Testbeam Studies of the LHCb Vertex Locator Modules Lisa Dwyer.

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


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LHCb VeLo


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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


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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


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Phi sensor

Inner strip pitch35.5μm – 78.3μm

Outer strip pitch39.3μm – 96.6μm


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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


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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


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Readout trace

Oscilloscope trace of chip readout Output in voltage and time

Header information

Data from chip


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Phi sensor readout – software strip

Inner regionStrip 0

Inner regionStrip 682

Outer regionStrip 683

Outer regionStrip 2047


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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


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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


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Data shows asymmetry No asymmetry in simulation

Simulation accounts for crosstalk on sensor but not in cables


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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


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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


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Effects of f & g

f

f

g

g


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Effect of f Negative f f=-0.2

Positive f f=0.2

Smeared

Not smeared


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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


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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


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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


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Crosstalk simulation

SW

SWHW

HW


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Noisy Strips


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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


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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

Testbeam Studies of the LHCb Vertex Locator Modules Lisa Dwyer.

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