Dipenguin-like contributions to D0 - anti-D0 mixing

Abstract

We show that because of the milder GIM suppression, the four-quark dipenguin operator contributes to the short distance piece of the D^0-\bar D^0 mixing amplitude at the same order of magnitude as the box diagram. In addition, we put an upper bound \Delta m_D^{LDR} \leq 5 \times \Delta m_D^{box} on a long-distance resonant contribution induced by the penguin mixing.Comment: 4 pages, 1 figure; to appear in the proceedings of HADRON'97, BNL, August 1997; preprint number is adde