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SiStrip Calibration, Local Reconstruction and Simulation meeting 27 km 100 m Status of Lorentz Angle Measurement Introduction Lorentz 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 L Cluster shift S. Frosali Th. Caebergs (UMons) – A. Nürnberg (KIT) – C.Vander Velde (ULB

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Introduction How 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 ² 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 L = track for minimum width (B. Betchart)

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SiStrip Calibration, Local Reconstruction and Simulation meeting 27 km 100 m Status of Lorentz Angle Measurement Introduction More 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 ( L ) = µ_ H B This work was started by Y. Gotra. 8 December 2011

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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 Gotraour analysis 8 December 2011 SiStrip Calibration, Local Reconstruction and Simulation meeting

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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 Gotraour analysis 8 December 2011 SiStrip Calibration, Local Reconstruction and Simulation meeting

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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-July 2010

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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 #

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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 hat Ex : TIB layer 1a – W=3 8 December 2011 Run (22/08/2010)

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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 tanθ L - (dx/dz) reco = / tanθ L - (dx/dz) reco = / Run (22/08/2010)

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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 tanθ L - (dx/dz) reco = / / Run (22/08/2010) SiStrip Calibration, Local Reconstruction and Simulation meeting Status of Lorentz Angle Measurement 8 December 2011 N w=1 / N clusters N w=1 / (N w=1 + N w=2 ) tanθ t - (dx/dz) reco

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The maximum probability of w = 1 method Change 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 (22/08/2010) Status of Lorentz Angle Measurement N w=1 / N clusters N w=1 / (N w=1 + N w=2 ) tanθ L - (dx/dz) reco = / tanθ L - (dx/dz) reco = / tanθ t - (dx/dz) reco

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Trying to rather clean the clusters SiStrip Calibration, Local Reconstruction and Simulation meeting 8 December 2011 Status of Lorentz Angle Measurement

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Trying to rather clean the clusters SiStrip Calibration, Local Reconstruction and Simulation meeting 8 December 2011 Status of Lorentz Angle Measurement Cleaning is effective

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Trying to rather clean the clusters SiStrip Calibration, Local Reconstruction and Simulation meeting 8 December 2011 Status of Lorentz Angle Measurement Variance method

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Trying to rather clean the clusters SiStrip Calibration, Local Reconstruction and Simulation meeting 8 December 2011 Status of Lorentz Angle Measurement Maximum probability method

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8 December 2011 SiStrip Calibration, Local Reconstruction and Simulation meeting 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 2a Prob12 End 2010 Beginning 2011

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CERN 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 Nürnberg SiStrip Calibration and Local Reconstruction meeting Expected µH temperature dependence (simulation) SIMULATION

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CERN Temperature effects: temperature & µH Andreas Nürnberg SiStrip Calibration and Local Reconstruction meeting µH - avgv2 – Run Silicon temperature – Run TIB & TOB Tracker module temperature quite inhomogeneous, even among modules of the same layer Inner layers warmer than outer layers Several closed cooling loops clearly visible Temperature distribution quite stable during a run Take average Calculate µH for each module individually Check for correlation between hall mobility and temperature

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CERN 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 Nürnberg SiStrip Calibration and Local Reconstruction meeting

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CERN 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 (V Bias = 300V) Andreas Nürnberg SiStrip Calibration and Local Reconstruction meeting

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CERN 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 Nürnberg SiStrip Calibration and Local Reconstruction meeting TIB TOB TIB TOB

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CERN 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 SIMULATION Andreas Nürnberg SiStrip Calibration and Local Reconstruction meeting

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CERN 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 ) Calculate „local“ shift in depth z Integrate over sensor thickness total shift Calculate tan(θ L ) = shift / thickness and divide by magnetic field (here fixed to 3.8T) to obtain µh Parametrization of hall mobility Andreas Nürnberg SiStrip Calibration and Local Reconstruction meeting

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CERN µh expectation vs. measurement Tested on 2 runs , 2nd May , 25th Sept Calculate expected µh per module using measured silicon temperature and V depl 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 , TOB Andreas Nürnberg SiStrip Calibration and Local Reconstruction meeting

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CERN 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 Nürnberg SiStrip Calibration and Local Reconstruction meeting

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Runs from April to October 2010 All methods quite stable results during the whole year for TIB1a AprilMayJuneJulyAugustSept.Oct. Status of Lorentz Angle Measurement

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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 AprilMayJuneJulyAugustSept.Oct. Status of Lorentz Angle Measurement

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8 December 2011 SiStrip Calibration, Local Reconstruction and Simulation meeting Monitoring for 2011 – shift after bias scan Jump after bias scan (beginning 2011) in TOB (here : TOB 2a) Status of Lorentz Angle Measurement

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SiStrip Calibration, Local Reconstruction and Simulation meeting Status of Lorentz Angle Measurement Conclusions To be written May 12th, 2011

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CERN 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 , 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 one Probably due to missing corrections for APV deconvolution mode Conclusions Andreas Nürnberg SiStrip Calibration and Local Reconstruction meeting

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CERN 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 Nürnberg SiStrip Calibration and Local Reconstruction meeting

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Backup

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Runs from April to October 2010 AprilMayJuneJulyAugustSept.Oct.

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Runs from April to October 2010 AprilMayJuneJulyAugustSept.Oct.

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Runs from April to October 2010 AprilMayJuneJulyAugustSept.Oct.

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Runs from April to October 2010 AprilMayJuneJulyAugustSept.Oct.

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Runs from April to October 2010 AprilMayJuneJulyAugustSept.Oct.

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Runs from April to October 2010 AprilMayJuneJulyAugustSept.Oct.

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Runs from April to October 2010 AprilMayJuneJulyAugustSept.Oct.

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CERN – avgv2 TIB TOB Andreas Nürnberg SiStrip Calibration and Local Reconstruction meeting

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CERN – avgv3 TIB TOB Andreas Nürnberg SiStrip Calibration and Local Reconstruction meeting

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CERN – avgv2 TIB TOB Andreas Nürnberg SiStrip Calibration and Local Reconstruction meeting

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CERN – avgv3 TIB TOB Andreas Nürnberg SiStrip Calibration and Local Reconstruction meeting

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