Transcript ppt

TKR Noise Flares observed in
TKR #11 and #8
Mutsumi Sugizaki, Hiro Tajima, and
TKR team
10/21/2005 Inst Ana
Meeting
TKR Noise Flares
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Noise flares observed in TKR #11
•
Test of noise occupancy monitor for TKR #11 in the acceptance test at SLAC
X11
X16
~ 2 hours
Y10
10/21/2005 Inst Ana
Meeting
 The strip occupancy occasionally
exceeds10-4 in the layer average during
some short terms (~10 min).
 These noise flares do not always
appear. It is rather rare.
 The noise flares appeared only in these
three layers on TKR #11.
 The flares were not synchronized layerto-layer.
TKR Noise Flares
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Strip profile of noise flares in TKR#11
X11
X16
Single strip flare.
It can be disabled by
data and trigger masks.
>> Solved.
Y10
Multi-strip noise flare?
It looks very strange.
Noisy strips are gathering on
the layer edge.
10/21/2005 Inst Ana
Meeting
TKR Noise Flares
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Noise flares observed in TKR #8
• The next noise flare was found during noise occupancy monitor for
TKR #8 in the TKR acceptance test at SLAC
Time profile
Strip profile
TKR #8 Y0
Ladder edge
Questions
 How can these multi-strip noise flare occur?
 Does it have a serious impact on the LAT performance?
 Flare strips seem to be confined by ladder boundary. Is it true?
 Are they also bunched by front-end chip (64 channels)?
 Why did it appear only in TKR #11 and #8?
10/21/2005 Inst Ana
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Strip multiplicity of noise flare
TKR#11 X11
TKR#11 Y10
GTRC event buffer
overflow
TKR #8 Y0
GTRC event buffer
overflow
Reference: normal layer
GTRC event buffer
overflow
 In the layers with noise flares, large-multiplicity events are increased.
 The gathering of the noisy strips on the layer edge can be explained by the
GTRC event-buffer overflow.
10/21/2005 Inst Ana
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Event selection with multiplicity
TKR #8 Y0
Time profile
Strip profile
Ladder edge
TOT distribution
0
 Selection condition:
(20<=Multiplicity<64)
 The noise flare can be mostly
explained by these large-multiplicity
events.
 TOTs of the noise flare events are
longer than a few ms.
10 20 30 40 50us
10/21/2005 Inst Ana
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TKR Noise Flares
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Layer (trigger) occupancy of noise flares
TKR#11 X11
TKR #8 Y0
10/21/2005 Inst Ana
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TKR#11 Y0
 Layer Occupancy is < 0.1, which
corresponds to the single-layer trigger
rate < 50 kHz.
(0.1/2ms=50 kHz in the worst case).
This still meets trigger specification at
GTRC OR_STRECH=31.
 The relation between strip and layer
occupancies in noise flare can be
explained by the large hit-strip
multiplicity.
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Other info. we have known about the noise flare
• According to the TKR group in Italy, similar noise flares were
observed in Towers A, #1, #4, #7, #8, #11, too, during the TVAC
test (L. Latronico NCR/FM/INFN/PI-592). They were considered to
be due to pickup of external noise because it seemed to be
synchronized with the time of the temperature change.
• The bias-voltage dependence of the noise flares is not clear, so far.
If it is caused by discharge on the detector, it should have some
bias-voltage dependence.
• I personally think that we cannot abandon the scenario of pickup of
external noise because we could not find any noise flare from the
data taken on last Sunday.
10/21/2005 Inst Ana
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Summary
• Current understanding about the noise flare
– Impact on the LAT performance is small.
• Frequency is very low.
• Single layer trigger rate still meets the requirement even
during the intense noise flare.
• The effect on the TKR 6-in-a-row trigger is negligible.
– We did not know the root cause.
• Analysis tools to monitor flare activities during normal data taking
are under development. We plan to involve them in the regular data
processing.
• TKR #8 is supposed to go to a beam-test tower. We are thinking
more tests using TKR #8 to reveal the root cause.
10/21/2005 Inst Ana
Meeting
TKR Noise Flares
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