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

3

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

4

Prob consecutive triggers 1.2·10-

5

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

5

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

6

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

7

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

11

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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16

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