TPC space point distortion and calibration Pass 0

TPC space point distortion and calibration. Pass 0 and Pass. X calibration marian ivanov for the TPC OFFLINE group 10 th March 2011 1

Outlook TPC correction framework Physical Models Distortion/alignment calibration Pass 0, Pass X calibration 10 th March 2011 2

TPC correction framework (Jim. Thomas, Stefan Rossegger, Magnus Mager, MI, . . . ) 10 th March 2011 3

Composed correction framework for modeling the TPC field distortions in Ali. Root, Alice Internal Note, 2010 This document provides a description of a group of C++ classes, which we have developed in order to model, distortions due to the different electric and magnetic field inhomogeneities in the ALICE TPC. The different models have been grouped together in a composed correction framework to simplify their usage and not to duplicate common code structures like the correction, distortion, print and plot functionality. The models were chosen to give a physical description of the distortions in order to achieve a step-by-step description of the geometrical details of the TPC itself. A complete list of field distortions and their resulting space point distortions can be formulated and the classes described here constitute a good description of the most important space-point distortions in the TPC. [1] M. Mager, S. Rossegger and J. Thomas, Composed correction framework for modeling the TPC field distortions in Ali. Root, Alice Internal Note, 2010, ALICE-INT-2010 -018. url: https: //edms. cern. ch/file/1113105/1/ALICE-INT-2010 -018. pdf [2] S. Rossegger and J. Thomas, Space-charge effects in the ALICE TPC: a comparison between expected ALICE performance and current results from the STAR TPC, Alice Internal Note, 2010, ALICE-INT-2010 -017. url: https: //edms. cern. ch/file/1113087/1/ALICE-INT-2010 -017. pdf [3] M. Mager, S. Rossegger and J. Thomas, The Langevin equation expanded to 2 nd order and comments on using the equation to correct for space point distortions in a TPC, Alice Internal Note, 2010, ALICE-INT-2010 -016. url: https: //edms. cern. ch/file/1108138/1/ALICE-INT-2010 -016. pdf 10 th March 2011 4

Composed correction framework 10 th March 2011 5

TPC composed correction Composed of: 1. TPCEx. BShape 2. align. Global 3. align. Local 4. align. Quadrant 5. FCVolt. Error 3 D 6. Fit. Boundary 7. Fit. Ex. BTwist 8. Fit. Align. TPC 9. Fit. Roc. Align. ZSum 10 th March 2011 6

Space point distortion due B field. Input data – integral of B field map Parameters to validate/fit: – – T 1, T 2, omega-tau Gas dependent Special runs to validate models and to extract parameters: – – B-field scan E-field scan Time dependence: – 10 th March 2011 Omega-tau – depends on the time in similar way as the drift velocity 7

Ex. B twist Space point distortion due global misalignment of the magnetic field and E-field in the TPC drift volume 2 parameters to fit Time dependence: – 10 th March 2011 Following the aligment 8

Boundary voltage 10 th March 2011 9

Field cage and Rod alignment 18 (rods) x 2 (IFC, OFC) x 2 (A side, C-side) 2 rotated clips x 2 (A side, Cside) B field 0 data used for the alignment/calibration 10 th March 2011 – Fitting of the distortion 10

Alignment 10 th March 2011 11

ROC z alignment 10 th March 2011 12

Time dependent alignment The default calibration entry for the space point distortion extracted using the data from the LHC 10 b, LHC 10 c and LHC 10 e period Additionally time dependent alignment correction applied on the top of mean correction Calibration entry granularity - run by run – Detector movement mainly switching the magnetic field polarity Two models: – – 10 th March 2011 Alignment in respect with other detectors Alignment in respect to the magnetic field (Ex. B Twist) 13

TPC-ITS alignment B=-0. 5 T B=0. 5 T Delta X and delta Y of the TPC-ITS translation (mm) Calibration part of the Pass 0. Used later in the reconstruction. 10 th March 2011 14

Ex. B twist B=-0. 5 T B=0. 5 T Ex. B twist angle parameters (rad) Calibration part of the Pass 0. Used later in the reconstruction. 10 th March 2011 15

Global fits and linear models (MI, Ana Kreshuk) 10 th March 2011 16

Distortion/alignment calibration Assumptions/Approximations: Space point distortion commute (the order of applying of corrections is not important) Space point distortion can be approximated as a linear combination of the “partial distortion” functions with given parameter: • = ki*Ei Space point distortion not directly observed. We define the set of observables O. • = ki*Oei Under given assumption the analytical (not iterative) Global minimization can be performed solving the set of linear equations. • Important to use unbiased set of observables Assumptions were tested for the “typical” distortion in the TPC, moreover the assumption were tested also for the fitted parameters. 10 th March 2011 17

Observable models example: Ex. B effect due B field non linearities Observed distortion linear combination of partial distortions Internal TPC calibration (2 parameters) 10 th March 2011 18

Fitting/minimization Numerical part based on the linear fitting package implemented in the ROOT (Tmatrix. D, Tlinear. Fitter) Additional functionality implemented in the class Tstat. Toolkit – – 10 th March 2011 Input data observables and fit models from the tree Possibility to add constrains Possibility to check the fit values (return value of the Fit. Plane. Constrain can be used as a alias in tree) Extraction of the partial fits 19

Pass 0 -Gobal fit example - Ali. TPCPreprocessor. Offline Define the model Fit model Additional constraints of particular parameters Create calibration entry 10 th March 2011 20

Pass 0, Pass X calibration (MI, Jacek Otwinowski, Alexander Kalweit, Jens Wiechula, ++) 10 th March 2011 21

TPC calibration train – calibration and calibration validation Raw data Reconstruction on Alien Calibration trains N iterations ESD + ESD friends (all information Tracks+Clusters) OCDB configuration Calibration train: Apply calibration Refit the track Recook variables (e. g d. Edx) Fill calibration components Merge calibration components Fits Extract new/residual calibration entry Store new OCDB entry (specific storage) Validation of OCDB entry (0 residual calibration) Port the OCDB entry to Alien OCDB 10 th March 2011 22

TPC calibration components Ali. TPCcalib. Calib Reapply transformations According OCDB setting Refit the track Ali. TPCcalib. Time Drift velocity calibration Inter-detector alignment Filing of the detector matching residual Histograms Time granularity – 15 min Ali. TPCcalib. Laser residual histograms Used later for global space point distortion calibration Ali. TPCcalib. Align Cluster residual histograms Tracklet residual histograms Ali. TPCcalib. V 0 Filtering of the high pt V 0 Ali. TPCcalib. Time. Gain equalization in time and space (el. Attachment) Time granularity – 15 min Ali. TPCcalib. Cosmic Filtering of the cosmic track candidates Light calibration OCDB entries per run Used for space point calibration OCDB entries per group of runs 10 th March 2011 23

Pass 0 / Pass. X (TPC oriented view) Raw data reconstruction per chunk ESD + ESD friends (all information Tracks+Clusters) Pass 0 only Apply calibration Refit the track Recook variables (e. g d. Edx) Fill calibration components Merge calibration components Fits Extract new/residual calibration entry Validation of OCDB entry Port the OCDB entry to Alien OCDB 10 th March 2011 N jobs 1 Alien job per chunk 2 independent Ali. Root processes 1 job per run CPU and memory consuming Improvement needed: Recursive merging Mering per calibration component 24

Binned Observables / Global alignment Generalization of the algorithm for all outer detectors – Global alignment Possible to integrate the algorithm in the Pass 0 or Pass. X Central train calibration • Detector matching – residual histogram – Differential Residual (4 D) histogram in bins of phi, eta, 1/pt • • 20 000 bins 10^6 events - 10^7 tracks ==>5000 entries in bin • Creation of distortion maps – Very small Statistical error = rms/sqrt(entries) e. g • • TPC-ITS ~ 20 microns TPC-TOF ~ 300 microns March 2011 fitting of distortion parameters • Global 10 th Calibration train (Grid) histogram Merging Creation of distortion Maps Distortion models fitting Distortion parameters Fitting 25

Steering macro run. Pass 0. sh 2 aliroot processes – – merge. Make. OCDB. sh - 2 processes – – 10 th Reconstruction (rec. Pass 0. C) Calibration (run. Calib. Train. C) Merging – merge. C OCDB extraction - make. OCDB. C validation. Merging. sh validation. sh March 2011 26

Detector specific code should be implemented in the code loaded with Ali. Root, the rest (ANLAYSIS dependent) in the lib. XXXcalib library e. g lib. T 0 calib. so custom par file are not allowed – Example compiled code to create detector calibration library: : – – 10 th Library needed for the pass 0, Pass. X calibration loaded in the STEERING macro Load. Libraries March 2011 https: //alisoft. cern. ch/Ali. Root/trunk/T 0/CMakelib. T 0 ca lib. pkg https: //alisoft. cern. ch/Ali. Root/trunk/T 0 calib. Link. De f. h https: //alisoft. cern. ch/Ali. Root/trunk/T 0/Ali. T 0 Preproce ssor. Offline. cxx => Resonsible to create OCDB https: //alisoft. cern. ch/Ali. Root/trunk/T 0/Ali. T 0 Calib. Off set. Channels. Task. cxx ==>Calibration task(s) itself 27