Testbeam Studies of the LHCb Vertex Locator Modules Lisa Dwyer

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting Overview  Vertex Locator  Testbeam overview  Cluster analysis

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting LHCb VeLo

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting 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

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting 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

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting Phi sensor Inner strip pitch 35.5μm – 78.3μm Outer strip pitch 39.3μm – 96.6μm

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting 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

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting 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

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting Readout trace  Oscilloscope trace of chip readout  Output in voltage and time Header information Data from chip

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting Phi sensor readout – software strip Inner region Strip 0 Inner region Strip 682 Outer region Strip 683 Outer region Strip 2047

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting 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 stripsInner strips HW SW Crosstalk in hardware channel adjacent 4 apart 3 apart

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting 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

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting Data shows asymmetry No asymmetry in simulation Simulation accounts for crosstalk on sensor but not in cables

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting Crosstalk simulation  Simulate testbeam events in MC  Add noise and smear data (hardware channel order)  Re-cluster (software strip order)  Compare results to data

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting 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

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting Effects of f & g f f g g

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting Effect of f  Negative f  f=-0.2  Positive f  f=0.2 Smeared Not smeared

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting Phi sensor data Before smearingWith best fit f= g=

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting Conclusion and outlook  Adjacent channels f= g=  Channels separated by 3 f = g =  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

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting 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 Noise Signal

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting Crosstalk simulation SW HW

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting Noisy Strips

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting 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

17/12/2007Lisa Dwyer - Liverpool HEP Christmas meeting Results Modulefg M30p adjacent M30p 3 apart M31p adjacent M31p 3 apart M30p –least affected by crosstalk M31p –most affected by crosstalk