The MUON trigger in AliRoot

1
The MUON trigger in AliRoot

• Overview
• Geometry
• Segmentation
• Chamber response
• Decision
• Outputs
• How to run
• Future developments

2
Overview

• AliMUONChamberTrigger,
• AliMUONTriggerGeometryBuilder,
• AliMUONSegmentationTrigger,
• AliMUONSegmentationTriggerX,
• AliMUONSegmentationTriggerY,
• AliMUONResponseTrigger,
• AliMUONResponseTriggerV1,
• AliMUONTriggerConstants,
• AliMUONTriggerLut,
• AliMUONTriggerDecision,
• AliMUONTriggerCircuit,
• AliMUONLocalTrigger,
• AliMUONGlobalTrigger,
• AliMUONTriggerTrack,
• MUONTriggerLut.root,
• MUONTriggerLutPtCal.root,
• MUONtrigger.C,
• MUONTriggerLut.C
• MUONTestTrigger.C,

• 14 classes
• 2 root files
• 4 macros
• framework for geometry, segmentation,
  digitalization, clusterization reconstruction
  heritated from tracking

3
Geometry

• AliMUONTriggerGeometryBuilder

• very compact thanks to design
• all planes identical, scaling with zpos/zpos1
• 5 chamber types per plane
• makes use of the virtual envelopes (Eric, Gines,
  Ivana)

4
Segmentation

• AliMUONSegmentationTrigger
• AliMUONSegmentationTriggerX, AliMUONSegmentationTr
  iggerY

• loop over 2 63 modules
• assign X Y strips according to
  AliMUONTriggerConstants

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Segmentation (frames)
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Segmentation (strips)
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Chamber Response

• AliMUONChamberTrigger,
• AliMUONResponseTrigger, AliMUONResponseTriggerV1

• digits are flagged according to ToF
• a digit is taken into account into L0 decision if
  ToF lt 75 ns
• default chamber response AliMUONResponseTrigger
• a hit fires one and only one strip
• realistic response AliMUONResponseTriggerV1
• a hit can fire several strips according to a
  parameterization of the cluster-size measured in
  test-beam (ALICE INT/DIM/01-04). this response
  can be activated in AliMUONFactory

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Display hits, digits color code

• this digit will not be taken into account into
  L0 decision
• this hit fires 2 strips

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L0 Trigger Decision

• AliMUONTriggerDecision,
• AliMUONTriggerCircuit, AliMUONTriggerLut

• feed TriggerCircuits with digits (a
  TriggerCircuit is a standalone L0 trigger
  board)
• loop over TriggerCircuits
• get X Y answers of L0 trigger (see algorithm
  in L0-PRR ALICE EN/2003-010)
• get L0 local answer (Xstrip11, Ystrip11, dev,
  sign, pt)
• get global answer (number of single -, single ,
  single undefined, unlike-sign pairs, like-sign
  pairs, with All pt, Low pt, High pt)

• X Y algo. are copy paste from FPGA of L0
  trigger board
• ? powerful for debugging both software hardware
• pt is given from LUTs

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pt calculation

• AliMUONTriggerLut, MUONTriggerLut.root

• for each combination of (circuit, Xstrip11,
  Ystrip11, deviation) we need to know whether the
  corresponding pt is larger than 1 GeV/c (low pt
  cut) and larger than 2 GeV/c (high pt cut)
• this pt can be calculated via

fast procedure but does not take into account
field asymmetries energy losses
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Realistic pt estimation (currently in
AliRoot)B.Forestier PhD Thesis

• shoot 1 GeV/c and 2 GeV/c pt muons into the
  spectrometer
• get deviation corresponding to each triplets
  (circuit, Xstrip11, Ystrip11)
• store output in 4D histograms (MUONTriggerLut.roo
  t)

in AliRoot, AliMUONTriggerDecision reads
MUONTriggerLut.root via AliMUONTriggerLut
old LUT can be re-activated
(MUONTriggerLutPtCal.root) and re-generated
(MUONTriggerLut.C)
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How to run (local global trigger answer)

• MUONtrigger.C, AliMUONLocalTrigger,
  AliMUONGlobalTrigger

• from ALICE_ROOT/MUON/README
• IMPORTANT!!!
• create write digits
• create write raw clusters
• create write trigger response

at this step local global trigger answers are
written in TreeR of MUON.RecPoints.root
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Getting more information online
from fDebug of AliMUONTriggerDecision
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How to retrieve local global trigger answers
1 from a TBrowser
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How to retrieve local global trigger answers
2 from MUONdisplay
Trigger button reads global trigger information
from MUON.RecPoints.root and prints it in the
terminal
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How to retrieve local global trigger answers
3 from MUONCheck.C
loop over events, reads global local trigger
information from MUON.RecPoints.root and prints
it in the terminal
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Making tracks with trigger info (1)
MUONTriggerTracker.C, AliMUONTriggerTrack,
AliMUONEventReconstructor

• loop over local triggers
• build human readable info.
• fill TreeT of MUON.Tracks.root

AliMUONEventReconstructor from Dr.Finck
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Making tracks with trigger info (2)

• X pos on MC11
• Y pos on MC11
• Theta X
• Theta Y
• Global trigger (Long_t)

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Future developments
20
The MUON trigger in reality

• 234 Local Trigger Boards
• adopted official numbering (PRR)
• all identical
• 10 configuration switches
• up-down neighbors are connected
• 3 trigger levels (local, regional, global)

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The MUON trigger in AliRoot

• 234 TriggerCircuits (equivalent to standalone
  Local Trigger Boards)
• numbering from AliMUONTriggerConstants
  (different from reality)
• (some) switches are hard-coded in the Loadxxx
  methods
• some other switches are not defined (e.g. no
  connections needed between 2 circuits since, in
  contrast to a local board, a circuit has, by
  definition, all needed information to deliver its
  local trigger decision)
• regional global trigger levels not implemented
  in a realistic way (regional trigger skipped,
  global trigger loop over 234 TriggerCircuits)

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What cannot be done with the present version of
the code

• easily assign a TriggerCircuit to a local board
  (because of different numbering)
• estimate the effect of mismatching in a local
  board configuration (because switches are
  hard-coded)
• estimate the effect of a non-working local board
  on the global trigger performances (because some
  switches are not simulated)
• investigate regional algorithm performances

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To do list

• redefine TriggerCircuit numbering like in
  reality
• redefine TriggerCircuit objects as closer to
  real local boards
• switches (data members) to be read from a
  database (234?10 entries)
• define a new interface between digits
  TriggerCircuits
• allow TriggerCircuits to talk between each other
  via switches
• simulate 16 virtual crates, fill-in the
  corresponding TriggerCicuits, implement regional
  global trigger algorithms like in reality

note needs Local2Global Global2Local to be
implemented first