c$, where gluon saturation effects may play a role, and the high-$p_T$ region, $p_T>2.5$ GeV/$c$. It is further observed that the value of $A_N$ is significantly larger for events with a large-$p_T$ isolated $pi^0$ than for events with a non-isolated $pi^0$ accompanied by additional jet-like fragments. The nuclear dependence $r(A)$ is similar for isolated and non-isolated $pi^0$ events.

• Huang, Tingwen
• Tribble, Robert
• Ma, Guolin
• Gagliardi, Carl

PHYSICAL REVIEW D

• Nucl-ex
• Hep-ex

1.1

7