JRA4-TMD-neXt: 3D structure of the nucleon in momentum space

The exploration of the internal structure of hadrons is one of the core missions of hadronic physics. TMD-neXt will join together a network of experimentalists and theorists with the aim of mapping the distributions of partons inside hadrons in momentum space, including their dependence on spin. The complete three-dimensional information on these distributions is encoded in Transverse-Momentum Dependent Parton-Distribution Functions (TMD PDFs). In experimental observables, they are often combined with Transverse-Momentum Dependent Fragmentation Functions (TMD FFs). During the last ten years, pioneering advances have opened up a broad vision of this multidimensional landscape. The time has come to sharpen this vision and make a transition from an exploration phase to a precision phase. TMD-neXt will open the way to the next-generation extractions of Transverse-Momentum Distributions (TMDs). In the envisaged four years’ running of the work package, we will lay the cornerstones for precision mapping of partonic structure in momentum space. In terms of concrete objectives, TMD-neXt plans to:

• increase the amount of data available for TMD studies,
• test the validity and limits of applicability of the TMD framework,
• extract TMDs from available data,
• extend the formalism in particular to gluon-dominated processes.

The successful completion of these objectives requires us to collect, analyze, interpret data of increasing quality and quantity from several different experiments around the world (e.g., COMPASS, CMS, TJNAF, BELLE), as well as plan new experimental measurements (e.g., EIC, fixed target at LHC). This endeavor calls for a close interaction between experimentalists and theorists, which is at the heart of this research activity.