Introduction to heavy quarks (charm and beauty)

Perturbative QCD is expected to provide reliable predictions for the production of bottom and (to a lesser extent) charm quarks since their masses are large enough to assure the applicability of perturbative calculations. A direct comparison of perturbative QCD predictions to heavy-flavour production data is not straightforward. Difficulties arise from the presence of scales very different from the quark masses that reduce the predictivity of fixed-order theory, from the non-perturbative ingredients needed to parametrize the fragmentation of the heavy quarks into the observed heavy hadrons, and from the limited phase space accessible to present detectors. Moreover, a breakdown of the standard collinear factorization approach can be expected at low-x. The study of heavy-quark production in hadronic interactions and in e–p collisions at HERA has been therefore an active field in the effort to overcome these difficulties and to get a deeper understanding of hard interactions. Besides its intrinsic interest, a precise understanding of heavy-quark production is important at the LHC because charm and beauty from QCD processes are relevant backgrounds to other interesting processes from the Standard Model (e.g., Higgs to bb) or beyond. Theoretical and experimental techniques developed at HERA in the heavy-quark field, such as heavy-quark parton densities or b-tagging, are also of great value for future measurements at the LHC. The present status of heavy-quark production theory is critically reviewed in the first contribution. The second contribution summarizes the present heavy-flavour data from HERA and gives an outlook of what can be expected from HERA-II. The potential of the LHC experiments for charm and beauty physics is reviewed in the third contribution. Then the relevance of saturation and low-x effects to heavyquark production at HERA and at the LHC are discussed. The non-perturbative aspects of heavy-quark fragmentation and their relevance to HERA and LHC are discussed in the next contribution. Finally, a comparison of different theoretical predictions for HERA and the LHC based on different approaches is presented.