Heavy flavours

Red mandarin is characterised by its amine-like top note. The sweet, heavy flavour with its floral base does, in contrast to all other citrus oils, not possess a refreshing, but a more fatty character. 

S. Frixione, P. Nason, B.R. Webber, Matching NLO QCD and parton showers in heavy flavour production. JHEP 0308, 007 (2003)... 

While the non-relativistic potential remains the most successful and simplest approach for calculating and predicting energy levels mid decay rates, other, more sophisticated, methods have been devised including bag models, QCD sum rules (Shifman et al., 1978 Reinders et al., 1985) and lattice calculations (Rebbi, 1983 Creutz, 1983 Creutz et al., 1983). The properties of quarkonia test some aspects of both perturbative mid non-perturbative QCD the heavier the quarkonium system, the less important are both relativistic effects and higher order perturbative QCD corrections. For a more recent approach to the problem of heavy flavours, see Isgur and Wise (1989, 1990) and for a comprehensive review, Neubert (1992). 

The subject of heavy flavours has e3q>anded tremendously in recent years stretching from the static properties (mainly spectroscopy, i.e. energy levels, lifetimes, branching ratios, decays, mixing etc.) of hadrons with one or more heavy quarks, e.g. bottom or charm, to more dynamical properties (like fragmentation, structure functions, jets etc.) and on to more exotic topics, e.g. production and decay of as yet undiscovered flavours like top, or speculations on a fourth generation or imphcations on Higgs or on non-standard effects and so on. 

Some of these topics are covered in other chapters (for energy levels, see Chapters 11 and 12 for Kobayashi-Maskawa matrix elements and CP violation, see Chapters 18 and 19 for structure functions, see Chapters 16 and 17). Here we discuss the discovery of particles with heavy flavours, their hfetimes, decays, mixing and other properties. For more detailed discussions, we refer to the specialized literature (see e.g. Ellis and Kernan, 1990, Kiihn et cd., 1989 and references therein). 

We note that if the electromagnetic and strong interactions conserve flavour, then we should expect associated production of heavy flavours, i.e. that production always occurs with pairs of particles of opposite charm or bottom (this is, of course, not the case for production in neutrino interactions via weak forces). Further, the decay of a heavy particle should be generated by the weak interactions, implying very narrow widths and effects of parity non conservation. 

As compared with the case of hidden charm, discussed in the previous chapters, the spectroscopy of heavy flavoured particles, especially charm... 

Some calculations use very general arguments to derive bounds for as yet undiscovered heavy flavoured particles. For example, Anselmino et al., (1990a) isolate the effects of colour-hyperflne terms and use experimental information to make predictions about the masses of baryons containing at least one heavy quark. Typical results are the predictions 64 < ft — ftc < 107 MeV/c, and 23 < ftj — ftj, < 39 MeV/c. These imply that ft and ftj cannot decay strongly. By the same technique one finds also 23 < EJ — Efc < 39 MeV/c so EJ cannot decay strongly into Ej, but both decay strongly into Aj,. 

If we assume charm to be a good quantum number under strong and electromagnetic interaction (see Section 13.3), the pseudo-scalar chmm mesons D, D and Df can only decay weakly into old mesons. By contrast, D s can decay both strongly and electromagnetically whereas only the latter mode is available to T> due to its mass threshold, as can be seen from Table 13.1. The naive expectation that heavy flavoured hadron decays are entirely determined by the so-called spectator diagram (Fig. 13.13) leads to immediate predictions for the lifetimes of these... 

The production of heavy flavours is a classical process in QCD and is linked with jet physics (Chapters 24, 25). Here, we limit ourselves to a few qualitative considerations. 

Fig. 13.19. Cross-section for bottom production (from Ellis and Keman, 1990). 13.5 Heavy flavours at LEP...

A new chapter on heavy flavour physics has been initiated at LEP in its studies of decays. The main motivation for heavy flavour searches, i.e. the quest for top (and Higgs), has been frustrating so far and we have repeatedly commented about the top mass limits set by LEP [eqn (8.6.20)] ... 

If the above estimate is correct, the direct detection of top in e e colliders is not just around the corner. Nonetheless LEP 1 has already given much information on heavy flavours (for a detailed review, see Tenchini, 1990). 

Heavy flavour physics has really just begun. We expect it to become one of the major subjects of the next few years with an impact on all aspects of the standard model on QCD and on CP violation. 

A large part of the present experimental activity concerns baryons with heavy flavours, Qqq or Qqs or Qss, where q means u or d. These states, with their helium-like structure, are much more asymmetric the two light quarks are rotating rather fast around a flavoured quark which remains almost static. In the near future, double-charm baryons QQq should provide interesting information on quark dynamics with the superposition, within the same hadron, of the slow motion of two heavy quarks experiencing the short-range QCD potential, and of the fast motion of a light quark around them [7,8]. 

A. Martin, in Heavy Flavours and High Energy Collisions in the 1-lOOTeV Range, Proc. Erice Workshop (1988), eds A. Ali and L. Cifarelli (Plenum, New York, 1989). 

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