Breakup of11Be: Prompt or Delayed?

The disintegration of a secondary beam of ${}^{11}\mathrm{Be}$ has been studied in the Coulomb plus nuclear field of Au and Be targets. The vector momentum (longitudinal and transverse components) was measured with a magnetic spectrograph with sufficient precision to detect previously reported differences in the velocity of the ${}^{10}\mathrm{Be}$ fragments and the incident beam. Coincident $\gamma$ rays, detected by an array of ${\mathrm{BaF}}_2$ scintillators surrounding the target, were used to identify events in which the target was simultaneously excited. No evidence for the previously suggested velocity difference was observed.