Building events

Event building is the process of combining the information from various subsystems. This also includes splitting simulated files into subsections corresponding to different runs or periods in data taking.

Time-coincidence map (TCM)

The basis of event building is the time-coincidence map or (TCM).

The TCM tells us which hits in the various subsystems happened close enough in time to be considered part of the same “event”.

The TCM is a lgdo.Table with two fields, both of which are lgdo.VectorOfVectors:

• row_in_table: which row of the file contains this hit

• table_key: which channel was the hit in.

The mapping from table keys to detector names is contained in the “tables” attribute of the TCM. This can be converted to a python dictionary with the function reboost.utils.get_table_names().

Since version 0.12.0 remage can compute the TCM directly and store it in the output file. However, in case a custom TCM is desired or an older version of reboost is used this can be computed with pygama.evt.build_tcm().

Warning

In case a non-trivial table mapping is used in reboost.build_hit.build_hit() the TCM to describe the hit files may be different.

Gathering data from other fields

The first step of event building is to gather data from the various tiers. This can be done with reboost.core.read_data_at_channel_as_ak(). This will return the data as a awkward.Array with the same shape as the TCM.

From this more manipulation can be applied using awkward manipulations, or custom written processors.

Filtering channels

One useful functionality is to select groups of channels. To do this the function reboost.shape.group.get_isin_group() can be used. This will return an awkward array with the same shape as the channels input of booleans indicating if a given channel was part of the group>

Full event tier post-processing

An example of a full post-processing of the event tier can be found in reboost.build_evt.build_evt().