(ITS) ALIGNMENT: status, problems, planning etcAlignable elements:SPD -- 240SDD -- 260SSD - 1698Total 2198 * 6 d.o.f + ~12 collective dof

(Slightly updated version of the Physics Board presentation on the 19th of July)

Prolegomena (1)Why (only/mainly) ITS ?Most difficult sub-detector and most demanding concerning alignment precisionOuter Barrel (TPC,TRD) not purely geometrical alignment, convolution with calibration, in hands of TPC experts (Marian Ivanov, Marek Kowalski et al)MUON standalone detector, has solved the alignment problem in an independent way : only 156 * 3 = 468 d.o.f. http://indico.cern.ch/conferenceDisplay.py? confId=3026 (Javier Castillo)

Prolegomena (2)Alice/ITS vs other LHC experimentsALICE/ITS alignment activity not yet commensurable with the importance and difficulty scale of the task, especially in comparison with other LHC experimentsSee for ex. links of the LHC ALIGNMENT WORKSHOP (4-6 Sept. 2006): http://lhc-detector-alignment-workshop.web.cern.ch/But not only Alice/ITS has alignment problems

Motivation of the

STATUS (1)Software Alignment Framework ok, ALICE Internal Note to be submitted (Raffaele, Cvetan, Andrei)Geometrical Modeler (based on TGeo/ROOT)Tools to manipulate geometry/modulesAlignment information management (CDB) Zero mis-alignment for testsResidual mis-alignment Full mis-alignmentAlignment monitoring & validation startingAlignment algorithm(s) general concepts & toolsFirst alignment scenario (cosmics, beam gas, pp) ??

(used in PDC06)

Framework for Software AlignmentGeometrical Modeler fully based on TGeo(metry) (ROOT) AliITSgeom TGeo Some problems due to volume overlaps and extrusions virtual volumes substituted by assembliesParameterized distortions not (yet) implemented Methods developed for mis/re-aligning the geometry (simulation and/or reconstruction) using information stored in CDB or in a standalone file, used in PDC06 (AliAlignObj classes)misaligned_geometry.root ~30 Mb, of that ITS (?) (Andrea Gheta, Raffaele Grosso offline week pres., March 2006)

General re-alignment Tools Principle: fit detector positions via minimizing residuals, grouping sensors by module, ladder or layerBased on good ESD tracks (found with open tolerances) from events easy for PatRec (low mult, high momenta)Special classes created in order to make it operational: AliAlignmentTracks base class + AliTrackFitter + AliTrackResiduals etc.Survey info necessary as a starting point and for constraining the alignment parameters freedomLocal Method a group of modules aligned relatively to another group (reference) of modulesTested on TPC and TRD simulated data, not yet tried for ITS ( precision unknown)

(Cvetan Cheshkov see March 2006 offline week pres.)

Example of some problems -overlapping clusters investigation An auxiliary method to control and monitor alignmentExploiting small (1-2%) sensor overlaps in R-phi and in Z (not SPD)Sensitivity to the misalignmentCross-check : simulation versus geometryA method to stress the alignment software

Overlapping clusters study method (simulation)

Look for clusters in the overlapping regions with the same (particle) labelsInvestigate characteristics of such double clustersDistancesSpread etc.Create reference (pseudo) real life distributions

R-phi overlapping clusters (1)Red and blue two correspondingclusters, about 1-2%of the total

R-phi overlapping clusters (2)~size of a module,V2 clustering bug(?)cut

Display(XZ) of Z overlapping clustersNot all pairsoverlap !

Z-overlapping clustersNote: no Z- overlaps (gaps) in SPDcut

Case of Z-overlaps: Dist(XY)

Explanation of the Anomaly(?) When E()< 20 MeV, its hit acquires mother particle labelpseudo-overlapsOther pathological cases large clusters splitting many same label clusters xxclusterclusterCONCLUSION careful selection of clusters for alignment (no outliers!)(suggested by Marian Ivanov)

Cluster correlations in (pseudo) raw data: R- overlapping modulesdPerfect GEOMETRY Clear (and narrow) peaksat d =0, dN/dy = 1000(1 mrad binning)

Cluster correlations in (pseudo) rawdata: Z modules overlaps (no SPD!)d Higher combinatorial background but clear central peaks

Overlaps from Rays in TGeo NEW GEOMETRYOLD GEOMETRYZRays generated from (0,0,0)(Ludovic Gaudichet SDD1 example)

Comparison: geometry - overlapclusters (in %)RZLoss of clusters in SSD !

SPD1SPD2SDD1SDD2SSD1SSD2GEOM+2.0+2.1+2.2+2.1+2.2+1.0CLUST 1.9 2.2 2.0 2.2 1.3 0.6GEOM-1.9-1.9+1.6+1.5+2.0+2.2CLUST -- -- 1.7 1.7 2.0 1.7

Another (recent) problemFull mis-alignment generation : sim.SetAlignObjArray( ITSAlignObj )Large loss of hits (mainly in SSD) due to: hit out of detectorPointing to some mix of different geometries in the simulation (misaligned in simulation, perfect in AliITS::Hits2Digits) Bug fix (Ludovic) - before PDC06 partial production with the full mis-alignment (for training the alignment algorithms) (found by Raffaele and AJ)

ManpowerFramework and the main alignment tools Alice offline core-teamGeometry maintenance and update Ludovic Gaudichet and Bjorn NilsenAuxiliary alignment checks and monitoring only AJ (with help of Youri) for the momentGeneral (re)alignment tools Cvetan Cheshkov Hardware and software ITS alignment ( Bjorn Nilsen and David Truesdale from OSU) (ITS offline leader Massimo Masera)

Planning (1) TO DO listDevelopment of the small auxiliary tools to monitor and constraint alignmentOverlapping clusters , cosmic tracksB=0 events/tracks reconstruction & analysisDisplay adapted to inspect alignment (zooms, projections)QA histograms of the relevant quantities (res.,Minv etc)Impact of the residual misalignment on physics (heavy flavors !)Testing/tuning of the existing alignment framework for ITS (optimal procedures, precision residual misalignment)Trying to get a more realistic estimate of the initial misalignment (mechanical precision, installation, survey..)Global 2 approach (Millepede algorithm) ? Maybe only at the level of the ladders (148 instead of 2198 alignable elements) ?AliMillepede already exists (developed by the MUON) in a general form ready to be used !!

Planning (2):possible first alignment passesFIRST, CALIBRATION and DATA INTEGRITY tests (channels mapping, event building) necessary !Cosmic muons: no primary vertex, only ~vertical tracks limited sensitivity of some elements ( 0, )Beam-gas: primary vertex poorly constrained, no possibility to use azimuthal symmetry, rather z collimated tracks (sensitivity to the radial direction?), then ppFIRST test the procedures on the corresponding simulated events residual misalignment Goal REACHING 10-m residual internal mis-alignment (if not too far from the ideal geometry)

Planning (3):pre-alignment toolsWhat to do if messy events at the start - no tracks found by the standard methods ??Many possible problems: DAQ, trigger, channels mapping, software bugs (raw data!); what can go wrong will go wrongThen careful debugging using display (well adapted) , histogramslooking for hit correlations, exploiting detector overlaps etc.REMEMBER hard competition with ATLAS and CMS (first pp run) stay ready to face all sort of possible problems and be able to solve them quickly

Conclusion(s) A big effort still needed, a larger participation of theITS (offline) group members welcome September (4-6) - firstconfrontation with other LHCexperiments (the Workshop)

Backup SlidesEXEMPLE OF AN ASSEMBLY

Comment on CR alignmentPPR II part 2, $6.11.6 : From this figure (6.475) and the coverageof the CR trigger chambers, we can estimate the time necessaryto calibrate and align any given detector in ALICE.Corresponding request sent to the Mexican Team (Arturo Fernandez),answer promised to be given during two weeks but nothing arrivedNote: two hits per layer tracklets from individual layers, but small (projected) ITS surface, long time expected to accumulate sufficient statistics, but precious infor- mations on track rec precision !x

Examples of alignment applications(only SPD case)Test for azimuthal distortions

Non centered layers non parallel, displaced tracklets

Z shifted layers

2C fits (4 points 2 param) residues analysistrackletsacquire an IP

Cosmic muons rec. points: 100 evtsAdditional problem noisy stripsSingle clean muon

IP resolution in R-phi (only SPD)null vs full mis-alignment (extra 20m)Infinite momentum limitsigma/sqrt(2) = 28 microns ! resolution 12 microns (ok)sigma/sqrt(2) = 35 microns whileexpected 54 microns (!) problem

Null vs Residual vs Full misalignmentProblem whyFull misalignment residual ???(expected 37 mic)found 35 micOffline ladder countingnot in agreement with online (!?)

ALICE

Alignment data flowAlignment - mainly needed in offline software, with exception of HLTIt can take some time before the first alignment data will be stored in the CDB (needs a lot of data and quite a lot of CPU + testing)To be decided where this will be done (locally at CERN ?) no need of data distribution via GRID (?)Monitoring of alignment/track quality special alignment runs if necessary (alignment trigger ?) , eventually with B ON and OFF

Comment on correlations in SPDGeneration vertex Xver = Yver = 0. just to see(d-phi) according to R resolution 0.5 mradPhi(SPD1) vs phi(SPD2) using correct hitsCorrelation shows effective Pt cut depending on the delta() used by VertexerZ

INVENTING PERTINENT DIAGNOSTIC TOOLS a huge task given complexity of ALICE Looking for global ways of data projections as checks of alignment and tracking , talk by Hans Drevermann from ALEPH/ATLAS (23 March 2005)http://ipt.web.cern.ch/IPT/PINS/DALI.html

The Feynman Tufte Principle:A visual display of data should be simpleenough to fit on the side of a vanEdward R. Tuft (the da Vinci of data) Information displays should be documentary comparative causal and explanatory quantified multivariate exploratory skeptical

ALICE coordinates

B = 0.4 TITS DISPLAYXYcenter of LHC

Some results on the ovlp clustersOvlp clusters identified by the labels a problem as small energy electrons (< 20 MeV) keep the mother particle label use of the PDG codesSearch only in pair of modules overlapping in R and/or Z Filtering only of good/small clusters (also important for real alignment !) Problem tracking ignoring double clusters

Comment on correlations in SPDNot so evidentXver=Yver=0

ITS HITS (60000 tracks)PIXELSSi DRIFTSSTRIPS[cm][rad]

Single sector SPD phi correlations

RHO-PHI slice zoom[rad][cm]fairly straighttracks

Rho-Z projection

INVERSE GEOMETRYTRANSFORMATION(Conformal mapping)some sensitivity tothe impact parameter

PHI SLICE in INVERSE GEOMETRYXinvYinvfirst layerlast layer

V (not V0 !) track representation[rad] +- kD pseudo-rapidity k - a constant D - | - max |track diagnostics(simple design,intense content)H. Drevermann fromALEPH/ATLAS

An (artificial pileup) high multiplicity ALEPH event221 tracks

UNIVERSAL PLOT(p alias R known)Perfect circlesZero impacts-ve+veglobal viewof tracksquality

WHERE ARE WE TO GO FROM HERE ??

SOME IDEAS and SUGGESTIONSSimple histograms - exploiting detector overlaps (if any) and some evident (a priori) correlations/knowledge: MOOD and OFFLINEStraight tracks (B=0) tracking for analysis of the special alignment runs DB stored informationVisual tools (like display) to assess, via human intelligence, the possible problems in tracking and alignment (and not only)Special version of tracking (Kalman with open tolerances?) in order to allow for misalignments, or/and alternative (validating) methodsStandard tests of the tracking quality through residues, K0 mass etcAnticipate in software all kinds of corrections via rotations, shifts, distortions (local, collective)Use experience of other experiments (ALEPH/ATLAS, STAR, others)Inter-detector coordination and cooperation strongly needed!Other ideas are WELCOME(instead of summary and conclusions)

A ROAD AHEAD