Page 1 of 18 Bjorn S. Nilsen, ALICE November 16 ITS Software meeting ITS Alignment Status Plus other...

of 18Bjorn S. Nilsen, ALICE November 16 ITS Software meeting

ITS Alignment StatusPlus other things

ByBjørn S. Nilsen

The Ohio State University


Outline

● ITS internal Alignment● Open questions about calibration● Changes in Tgeant3 and the Virtual MC interface● Speeding up of SPD simulation● planned Changes to AliITSgeom● Conclusions


ITS Alignment

● 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.


Alignment view● Offline wants new ITS

geometry to have “movable” parts.– In principle do-able, but...– Moving part of the ITS

geometry leads to overlaps..– To make remove the

modified geometries overlaps, shapes must change (e.g. box->Trap)

– This is a problem difficult to solve even in principle.

Parts of “Detector response Analysis and Alignment”may be done before “Reconstruction” and may usesome of the results from the Tracking and PID.


ITS view (my opinion)● We align using AliITSgeom (the geometry of our

sensitive volumes)– This isn't quite good enough for tracking, the need to

know about the material budget between layers– Don't know quite how to solve this.

● Using reconstructed virtual photons converted within the ITS, we can know about all of the material within the ITS– This, along with the corrected AliITSgeom, will be

used to rewrite a new ITS geometry (up to some possible limits to be determined)


Alignment Status

● new AliITSAlignRecPoint (derived from AliITSRecpoint)

– Adding data members needed for Alignment (Event#, Det#, Global coordinate,...)

– Adding functionality, not found in AliITSRecPoint

● new memory resident array classes for AliITSAlignRecPoint (by detector, track, ...)

● More still to come

Work just starting up again (see ITS TDR for original results)


Calibration● We had a long and active meeting about

calibration at the last Offline week.– Offline want to know, from us(?)

● What data will be stored in the different data bases● What data “we” need for the Offline● And where all of this data can be found.

– Offline presented a prototype “framework” to get access to information kept in ALICE data bases

● Prototype only worked with DCS data base● Most ITS information “we” need is not in DCS data base● “User” interface very poor

– must give an ascii input file with a list of all data possibly wanted– ascii file must also contain address of data base– format of ascii file dependent on which data base accessing

● Seems as cumbersome as accessing data bases directly– Aren't there supposed to be API's for all Data Bases?– Isn't there ROOT interfaces to all of these Data Bases?


Process to Get Calibration Data

Peter Chochula

Boyko Yordanov


Calibration InformationWhole ITS

Incom

plete

Prelim

inary

● Cooling: Air (flow rate, humidity, Temperature), Water Cooling {1/half-Barrel (Flow meter, Waist Oxygen Levels), 26 each side

(Cooing circuit on/off, Temperature, Pressure)}, 2 Phase (?)● ITS Alignment monitoring System:● Racks: ?● Inter Lock: ?● ?● Geometry, Survey (not in any data base, Alice Note?)

Sim

ulat

ion

Rec

onst

ruct

ion


Calibration InformationSPD

Incom

plete

Prelim

inary

● 10 Sectors, 6 Staves/sector, 4 detectors/Stave, 5 readout chips/detector, 256×32 pixels/readout chip

● ?● Dead pixels/readout chips/Staves, Noisy pixels,

Geometry● Noise levels, Thresholds, Temperature, Bias

voltage, GeometrySim

ulat

ion

Rec

onst

ruct

ion


Calibration InformationSDD

Incom

plete

Prelim

inary

● 22 [14] ladders/layer, 2 sets of ladder end boards/ladder , 8 [6] detectors/ladder, 2 hybrids/detector 3 Ambra+Pascal/hybrid, 256 Anodes/hybrid

● Power supply, low voltage, medium voltage, high voltage● Hybrid: Temperature, over current, voltage setting, readout

frequency, ● CARLOS: low & high thresholds, enable/disable zero

suppression● ?● High & low thresholds, baseline, noise level, temperature

(injectors), Geometry● Correction maps (?)Si

mul

atio

nR

econ

stru

ctio

n


Calibration InformationSSD

Incom

plete

Prelim

inary

● 2 Layers, 33 [33] ladders/layer, 25 [22] detectors/ladder, 2 hybrids/detector, 768 strips/hybrid

● ?● Threshold, Baseline, noise level, temperature,

bias voltage, Geometry

Sim

ulat

ion

Rec

onst

ruct

ion


Calibration Sources (?)

Incom

plete

Prelim

inary

● Detector Construction Data base– Detector & other positions,

● Special data and none data runs (after some analysis)– noise, temperature,...

● Regular data runs, calibration event (after some analysis)– temperature (injector events), ...

● Data runs, real data (after some analysis)– noise (zero non-suppressed data), alignment,...


TGeant3and

AliITSgeom initializationChanges to TGeant3, TGeant3TGeo...,

and TVirtualMC.● Added function, GetTransformation, GetShape,

GetMaterial, & GetMedium● Now we can remove the use of TGeant3 functions● This will now allow all of our geometries to be use

with Geant3 (native/TGeo), Geant4, and Fluka (except for the use of MANY)

● Waiting for, Update of Geant3, ROOT, and OK from Peter


SPD SimulationdubnaUpdates, to come

Presently1 Trapezoidal Integration along

track path between hits. - Easy to code & debug- Inefficient

2 Step size is of the order 1µm- Much smaller than needed- Guarantees accuracy

3 4 evaluations of Tmath::Erfc- ~exp(8th order polynomial)

4 Loop over ±3 (x), ±2 (z) pixels

Under Development1A Gaussian Integration along

track path between hits. - Very efficient- Many fewer steps (~10 compared to

~200)- Require 4 evaluations of Erfc

functions1B And/Or Analytic Integration

- Must be done via an expansion- Includes evaluation of Erfc functions

2 Loop over ±3 (x), ±2 (z) pixels Max

- Only as needed3 More general algorithm

- Applicable to SPD and SSD- May be expendable to SDD


● All parameters will be unchanged– Work on optimizing parameters can use existing code– Only algorithm will change

● Code ready by End of November● Code tested by End of December

– Comparison of SDigits between versions– Require same numbers up to ±1 electron or better

SPD SimulationdubnaUpdates, to come


Changes to AliITSgeom● Allow it to work with the “new” tracking

standard detector local coordinate system (see presentation by Juira)

● Give AliITSgeom direct access, if not complete ownership of, the segmentation class– AliITSgeom would then do transformation from

module index coordinates through ALICE global coordinates.

– With one call/function one can go from any set of coordinates to any other.


Conclusions

● ITS internal Alignment work started● Open questions about calibration ????????? help!● Changes in TGeant3 and the Virtual MC interface

ready to be put to use● Speeding up of SPD simulation coming soon● planned Changes to AliITSgeom coming soon

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