Measurements of transverse spin effects in the forward region with the STAR detector

TL;DR

This paper reports on measurements of transverse spin effects in forward neutral pion production at STAR, exploring asymmetries and correlations to distinguish underlying mechanisms like the Sivers and Collins effects.

Contribution

It presents new experimental data from the STAR detector with extended forward calorimetry, enabling analysis of heavier mesons and c0^0-c0^0 correlations to better understand spin asymmetries.

Findings

Extended forward calorimetry at STAR enhances meson detection.

Preliminary results on c0^0-c0^0 correlations are discussed.

Plans for future analyses to discriminate spin effects are outlined.

Abstract

Measurements by the STAR collaboration of the cross section and transverse single spin asymmetry (SSA) of neutral pion production at large Feynman x (x_F) in pp-collisions at \sqrt{s}=200 GeV were reported previously. The x_F dependence of the asymmetry can be described by phenomenological models that include the Sivers effect, Collins effect or higher twist contributions in the initial and final states. Discriminating between the Sivers and Collins effects requires one to go beyond inclusive \pi^0 measurements. For the 2008 run, forward calorimetry at STAR was significantly extended. The large acceptance of the Forward Meson Spectrometer (FMS) allows us to look at heavier meson states and \pi^0-\pi^0 correlations. Recent results, the status of current analyses and near-term plans will be discussed.