EMCal Jet Trigger Analysis for ALICE* - PowerPoint PPT Presentation

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EMCal Jet Trigger Analysis for ALICE*

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Title: EMCal Jet Trigger Analysis for ALICE*


1
EMCal Jet Trigger Analysisfor ALICE
  • Christopher Anson
  • Creighton University
  • Supported by the U.S. DOE Office of Science

2
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

3
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

4
Trigger Requirements
  • Reduce data rate into higher level trigger
  • Efficient jet selection at lowest possible energy
  • Use most efficient patch size

5
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
6
  • 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

7
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

8
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
9
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)

10
  • 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

11
  • 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
12
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

13
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

14
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.

15
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)

16
  • 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.

17
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
18
Backup Slides
19
  • 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.
20
  • 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

21
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.

22
Smallest towers ??x?? 0.02x0.02
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