Towards an explanation of transverse single-spin asymmetries in proton-proton collisions: the role of fragmentation in collinear factorization

Abstract

We study the transverse single-spin asymmetry for single-hadron production in proton-proton collisions within the framework of collinear twist-3 factorization in Quantum Chromodynamics. By taking into account the contribution due to parton fragmentation we obtain a very good description of all high transverse-momentum data for neutral and charged pion production from the Relativistic Heavy Ion Collider. Our study may provide the crucial step towards a final solution to the longstanding problem of what causes transverse single-spin asymmetries in hadronic collisions within Quantum Chromodynamics. We show for the first time that it is possible to simultaneously describe spin/azimuthal asymmetries in proton-proton collisions, semi-inclusive deep-inelastic scattering, and electron-positron annihilation by using collinear twist-3 factorization in the first process along with transverse momentum dependent functions extracted from the latter two reactions.

Figures (4)

• Figure 1: Fit results for $A_N^{\pi^0}$ (data from Adams:2003fx:2008qbAdamczyk:2012xd) and $A_N^{\pi^\pm}$ (data from Lee:2007zzh) for the SV1 input. The dashed line (dotted line in the case of $\pi^-$) means $\hat{H}_{FU}^{\Im}$ switched off.
• Figure 2: Results for the FFs $H^{\pi^+/q}$ and $\tilde{H}_{FU}^{\pi^+/q}$ (defined in the text) for the SV1 input. Also shown is $H^{\pi^+/q}$ without the contribution from $\hat{H}_{FU}^{\Im}$ (dashed line).
• Figure 3: Individual contributions to $A_N^{\pi^0}$ (data from :2008qb) for SV1 and SV2 inputs.
• Figure 4: $A_N$ as function of $P_{h\perp}$ for SV1 input at $\sqrt{S} = 500 \, \textrm{GeV}$ (data from Heppelmann:2013ewa).