Polarization in double parton scattering

TL;DR

This paper reviews the current understanding of double parton scattering, emphasizing the role of polarization arising from spin correlations between partons, and discusses how techniques from transverse momentum dependent distributions can be applied.

Contribution

It highlights the importance of polarization effects in DPS, which are often neglected, and explores their theoretical and phenomenological implications.

Findings

Polarization effects in DPS are significant and calculable.

Techniques from TMD parton distributions can be adapted to DPS.

Neglecting polarization may overlook important correlations in DPS.

Abstract

We briefly discuss the status of double parton scattering (DPS) on both theoretical and experimental sides and summarize the state of the naive DPS model, where the scatterers are taken completely independent. We then elaborate on some of the effects which are neglected in such an approach, and often ignored in phenomenological studies, with focus on polarization - which arises from the correlation between the spin of two partons inside a proton. Polarization is of particular interest, thanks to its direct and calculable connections to the distribution of particles in the final state. Although the physics described is different, there are strong similarities between polarization in DPS and in single partons scattering with measured transverse momentum, and several of the techniques and results from studies of transverse momentum dependent parton distributions can be translated into the setting of double parton scattering.