  The production of a heavy quark is accompanied by gluon bremsstrahlung which
is suppressed at small angles $\Theta\lesssim M_Q/E$ for mass $M_Q$ and high
energy $E$ according to perturbative Quantum Chromo Dynamics (QCD) (``dead cone
effect''). As particles at small angles typically have large momenta, the heavy
quark mass also causes a suppression of high momentum particles. In this paper,
we studied this effect in c- and b-quark events using data from Z boson decays
in $e^+e^-$ annihilation. The heavy quark fragmentation function for charged
particles is reconstructed in the momentum fraction variable $x$ or
$\xi=\ln(1/x)$ by removing the decays of the heavy quark hadrons. Indeed, we
find an increasing suppression of particles with rising $x$ down to a fraction
of $\lesssim 1/10$ for particles with $x\gtrsim0.2$ in b-quark and
$x\gtrsim0.4$ in c-quark jets in comparison to light quark fragmentation. The
sensitivity to the dead cone effect in the present momentum analysis is
considerably increased in comparison to the recently presented angular
analysis. This amount of suppression and the differences between c- and b-quark
fragmentation are in good quantitative agreement with the expectations based on
perturbative QCD within the Modified Leading Logarithmic Approximation (MLLA)
in the central kinematic region. The data also support a two parameter
description in the MLLA of these phenomena (``Limiting Spectrum''). The
sensitivity of these measurements to the heavy quark mass is investigated.
