Jets from quark fragmentation: treatment of flavour and new power counting rules at x → 1

Allowing for the possibility of many quark flavours in a crossing symmetric manner, the general problem of quark fragmentation into a jet of mesons via successive breakups (quark → meson + quark) is formulated and solved. Simple power counting rules for the behaviour of various fragmentation functions at x → 1 are derived and compared with experiment. Meson multiplicities are found to grow logarithmically with a slope independent of the jet-initiating quark, but dependent on the type of meson. (Auth.)