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Tracker Alignment with MillePede. 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. Outline. Why we need alignment?. - PowerPoint PPT Presentation
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CMS Torino meeting,
4th June, 2007
R. Castello on behalf of Torino Tracker’s group
Tracker Alignment with MillePede
CMS Torino meeting R.Castello4th June 2007
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
CMS Torino meeting R.Castello4th June 2007
Why we need alignment?
• The CMS tracker is build in order to optimize the particle momenta resolution.
• It depends on two factors:
21 CpCp
p
C2 depends on MCS
C1 is geometry -dependent
B = magnetic field
L = track length
n = # hit of the track
σx = resolution on the measured point
sistx2
int2
21LBn
C x
~ 10 μm (Si)
Systematic error can be minimized by a correct alignment
CMS Torino meeting R.Castello4th June 2007
The tracker alignment
1. Survey measurements (during assembly) = 100-200 m2. Laser Alignment System (LAS) : alignment of TIB vs TOB etc ...3. Track Based Alignment (cosmics, Z→ etc) = 10 m
The problem16k microstrip modules
6 d.o.f per moduleO (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)
CMS Torino meeting R.Castello4th June 2007
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 mk is the
measurement with uncertainty k and dk is the
coefficient vector.
the idea : minimize square of residuum.
fitk
hitkk
Tkk uudamr
kk
kT
k dama
2
2 )(
jj
ji
n
ii daz
11
global
local
CMS Torino meeting R.Castello4th June 2007
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 ~ n3 )
• With MillePede you can align @ 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
),,,,,( wvua
baC '' baC global
CMS Torino meeting R.Castello4th June 2007
MillePede Algorithm in CMSSW(implemented by G. Flucke, Hamburg)
- CMSSW 1_3_1 version - Alignment/MillePedeAlignmentAlgorithm (tag branchV00-07-0X-01) - Cfg file: AlignmentTrackSelectorModule:- selection of Tracking algorithm
- set APE - set cut for tk selection
(pt, #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
CMS Torino meeting R.Castello4th June 2007
Cosmics simulation @TIF (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
CMS Torino meeting R.Castello4th June 2007
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)
CMS Torino meeting R.Castello4th June 2007
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.
CMS Torino meeting R.Castello4th June 2007
Simulated cosmic sample with old scintillator configuration (x axis)
Sim
ula
ted c
osm
ic s
am
ple
wit
h n
ew
sci
nti
llato
r co
nfig
ura
tion (
y a
xis
)
agreement for u
Old and new MC configuration
To be understood..
CMS Torino meeting R.Castello4th June 2007
u and for real data (10th March run)
RMS =21 m
RMS =79 rad
Rod Level (71 alignment
parameters)
Too precise if compared with the “expected” results
under studying…
CMS Torino meeting R.Castello4th June 2007
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:
http://indico.cern.ch/conferenceDisplay.py?confId=16095
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