New experimental tools for exploring in-medium parton propagation in QCD
Proceedings of Sixth International Conference on Quarks and Nuclear Physics — PoS(QNP2012)
Atomic nuclei can be employed as spatial analyzers of the propagation of partons in-medium and of the hadronization process. The study of semi-inclusive deep inelastic scattering on nuclei using fully-identified final state hadrons began with the HERMES program in the late 1990s, and is now continuing at Jefferson Lab. In the Jefferson Lab measurements, electrons and positive pions were measured from a 5 GeV electron beam incident on targets of liquid deuterium, carbon, iron, and lead using
... and lead using CLAS in Hall B. The broadening of the transverse momentum of positive pions has been studied in detail as a function of multiple kinematic variables, and interpreted in terms of the transport of the struck quark through the nuclear systems. New insights are being obtained from these data concerning the roles of current and target fragmentation, characteristic time scales of the processes, and quantum interferences, in the interpretation of what is observed. Another new probe of parton propagation through nuclear systems is provided by the protonlead collisions planned for the LHC later this year. The initial tests and plans for proton-lead collisions at the LHC will be described, and the physics that could be obtained from an extended p-Pb run will be discussed; topics include gluon shadowing, nuclear parton distribution functions, and estimates of the saturation scale in cold nuclear matter. These studies of the parton propagation and hadronization processes expose important connections between the DIS data, deuterium-gold collisions at RHIC, proton-nucleus interactions in Fermilab experiment E-906 at 120 GeV, and proton-nucleus collisions at the LHC with multi-TeV beams. They are providing new tools for understanding the fundamental QCD processes at play. In addition, they may help to constrain the interpretation of the jet quenching seen in heavy ion collisions at the LHC and at RHIC. The DIS measurements will be extended in the next few years with the approved JLab experiment E12-06-117, and later will be pursued at the future Electron-Ion Collider.