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The Level 3 Event Display


Rainer Bartoldus, SLAC

Event Display

[Setting things up] [Running from a trickle stream] [Running from an xtc file] [What you see] [More options]

Setting things up

The Level 3 Event Display can basically be run in two modes; it can be run live from a trickle stream or in playback mode from an xtc file.

Running it from a trickle stream usually means to connect the display to a Level 3 farm node in IR2 and to display events as they are being taken. Running it in playback mode means to display events that have previously been recorded, or skimmed, into an xtc file. (About skimming events from and to xtc files, see the instructions on runL3TSkimApp .)

In both cases, the display application is run via a wrapper script called runL3TDisplay. This script is part of any recent BaBar release. There is no need to create a test release, or run out of a workdir etc. The display can be run from anywhere. All that is needed is access to an installed release, to the configuration/conditions database and, of course, to the event data, either on disk via the network.

To set up the path to a release do, as usual:

$ srtpath
You can specify a particular release, if you know of a reason to, but generally the default should be fine.

To be able to process event data, the application needs access to the configuration/conditions database. Simply set up the appropriate boot file for this. Typically you would do:

$ ambientboot

That is all. Depending on the options you specify the script will start the appropriate framework executable with the necessary command line arguments.

Running live from a trickle stream

Note that in this mode you are interfering with the BaBar data acquisition. It is understood that you request permission from IR2 and give appropriate notice.

To run the Level 3 display live from a trickle stream use the command:

runL3TDisplay [ -h <hostname> ] [ -p <port number> ]

The first optional argument is the host name to connect to. This should be one one of the farm nodes running the live Level 3. The second argument is the port number to use. This defines the event selection you are going to see.

For example:

 $ runL3TDisplay -h bfo-farm100 -p 10080
The hostname and port number default to the ones above.

There are typically three trickle streams served by each farm node,

  • port 10080 is connected to the L3 input (serving L1 accepts)
  • port 10081 is connected to the L3 output (serving L3 logged events)
  • port 10082 is connected to the beam spot monitor (serving two prong events)

Running playback from an xtc file

To display events from an xtc file, you use the command:
runL3TDisplay -f <xtc file>
For example:
$ runL3TDisplay -f /nfs/babar/tcfiles/babar-0020029-001.xtc
This particular path corresponds to the HPSS staging area. You can stage any xtc file via the command tcstage.

Alternatively, you can pick the latest xtc file that was written to disk by giving an empty file argument:

$ runL3TDisplay -f ""

What you see

At this point you should have a display window on your screen.

The window shows an r-phi view of the Drift Chamber surrounded by the Calorimeter. The drift chamber volume is divided in 120x10 cells as used for the track finding. The calorimeter shows the 120 crystals of the barrel.

The drift chamber hits are drawn as blue circles with their radius corresponding to the drift distance. Red crosses indicate associated hits from the TSF segments. Red squares are TSF hits not associated with DCH hits. Level 3 tracks are drawn in red.

The calorimeter shows EMC digis as solid red bars and EMT towers as hatched red bars. The height of the bars is proportional to the deposited energy, where the depth of one crystal corresponds to a scale of 2 GeV. Level 3 clusters are indicated by blue triangles pointing to the calorimeter surface, with their position corresonding to the cluster centroid.

The display window shows the L1 trigger lines on the left, with the ones that fired on the particular event in red (prefixed by a "1"), the ones that fired the GLT but were prescaled in the FCT in green ("-1"), and the ones that did not fire in black ("0"). On the right, it shows the status of the L3 output lines with a similar code: in red the ones that contributed to the logging decision ("on"), in green the ones that fired but were prescaled in OEP ("pre"), and in black the ones that did not fire ("off").

The window also shows the event time stamp, the Level 3 event t0, and the number of tracks and clusters.

There is a bar with controls. These should be pretty self-explanatory.

More options

If you run the display script with a -?, it prints a usage message. Currently this says:
$ runL3TDisplay -?

usage: runL3TDisplay [options]

  -f <xtc file>   use xtc file to playback,
                  with "" as filename argument, the latest file is taken from
  -h <host>       specify host for running from trickle stream,
                  default: bfo-farm100
  -p <port>       specify port number for trickle stream,
                  default: 10080
  -t <tcl file>   use specified tcl configuration,
                  default: L3Trigger/L3TDisplayApp.tcl
  -g              start in continuous mode (as if the "Go" button was hit)
  -?              this help
The additional options make it possible to supply your own tcl file, or start the display in continuous mode.
Page author: Rainer Bartoldus
Last update: 08-Mar-2005 Expiry date: 31-Dec-2006

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