Abstract
Single spin asymmetry measurements ([Formula: see text]) of the azimuthal distribution of charged pions inside jets produced in transversely polarized proton collisions are sensitive to the transversity distribution and the Collins fragmentation function. The STAR Detector at the Relativistic Heavy Ion Collider is well suited for these types of measurements as it is capable of full jet reconstruction and charged pion identification in the mid-rapidity region ([Formula: see text][Formula: see text][Formula: see text][Formula: see text]). We report here the first observation of Collins [Formula: see text] asymmetries in [Formula: see text] GeV [Formula: see text] collisions.
Highlights
A complete, fundamental understanding of the proton must include knowledge of the underlying spin structure
Drachenberg asymmetries of charged pions have been observed in semi-inclusive deep inelastic scattering (SIDIS) data.[3, 4]. These SIDIS asymmetries combined with measurements in e+e− annihilation at Belle and BABAR permit the extraction of h1 x, Q2 and ∆D (z, jet axis (jT) ).[5, 6]
A significant asymmetry in this channel would provide access to h1 x, Q2 at higher average x ranges than in SIDIS and sensitivity to the ∆D (z, jT ) at the same scales measured at Belle and BaBar
Summary
A complete, fundamental understanding of the proton must include knowledge of the underlying spin structure. Transversity extractions have focused solely on data from SIDIS and e+e− experiments.[9] asymmetry measurements of the azimuthal distribution of charged pions inside jets in polarized proton collisions provide a unique tool to constrain transversity distributions.[10, 11]
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