spd consecutive triggers
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SPD consecutive triggers
Míriam 21 April 2010
Introduction Afterpulse-like activity at the SPD noticed in
different contexts like calibration triggers or LHC collisions. What are the sources? Are they common?
SPD>0 (cosmic) run Collisions
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High rate SPD>0 in BXIds:882910…26612690…
Calibration BXIds: 876 y 2655
BXId
N S
PD
40
LED system
Cosmics + noise
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SPDMult>0 trigger run No LHC beam
~470Hz (Threshold 0.5 MIP)
637134 events
Fract
ion o
f events
---- no cells or PMT in commonAt least one cell in commonPMT in common, but no cells
‘Next2’could include spill-over
Consecutive triggers
Fraction of triggers which could be afterpulse: 2.4·10-4
(integrated tail from >Next2)Compatible with BCN measurements
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Prob consecutive triggers 1.2·10-
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From BX>40 2.5·10-5 vs 5.4·10-6 of same VFE random coincidence 9.5·10-6 vs 9·10-9 of same cell coincidence
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Afterpulse candidates (same hit or VFE also at T0)
Number of consecutive triggers from the same event
Same cell
Same VFE
SPD Multiplicity of afterpulse candidates
afterpulse candidates
Collisions
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SPDMult>0 (downscaled by factor 40) and SPDMult>2 trigger channels.
SPD>0 triggersAt least one PMT in commonAt least one cell in common
+67% SPD40 triggers wrt collision BXID
Relative 54.7% of tail (>33%) 15.1% of tail (>1.3%)
SPD>2 triggersAt least one PMT in commonAt least one cell in common
+1.7% SPD triggers wrt collision BXID
82.5% of tail45.7% of tail
45% of the tail unrelated with collision signal
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No cells or PMT in commonAt least one cell in commonPMT in common, but not same cell
SPDMult>0 trigger Threshold 0.8 MIP
SPDMult>2 trigger
Integrated tail (blue + red) 1.4%(0.8%)
Integrated tail (blue + red) 37% aditional triggers(10.2%) Not compatible with ~2% expected from afterpulsing (from cosmic + noise run)BUT related with regions with signal in the collisions
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SPD Multiplicity of events at BXId 1786 (‘T0’)
<>=34 VFEs
<>=53 VFEs
SPD Multiplicity of events with after-trigger
SPD Multiplicity of after-triggers
<>=1.04 VFEs
SPD>0
Only one consecutive trigger from the same event (rejection factor 40)
After-triggersmainly 1 VFE
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SPD Multiplicity of after-triggers
SPD Multiplicity of events with after-triggers
SPD Multiplicity of events at BXId 1786 (‘T0’) Number of consecutive
triggers from the same eventMainly once
<>=33 VFEs
<>=52 VFEs
<>=1.5 VFEs
SPD>2
After-triggersmainly 1 or 2 VFE
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SPD PS
T0
Next 32
SPD>2
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SPD PS
Next 37
~half of after-trigger events >1 VFE
But distance between hits from different VFE is below 50 cm for 70% of these
Physics bkg?
Increasing the SPD Multiplicity cut
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SPDMult> Eff (%) After-triggers (%)
2 98.5 1.4
3 98.4 0.4
4 96.6 0.11
5 95.7 0.03
Eff = efficiency on SPD>0 events at BXID 1786
After-triggers = fraction of events with a consecutive trigger (up to 200 BX)
SPDMult>4
Current level of after triggers is not a problem. (If at some point it become a problem, the cure can be to increase the threshold).
Summary
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Trying to find if SPD trigger tails is consistent with possible afterpulsing 0.025 % is too low to explain ~10-40% tail in the
SPD>0 trigger Barcelone measurements estimate 0.01%
Tail duration does not fit with AP duration For beam-beam interactions is about 200 cycles (5 s) Barcelone measurements, AP duration is < 1 s
Physics background? For the long-lived component of the after-triggers (SPD>2),
a clear tendency is seen for the hits to be clustered in the same detector region. The fact that this happens also in contiguous VFEs points towards physics origins.
Backup
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Multi> 0.5 MIP0 4701 5.52 1.63 0.764 0.475 0.296 0.21
SPD rates in Hz (LHC off)
SPD40: 11.75 Hz
SPD: 1.6 Hz
Cosmics + noise
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Initially one cell (629631 evts)
same VFE 1.2·10-7
same cell 3.2·10-9
Prob consecutive triggers 1.2·10-
5
Integrated tail (red+ blue >=Next3) 2.3·10-4
AP
Cosmics + noise
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Next2
Next4 Next6
Next8
Cosmics + noise
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‘T0’ with afterpulses
Any event
SPD Multiplicity of events with afterpulsing (*)
(*) >Next2 triggers with at least one PMT in common
No afterpulses
Cosmics + noise
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