A muon can produce a bremsstrahlung shower in or near the wave length shifter ( WLS). Such a shower will not be localized to the cell it occurred in but also cause the photomultipliers of neighboring cells to record energy.
Figure 6.7 illustrates this for two neighboring modules. Since the cells are neighboring and since MUFFIN is largely based on condensates these cells (the EMC cells in figure 6.7) which have not been traversed by the muon are part of the candidate. When MUFFIN tries to perform the trajectory fit these cells will reduce the hit ratio of the candidate and thus reduce the efficiency of the finder for such events.
One possibility to deal with this problem would be to perform a cut on the imbalance in a cell. This however would compromise the muon finder efficiency for muons which only traverse a few cells.
Instead MUFFIN uses CONDENSOR to find all cells which could have energy just because there was a shower that leaked into their WLS:
CONDENSOR first tries to identify the cell that contains the center of the shower. Such a cell has to have imbalance bigger than and more than energy. The imbalance of the cell points to the side where the shower occurred. Due to the geometric structure of the UCAL only cells in front of the cell that contained the shower can be potential candidates for cells with energy due to a shower. Also cells in neighboring towers can be candidates, so MUFFIN scans the next towers.
For this WLS shower topology CONDENSOR requires at least one cell on the other side of the WLS-gap to have a large imbalance of . Only then will it use a lower imbalance cut of to find the other cells. Moreover CONDENSOR requires that for all candidate cells the channel that is not on the WLS-side recorded energy below the noise cut value. This value is the per-cell noise cut value (see section 6.3.1) divided by .