Cambining the experimental data on the inclusive decays $D\to X e\nu$, $B\to X e\nu$, and $B\to X \tau \nu$, we find severe constraints on the $\overline{\Lambda }$ and ${\lambda }_1$ parameters of the heavy quark effective theory. In particular, we get $\overline{\Lambda }<0.7\mathrm{}$ GeV. Our constraints further imply $m_c\ge 1.43$ GeV and $m_b\ge 4.66$ GeV. We discuss future prospects of improving these bounds and their phenomenological implications.

• Received 19 January 1994

DOI:https://doi.org/10.1103/PhysRevD.49.R4331