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From 1D Fragmentation towards 3D Correlated Fragmentation
Our understanding of the fragmentation functions, or of the process how massive and colorless hadrons emerge from near-massless and color-charged quarks and gluons, suffers from the same shortcomings as the one-dimensional (1D) parton (spin and momentum) distributions in the description of nucleon structure. The partons exhibit three-dimensional (3D) confined motion inside nucleons, reflecting the 3D structure of the nucleon. Hadrons can emerge from a vehement electronquark scattering process only by the struck quark binding with another. At minimum, one additional antiquark is required, to be picked up either from the QCD vacuum or the remnant beam (target) fragments. The final hadron can accumulate a momentum transverse to the beam direction by a convolution of the transverse momentum of the struck quark and the transverse momentum of the additional antiquark. This then turns the understanding of the emergence of hadrons from color charge into a correlated 3D problem. This workshop goal is to consider and develop a necessary extension of the usual 1D fragmentation approach. Even if this is a significant hurdle to take, this is the time to start considering more seriously unintegrated fragmentation or fracture functions, including potentially defining a more intuitive class of functions for the latter to express the correlated nature of the fragmentation process.
|Alessandro Bacchetta||INFN Pavia and Pavia University|
|Vincenzo Barone||Piemonte Orientale Univeristy - Alessandria|
|Rolf Ent||Jefferson Lab|
|Ted C. Rogers||Jefferson Lab and Old Dominion University|