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Cosmics in ITS: tracking & alignment

Cosmics in ITS: tracking & alignment. A.Dainese (INFN Legnaro). ITS alignment group: LNL, PD, TS, CT, TO, Nikhef. Layout. ITS alignment strategy Cosmics reconstruction in ITS Summer cosmics sample for alignment First alignment results: Millepede Iterative residuals minimization

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Cosmics in ITS: tracking & alignment

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  1. Cosmics in ITS: tracking & alignment A.Dainese (INFN Legnaro) ITS alignment group: LNL, PD, TS, CT, TO, Nikhef IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  2. Layout • ITS alignment strategy • Cosmics reconstruction in ITS • Summer cosmics sample for alignment • First alignment results: • Millepede • Iterative residuals minimization • Alignment monitoring • First attempts of TPC-ITS matching  S.Moretto IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  3. Inner Tracking System (ITS) • Silicon Pixel Detector (SPD): • ~10M channels • 240 sensitive vol. (60 ladders) • Silicon Drift Detector (SDD): • ~133k channels • 260 sensitive vol. (36 ladders) • Silicon Strip Detector (SSD): • ~2.6M channels • 1698 sensitive vol. (72 ladders) SSD ITS total: 2198 alignable sensitive volumes  13188 d.o.f. SPD SDD IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  4. yloc zloc xloc ITS detector resolutions & target alignment precisions Residual: expected misalignment left after applying the realignment procedure(s). Target ~0.7resol. ~20% degradation of the resolution detector local c.s.: xloc~rfglob, yloc~rglob, zloc = zglob IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  5. ITS alignment with tracks:general strategy • Data sets: cosmics + first pp collisions (and beam gas) • use cocktail of tracks from cosmics and pp to cover full detector surface and to maximize correlations among volumes • Start with B off, then switch on B (pp)  possibility to select high-momentum (no multiple scattering) tracks for alignment • General strategy: • start with layers easier to calibrate: SPD and SSD • good resol. in rf (12-20mm), worse in z (120-830mm) • global ITS alignment relative to TPC (already internally aligned) • finally, inclusion of SDD, which need longer calibration (interplay between alignment and calibration) • Two independent track-based alignment methods in preparation: • global: Millepede (ported to ALICE for muon arm alignment) • local: iterative method based on residuals minimization IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  6. Cosmics!1st muon in SPD: Feb 17, 2008 IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  7. Tracking cosmics in ITS • Cosmics tracking in ITS: • adapted stand-alone ITS tracking (Torino) • enlarged search windows to account for large misalignments • start from “fake” vertex built from the two tracklets in inner two layers IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  8. Cosmics with SPD trigger • Pixel FastOR trigger since May 25: first side C, then also side A • Trigger configuration: • rate: 0.05 Hz (June)  0.18 Hz (Aug) • purity (reconstructed with 3-4 cls/triggered): about 30% • about 85% of SPD taking data in August • Statistics collected (till Sept 3rd): about 55k good events • events with 4-cls in SPD: 30k • events with 3-cls in SPD: 25k AND IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  9. ITS points IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  10. Cosmics statistics (SPD) • 220/240 (92%) modules with at least one hit • 200/240 (83%) modules with at least 50 hits IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  11. Cosmics statistics (SDD) • Low statistics on inner layer (switched on later than outer) • Limited statistics on the sides (outer layer: about 50% of modules have sufficient statistics to try alignment) IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  12. Cosmics statistics (SSD) • Limited statistics on the side and edges in z • aligned in Millepede down to the ladder level: about 55/72 ladders have sufficient statiscs IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  13. SPD  S.Moretto • Millepede alignment quite advanced • Most of the detectors that are currenltly switched on have some alignment • Alignment of side detectors may be less realiable • need quick checks with first pp data! SDD • Calibration of time offset is in progress (Torino) • Use Alignment Monitoring tool for validation (C.Bombonati) • Almost ready to be included • Survey (modules on ladders) is ready to be used (M.Poghosyan) SSD  S.Moretto • Included in Millepede since mid-July • Alignment exercises usefull to spot / understand possible problems in geometry / hardware • Survey (modules on ladders) ready to be used IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  14. Checking the quality of realignment y • Main variable: track-to-track Dx at y=0 • Acceptance overlaps  “extra” clusters • Alignment monitoring tool x IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  15. Millepede SPD realignment:Dx at y=0 DATA: Sim, ideal geom: not realigned realigned 43 mm 56 mm Expected spread  sspatial=15 mm  sspatial=11 mm (Sim) IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  16. Millepede SPD realignment:“extra” clusters DATA: Sim, ideal geom: not realigned realigned 22 mm 15 mm Expected spread  sspatial=16 mm  sspatial=11 mm (Sim) IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  17. Alignment Monitoring: SPD • Track fit + residuals analysis • Check and monitor in time the quality of realignment • (try to “guess” high-level or correlated misalignments) Millepede Ideal sim. s=70mm s=44mm Mille/Sim ~ 70/44 ~ 22/15 extra clusters C.Bombonati, A.Rossi x residual [cm] IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese x residual

  18. ITS alignment with tracks: iterative local method • Alignment params from minimization of track-to-points residuals • Local: works on a module-by-module basis • Iterations are used to take into account correlations between the alignment params of different modules • difficult with SPD alone: only 4 points (modules) per track about 50% worse than Millepede; difficult to account for correlations A.Rossi IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  19. SDD: time0 calibration and alignment • Residuals: • fit su SPD+SSD • residuals su SDD (up, down) • Not indep. of misalignment C.Garcia, C.Bombonati • Complementary procedure: estimate time0 from minimum time (F.Prino) -130mm -10mm IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  20. TPC-ITS matching with large misalignment/miscalibration • Misalignments (internal & TPC vs ITS) and miscalibration (drift velocity, time0, ExB) reduce matching efficiency • A set of knobs to enlarge track/cluster errors should allow to recover the efficiency • TPC: add systematic errors (drift velocity, time0, ExB) to the track covariance matrix before prolongation to ITS • ITS: add misalignment errors to cluster errors (~ 1 mm) • Matching efficiency (prel.): TPC+ITS (4cls) / ITSsa (4cls) • B=0: >90% • B=0.5T (enlarged errors): ~85% IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  21. B=0.5 T cosmics in ITS+TPC pT = 2 GeV pT = 1 GeV pT = 0.2 GeV noise SDD ora risolto IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  22. Check of ITS alignment with ITS+TPC tracks, B=0.5 • Use Millepede realignment SPD+SSD Track-to-track distance Dx pull = Dx / √stop2+sbottom2 3or4 + 3or4 ITS points ITS+TPC SPD+SSD+TPC mean 6 mm s = 54 mm IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  23. Summary • Large sample of cosmics collected during Summer • SPD FastOR trigger gave a big boost • All alignment machinery (reconstruction, realignment, monitoring) working from the very beginning • Good results from Millepede • Most of SPD realigned to 10 mm • need cross-checks with pp, especially on the side • Started to include SSD (limited statistics for cosmics) • SDD will come soon • Next step: ITS-TPC alignment • need to understand TPC calibration first... IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  24. EXTRA SLIDES IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  25. rec. track e Primary Vertex B X d0 Impact of ITS misalignmenton tracking performance • Effect of misalignment on d0 (and pt) resolutions studied by reconstructing misaligned events with ideal geometry • Estimated effect on D0Kp significance null residual full full+ A.D, A.Rossi IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  26. Millepede: cross-checks (3) • Use f-acceptance overlaps in SPD (“extra” clusters) • Check on simulation with ideal geometry: outer SPD layer: s(Dxy) = 15 mm s(Dz) = 165 mm “extra” clusters not (yet) used for realignment  cross-check IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

  27. Millepede: cross-checks (3) • Use f-acceptance overlaps in SPD (“extra” clusters) • Check on simulation with ideal geometry: outer SPD layer: s(Dxy) = 22 mm s(Dz) = 163 mm high-stats sectors selected realigned raw IV Convegno Nazionale Fisica ALICE, Palau, 28.09.2008 Andrea Dainese

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