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Testbeam Studies of the LHCb Vertex Locator Modules
Lisa Dwyer
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Overview
Vertex Locator
Testbeam overview
Cluster analysis
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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LHCb VeLo
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Testbeam overview Data taken with 10 production
modules Capability to read out 6 Cooling and electronics used in final
experiment Check response of modules My analyses:
Signal to Noise ratio Clusters
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Cluster analysis Fraction of two strip clusters Ratio of charge Crosstalk
Zero suppressed data Zero degree tracks Clusters on tracks Look at R and Phi
sensors separately
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Phi sensor
Inner strip pitch35.5μm – 78.3μm
Outer strip pitch39.3μm – 96.6μm
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Fraction of two strip clusters
Fraction of two strip clusters as a function of pitch
Expect similar fractions of two strip clusters in each sensor
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Possible causes for distribution
Noisy strips X All noisy strips removed
Operational settings X
Crosstalk ? Charge sharing between strips Alters the actual number of two strip
clusters
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Readout trace
Oscilloscope trace of chip readout Output in voltage and time
Header information
Data from chip
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Phi sensor readout – software strip
Inner regionStrip 0
Inner regionStrip 682
Outer regionStrip 683
Outer regionStrip 2047
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Phi sensor readout - Hardware channel
0 (682)1 (2046)2 (2047)3 (2045)
4 (681)5 (680)6 (2044)
7 (2043)8 (2042)
9 (679)10 (2041)11 (2040)
12 (678)13 (2038)14 (2039)15 (2037) 16 (677)
17 (676)
Outer strips Inner stripsHW
HWSW
SW
Crosstalk in hardware channel
adjacent
4 apart
3 apart
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Measuring crosstalk Look at two strip clusters Look at ratio of charge Check if crosstalk is asymmetric
Ratios > 1 Earlier >Later Later > Earlier
Comparison between testbeam data and simulation
Crosstalk found to be asymmetric
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Data shows asymmetry No asymmetry in simulation
Simulation accounts for crosstalk on sensor but not in cables
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Crosstalk simulation
Simulate testbeam events in MC Add noise and smear data (hardware
channel order) Re-cluster (software strip order) Compare results to data
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Smearing data To model crosstalk Smearing formula:
Negative f & g values → charge sucked in from neighbouring strips
Positive f & g values → charge dispersed to neighbouring strips
jjijjiinew gadcfadcgf
adcadc1
1
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Effects of f & g
f
f
g
g
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Effect of f Negative f f=-0.2
Positive f f=0.2
Smeared
Not smeared
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Phi sensor data
Before smearing With best fit
f=-0.2+0.05-0.02
g=-0.22+0.04-0.08
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Conclusion and outlook Adjacent channels
f=-0.2 +0.05-0.02
g=-0.22 +0.04-0.08
Channels separated by 3 f = -0.12 +0.02 -0.06
g = -0.1 +0.06 -0.01
Obtain smearing factors (f & g) for all modules Use smearing factors to remove crosstalk from data Re-calculate signal to noise Prepare J/ψ analysis for first physics at LHC
Back up
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Signal to Noise ratio Theoretical value for 300μm
Silicon sensor is 28 S/N for R sensors 21.7 – 29.4 S/N for Phi sensor 22.8 – 27.7
NoiseSignal
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Crosstalk simulation
SW
SWHW
HW
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Noisy Strips
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Clustering process Use standard algorithm Looks for strip with ADC value > 10 Then looks at adjacent strips ADC value >5
Produces 1, 2 and 3 strip clusters If two strip cluster consider its neighbouring
strips Produces 2, 3 and 4 strip clusters
17/12/2007 Lisa Dwyer - Liverpool HEP Christmas meeting 2007
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Results
Module f g
M30p adjacent -0.2 +0.05 -0.02
-0.22 +0.04 -0.08
M30p 3 apart -0.12 +0.02 -0.06
-0.1 +0.06 -0.01
M31p adjacent +0.12 +0.005 -0.01
-0.28 +0.01 -0.02
M31p 3 apart -0.16 +0.04 -0.05
-0.18 +0.04 -0.02
M30p –least affected by crosstalkM31p –most affected by crosstalk