Title: Muon Reconstruction in the Daya Bay Water Pools,
Abstract: Muon reconstruction in the Daya Bay water pools would serve to verify the
simulated muon fluxes and offer the possibility of studying cosmic muons in
general. This reconstruction is, however, complicated by many optical obstacles
and the small coverage of photomultiplier tubes (PMTs) as compared to other
large water Cherenkov detectors. The PMTs' timing information is useful only in
the case of direct, unreflected Cherenkov light. This requires PMTs to be added
and removed as an hypothesized muon trajectory is iteratively improved, to
account for the changing effects of obstacles and direction of light.
Therefore, muon reconstruction in the Daya Bay water pools does not lend itself
to a general fitting procedure employing smoothly varying functions with
continuous derivatives. Here, an algorithm is described which overcomes these
complications. It employs the method of Least Mean Squares to determine an
hypothesized trajectory from the PMTs' charge-weighted positions. This
initially hypothesized trajectory is then iteratively refined using the PMTs'
timing information. Reconstructions with simulated data reproduce the simulated
trajectory to within about 5 degrees in direction and about 45 cm in position
at the pool surface, with a bias that tends to pull tracks away from the
vertical by about 3 degrees.