(ITS) ALIGNMENT : status, problems, planning etc

1. (ITS) ALIGNMENT: status, problems, planning etc 2007 Alignable elements: SPD -- 240 SDD -- 260 SSD - 1698 Total – 2198 * 6 d.o.f + ~12 collective dof (Slightly updated version of the Physics Board presentation on the 19th of July) Adam Jacholkowski

2. Prolegomena (1)Why (only/mainly) ITS ? • Most difficult sub-detector and most demanding concerning alignment precision • Outer 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) Adam Jacholkowski

3. Prolegomena (2)Alice/ITS vs other LHC experiments • ALICE/ITS alignment activity not yet commensurable with the importance and difficulty scale of the task, especially in comparison with other LHC experiments See 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 Adam Jacholkowski

4. Motivation of the Adam Jacholkowski

5. 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/modules • Alignment information management (CDB) • Zero mis-alignment – for tests • Residual mis-alignment • Full mis-alignment • Alignment monitoring & validation – starting • Alignment algorithm(s) – general concepts & tools • First alignment scenario (cosmics, beam gas, pp) ?? (used in PDC06) Adam Jacholkowski

6. Framework for Software Alignment (Andrea Gheta, Raffaele Grosso  offline week pres., March 2006) • Geometrical Modeler fully based on TGeo(metry) (ROOT) AliITSgeom  TGeo • Some problems due to volume overlaps and extrusions  virtual volumes substituted by assemblies • Parameterized 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, ½ of that ITS (?) Adam Jacholkowski

7. General re-alignment Tools (Cvetan Cheshkov  see March 2006 offline week pres.) • Principle: fit detector positions via minimizing residuals, grouping sensors by module, ladder or layer • Based on good ESDtracks (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 freedom • Local Method – a group of modules aligned relatively to another group (reference) of modules • Tested on TPC and TRD simulated data, not yet tried for ITS ( precision unknown) Adam Jacholkowski

8. Example of some problems -overlapping clusters investigation • An auxiliary method to control and monitor alignment • Exploiting small (1-2%) sensor overlaps in R-phi and in Z (not SPD) • Sensitivity to the misalignment • Cross-check : simulation versus geometry • A method to stress the alignment software Adam Jacholkowski

9. Overlapping clusters study method (simulation) • Look for clusters in the overlapping regions with the same (particle) labels • Investigate characteristics of such double clusters • Distances • Spread etc. • Create reference (pseudo) real life distributions Adam Jacholkowski

10. R-phi overlapping clusters (1) Red and blue – two corresponding clusters, about 1-2% of the total Adam Jacholkowski

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

12. Display(XZ) of Z overlapping clusters Not all pairs overlap ! Adam Jacholkowski

13. Z-overlapping clusters cut Note: no Z- overlaps (gaps) in SPD Adam Jacholkowski

14. Case of Z-overlaps: Dist(XY) ? Adam Jacholkowski

15. Explanation of the Anomaly(?) (suggested by Marian Ivanov) δ π x cluster cluster x • When E(δ)< 20 MeV, its hit acquires mother particle label • pseudo-overlaps Other pathological cases – large clusters splitting  many same label clusters CONCLUSION – careful selection of clusters for alignment (no outliers!) Adam Jacholkowski

16. Cluster correlations in (pseudo) raw data: R-φ overlapping modules dφ (1 mrad binning) Perfect GEOMETRY  Clear (and narrow) peaks at dφ =0, dN/dy = 1000 Adam Jacholkowski

17. Cluster correlations in (pseudo) rawdata: Z modules overlaps (no SPD!) dφ  Higher combinatorial background but clear central peaks Adam Jacholkowski

18. Overlaps from Rays in TGeo (Ludovic Gaudichet – SDD1 example) Z φ OLD GEOMETRY NEW GEOMETRY Rays generated from (0,0,0) Adam Jacholkowski

19. Comparison: geometry - overlapclusters (in %) Rφ Z Loss of clusters in SSD ! Adam Jacholkowski

20. Another (recent) problem (found by Raffaele and AJ) • Full mis-alignment generation : sim.SetAlignObjArray( ITSAlignObj ) • Large loss of hits (mainly in SSD) due to: hit out of detector • Pointing 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) Adam Jacholkowski

21. Manpower (ITS offline leader – Massimo Masera) • Framework and the main alignment tools – Alice offline core-team • Geometry maintenance and update – Ludovic Gaudichet and Bjorn Nilsen • Auxiliary alignment checks and monitoring – only AJ (with help of Youri) for the moment • General (re)alignment tools – Cvetan Cheshkov • Hardware and software ITS alignment ( Bjorn Nilsen and David Truesdale from OSU) Adam Jacholkowski

22. Planning (1) – TO DO list • Development of the “small” – auxiliary tools to monitor and constraint alignment • Overlapping clusters , cosmic tracks • B=0 events/tracks reconstruction & analysis • Display 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 χ2 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 !! Adam Jacholkowski

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

24. Planning (3):pre-alignment tools • What 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 wrong” • Then careful debugging using display (well adapted) , histogramslooking 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 Adam Jacholkowski

25. Conclusion(s) ♪ A big effort still needed, a larger participation of the ITS (offline) group members welcome ♪ September (4-6) - first confrontationwith other LHC experiments (the Workshop) Adam Jacholkowski

26. Backup Slides EXEMPLE OF AN ASSEMBLY Adam Jacholkowski

27. Comment on CR alignment PPR II part 2, $6.11.6 : From this figure (6.475) and the coverage of the CR trigger chambers, we can estimate the time necessary to 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 arrived x Note: 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 ! Adam Jacholkowski

28. Examples of alignment applications(only SPD case) tracklets acquire an IP • Test for azimuthal distortions • Non centered layers  non parallel, displaced tracklets • Z shifted layers • 2C fits (4 points – 2 param)  residues analysis Adam Jacholkowski

29. Cosmic muons rec. points: 100 evts Additional problem – noisy strips Single clean muon Adam Jacholkowski

30. IP resolution in R-phi (only SPD)null vs full mis-alignment (extra 20μm) Infinite momentum limit sigma/sqrt(2) = 28 microns !  resolution 12 microns (ok) sigma/sqrt(2) = 35 microns while expected 54 microns (!) problem Adam Jacholkowski

31. Null vs Residual vs Full misalignment Problem – why Full misalignment ≈ residual ??? (expected 37 mic) found 35 mic Offline ladder counting not in agreement with online (!?) Adam Jacholkowski

32. ACCORDE TOF TRD HMPID TPC PMD PHOS ITS Muon arm ALICE Adam Jacholkowski

33. Alignment data flow • Alignment - mainly needed in offline software, with exception of HLT • It 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 Adam Jacholkowski

34. Comment on φ correlations in SPD • Generation vertex Xver = Yver = 0. just to see… • Δ(d-phi) according to Rφ resolution ≈ 0.5 mrad • Phi(SPD1) vs phi(SPD2) using correct hits • Correlation shows effective Pt cut depending on the delta(φ) used by VertexerZ Adam Jacholkowski

35. z ཛྷ 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 ρ Adam Jacholkowski

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

37. ALICE coordinates Adam Jacholkowski

38. ITS DISPLAY Y ρ φ X center of LHC B = 0.4 T Adam Jacholkowski

39. Some results on the ovlp clusters • Ovlp clusters identified by the labels – a problem as small energy electrons (< 20 MeV) keep the mother particle label  use of the PDG codes • Search only in pair of modules overlapping in Rφ and/or Z • Filtering only of good/small clusters (also important for real alignment !) • Problem – tracking ignoring double clusters Adam Jacholkowski

40. Comment on φ correlations in SPD Not so evident Xver=Yver=0 Adam Jacholkowski

41. ITS HITS (60000 tracks) STRIPS ρ [cm] Si DRIFTS PIXELS φ[rad] Adam Jacholkowski

42. Single sector SPD phi correlations Adam Jacholkowski

43. RHO-PHI slice zoom ρ [cm] fairly straight tracks φ[rad] Adam Jacholkowski

44. Rho-Z projection Adam Jacholkowski

45. INVERSE GEOMETRYTRANSFORMATION (Conformal mapping) some sensitivity to the impact parameter Adam Jacholkowski

46. PHI SLICE in INVERSE GEOMETRY Yinv first layer last layer Xinv Adam Jacholkowski

47. V (not V0 !) track representation φ[rad] η – pseudo-rapidity k - a constant D - | ρ - ρmax | track diagnostics (simple design, intense content) H. Drevermann from ALEPH/ATLAS η +- kD Adam Jacholkowski

48. An (artificial pileup) high multiplicity ALEPH event 221 tracks Adam Jacholkowski

49. UNIVERSAL PLOT(p alias R known) Perfect circles Zero impacts -ve +ve global view of tracks quality Adam Jacholkowski

50. WHERE ARE WE TO GO FROM HERE ?? Adam Jacholkowski