1. Adam Jacholkowski Catania & CERN 1 24-25/01/05 GSI Silicon Tracking at WA97 and NA57 introduction to WA97/NA57 : setup & physics silicon pixels – hardware aspects alignment pattern recognition & track fit vertex finding summary & final remarks

2. Adam Jacholkowski Catania & CERN 2 24-25/01/05 GSI The NA57 Experiment Study of the dependence of hyperon enhancements on: WA97 p-Be sample used as reference data at 158 A GeV.  Data samples: Interaction volume - centrality down to N wound ~ 50 Collision energy - data at two beam momenta - 158 and 40 A GeV/c INTRODUCTION(1) 3-4 Tb in CASTOR (mass storage) SystemBeam energySample sizeData taking year Pb-Pb158 A GeV230+230 x 10 6 evts1998+2000 Pb-Pb40 A GeV240 x 10 6 evts1999 p-Be*40 A GeV60+110 x 10 6 evts1999+2001 (continuation and extension of WA97)

3. Adam Jacholkowski Catania & CERN 3 24-25/01/05 GSI INTRODUCTION  Example: INCREASES WITH STRANGENESS CONTENT ! systematic error  NA57 – example of the enhancement study result: for more see  G. Bruno plenary talk at QM2004 INTRODUCTION(2) Enhancement def. central rapidity (one unit) yield statistical error

4. Adam Jacholkowski Catania & CERN 4 24-25/01/05 GSI WA97 (predecessor of NA57) set-up in the OMEGA magnet  Target: Be, Pb;  Beam: p, Pb, 158 A GeV/c momentum  Magnetic field: 1.8 T  Silicon telescope: tracking device (7 pixel and 10 microstrip planes, 5cm x 5cm)  Pad chambers: lever arm  Scintillation petals: lead run centrality trigger (40%  inel )  Multiplicity detectors: off-line event centrality analysis d  L L = 30 cm d = 60 cm (Pb-Pb), 90 cm (p-A)  = 40 mrad (Pb-Pb), 48 mrad (p-A) (~ 0.5 M pixels)

5. Adam Jacholkowski Catania & CERN 5 24-25/01/05 GSI B=0 event

6. Adam Jacholkowski Catania & CERN 6 24-25/01/05 GSI NA57 SETUP (Pb - Pb run) 1.4 T Target: 1% Pb Scintillator Petals: centrality trigger MSD: multiplicity silicon detector Tracking device: silicon pixel planes (5 x 5 cm 2 cross section) Lever arm: double side  strips 5 cm X (~ 1.0 M pixels)

7. Adam Jacholkowski Catania & CERN 7 24-25/01/05 GSI

8. Adam Jacholkowski Catania & CERN 8 24-25/01/05 GSI

9. Adam Jacholkowski Catania & CERN 9 24-25/01/05 GSI Ω3 pixel (single) card Ω2 pixel plane (box) 5 cm

10. Adam Jacholkowski Catania & CERN 10 24-25/01/05 GSI Single pixel cell of the LHC1/Ω3 chip LHC1: A semiconductor pixel detector readout chip with internal, tunable delay providing a binary pattern of selected events Erik H. M. Heijne et al Nucl. Instr. & Methods A 383 (1996) 55 ( RD19 & WA97 collaboration)

11. Adam Jacholkowski Catania & CERN 11 24-25/01/05 GSI Pixel Maps (full planes) 1 as seen by the beam (along X) (98256 pixel cells) Z Y Ω3Y double length pixels (chip border) 10 000 events

12. Adam Jacholkowski Catania & CERN 12 24-25/01/05 GSI Pixel Maps (full planes) 2 (73656 pixel cells) only one card switched ON Ω2Z 10 000 events

13. Adam Jacholkowski Catania & CERN 13 24-25/01/05 GSI Dead Time (1) LDC – Local Data Collector (group of pixel cards) ms DT – proportional to amount of fired pixels (hits + noise)

14. Adam Jacholkowski Catania & CERN 14 24-25/01/05 GSI Dead Time (2) Risk of saturating DAQ in case of high level of noise, but exaggerated noise suppression  lowering planes efficiency compromise Importance of masking noisy pixels and (chips) efficiency monitoring Data Base

15. Adam Jacholkowski Catania & CERN 15 24-25/01/05 GSI MAIN ANALYSIS STEPS ALIGNMENT and CALIBRATION  DATA BASE GEOMETRICAL RECONSTRUCTION  clusters, tracks V0 FINDING  Λ and K0 candidates CASCADE RECONSTRUCTION (V0s + tracks) PARTICLE SIGNALS EXTRACTION (selection cuts)  Gold-Plated ntuples CORRECTING for ACCEPTANCE and LOSSES  EVENT-BY- EVENT WEIGHTING (and/or de-convolution) EXTRAPOLATION TO FULL Pt AND ONE UNIT OF rapidity NORMALIZATION (beam flux,target) YIELDS MULTIPLICITY RECONSTRUCTION  CENTRALITY

16. Adam Jacholkowski Catania & CERN 16 24-25/01/05 GSI ALIGNMENT(1)  Starting point – optical bench survey measurements + internal pixel ladder positions (known from construction)  Internal pixel alignment cross checks using strips tracks (WA97) and exploiting ladder overlaps  Transverse & longitudinal alignment using straight tracks (special B=0 and telescope in proton beam runs)  Small correction tilt angles relative to the telescope axis  Cross-alignment of the Z and Y planes  Alignment data taken periodically and/or after each intervention on the optical bench ( results stored in the DB)

17. Adam Jacholkowski Catania & CERN 17 24-25/01/05 GSI Alignment (2) Single Y (vertical) ladder Y-plane tilt test mm Z Z Y microns

18. Adam Jacholkowski Catania & CERN 18 24-25/01/05 GSI Parabolic Approximation (used in Pat. Rec.) circle parabola Y X 31 cm Example: p = 2 GeV/c φ = 0.  ρ = 5m Sagitta = L 2 /8ρ= ¼ cm (50 pixels) 10 μ diff.

19. Adam Jacholkowski Catania & CERN 19 24-25/01/05 GSI Polynomial Parameterization Fit (example)

20. Adam Jacholkowski Catania & CERN 20 24-25/01/05 GSI TRACK RECONSTRUCTION PRECISION (3 points parabolic approximation) B in kGs, p in GeV/c, L in cm σ 0 = pitch/sqrt(12) R.L. GLUCKSTERN Nucl. Instr. & Methods 24(1963) 381

21. Adam Jacholkowski Catania & CERN 21 24-25/01/05 GSI NA57 case : λ ≈ 0, L ≈ 30cm, B ≈ 14kGs, X 0 ≈ 30cm/(9x 0.012) = 277cm, pitch = 50μm Δp/p meas and msc errors equal at p ≈ 12.2 GeV/c (4.5%) p = 12.2  Δφ = 0.25 & 0.17mrad → 0.3 mrad measmsc.

22. Adam Jacholkowski Catania & CERN 22 24-25/01/05 GSI Pattern Recognition(1)  Parabolic track model (very good approximation!) in the bending plane  Starting from 3 points (e.g. in the first and the last plane + in one of the intermediate planes) then adding other points lying within the predetermined limits relatively to the predictions  Constraints: N points ≥ N min (for example 6-7 out of 9-11 possible) with a requirement of a minimum number of points in each type of pixels (Z or Y-like) Semi-combinatorial, using predefined plane configurations of the compact part only

23. Adam Jacholkowski Catania & CERN 23 24-25/01/05 GSI     - ) Pattern Recognition(2) x x x

24. Adam Jacholkowski Catania & CERN 24 24-25/01/05 GSI Pattern Recognition (3)  2D - PR+ matching in WA97, 3D - PR in NA57  Hit sharing level controlled according to the chosen tolerance: ambiguities resolved on the basis of χ 2  Track finding efficiency bigger than 95%, while Kalman Filter ε ≈ 50% ! ( sparse points + multiple scattering)  Ghosts kept at a negligible level (below 1% )  PR optimization - multiplicity dependent (different in Pb-Pb and p-Be)

25. Adam Jacholkowski Catania & CERN 25 24-25/01/05 GSI Track Fit (Quintic Spline) H. Wind Nucl. Instr. & Methods 115 (1974) 431

26. Adam Jacholkowski Catania & CERN 26 24-25/01/05 GSI ORHION – reconstruction programme  Fortran code developed under Patchy: new versions kept backward compatible (useful for reprocessing !)  Working both on real and simulated (GEANT MC) data  Internally split into different (main) sub processes: OR – steering ST – pattern recognition TF – track fit XC – lever arm track improvement V0 – secondary vertices finder  DST-output files of different formats  input for the analysis programs

27. Adam Jacholkowski Catania & CERN 27 24-25/01/05 GSI p-Be 40 GeV/c Ξ event [cm] Y X Ω3YΩ3ZΩ2YΩ2ZΩ3YΩ2YΩ2ZΩ2Y Ω2Z Ω3YΩ3Y planes sequence aspect ratio ≈ 9 !

28. Adam Jacholkowski Catania & CERN 28 24-25/01/05 GSI p-Be 40 GeV/c Ξ event [cm] Z X Ω3YΩ3ZΩ2YΩ2ZΩ3YΩ2YΩ2ZΩ2Y Ω2Z Ω3YΩ3Y planes sequence aspect ratio ≈ 9 !

29. Adam Jacholkowski Catania & CERN 29 24-25/01/05 GSI Vertex Finding  Primary vertex – from secondary tracks extrapolation (the μ- strips beam telescope used only in the WA97 p-Be run ) : - event-by-event (WA97) or - run-by-run (to handle more peripheral collisions in NA57)  V0 finding – pairs of oppositely charged tracks extrapolated first to a ref. plane, then search for the point of nearest approach using helix parameterization  The nearest approach distance – a crucial parameter in selecting clean signals (removing background): a typical cut value d max /2 (alias close) = 0.04 cm

30. Adam Jacholkowski Catania & CERN 30 24-25/01/05 GSI HYPERON DETECTION 30 cm 5 cm    byby byby Plus many other associated tracks Each hyperon (particle) assigned to a centrality class according to MSD  N charged X

31. Adam Jacholkowski Catania & CERN 31 24-25/01/05 GSI Mass Resolution: Ξ 158 A GeV/c 40 A GeV/c

32. Adam Jacholkowski Catania & CERN 32 24-25/01/05 GSI Mass Resolution: K 0 s 158 A GeV/c 40 A GeV/c FWHM = 24 MeVFWHM = 16 MeV

33. Adam Jacholkowski Catania & CERN 33 24-25/01/05 GSI Summary  WA97  first application of pixel technology (Ω2 then Ω3/LHC1 chips) in conjunction with strips  NA57  pattern recognition and tracking entirely based on pixel detectors  WA97 and NA57 experience  pixel detectors – a powerful tool for high precision tracking (3D)

34. Adam Jacholkowski Catania & CERN 34 24-25/01/05 GSI Technology still in rapid evolution, future  CERN LHC experiments/NA60 Final Remarks (1)

35. Adam Jacholkowski Catania & CERN 35 24-25/01/05 GSI Message to CBM Final Remarks (2) PIXEL TECHNOLOGY is a powerful tool for physics once good care is taken of all necessary elements of hardware (calibration) and software (alignment, noise and efficiency control) environment

36. Adam Jacholkowski Catania & CERN 36 24-25/01/05 GSI Physics Department, University of Athens, Greece; Dipartimento IA di Fisica dell'Università e del Politecnico di Bari and INFN, Bari, Italy; Fysisk Institutt, Universitetet i Bergen, Bergen, Norway ; Høgskolen i Bergen, Bergen, Norway; University of Birmingham, Birmingham, UK; Comenius University, Bratislava, Slovakia; University of Catania and INFN, Catania, Italy; CERN, European Laboratory for Particle Physics, Geneva, Switzerland; Institute of Experimental Physics Slovak Academy of Science, Kosice, Slovakia; P.J. Safárik University, Kosice, Slovakia; Fysisk institutt, Universitetet i Oslo, Oslo, Norway; University of Padua and INFN, Padua, Italy; Collège de France, Paris, France; Institute of Physics, Prague, Czech Republic; University “La Sapienza'' and INFN, Rome, Italy; Dipartimento di Scienze Fisiche “E.R. Caianiello'' dell'Università and INFN, Salerno, Italy; State University of St. Petersburg, St. Petersburg, Russia; IReS/ULP, Strasbourg, France; Utrecht University and NIKHEF, Utrecht, The Netherlands. THE NA57 COLLABORATION

37. Adam Jacholkowski Catania & CERN 37 24-25/01/05 GSI CENTRAL RAPIDITY YIELD MEASUREMENT ONE UNIT OF RAPIDITY FULL P t RANGE INTRODUCTION T from Max-Log-Likelihood

38. Adam Jacholkowski Catania & CERN 38 24-25/01/05 GSI Hyperon reconstruction Λ(cowboy) acceptance  -- d Δ

39. Adam Jacholkowski Catania & CERN 39 24-25/01/05 GSI Pixel maps (single cards) Importance of masking noisy pixels and (chips) efficiency monitoring Data Base (36828 pixel cells)(49128 pixel cells)

40. Adam Jacholkowski Catania & CERN 40 24-25/01/05 GSI EXAMPLE OF ORHION PROCESSING (Pb-Pb 2000 Background) Background data – representative sample of all data (each 200 th event – 5%), 24 files Parallel running at CERN (Linux Batch)  overall 1 day and 1 night human time About 3-4 NCU hours per file 1440-1920 NCU hours of full 2000 data ( 230 Mevts ) ORHION processing (distributed between all labs !!) Slightly less for Pb-Pb at 40 GeV/c, then still less for p-Be (one week)

41. Adam Jacholkowski Catania & CERN 41 24-25/01/05 GSI Selection of Hyperons (and K S 0 ) X-Ξ vertex close Λ impact  Cleaning of the signals via geometrical cuts

42. Adam Jacholkowski Catania & CERN 42 24-25/01/05 GSI WEIGHTING PARTICLES A weight is associated with each selected particle to correct for acceptance, efficiencies and cuts ( ~few thousands) 2 different selections (cuts) spread

43. Adam Jacholkowski Catania & CERN 43 24-25/01/05 GSI WEIGHTING PROCEDURE (2) Weights are calculated by Monte Carlo: - generated hyperons (N gen ) are traced through a GEANT simulation of the NA57 apparatus - track hits are merged with true events - resulting events are processed through the reconstruction and analysis chain - reconstructed hyperons are counted (N rec ) Simulation thoroughly checked against real data

44. Adam Jacholkowski Catania & CERN 44 24-25/01/05 GSI WEIGHT STATISTICS at 158 GeV/c Particle weighted collected 3340 2350 2718 6444 936 432 192 x400 x400 x50 x1 x1 x1 x1 Most expensive cascade particles:1-3 NCU hours on LXPLUS, 10000 Λs and 10000 K0s  about 40K NCU hours, alias 1 working month (estimate) 2001 p-Be data weighting ( 4000 Λs only) just in one week at CERN

45. Adam Jacholkowski Catania & CERN 45 24-25/01/05 GSI DECONVOLUTION An alternative method to weighting (which is precise but CPU expensive), applicable to high statistics samples F. Antinori et al Transverse mass spectra of strange and multi-strange particles in Pb-Pb collisions at 158 A GeV/c Eur. Phys. J. C 14, 633-641 (2000)

46. Adam Jacholkowski Catania & CERN 46 24-25/01/05 GSI Energy multiplicity dependence logarithmic scaling