SPD commissioning
Ricci, Míriam, Daniel, Edu, Hugo et al. from
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Outline
• SPD calibration with cosmics• Vref calibration
• LED intensity: limits and current status• SPD hardware• LED features
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Calibration with cosmics
• Have to set threshold @ 0.5 – 0.7 MIP• MIP computed by multiplying calibration of
components– nPhes from Evgeni: cosmics with the detector “on
a table”
• Check MIP computation with cosmics:1) Make sure that SPD occupancy looks uniform on
ECAL&&HCAL cosmics2) Try to compare efficiency with expectation
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Uniformity• Cosmics allowed to solve a bug in HV settings
in a few PMTs• Reasonable uniformity after correction:
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Threshold @ 0.5 MIP1 M events
Threshold @ 1.5 MIP0.5 M events
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Global SPD efficiency
• Tried to define a clean sample:– Track extrap. >2 away from acceptance limits– No multiple hits in SPD– Track extrap. x, y < 150 mm– Energy in PS > 40 ADCs– PS cell and track extrap. in 3 & only 1 cell– Look in any BX
• Still, efficiency lower than expected– Reason: time of arrival
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Efficiency vs arrival time
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0.5 MIP 1.5 MIP
100% 50%
Arrival time (ns) Arrival time (ns)
With perpendicular cosmics
• Selecting cosmics with x/x < 1.2
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0.5 MIP 1.5 MIP100% 50%
Arrival time (ns) Arrival time (ns)
Threshold voltage vs Vref
Vth = 0.65 · Vref ·(n/63), n internal DAC reg.
• Physics setting: in each VFE, minimum Vref that can provide 1 MIP in all channels– To minimize step size, hence resol on threshold
• But will need 2 MIPs for threshold scans• How stable is calibration under changes in Vref?
• Checked by measuring noise offset by performing threshold scans with different Vref
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Threshold dependence of Vref
• Checked with Vref = 555 mV vs Vref = 1560 mV
• Dispersion lower than 1 step (5-15 mV)• Slight bias due to choice of step (will be optimized)
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Míriam
Voff (V)
LED system
• Light intensity being adjusted by Evgeni• Limit on LED light?
– Occupancy wrt 40 MHz @ 2·1032: (0.001,0.03) (40K, 1.2M) MIP·s-1
– LED system: 40 MHz / (3564 * 5 ) = 2.2 KHz
• A LED flashing @ 20 MIP is contributing between 3% and 100% of the light from physics
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Measuring LED intensity
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• Idea: change SPD threshold to a very high value and look for signal
• Electronics allows for a maximum of 6 MIPs if we want to have uniform thresholds in the whole SPD
Max SPD threshold in MIPs
LED results: intensity
• Complete results from runs from 25th Jan at: http://lhcb.ecm.ub.es/~lhcb/2009/jan/27/
• All in the form of LED-timing scans: LED trigger delay from 0 to 25 ns with steps of 1ns
• Look at many BXs: can study duration of signal• Edu, Evgeni will explain details, here just flash
some results
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Míriam/Daniel
VFE 35 / Trigger 40 / Vled(8) = 1750
0.5 MIPs
0.5 MIPsOld HV settingsVled = 1700
2 MIPs
6 MIPs
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Míriam/Daniel
C side
Too much light!
VFE 21 / Trigger 43 / Vled(7) = 1750
0.5 MIPs
0.5 MIPsOld HV settingsVled = 1700
2 MIPs
6 MIPs
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Míriam/Daniel
C side
Far too much light!Remember subtractor 20% of previous BXHow many MIPs?
VFE 40 / Trigger 40 / Vled(8) = 1750
0.5 MIPs
0.5 MIPsOld HV settingsVled = 1800
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Míriam/Daniel
C side
Too little light
VFE 91 / Trigger 41 / Vled(8) = 1700
0.5 MIPs
0.5 MIPsOld HV settingsVled = 1700
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Míriam/Daniel
A side
Far too little light
2/Feb/2009 SPD shutdown activities and LED checks
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SPD electronics status
• Checks on 1 VFE which showed problems:– VFE number 2 (crate PRS0, CB5, channel2) on C-side
– No communication between VFE and CB before Christmas. Now OK.
– Possible causes:• VFE problem• Control/clock cable problem (as 2 other from same bundle)• Metal dust inside EE box
– Actions done:• As VFE worked last week, just clean all dust.• Wait until all detectors are closed on C-side (if the cable is the problem) or the
problem apears again
– Solution if the cable is found broken:• Use another box control/clock spare cable and extension.• It is not feasible to pass a few new control/clock cables to the problematic zone
through the chain.
2/Feb/2009 SPD shutdown activities and LED checks
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SPD shutdown activities: tests
• VFE tests:– LED measurements
• Uniformity study and adjustment (Evgeny)• Run types:
– Simple measurement (just apply a trigger pattern)
– Time alignment scan (change delay on the trigger of the LEDs)
– Threshold scan (modify threshold values on each step)
– Offset measurements• Threshold scan with and without HV• Repeat for various Vref and to check stability
– Mapping test• Check the DAQ vs. VFE channel mapping• To do it once
A-side V(2)=2800V(7)=2450V(8)=1700V(9)=2400
V(10)=2500
C-side V(2)=2100V(7)=1750V(8)=1750V(9)=2100V(10)=1750
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Bias applied
2/Feb/2009 SPD shutdown activities and LED checks
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VFE 33 / Trigger 42 / Vled(8) = 1750
0.5 MIPs
0.5 MIPsOld HV settingsVled = 1700
2 MIPs
Problems with LEDTSB, VFE configuration?
2/Feb/2009 SPD shutdown activities and LED checks
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VFE 38 / Trigger 41 / Vled(8) = 1750
0.5 MIPs
0.5 MIPsOld HV settingsVled = 1700
2 MIPs
6 MIPs
Trigger signal reflections
BACK-UP
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Occupancieslumi2 lumi2 lumi2
lumi5 lumi5 lumi5
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Conclusions on LEDs
• C-side:– Most VFE have signal with threshold @ 6 MIPs
• VLED(2, 7, 9, 10) too low; V(8)~OK?
• A-side:– Some VFE signal too low (@ 0.5 MIP)
• VLED(2,8) too high; V(7, 9, 10) ~OK?
– Problems with triggers 31, 32, 38, 39 (VLED not controlled) and 42, 56 (not triggered)
– VFE 65(?), 66 no HV
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‘Teor’Delays from data
Some discrepancies for inner, ~ 3ns. (Check teor fiber delays.)Wait for fine time alignment with first collisions. 25
Time alignmentMíriam
With 2.6 M cosimic events analyzed:
Material traversed by cosmics
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(-5<t<5) (15<t<25)
Offset difference in Volts
V V
VV
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RUN 36187 (Vref = 555 mV) vs RUN 36204 (Vref = 1560 mV)Míriam