ITS Detector Alignment Status

Oct. 5 2005

ALICE Offline Week

By: Bjørn S. Nilsen

Outline

Alienable Parts

Effects on Hits, SDigits, Digits, RecPoints, Tracks

Simulations with misaligned data

Software realignment

Other Stuff

Alienable Parts

2198 Si detector wafers

240 SPD wafers

260 SDD wafers

1698 SSD wafers

X 6 DoF = 13188 DoF

All of the other Radiation thick Materials of ITS.

Effects on Hits, SDigits, Digits, RecPoints, and Tracks

Simulation Uses AliITSgeom

Hits

SDigits

Digits

AliITSgeom Must be Exactly from geometry at all times

Reconstruction Uses AliITSgeom

RecPoints

Tracks

AliITSgeom should never be Exactly from geometry

AliITSgeom can be modified before using in Reconstruction

How to Reconstruct
Unaligned data

Run Standard AliRoot (ITS) simulation through Digit creation. AliITSgeom is filled from geometry (or file) and is exact.

Initialize reconstruction and load in the AliITSgeom data used during simulation.

AliITSgeom dealignedGm,*exactGm = its->GetITSgeom(); dealignedGm = *exactGm; dealignGm.RandomChange(strans,srot); its->SetITSgeom(&dealignedGm);

Now Run reconstruction all the way through. Results will be using a de-aligned ITS.

Simulations with Misaligned data

Uses AliITSgeom.

Used in all ITS code from simulation to tracking.

Not tested with most recent uncommitted code. No reason why is should not work.

Simulation was done using straight tracks.

Simulation and Analysis was done during this last Millennium. See ITS TDR section 6.3

Software realignment

Waiting on ...

Has not been done to date

Expect a reasonable version based on TTask in about 6 months

Results of realignment will be reflected in a new ITS geometry

Specifically, will be in reconstruction version of AliITSgeom

Some misalignments break symmetries in such a way that the use of copies is excluded and cost too much in new volumes. Will only be reflected in AliITSgeom

Software realignment
Outline

Require primary tracks with unambiguous digits.

No hypothesis tree for digits/tracking.

Tracks come from a well defined point and must have digits in all 6 layers, preferably more (det. Overlaps).

Suggest better to use low multiplicity or even p-p data

Prefer to use high Pt tracks.

Track model is better defined (material is clumped).

Fits to track shape are better, smaller c2.

Since multiple scattering averages out, even low Pt tracks might be used.

Software realignment
Outline

Group detectors by ladder, layer, or individually.

Perform fit of detector position to minimize separation between track and associated digit.

Note, average track-digit displacement gives new detector position to first order

Note, gradient in track-digit displacement gives rotation of detector to first order.

There are out of alignment modes which can not be found/corrected with tracks.

Conclusion
Alignment

Alienable Parts

2198 Si Wafers

All other central elements of the ITS

No effects on Hits, Sdigits, and Digits. Effects on RecPoints, and Tracks

Simulations with misaligned data - Done

Software realignment – To be done

Information still to get
SPD Configuration Data

4 bit Threshold/cell (computed based on noise [DCS-fecf])

Dead cell index (constDB and data analysis [ConstDB,?])

Noise cell index (no data noise run [DCS-fecf])

Multi-event buffer mode switch (by det chip [DCS])?

Voltage setting and current (1/power supply [DCS])?

Det chip on/off (indicated by V=0? [DCS])?

Detector chip index map [constDB]

Information still to get
SDD Configuration Data

Drift time residues (450/Det? [constDB])

Drift/Anode correction maps (2/cell [constDB])

Charge collection Efficiency (between 1/det to 1/cell, from data analysis [?])

Injectors/Thermal map (special trigger data [?})

Noise (no data noise run, zero unsuppressed [dcs-fecf])

2 Thresholds/anode (no data noise run/trigger, zero unsuppressed [dcs-fecf])

1 Baseline/anode (no data noise run/trigger, zero unsuppressed [dcs-fecf])

PreAmp gain (? [dcs-fecf])

High voltage/current (1/power supply [dcs])

Low voltage/current (1/power supply [dcs])

10 bit/8 bit data mode switch (2/det? [dcs-fecf])

Zero suppressed data switch (2/det? [dcs-fecf])

Sampling doubling switch (2/det? [dcs-fecf])

Clock frequency (2/ladder [dcs])

CARLOS Compression switch (2/ladder? [dcs-fecf])

CARLOS multi-event buffer switch (2/ladder? [dcs-fecf])

Detector index to location map [constDB]

Information still to get
SSD Configuration Data

Anode/Cathode index map [constDB]

Detector index map [constDB]

PreAmp gain (from noise run [dcs-fecf])

Baseline (from noise run [dcf-fecf])

Noise (from noise run [?])

Threshold (from noise run [dcf-fecf])

Detector voltage/current (1/power supply [dcf])

Low voltage/current (1/power supply [dcf])

Information still to get
Geometry Configuration Data

Base Geometry (constDB, survey, alignment [?])

AliITSgeom (alignment + Base Geometry [?])

AliITSAMS hardware alignment system alarm (1 type time? [dcs?])

AliITSAMS setup info (??? [?])

AliITSAMS voltage/current (1 [dcs?])

2005-10-03T16:12:05