Light-quark and heavy-quark fragmentation functions

The shape of the leading-fragment momentum distribution function in light- and heavy-quark fragmentation is discussed. The features of the u-quark and s-quark leading fragmentation functions extrapolated to higher quark masses lead to the conclusion that as the quark mass increases the average momentum carried by the heavy meson increases and the fragmentation function becomes narrower. This result fully supports Bjorken's proposal for heavy quark decay. Predictions are given for the shape of the c, b,...quark fragmentation functions. (Auth.)