Open heavy flavours

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. 

Chapter 19 and is in agreement with the non-existence of charm-changing neutrcd currents (as expected from the GIM mechanism, see Chapter 9). The decays, therefore, are due to the charged weak current. Nonetheless mixing is not negligible, as we will see, and this has important consequences for CP violation (see Chapter 19). 

In terms of quark diagrams (Fig. 13.1), a charm particle will decay into ordinary hadrons, according to the standard model, via the dominant quark transitions (see Section 9.2) 

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