  We use confocal microscopy to study a random close packed sample of colloidal
particles. We introduce an algorithm to estimate the size of each particle.
Taking into account their sizes, we compute the compressibility of the sample
as a function of wave vector $q$, and find that this compressibility vanishes
linearly as $q \rightarrow 0$. The particle sizes must be considered to
calculate the compressibility properly. These results also suggest that the
experimental packing is hyperuniform.

Soft Condensed Matter