sistrip calibration, local reconstruction and simulation meeting 27 km 100 m status of lorentz...
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SiStrip Calibration, Local Reconstruction and Simulation meeting
= 27 km100 m
Status of Lorentz Angle Measurement
IntroductionLorentz angle ?
Problem :• E varies with the depth ~ average LA• Average LA varies with :
• Temperature• Drift velocity• Depth of collected charge readout mode (peak vs deconvolution)
8 December 2011
The charges drift at an angle qL
Cluster shift
S. Frosali
Th. Caebergs (UMons) – A. Nürnberg (KIT) – C.Vander Velde (ULB
IntroductionHow to measure the average LA ?Several methods developped by our precursors:• Look for minimum cluster width in # of strips (S. Frosali)
Sensitive to the higher cross-talk in deconvolution mode
Does not work for collision data (not enough w = 1 clusters)• Look for maximum probability of cluster with only 1 strip (prob1)• Look for minimum sqrt (variance) for w=2 and w=3 (avgv2, avgv3)• Look for minimum rms, for w = 2 and w = 3 (rmsv2, rmsv3)
The extrema are search for using a minimum c² symmetry fit.
All these methods give different results and the correct way to proceed is not yet understood!
SiStrip Calibration, Local Reconstruction and Simulation meeting
Status of Lorentz Angle Measurement
8 December 2011
qL = qtrack for minimum width
(B. B
etchart)
SiStrip Calibration, Local Reconstruction and Simulation meeting
= 27 km100 m
Status of Lorentz Angle Measurement
IntroductionMore difficulties• The difference between the methods are not the same for all modules,
even not for a category, TIB – TOB, parallel – stereo• They depend on the readout mode (charge depth influence)• They are different for cosmic runs and collision data (angular
distribution of tracks)
Question?Is it possible to measure « something » leading to a cluster position shift such that the alignment remains the same as long as the detector is not moved? Presently, we can just monitor the changes with time!
What do we monitor?The hole mobility, µ_H, versus the run #:
tg (qL) = µ_H B
This work was started by Y. Gotra.
8 December 2011
SiStrip Calibration, Local Reconstruction and Simulation meeting
Comparison with former results
• Yuri Gotra looked at runs from April to mid-July 2010, last year
• We looked at the same runs, to check that we handle the analysis code in the right way
• We reproduced Yuri‘s results for most layers (all TIB, TOB 1-4). Example:
Yuri Gotra our analysis
8 December 2011
SiStrip Calibration, Local Reconstruction and Simulation meeting
Different result for TOB layer 5 and 6• For some runs, we reproduce the results exactly (e.g. first 5
runs in the plots)• For the other runs, our analysis looks more stable• Differences to be understood (same files!)
Yuri Gotra our analysis
8 December 2011
SiStrip Calibration, Local Reconstruction and Simulation meeting
Status of Lorentz Angle Measurement
Dispersion of mobility estimations• The dispersion of mobility estimations cannot be explained only by
temperature variations• There are unexplained variations with time
8 December 2011
Run #
April to mid-July2010
SiStrip Calibration, Local Reconstruction and Simulation meeting
Status of Lorentz Angle Measurement
Dispersion of mobility estimations• ... and the values obtained can be very different for each method.
We started to investigate the reasons for those behaviours
8 December 2011
Run #
SiStrip Calibration, Local Reconstruction and Simulation meeting
Status of Lorentz Angle Measurement
Too many high variance clusters at small angles
Typical patterns in TIB : the cowboy hatEx : TIB layer 1a – W=3
8 December 2011
Run 143657(22/08/2010)
Trying to adapt the variance methods for high variance spurious clusters
• As the average of clusters variance can be biased by the spurious clusters, we have tried other methods: the most probable value, the mean in the peak around the most probable value, the median No real improvement
Ex : TIB layer 1a (W=3) : mean most probable value
SiStrip Calibration, Local Reconstruction and Simulation meeting
Status of Lorentz Angle Measurement
8 December 2011
tanθL - (dx/dz)reco = - 0.00101 +/- 0.00032
tanθL - (dx/dz)reco = -0.01532 +/- 0.00038
Run 143657(22/08/2010)
Trying to adapt the prob1 method for high variance spurious clusters
Change of normalisation : the TIB case• Improvement of the shape (here : TIB layer 2s)
• Fit result for tanθL - (dx/dz)reco = 0.0185 +/- 0.0006 0.0015 +/- 0.0007
Run 143657(22/08/2010)
SiStrip Calibration, Local Reconstruction and Simulation meeting
Status of Lorentz Angle Measurement
8 December 2011
Nw=1 / Nclusters Nw=1 / (Nw=1 + Nw=2 )
tanθt - (dx/dz)reco tanθt - (dx/dz)reco
The maximum probability of w = 1 methodChange of normalisation : the TOB case• Also improvement of the shapes …• … but the statistics of W=1 clusters for TOB is too low, depleting the
center of the distribution.• and the Symmetry Fit to find the maximum seems sensitive to
asymmetry in statistics, even if symmetric in shape.
no improvement of the results (ex: TOB layer 2s)
SiStrip Calibration, Local Reconstruction and Simulation meeting 8 December 2011
Run 143657(22/08/2010)
Status of Lorentz Angle Measurement
Nw=1 / Nclusters Nw=1 / (Nw=1 + Nw=2 )
tanθL - (dx/dz)reco = 0.0059 +/- 0.0029
tanθL - (dx/dz)reco = - 0.0048 +/- 0.0032
tanθt - (dx/dz)recotanθt - (dx/dz)reco
Trying to rather clean the clusters
SiStrip Calibration, Local Reconstruction and Simulation meeting 8 December 2011
Status of Lorentz Angle Measurement
Trying to rather clean the clusters
SiStrip Calibration, Local Reconstruction and Simulation meeting 8 December 2011
Status of Lorentz Angle Measurement
Cleaning is effective
Trying to rather clean the clusters
SiStrip Calibration, Local Reconstruction and Simulation meeting 8 December 2011
Status of Lorentz Angle Measurement
Variance method
Trying to rather clean the clusters
SiStrip Calibration, Local Reconstruction and Simulation meeting 8 December 2011
Status of Lorentz Angle Measurement
Maximum probability method
SiStrip Calibration, Local Reconstruction and Simulation meeting
8 December 2011
Attempts to replace the Symmetry Fit• V-shaped fit function• Minimum or maximum of a fitted polynomial (order 3 or 4), around
the expected Lorentz angle
Status of Lorentz Angle Measurement
TIB 2aProb12
End 2010 Beginning 2011
CERN17 08.12.2011
Simulation originally written for lorentz angle measurement with laser in Karlsruhe
Use T-CAD simulation of electric field
Place charge carrier pairs according to laser type
Track charge through sensor volume
Electric field
Magnetic field
Diffusion
…
Calculate induced signal per strip
Up to now, no readout electronic effects included
Take gaussian fit of charge cluster to calculate lorentz shift and hall mobility
Simulation of 300um CMS sensor at different temperatures with red laser
Expected temperature coefficient:-0.16e-3 (1/Tesla)/Kelvin at 300V, 4T
Andreas NürnbergSiStrip Calibration and Local Reconstruction meeting
Expected µH temperature dependence (simulation)
SIMULATION
CERN18 08.12.2011
Temperature effects: temperature & µH
Andreas NürnbergSiStrip Calibration and Local Reconstruction meeting
µH - avgv2 – Run 161311
Silicon temperature – Run 161311
TIB & TOB Tracker module temperature quite inhomogeneous, even among modules of the same layer
Inner layers warmer than outer layersSeveral closed cooling loops clearly visible
Temperature distribution quite stable during a run Take average
Calculate µH for each module individuallyCheck for correlation between hall mobility and temperature
CERN19 08.12.2011
Average temperature depencence (from fit) in expected order of magnitude for this specific run (161311, 23 March 2011) for most layers
Expected value (0.16e-3 1/Tesla K) determined by simulation
TIB TOB
expected value
Temperature effects – Impact on Lorentz angle
There are temperature differences in a layer as large as 30°C for inner TIB layers. Such temperature differences should lead to µH differences and cluster shifts of the order of ~0.05 1/Tesla and ~5µm
A correction taking into account the module temperature is thus probably worth to be envisaged
SIMULATION
Andreas NürnbergSiStrip Calibration and Local Reconstruction meeting
CERN20 08.12.2011
Depletion Voltage
Depletion voltage in TIB and TOB ranges from 100V up to 300V
Depletion voltage depends on bulk doping concentration (and radiation induced damage)
Different depletion voltage of the sensors may have an effect on the Lorentz angle as it affects the electric field distribution in the sensor bulk even at the same bias voltage
Backplane Strips
V_depl=300V
V_depl=100V
|E| [V/cm]
Electric field(VBias = 300V)
300
0
Andreas NürnbergSiStrip Calibration and Local Reconstruction meeting
CERN21 08.12.2011
Depletion Voltage – Impact on Lorentz angle
Slopes mostly compatible to zero
No dependence of Lorentz angle to depletion voltage observed
Simulation shows no dependence as well
avgv3
expected value
avgv2
expected value
Andreas NürnbergSiStrip Calibration and Local Reconstruction meeting
TIB TOB TIB TOB
CERN22 08.12.2011
Use simulation code written for hardware LA measurements
Induce charge by laser pulse from backside
Track charge carrier drift through sensor
Reconstruct cluster and calculate shift
No dependence on depletion voltage observed
Depletion Votage – Monte Carlo
300V bias
SIMULATIONSIMULATION
Andreas NürnbergSiStrip Calibration and Local Reconstruction meeting
CERN23 08.12.2011
Parametrize electric field distribution in sensor (An algorithm for calculating the Lorentz angle in
silicon detectors, V. Bartsch et al., Nuclear Instruments and Methods in Physics Research A 497 (2003) 389–396)
Parametrize hall mobility / drift velocity depending on electric field and temperature (A REVIEW OF SOME CHARGE TRANSPORT PROPERTIES OF SILICON, C. JACOBONI et al., Solid-State
Electronics, 1977, Vol. 20, pp. 7749.)
Calculate „local“ shift in depth z
Integrate over sensor thickness total shift
Calculate tan(θL) = shift / thickness and divide by magnetic field (here fixed to 3.8T) to obtain µh
Parametrization of hall mobility
Andreas NürnbergSiStrip Calibration and Local Reconstruction meeting
CERN24 08.12.2011
µh expectation vs. measurement
Tested on 2 runs 163817, 2nd May 2011
177139, 25th Sept. 2011
Calculate expected µh per module using measured silicon temperature and Vdepl
from database
Compare µh value obtained from data by different estimators to this expected value
Histograms should be centered around zero
The narrower the better
Run 163817, TOB
Andreas NürnbergSiStrip Calibration and Local Reconstruction meeting
CERN25 08.12.2011
µh expectation vs. measurement
Measured µH is ~ 5-10% smaller than expectation
Possibly due to deconvolution mode of APV
Effective sensor thickness is reduced
Deco mode is not yet considered in calculation
avgv3 (filled symbols) seems to be closer to expectation than avgv2 (open symbols)
TOB
TIB
Andreas NürnbergSiStrip Calibration and Local Reconstruction meeting
Runs from April to October 2010
• All methods quite stable results during the whole year for TIB1a
April May June July August Sept. Oct.
Status of Lorentz Angle Measurement
Runs from April to October 2010
• Slight increase in avgv3 (black), slight decrease in avgv2 (blue) for TOB layer 2a• Drifts also in other layers and methods visible see backup for remaining layers
April May June July August Sept. Oct.
Status of Lorentz Angle Measurement
SiStrip Calibration, Local Reconstruction and Simulation meeting
8 December 2011
Monitoring for 2011 – shift after bias scan
• Jump after bias scan (beginning 2011) in TOB (here : TOB 2a)
Status of Lorentz Angle Measurement
SiStrip Calibration, Local Reconstruction and Simulation meeting
Status of Lorentz Angle Measurement
Conclusions• To be written
May 12th, 2011
CERN30 08.12.2011
Temperature dependence of µH is like it is expected, at least on average
However for the time being the methods to determine µH seem to produce dispersions not all explained by temperature differences
No impact of depletion voltage to Lorentz angle observed in data for Run 167674, 24 June 2011
Monte Carlo simulation shows no dependence from depletion voltage, as long as sensors are overdepleted (which is true for the strip tracker)
Implemented theoretical model to estimate Lorentz angle
Expected LA from model is 5-10% larger than measured oneProbably due to missing corrections for APV deconvolution mode
Conclusions
Andreas NürnbergSiStrip Calibration and Local Reconstruction meeting
CERN31 08.12.2011
Investigate bias scan at beginning of 2011 run for further testing of model
Implement corrections for deco mode
Get automated access to temperature database (?)
Outlook
Andreas NürnbergSiStrip Calibration and Local Reconstruction meeting
Backup
Runs from April to October 2010
April May June July August Sept. Oct.
Runs from April to October 2010
April May June July August Sept. Oct.
Runs from April to October 2010
April May June July August Sept. Oct.
Runs from April to October 2010
April May June July August Sept. Oct.
Runs from April to October 2010
April May June July August Sept. Oct.
Runs from April to October 2010
April May June July August Sept. Oct.
Runs from April to October 2010
April May June July August Sept. Oct.
CERN40 08.12.2011
163817 – avgv2
TIB
TOB
Andreas NürnbergSiStrip Calibration and Local Reconstruction meeting
CERN41 08.12.2011
163817 – avgv3
TIB
TOB
Andreas NürnbergSiStrip Calibration and Local Reconstruction meeting
CERN42 08.12.2011
177139 – avgv2
TIB
TOB
Andreas NürnbergSiStrip Calibration and Local Reconstruction meeting
CERN43 08.12.2011
177139 – avgv3
TIB
TOB
Andreas NürnbergSiStrip Calibration and Local Reconstruction meeting