Hadron multiplicities in semi-inclusive deep-inelastic scattering were measured on neon, krypton and xenon targets relative to deuterium at an electron-beam energy of 27.6 GeV at HERMES. These ratios were determined as a function of the virtual-photo
n energy nu, its virtuality Q2, the fractional hadron energy z and the transverse hadron momentum with respect to the virtual-photon direction p_t . Dependences were analysed separately for positively and negatively charged pions and kaons as well as protons and antiprotons in a two-dimensional representation. These results will help to constrain mechanisms and models of hadronization much more decisively than by the use of integrated results as traditionally done. A few features particular to the two-dimensional representation are highlighted in this contribution.
The standard model and Quantum Chromodynamics (QCD) have undergone rigorous tests at distances much shorter than the size of a nucleon. Up to now, the predicted phenomena are reproduced rather well. However, at distances comparable to the size of a n
ucleon, new experimental results keep appearing which cannot be described consistently by effective theories based on QCD. The physics of strange and charmed quarks holds the potential to connect the two energy domains, interpolating between the limiting scales of QCD. This is the regime which will be explored using the future Antiproton Annihilations at Darmstadt (PANDA) experiment at the Facility for Antiproton and Ion Research (FAIR). In this contribution some of the most relevant physics topics are detailed; and the reason why PANDA is the ideal detector to study them is given. Precision studies of hadron formation in the charmonium region will greatly advance our understanding of hadronic structure. It may reveal particles beyond the two and three-quark configuration, some of which are predicted to have exotic quantum numbers in that mass region. It will deepen the understanding of the charmonium spectrum, where unpredicted states have been found recently by the B-factories. To date the structure of the nucleon, in terms of parton distributions, has been mainly investigated using scattering experiments. Complementary information will be acquired measuring electro-magnetic final states at PANDA.
