CMS Torino meeting, 4 th June, 2007 R. Castello on behalf of Torino Tracker’s group Tracker Alignment with MillePede

4 th June 2007CMS Torino meetingR.Castello Outline Why we need alignment? Alignment with MillePede Algorithm Alignment with TIF trigger configuration on simulated cosmics data Preliminary results Status of the alignment with TIF real data Conclusions and outlook

4 th June 2007CMS Torino meetingR.Castello Why we need alignment? The CMS tracker is build in order to optimize the particle momenta resolution. It depends on two factors: C 2 depends on MCS C 1 is geometry - dependent B = magnetic field L = track length n = # hit of the track σ x = resolution on the measured point ~ 10 μm (Si) Systematic error can be minimized by a correct alignment

4 th June 2007CMS Torino meetingR.Castello The tracker alignment 1.Survey measurements (during assembly)  =  m 2.Laser Alignment System (LAS) : alignment of TIB vs TOB etc... 3.Track Based Alignment (cosmics, Z →  etc  )  = 10  m The problem 16k microstrip modules 6 d.o.f per module O (100k) unknowns Complex system of equation to solve efficient and fast algorithm For CMS tracker alignment 3 algorithms: HIP MillePede Kalman Filter (Helsinki, Milano, Perugia) (Hamburg, Torino) (Wien)

4 th June 2007CMS Torino meetingR.Castello MillePede Algorithm MILLE PEDE ( V. Blobel ) A measurement can be written as Linearised least square combined fit of alignment parameters (global) and track parameters (local) MIllePede uses the Method of the Least Squares residuum, where m k is the measurement with uncertainty  k and d k is the coefficient vector. the idea : minimize square of residuum. global local

4 th June 2007CMS Torino meetingR.Castello Alignment with MillePede Interested to the n global parameters. For a set of N measurements: from (n+N ) equations to n C ’ matrix inversion (Computational time ~ n 3 ) With MillePede you can different levels (Detectors, String, Layer level, etc…) 6 degrees of freedom for each alignable structure (6 parameters): 3 shifts (respectively along local x,y, z) and 3 rotations (around x,y,z) the aim it’s to find a with good uncertainty

4 th June 2007CMS Torino meetingR.Castello MillePede Algorithm in CMSSW (implemented by G. Flucke, Hamburg) - CMSSW 1_3_1 version - Alignment/MillePedeAlignmentAlgorithm (tag branchV X-01) - Cfg file: AlignmentTrackSelectorModule: - selection of Tracking algorithm - set APE - set cut for tk selection (p t, #hits,..) AlignmentProducer: - selection of alignment parameters - geometrical selection in eta, phi,z - selection of misalignment scenario - set solving method ( inversion, etc.) - set  2 range acceptance PoolSource: - selection of dataset - set number of events

4 th June 2007CMS Torino meetingR.Castello Cosmics (Tracker Integration Facility) Old scintillator configuration ( 36k events) New scintillator configuration ( 20k events) Since Feb.’07 the 25% of the tracker system is under commissioning

4 th June 2007CMS Torino meetingR.Castello RMS =263  rad Rod Level (79 alignment parameters) RMS =151  m Results on TIF cosmics simulated sample (old trigger configuration) with Short Term misalignment scenario (~100 pb -1 )

4 th June 2007CMS Torino meetingR.Castello  u (Strings level) Good correlation between  u at the start (misaligned) and at the end (after the alignment) Global correlation : largest correlation of a parameter with any linear combination of all other parameters. A value close to 1 means solution not well determined.

4 th June 2007CMS Torino meetingR.Castello Simulated cosmic sample with old scintillator configuration (x axis) Simulated cosmic sample with new scintillator configuration (y axis) agreement for  u Old and new MC configuration To be understood..

4 th June 2007CMS Torino meetingR.Castello  u and  for real data (10 th March run) RMS =21  m RMS =79  rad Rod Level (71 alignment parameters) Too precise if compared with the “expected” results under studying…

4 th June 2007CMS Torino meetingR.Castello Conclusions & outlook Preliminary results obtained running MIllePede alignment algorithm on TIF simulated sample for  u and  parameters at two different hierarchical levels (Strings & Layer ) No relevant differences between new and old scintillator configuration on simulated data (a first indication of algorithm stability) The exercise on real data is going on Good impression and relevant hints from recent Hamburg workshop: