Study of TKR Trigger Inefficiency from discrepancy between Trigger and Strip Data

1
Study of TKR Trigger Inefficiency(from
discrepancy between Trigger and Strip Data)

• Mutsumi Sugizaki

2
Purpose and Target

• Detection of gamma-rays in LAT is led by TKR
  3-in-a-row trigger. TKR-trigger efficiency is
  one of the most important issues.
• There are a lot of factors related with the
  efficiency. Some of them, such as dead strips,
  insensitive area of silicon detectors, can be
  estimated from strip data. They are not discussed
  here. (See talks by Hiro)
• Targets of this study are inefficiencies due to
  the trigger signal processing.
• Information of trigger signal itself (GEM data)
  are fairly limited. Thus, it is studied from
  discrepancy between trigger and strip data.

3
Overview of TKR trigger and strip data

• Trigger signal and strip data
• Trigger signal flow
• Comparator output of each strip ? layer-OR ?
  OR-stretch (3.2 ms one shot) ? TREQ ? GEM
  (Trigger information)
• Hit-strip data latch flow
• GEM ? TACK ? latch comparator output ? strip
  data
• Prospective issues related with the TKR trigger
• Inefficiency due to the trigger-time jitter
  between 3-in-a-row layers.
• Discrepancy for the time lags between trigger
  (TREQ) and data-latch (TACK) signals.
• Trigger dead time for noise occupation.

TREQ
OR-stretch(3.2 ms)
Comparator output
GEM
Trigger dead time in front-end electronics
TACK
Data latch delay
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Event classification by strip-data and trigger
combination
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Trigger information in standard data

• Available trigger information
• GEM conditions summary word 8 bits
• (Roi, Tkr, CalLe, CalHe, Cno, Periodic,
  Solicited, External)
• GEM TKR vector 16 bits, 1 bit (0/1) for each
  tower
• GEM ROI vector -- 16 bits, 1 bit (0/1) for each
  tower
• GEM CalLe(He) vector 16 bits, 1 bit (0/1) for
  each tower
• GEM CNO vector 12 bits
• Difficulty in the study of trigger efficiency
• TKR trigger information includes only an entire
  OR of 16 3-in-a-row combinations (0-1-2, 1-2-3,
  , 16-17-18) for each Tower.
• Status of trigger signal of every individual
  silicon layer can be obtained if diagnostic mode
  is enabled. However, the diagnostic data is
  latched in another timing. It just brings
  another timing issue.
• Patterns of TKR, ACD(Roi, Cno), CAL(Le,He)
  triggers are limited in standard data ? See past
  talks about trigger engine.

6
Analysis method

• Parameter of TKR trigger inefficiency per TKR
  3-in-a-row
• of events without TKR trigger
• of events with 3-in-a-raw strip data
• Event sampling
• Collect events triggered by another TKR, or ACD
  or CAL, then check status of trigger and strip
  data of the test-unit TKR.
• Number of TKR Track 1 to exclude pile-up
  events
• Data sample 1 MIP particle
• TkrClrMipslt2 in every layer in a Tower
• Data sample 2 Data with ACD-or-CAL trigger
• (CalLe)(CalHe)(Cno)gt0
• Dependence on the number of 3-in-a-row
• The trigger inefficiency should depend on the
  number of 3-in-a-row combinations.

Use data taken by FSW runs in April-May at
SLAC. of events 108
Quadruple 3-in-a-row ? The Trigger inefficiency
will be smaller than that for single 3-in-a-row
events.
Single 3-in-a-row
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Inefficiency for Data Sample 1MIP events
Example Tower0
of 3-in-a-row combinations
1 2 3 4 5 6

• The inefficiency is 10-310-2. (Specification
  total inefficiencylt10.)
• The dependence on the number of 3-in-a-row is
  clear. The gap between 3 and 4 will come from the
  number of isolated 3-in-a-row combinations.
• These events are triggered mostly with the
  adjacent TKRs. It might depend on the
  trigger-timing jitter between TKRs. (That effect
  would be maybe very small.)

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Inefficiency for Data Sample 2CNO/CalLe(He)
trigger events
Example Tower0
of 3-in-a-row combinations
1 2 3 4 5 6

• The inefficiency is 10-2, 510 times larger
  than that for MIP events.
• It will depend on jitter of trigger-timing lags
  between ACD, CAL, and TKR. Thus, the inefficiency
  for this data sample does not directly mean TKR
  trigger inefficiency.

9
Noise Dependence
Tower 13 MIP events

• Tower13-X13 is only a layer on which the
  relation between the noise and the trigger
  inefficiency can be seen.
• The noise layer occupancy is 3, which seems
  reasonably agreed with the trigger inefficiency
  3.

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Summary

• TKR trigger inefficiency is studied from the
  discrepancy between trigger and strip data.
• The trigger inefficiency of each 3-in-a-row is
  estimated at 10-2 against strip data, which is
  enough small comparing with the requirement.
  (Total inefficiency is lt 10)
• The noise dependence of the trigger efficiency is
  seen only in the noisiest layer. The level is
  currently enough small.
• The trigger inefficiency by noise can be naively
  estimated from layer-OR occupancy. We will have
  to keep monitoring the noise parameter.
  (Actually, the layer-OR occupancy occasionally
  exceeds 10 during extreme large noise flare)

11
A preliminary result from EMI test run

• RunID77006515-6521
• A large noise flare was observed on Tower15-X11.
  
• The layer-OR occupancy reached 20.
• It now returned to the quiet level.