EMCal Jet Trigger Analysis for ALICE*

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EMCal Jet Trigger Analysisfor ALICE

• Christopher Anson
• Creighton University
• Supported by the U.S. DOE Office of Science

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Introduction

• The goals of this study are to
• Investigate trigger properties starting with
  event simulations simple assumptions about
  detector.
• Compare conclusions with other results starting
  with advanced simulations of detector response.
• Investigate the underlying physics and behavior
  of triggers.
• By using
• 2 million jet events with AliPythia
• 1000 background events with HIJING PbPb

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Outline

• Jet Triggers with Pythia Jets
• a) Leading ?0 trigger
• b) Cone trigger
• c) Patch trigger
• Patch Triggers with Pythia Jets and HIJING
  Background
• Jet vs. background energy in patches
• Centrality dependence
• Patch Triggers with Rate Requirement Introduced

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Trigger Requirements

• Reduce data rate into higher level trigger
• Efficient jet selection at lowest possible energy
• Use most efficient patch size

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Rates at ALICE
Interaction Rate 4 kHz Into High Level Trigger
100 Hz Data to tape rate 100 Hz Need 100
efficiency above 100 GeV And enhancement at 50
GeV Must reduce data rate by 10-50 times
inclusive jets
10 Hz _at_ 50 GeV
few x 10
4
/year
for E
gt150 GeV
T
An EMC for ALICE
From Peter Jacobs
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• Leading ?0 Trigger
• Investigating efficiency for different cuts
• Conclusions
• Increasing cut reduces efficiency for high energy
  jets.
• Some higher energy jets have a low energy leading
  ?0.

• Cut Energy
• 2 GeV cut
• 4 GeV cut
• 6 GeV cut

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Cone Trigger with Different Cone Radii

• Cone is around Pythia jet axis
• 100 e,e-,? energy
• 25 hadron energy
• Conclusions
• Reduced efficiency for smaller cones
• Sometimes jet energy is not centralized near
  Pythia defined jet axis

• Cone Radius
• R 0.05
• R 0.10
• R 0.20
• R 0.30
• R 0.40

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Patch Trigger Slides Across the Detector
In reality the smallest 2x2 Tower units are
0.028x0.028 Smallest patches I use are
0.05x0.05 Larger patches are built from summing
the smaller patches The patches looked at in my
study are 0.05x0.05 1x1 0.10x0.10
2x2 0.15x0.15 3x3 0.20x0.20 4x4 0.25x0.25
5x5
?
?
?? 0.05
?? 0.05
??x?? 0.15x0.15
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Patch Trigger vs Cone Trigger

• 10 GeV cut
• ??x?? 0.15x0.15 patch
• Cone has equal area
• Conclusions
• Sometimes jet energy is not centralized near
  Pythia defined jet axis
• Cone trigger has poor efficiency

• Trigger Type
• 0.15x0.15 Patch Trigger
• Cone Trigger (Same Area)

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• Patch Size Dependance
• Energy is summed in d?xdf patches
• Cuts produce 50 efficiency at fixed 72 GeV to
  investigate behavior of trigger
• Conclusion
• Patch trigger efficiency is independent of patch
  size

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• Patch Size Dependance
• Pythia assumption of 25 hadron energy detected
• Agrees with full GEANT simulation
• Cuts produce 50 efficiency at 72 GeV to
  investigate behavior of trigger
• Conclusion
• Patch trigger efficiency is independent of patch
  size

Full GEANT simulation Bill Mayes, Houston
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Comparing Patch Trigger and Leading ?0 Trigger
1x1 patch trigger doesnt reduce to leading p0
trigger Turning off the energy deposited by
hadrons

• Trigger Type
• 0.05x0.05 Patch Trigger
• Leading p0 Trigger

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Comparing Patch Trigger and Leading ?0 Trigger

• With energy in patch only due to e,e-, and ?
  energy
• Now the two curves are similar
• Conclusions
• Hadronic energy is significant
• Efficiency increases as more hadron energy is
  deposited

• Trigger Type
• 0.05x0.05 Patch Trigger
• Leading p0 Trigger

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Summary using just Pythia

• Leading ?0 trigger efficiency decreases with
  larger cuts (6 GeV).
• Cone trigger is inefficient.
• - (Energy not always near jet axis).
• Patch trigger is most efficient.
• Small patches as efficient as large patches.
• Hadronic energy contribution enhances efficiency.

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Comparing Jet Energy to Background in Patches

• Central HIJING PbPb collisions
• Background increases monotonically with patch
  size
• Jet energy levels off with patch size
• Background decreases for peripheral collisions
• Conclusions
• Background comparable to jet energy for central
  collisions
• Need centrality dependent trigger (Agrees with
  Peter Jacobs and Andre Mischkes conclusion)

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• Patch Trigger with Rates
• The cuts here select 1/10 events (about what is
  needed in the Level 1 trigger)
• NOTE This is with central HIJING and should be
  redone with min-bias HIJING. Central HIJING may
  give a worst case scenario.
• Conclusion
• Only smaller patch is less efficient
• Larger patches make the trigger more robust
  against fluctuations
• This graph is also consistent with the Full GEANT
  simulation done by Bill Mayes.

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Summary

• Patch trigger is most efficient trigger for the
  EMCal.
• For p-p jets, efficiency is independent of patch
  size.
• For p-p background meeting required rate,
  larger patches are efficient.
• (smallest patch is not).
• Centrality dependent higher level trigger is
  required
• (due to decreasing background with decreasing
  centrality).

For more information refer to pages listed at
http//pdsfweb01.nersc.gov/canson/HijingHTMLStuf
f.html
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Backup Slides
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• Cone Radius
• R 0.05
• R 0.10
• R 0.20
• R 0.30
• R 0.40

• Cone Radius
• R 0.05
• R 0.10
• R 0.20
• R 0.30
• R 0.40

Larger cuts eliminate more low energy AND high
energy jets.
Increasing the Cut on the Energy in a Cone shifts
the efficiency curve downwards for smaller patch
energies.
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• Patch Trigger with Rates
• Only Pythia Jets
• 25 Hadron Energy contributed
• The reduction in rate is estimated by dividing
  the integrated jet spectra with a cut by that
  without a cut
• The cuts here select 1/50 of the events
• Conclusion
• Patch trigger is still efficient even for small
  patch sizes

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Calculation of Trigger Rate

1. Project jets above cut Et and count how many
   (integrate).
2. Project jets with higest patch Et above 0 gev and
   count how many.
3. Divide number in Step 1 by number in Step 2.
4. This give the number of events selected.

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Smallest towers ??x?? 0.02x0.02