the number of photoelectrons measured in the downstream PMT at 2 GeV for WbLS was substantially less than the number of photoelectrons measured in water at the same energy, which suggests that some proportion of the detectable Cherenkov light is absorbed or scattered by the WbLS. Due to the black detector walls, the upstream detector is largely insensitive to the direct Cherenkov light (as shown in figure \[fig:DetAResults\](b)), and therefore this signal can be used to estimate the number of photoelectrons that are measured due to the isotropic light emission processes – scintillation and WLS. The absorption probability of the detectable Cherenkov light in the WbLS is given to first order by: $$P_{abs} =   1-\frac{N_{down}(WbLS, 2~GeV)-N_{up}(WbLS, 2~GeV)}{N_{down}(Water, 2~GeV)}$$ where $N_{down}$ and $N_{up}$ are the mean numbers of photoelectrons in the downstream and upstream photomultipliers for a given measurement, respectively. Our measurements indicate that $P_{abs} \approx 58\%$; that is, 58% of Cherenkov photons that were measured in the water sample were instead absorbed in the WbLS sample measurement.

The large proportion of Cherenkov photons absorbed or scattered by the ${\mathcal O}(10 {\rm cm})$ path length in WbLS suggests that the optical attenuation length of the WbLS used in this measurement is 