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Using the LCSim Event Browser

The event data in LCIO files can be viewed using JAS3 with the LCSim Plugin. This tutorial will show you how to open an LCIO data file and browse through it using this tool.

Loading an LCIO Data File

Download this qqbar sample in the sid02 detector to your harddisk. This data file will be used throughout the example.

Open JAS3 by clicking on Start -> Programs -> JAS3 -> JAS3.

Browse to the data file by clicking on File -> Open, navigating to the directory where the file was saved, selecting the file, and pressing Enter.

If you are asked which plugin to chose for opening the file, choose org.lcsim. This query may or may not appear on your system. (It only shows up if you have multiple plugins installed that can open the file.)

JAS has changed a bit now that the LCIO file is loaded.

  • The name of the file is shown in the select box.
  • The JAS tree shows at the lefthand side of the screen with a folder called Datasets. The file is listed as a member of this folder.
  • The record toolbar shows on the toolbar. This is used to step through records one-by-one or process all of the records in a file.
  • The listing under File -> Recent Files shows the name of this file, for easy access in a later session.

This is the basic view for LCIO files.

Viewing Collection Data with LCSim Event Viewer

The LCSim Event Viewer shows event data from the collections in the LCIO file. (Collections are sets of objects with the same type, such as CalorimeterHits, TrackerHits or MCParticles.)

To open the browser, select File -> New -> LCSim Event Browser.

Only an empty tab reading "LCSim Event" shows, because the plugin requires some data to read.

To feed the LCSim plugin a record, press the Go 1 button. This button has a vertical bar plus a right arrow.

Now, the viewer should be filled with event information.

This is the event view. (Notice that Event is select in the lefthand menu.)

The LCIO Event Header section shows the information from the LCIO event header, including run and event numbers, the time stamp, and the name of the simulated detector.

The Blocks (basically meaning "Collections") area shows the data collections within this event. For simulated event files, these collections will usually consist of the Monte Carlo Particles (MCParticles) from the physics event, hits in the calorimeter systems (CalorimeterHit), and the hits from the trackers (TrackerHit).


The LCSim Event Viewer can also show reconstruction objects, such as clusters and tracks, but this tutorial will focus on the simulation classes mentioned previously, e.g. hits and tracks.

View a collection's data by clicking on its corresponding icon in the tree on the lefthand side of the LCSim Event Viewer.

Monte Carlo Particles

Open the MCParticleTree by clicking on it in the lefthand, event tree menu.

This shows the tree-like hierarchy of Monte Carlo Particles (MCParticles) in the event. A particles "children" can be viewed by expanding it using the "+" button.

More detailed information on MCParticles is available from the MCParticles collection, which has one record for every particle in the event.

From this table, you can see the type, energy, momentum, start and ending points, etc. of each particle.

Calorimeter Hit Collections

Select EcalBarrHits from the event menu.

This view shows one record for each hit in the "EcalBarrHits" collection. These hits are objects of type SimCalorimeterHit. All of the Calorimeter hit collections (including both endcaps and barrels) are decoded in an identical fashion, so the Hcal and Muon collections will look quite similar.

Not all of the fields may make sense to you, but ones to notice for Calorimeter hits include layer, which is the logical subdetector layer of the hit, energy (e.g. the raw, uncompensated energy deposition) and position (X, Y, Z).

Tracker Hit Collections

Now click on TkrBarrHits in the event tree menu.

Similar to the calorimeter view, this shows a record for each tracker in the collection.

The key values of interest are probably layer, position (x, y, z), dedx (e.g. raw energy deposition), and time.