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MUON Trigger

How to reprocess trigger decision from already produced digits

The MUONTrigger.C macro can be used to check the trigger algorithm w/o having to (re-)perform simulation and digitalization. It loads the digits, erase TreeR and store the current trigger output in TreeR.

The different trigger outputs can be compared by looking at the GLT branch of TreeD (filled during simulation) and the TC branch of TreeR (filled from a copy of TreeD during reconstruction or with this macro). Note: rec points from tracking chamber will be lost.


root [0] .L $ALICE_ROOT/MUON/MUONTrigger.C+
root [1] MUONTrigger("galice.root")

OFFLINE trigger Graphical User Interface (GUI) data quality and debugging tool

  • read digits and local trigger decision from simulated/real data
  • display the strips in local boards
  • reprocess trigger decision inside AliRoot
  • set x/y strips interactively on boards and transfer them to the AliRoot TriggerElectronics, execute trigger algorithm and recover the local trigger decision

Usage (aliroot):

root [0] new AliMUONTriggerGUI

Main window shows the map of the local boards as seen from the I.P. The main window is position sensitive: by focusing a board, the "tip text" shows the board name, the crate name, the board ID and the board internal number in the GUI.



  • "Run input" - open a file and start with a given event number:
    • "your_path/galice.root" to use simulated (or re-created) aliroot digits
    • confirm with "Apply (galice)"
    • "your_path/rawfilename.root" to use raw data in root format
    • confirm with "Apply (raw)"
  • "Control" - navigate in the tree with events
  • "Exit" - exit the main application


  • "Digits map" - graphical map showing digits in the four chambers, MT11 ... MT22
  • "Reset digits" - clean the digits map

Chambers digit maps

  • "Update" - update the map after:
    • loading of another event
    • changing interactively the strip signals in boards GUI


  • "Open" - open a board GUI by circuit (board) number

TriggerDSET, run the trigger algorithm with interactively set strips

  • this is an interface to AliMUONTriggerElectronics
  • "Digit store" - create a digit store (object) with the current board digits (input from the circuit GUI)
  • "Trigger store" - create a trigger store (object) from the digit store, using AliMUONTriggerElectronics; each type of store can be "cleared" and "printed"
  • "Front End Test" - simulate a FET (all strips fire) on all boards or on a regional board
  • "Write raw data" - save the trigger store in a raw data file (DATE and ROOT) format

Circuit GUI ("Circuit/Open" or click on boards map)

  • the window title shows the name of the board, the number and the status
  • "Draw" visualize x/y strips
  • "Set/unset" x (or) y strips, on mouse click
  • "Digits" create board digits from the actual configuration created in the GUI
  • "Reset" reset modification on strips done interactively

The sequence to test the trigger algorithm is:

  • open a board GUI
  • set some x/y strips
  • press "Digits" to create board digits
  • from the TrigerDSET menu create a digit store, then a trigger store and print it to see the trigger decision
  • write raw data for further investigation

How to check integrated trigger efficiency

The MUONTriggerEfficiency.C macro (included in the check scripts) calculates the trigger efficiency for the 2 pt cuts. The output is stored in MUONTriggerEfficiency.out file.


root [0] .L $ALICE_ROOT/MUON/MUONTriggerEfficiency.C+
root [1] MUONTriggerEfficiency()

Two LUTs are stored in the CDB (/Calib/TriggerLut/):

  • Run0_999999999_v0_s0.root with Lpt 1.0 GeV and Hpt 1.7 GeV
  • Run0_999999999_v1_s0.root with Lpt 0.0 GeV and Hpt 1.0 GeV (default)

and can be built with the AliMUONCDB class taking as source the root files (found in $ALICE_ROOT/MUON/data/):

  • lutAptLpt1Hpt1p7.root
  • lutAptAptLpt1.root


The reference for J/psi and Upsilon is as below For 1000 Jpsi events with:

    AliGenParam *gener = new AliGenParam(1, AliGenMUONlib::kJpsi);
    gener->SetPhiRange(0., 360.);

the output should be

  Efficiency Lpt cut = 0.9061 +/- 0.0456
  Efficiency Hpt cut = 0.6943 +/- 0.0376

Similarly, for 1000 Upsilon events (replace kJpsi by kUpsilon), the output should be

  Efficiency Lpt cut = 0.9872 +/- 0.0458
  Efficiency Hpt cut = 0.9851 +/- 0.0457

How to check single muon trigger efficiency versus pt

The MUONTriggerEfficiencyPt.C macro produces trigger single muon efficiency versus pt plots for the 2 pt cuts. Results are compared to the reference (red curves). To be used with (at least) 10000 events as follows

   AliGenBox * gener = new AliGenBox(1);
   gener->SetPhiRange(0., 360.);         
   gener->SetPart(13);           // or -13
   gener->SetOrigin(0.,0., 0.);  
   gener->SetSigma(0.0, 0.0, 0.0);     

Outputs are stored in MUONTriggerEfficiencyPt.gif/eps/out files Important note: this macro works with one (real) muon track per event only


root [0] .L $ALICE_ROOT/MUON/MUONTriggerEfficiencyPt.C+
root [1] MUONTriggerEfficiencyPt()

How to get trigger chamber efficiency from data

Trigger chamber efficiency map is calculated from AliESDs.root with the analysis task: PWG3/muon/AliMUONTriggerChamberEff. The output of the task is a file filename="MUON.TriggerEfficiencyMap.root" containing the numerator and denominator histograms for the efficiency calculation. In order to view and save the map, use macro MUONTriggerChamberEfficiency.C

To compile MUONTriggerChamberEfficiency.C

.includepath $ALICE_ROOT/MUON
.L $ALICE_ROOT/MUON/MUONTriggerChamberEfficiency.C+

To run MUONTriggerChamberEfficiency.C


If you want to make the calculated map available for next simulation use option kTRUE, and specify the run validity:


The last option allows to set the efficiency of each board of an RPC with the mean value of the chamber: this is useful when the efficiency was calculated with low statistics (like in cosmic runs).


Finally, to have a look to the map stored in the OCDB for the run runNumber, do:

.includepath $ALICE_ROOT/MUON
.L $ALICE_ROOT/MUON/MUONTriggerChamberEfficiency.C+

When running next simulation, please remember to activate trigger efficiency by adding in Config.C:


This chapter is defined in the READMEtrigger.txt file.