Measurement by penetrating muon
Cosmic ray muons which penetrate through the detector are also used to check the water transparency. When a penetrating muon traverses the detector, the charge observed in each PMT has approximately the following relation;
|
(1) |
,where, Li is the distance from muon track to i-th PMT along a ray at 42
from the muon track, 
is the opening angle between the direction of the photon on the
surface of i-th PMT and the relative direction that this PMT is facing, 
is
the PMT acceptance function, A is a constant parameter, and 
indicates
the water transparency. Fig 1 shows the relation between 
and 
.
This slope in the figure indicates 1/, and the water transparency is calculated to 5615cm.
Fig 2 shows the water transparency as a function of time calculated by this method,
and the time variation is consistent with the method using stopping muon event.
|
|
Figure 1: |
The relation between and . The calculated water
transparency is 5615cm. |
|
Figure 2: The water transparency as a function of time. The through going muon events are used for this calculation. |
