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;



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.

watmu2.eps.gif (8691 ?o?C?g)

Figure 1:

The relation between and . The calculated water transparency is 5615cm.


muthr.eps.gif (9425 ?o?C?g)

Figure 2: The water transparency as a function of time. The through going muon events are used for this calculation.


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revised on 1999/09/27