10/21/2005 Inst Ana Meeting TKR Noise Flares1 TKR Noise Flares observed in TKR #11 and #8 Mutsumi Sugizaki, Hiro Tajima, and TKR team

10/21/2005 Inst Ana Meeting TKR Noise Flares2 Noise flares observed in TKR #11 Test of noise occupancy monitor for TKR #11 in the acceptance test at SLAC X11X16 Y10 ~ 2 hours  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 layer- to-layer.

10/21/2005 Inst Ana Meeting TKR Noise Flares3 Strip profile of noise flares in TKR#11 X16X11 Y10 Single strip flare. It can be disabled by data and trigger masks. >> Solved. Multi-strip noise flare? It looks very strange. Noisy strips are gathering on the layer edge.

10/21/2005 Inst Ana Meeting TKR Noise Flares4 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 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? TKR #8 Y0

10/21/2005 Inst Ana Meeting TKR Noise Flares5 Strip multiplicity of noise flare TKR#11 X11 TKR#11 Y10 TKR #8 Y0 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 Meeting TKR Noise Flares6 Event selection with multiplicity TKR #8 Y0 Ladder edge Time profileStrip profile TOT distribution  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  s us

10/21/2005 Inst Ana Meeting TKR Noise Flares7 Layer (trigger) occupancy of noise flares TKR#11 X11TKR#11 Y0 TKR #8 Y0  Layer Occupancy is < 0.1, which corresponds to the single-layer trigger rate < 50 kHz. (0.1/2  s=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.

10/21/2005 Inst Ana Meeting TKR Noise Flares8 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 Meeting TKR Noise Flares9 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.