Files, reconstructed with nemor have H10 tree of events inside (see later about the H10 itself). They are quite big and need to be preselected before the final usage.
The idea of preselecting is to select a fairly small amount of data (
few hundreds megabytes, less than 2G anyway) for every MC component (component means a background from specific radioactive isotope in the specific locations, i.e. B214 from PMT glass, Tl208 from PMT glass, Bi214 from the surface of wires etc.). Usually one applies quite broad cuts to pre select the events. A reasonable compromise has to be achieved here. First, using too loose cuts will lead to the too big files, and slower analysis performance in the end. Second, too tight cut will restrict the flexibility of the analysis later. E.g. if there might be a need to investigate events with multiple gamma deposits, and one selects only events with one track and two PM hits a new preselecting would need to be run for that.
In short, preselecting cuts have to be planned and thought through carefully.
Final step is the analysis itself, which loops over the data and all MC components, fills histograms, performs fits and plots result in the form of nice colourful plots to trigger WOW effect in the audience.