Jet Finder with Association Maker

The Backstory

In May 2013, I started putting together the initial tiny embedding request for the 2011 Collins analysis. I wanted to do a reco-thrown association study, matching both jets and pions within the jets. My initial thought was to use the association maker, as had been done for the FTPC efficiency embedding produced for my dissertation. Pibero noted that the jet trees were not set up to use the association maker, as it had never been needed. Out of the goodness of his heart, he edited the standard jet code to utilize the association maker, to match reconstructed tracks with generated tracks. Ultimately we decided to go with a simple geometric association for the 2011 Collins analysis. However, the tool Pibero developed may prove useful for hadron-within-jet efficiency calculations, e.g. needed for fragmentation function measurements.

The Association Maker

In brief, the association maker matches reconstructed hits with simulated hits at the TPC padrow level. It then associates a reconstructed track with the simulated track on the basis of the matched hits, in contrast to a simple geometric matching of reconstructed and generated tracks. By default the hits must reconstruct within a 5 mm × 5 mm × 5mm box of each other in order to count as a matched hit. Additionally, three associated hits are required for a track to be considered matched. Documentation on the association maker may be found here

Updates to Jet Code

Pibero updated the Monte Carlo jet finding code to utilize the association maker for generated tracks. For each MC track in the jet tree, there is a new function recoTrackId() that returns the reconstructed track ID of the most closely associated reconstructed track to the MC track, according to the association maker. In the analysis, one may loop over the MC tracks in the particle jets and look up the corresponding reconstructed tracks in the detector jets using the reconstructed track ID.

Because the μDST do not store track hits, one must have the event.root files available for the association maker to work. These files are generally large and not kept on disc during the embedding production. This represents a major but necessary change to how one handles the embedding productions.

First Try

As a first try, I requested some of the event.root files be restored from Kevin's 2012 200 GeV embedding on PDSF. I compiled the edited jet finding code using SL18b. The code appeared to run successfully for the 90 events contained within the file. The following histograms demonstrate the resulting geometric associations (and shift in pT) for the matched tracks according to the association maker.

Figure 1: Reco vs. Thrown for η, φ, and pT

Figure 2: Reco - Thrown for η, φ, and pT