Paint $($a Bingham fluid$)$ is applied with a spray gun by forcing it under high pressure through a small orifice. The average diameter of the droplets $($d$)$ produced is known to be a function of

${}_0$: yield stress

$$ : Bingham liquid viscosity

$$ : liquid density

$P$ : pressure at the spray gun

$$: surface tension

$Q$ : volumetric flow rate

D : orifice diameter

Use dimensional analysis to find a dimensionless expression for $d.$