Double Longitudinal Spin Asymmetry in Neutral Pion Production in Polarized p+p Collisions at sqrt(s)=200 GeV at PHENIX

TL;DR

This paper reports measurements of double longitudinal and transverse spin asymmetries in neutral pion production at RHIC, providing constraints on the gluon contribution to proton spin and exploring spin effects in polarized proton collisions.

Contribution

It presents new experimental results from RHIC runs that constrain g and include the first measurement of azimuthally independent double transverse spin asymmetry.

Findings

Results disfavor maximal positive and negative g values.

Provides constraints on gluon polarization in the proton.

Includes the first measurement of A_TT in this context.

Abstract

A major goal of the RHIC spin program is to measure \Delta g, the gluon contribution to the proton's spin. Measurements by PHENIX of the double longitudinal spin asymmetry, A_LL, of the neutral pion production at mid-rapidity in polarized proton collisions have been shown to constrain \Delta g. Results from the 2005 RHIC run, as well as high p_T data from the 2006 RHIC run, are presented. The results disfavor maximal positive and negative values of \Delta g. A measurement of azimuthally independent double transverse spin asymmetry, A_TT, is also presented.