Narrow Results

During the last three years strong experimental evidence from B and charm factories has been accumulating for the existence of exotic hadronic quarkonia, narrow resonances which cannot be made from a quark and an antiquark. Their masses and decay modes show that they contain a heavy quark-antiquark pair, but their quantum numbers are such that they must also contain a light quark-antiquark pair. The main theoretical challenge has been to determine the nature of these resonances. The main possibilities are that they are either "genuine tetraquarks", i.e. two quarks and two antiquarks within one confinement volume, or "hadronic molecules" of two heavy-light mesons. In the last few months there is more and more evidence in favor of the latter. I discuss the experimental data and its interpretation and provide fairly precise predictions for masses and quantum numbers of the additional exotic states which are naturally expected in the molecular picture but have yet to be observed. I also provide arguments in favor of the existence of an even more exotic state – a hypothetical deuteron-like bound state of two heavy baryons.

The high gluon density in the initial state of hadronic collisions at LHC energies implies that the probability of multiple parton interactions within one proton-proton collision increases. In particular, this motivates one to investigate the importance of Double Parton Scattering (DPS) processes at the LHC. In a DPS process one can have, from one proton-proton collision, two interacting partons coming from each colliding hadron. In this context, the relation between the double parton distribution functions (dPDF) and the usual parton distribution functions (PDF) is discussed, and some formulae for the DPS cross section are compared. Our results focus on the production of different final states related to two heavy quark-antiquark pairs. Those include $c\bar{c}c\bar{c}$, which is called the golden channel of DPS, $b\bar{b}b\bar{b}$ and $c\bar{c}b\bar{b}$.

Some of the currently most popular conjectures for the structure of the recently discovered heavy mesons that do not find a place in the quark model quarkonium spectrum are sketched. Furthermore, some observables are identified that should allow one to identify the most prominent components of individual states.