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LHCb Alignment

LHCb Alignment. 1. Introduction 2. The alignment challenge 3. Conclusions. Cosener’s Forum « LHC Startup ». S. Viret. 12 th April 2007. 1. Introduction 2. The alignment challenge 3. Conclusions. 1. Introduction 2. The alignment challenge 3. Conclusions. 1. Physics justification

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LHCb Alignment

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  1. LHCb Alignment 1. Introduction 2. The alignment challenge 3. Conclusions Cosener’s Forum « LHC Startup » S. Viret 12th April 2007

  2. 1. Introduction 2. The alignment challenge 3. Conclusions

  3. 1. Introduction 2. The alignment challenge 3. Conclusions 1. Physics justification 2. The detector 3. LHCb startup program They will be difficult to characterize Heavy-flavor physics will provide plenty of discriminating observables LHC Startup S. Viret 1  Why LHCb ? New-physics signs are expected at the LHC

  4. 1. Introduction 2. The alignment challenge 3. Conclusions g g g b s s s 1. Physics justification 2. The detector 3. LHCb startup program  W± Involves FCNC, forbidden by Standard Model s s s b b b t t ~ ~ LHC Startup S. Viret 2  Example : bsg g Need for loops involving heavy particles Bsfg decay New contributions could arise and affect observable parameters (BR, ACP, Aisospin)

  5. 1. Introduction 2. The alignment challenge 3. Conclusions 1. Physics justification 2. The detector 3. LHCb startup program LHC Startup S. Viret 3  If you want to study B-physics, it’s nice to have :  A large b quark production in the acceptance  A precise vertex reconstruction A very good particle ID  An efficient trigger system

  6. 1. Introduction 2. The alignment challenge 3. Conclusions 1. Physics justification 2. The detector 3. LHCb startup program Beam line LHC Startup S. Viret 4  The LHCb experiment :

  7. 1. Introduction 2. The alignment challenge 3. Conclusions b quark production cross-section largerat high h 100 mb 1. Physics justification 2. The detector 3. LHCb startup program pT 230 mb 105 b-hadrons per secondeatL=2x1032cm-2s-1 (LHCb nominal lumi.) h b & b quark directions highly correlated. Production cross-section (Pythia) b b Beam qb qb LHC Startup S. Viret 5 A forward geometry A large b quark production in the acceptance

  8. 1. Introduction 2. The alignment challenge 3. Conclusions 1. Physics justification 2. The detector 3. LHCb startup program Beam line LHC Startup S. Viret 6 VELO (VErtex LOcator) A precise vertex reconstruction An efficient trigger system

  9. 1. Introduction 2. The alignment challenge 3. Conclusions 1. Physics justification 2. The detector 3. LHCb startup program LHC Startup S. Viret 7  VELO ~1m VErtex LOcator  VELO :  Innermost part of LHCb.  A detector very close to the beam (~8 mm). 42 detection modules in 2 boxes.

  10. 1. Introduction 2. The alignment challenge 3. Conclusions 8 mm z (beam) f R y 1. Physics justification 2. The detector 3. LHCb startup program x Module = 2 sensors (1R/1f) glued together LHC Startup S. Viret 8  VELO modules 4.2 cm

  11. 1. Introduction 2. The alignment challenge 3. Conclusions 1. Physics justification 2. The detector 3. LHCb startup program VELO box (empty here) LHC Startup S. Viret 9  VELO is a moving detector !  During LHC beam injection, each box is retracted by 3cm from its nominal position.  Then the boxes are moved back close to the beam, and data taking starts.

  12. 1. Introduction 2. The alignment challenge 3. Conclusions 1. Physics justification 2. The detector 3. LHCb startup program Beam line LHC Startup S. Viret 10 RICH 1&2 A very good particle ID

  13. 1. Introduction 2. The alignment challenge 3. Conclusions 1. Physics justification 2. The detector 3. LHCb startup program LHC Startup S. Viret 11  2 complementary detectors : RICH 1 RICH 2

  14. 1. Introduction 2. The alignment challenge 3. Conclusions 1. Physics justification 2. The detector 3. LHCb startup program Some advertising… LHC Startup S. Viret 12  RICH design :  Photon collected by HPD detectors (484 in total RICH 1&2)  Number of mirrors: RICH 1 : 4 sphericals / 16 planes RICH 2 : 56 sphericals / 40 planes

  15. 1. Introduction 2. The alignment challenge 3. Conclusions 1. Physics justification 2. The detector 3. LHCb startup program Beam line LHC Startup S. Viret 13 Tracking System A precise vertex reconstruction An efficient trigger system

  16. 1. Introduction 2. The alignment challenge 3. Conclusions 1. Physics justification 2. The detector 3. LHCb startup program LHC Startup S. Viret 14  Tracking stations Outer Tracker (3 stations)  5.0 mm Straws  Double-layer straws  4 layers: X:U(5o):V(-5o):X Overlap regions between IT/OT to facilitate relative alignment Outer Tracker Trigger Tracker Inner Tracker 20% of the tracks Silicon Strips  198 mm pitch  1-2 sensor ladders (336 ladders)  4 layers: XUVX Inner Tracker Trigger Tracker (1 station) Silicon Strips  183 mm pitch  128 7-sensor ladders  4 layers: X:U(5o):V(-5o):X  128 ladders to be aligned 125.6 mm 41.4 mm 125.6 mm

  17. 1. Introduction 2. The alignment challenge 3. Conclusions  LEVEL 0 (4ms): purely hardware. Select the events containing interesting info (m, di-muons, e, g & hadrons with high pT). Pile-up rejection. L0 107 1. Physics justification 2. The detector 3. LHCb startup program 1 MHz 106  LEVEL 1 (1ms): purely software. Look for a displaced vertex in the VELO (good detector alignment mandatory here). L1 Rate (in Hz) 105 40 kHz 104  HLT (10ms): purely software. Fine event selection (streaming). HLT 103 ~2 kHz LHC Startup S. Viret 15 Trigger strategy An efficient trigger system

  18. 1. Introduction 2. The alignment challenge 3. Conclusions 1. Physics justification 2. The detector 3. LHCb startup program LHC Startup S. Viret 16  2007: startup • Pilot run at 450 GeV per beam • Establish running procedures, align detectors in time and space • Integratedluminosity for physics ~ 0 fb–1  2008: early phase • Complete commissioning of detector and trigger at s=14 TeV • Calibrate momentum, energy and particle ID • Start first physics data taking, assume ~ 0.5 fb–1 • Establish physics analyses, understand performance  2009–20xx: stable running • Stable running, assume ~ 2 fb–1/year • Develop full physics program • Exploit statistics, work on systematics

  19. 1. Introduction 2. The alignment challenge 3. Conclusions

  20. 1. Introduction 2. The alignment challenge 3. Conclusions 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview A particle passes trough a misaligned detector What happens if track is fitted using uncorrected geometry  With no correction, one gets a bad quality track (or even no track at all)  How could this affect LHCb results ? LHC Startup S. Viret 17  The alignment problem:

  21. 1. Introduction 2. The alignment challenge 3. Conclusions d · mB t= c · |pB| 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview dnew d Proper-time  LHC Startup S. Viret 18  Example 1 : proper-time estimation Detector Primary vertex B-decay vertex Tracks

  22. 1. Introduction 2. The alignment challenge 3. Conclusions Y axis 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview LHC Startup S. Viret 19  Example 2 : trigger efficiency BsKK events HLT trigger efficiency  With 0.5 mrad tilt of one VELO box, 30% less events selected  These events are definitely lost!!!

  23. 1. Introduction 2. The alignment challenge 3. Conclusions 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview LHC Startup S. Viret 20  A 3 steps procedure : Complete survey of every sub-detector and of all the structure when installed in the pit  Hardware alignment (position monitoring):  Stepping motors information during VELO boxes closing  OT larges structures positions constantly monitored (RASNIKs system)  Laser alignment for RICH mirror positioning Alignment precision  Software alignment

  24. 1. Introduction 2. The alignment challenge 3. Conclusions 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview LHC Startup S. Viret 21  Software alignment strategy : Align all sub-detectors (VELO, IT, OT, RICHs) internally Align the sub-detectors w.r.t. the VELO (Global alignment). Start IT & OT, then TT (not alignable internally), RICH and finally Ecal, Hcal and Muon.

  25. 1. Introduction 2. The alignment challenge 3. Conclusions Start of run : VELO is closed 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview Residuals monitoring If necessary… Software alignment procedure Data taking End of run : VELO is open LHC Startup S. Viret 22  VELO alignment : how to proceed ? Alignment should be designed to be FAST (few minutes)and PRECISE (<5 mm precision)

  26. 1. Introduction 2. The alignment challenge 3. Conclusions 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview Step 1 Internally-aligned VELO Global fit applied on tracks (classic & beam gas/halo) in the two boxes Step 2 Aligned VELO Align the boxes using global fit again on primary vertices, overlapping tracks,... Step 0 Misaligned VELO LHC Startup S. Viret 23  VELO: the strategy

  27. 1. Introduction 2. The alignment challenge 3. Conclusions  Residualsare function of the detector resolution, but also of the misalignments 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview  The geometry we are looking for is the one which minimizes the tracks residuals (in fact there are many of them but there are ways to solve this problem). … to that LHC Startup S. Viret 24  Global fit ? From this…

  28. 1. Introduction 2. The alignment challenge 3. Conclusions xclus =∑ai∙di+∑aj∙Dj LINEAR sum on misalignment constants Di 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview LINEAR sum on track parameters di (different for each track) LINEAR sum on track parameters di (different for each track) xclus =∑ai∙di+ ex LHC Startup S. Viret 25 GLOBAL FIT IDEA :Express the residuals as a linear function of the misalignments, and fit both track and residuals in the meantime: xclus =xtrack + ex LOCAL PART GLOBAL PART  Taking into account the alignment constants into the fit implies a simultaneous fit of all tracks (they are now all ‘correlated’):  We get the solution in only one step.  The final matrix is huge (Ntracks∙Nlocal+Nglobal)  But inversion by partitioning (implemented in V.Blobel’s MILLEPEDE algorithm), reduces the problem to a Nglobal xNglobal matrix inversion !!!

  29. 1. Introduction 2. The alignment challenge 3. Conclusions 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview LHC Startup S. Viret 26  VELO : MC results (STEP 1: modules alignment) dx  Code integrated into LHCb software. MC tests made with different misaligned geometries. Before After  Resolution on alignment constants (with ~20000 tracks/box) are 1.2 mm (dx and dy) and 0.1 mrad (dg) dy  Algorithm is fast (few minutes on a single CPU) dg  STEP 2 results also within LHCb requirements

  30. 1. Introduction 2. The alignment challenge 3. Conclusions 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview 10 modules installed LHC Startup S. Viret 27  VELO : testbeam results (Nov.06)     4 configurations (6 modules cabled) tested  The testbeam setup

  31. 1. Introduction 2. The alignment challenge 3. Conclusions 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview LHC Startup S. Viret 28  VELO : testbeam results Before alignment After alignment 1 2 • +26% vertices in target 1 • +10% vertices in target 2 Track residuals Vertexing

  32. 1. Introduction 2. The alignment challenge 3. Conclusions 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview LHC Startup S. Viret 29  Tracking system alignment  IT and OT are internally aligned separately, then w.r.t. each other using the overlap areas.  Use the same method as the VELO (global fit via Millepede) via a common alignment software framework (currently under development).  Interface with Millepede is more complex than in the VELO,due to different track shapes (parabolas inst. of straight tracks). On the other hand detectors are not moving, alignment might be less frequently processed.  Work is ongoing. Results expected soon.

  33. 1. Introduction 2. The alignment challenge 3. Conclusions 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview : Expected Cherenkov angle : Measured angle : Distortion due to mirror tilts LHC Startup S. Viret 30  RICH alignment : principle Mirror tilt

  34. 1. Introduction 2. The alignment challenge 3. Conclusions Alignment code implemented Minimization using MINUIT 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview ax RICH 2 Measured - expected 0.1 mrad resolution obtained, well within requirements LHC Startup S. Viret 31  RICH alignment : results Fit those distributions for all the mirrors combinations in order to get their individual orientation (tilt around X and Y axis).

  35. 1. Introduction 2. The alignment challenge 3. Conclusions 1. What’s the problem with alignment ? 2. LHCb alignment strategy 3. Sub-detectors overview LHC Startup S. Viret 32  Global alignment  Most critical step is tracking system alignment: VELO to T-stations (IT & OT) TT to VELO/IT/OT  Strategy for step  has been defined (match tracks fitted independently in both tracking systems) and successfully tested on MC. Has to be extended to step   Work is ongoing.

  36. 1. Introduction 2. The alignment challenge 3. Conclusions

  37. 1. Introduction 2. The alignment challenge 3. Conclusions LHC Startup S. Viret 33  LHCb has been designed to hunt New Physics sign in the heavy flavours sector.  But in order to reach our objectives, a perfect understanding of the detector will be necessary.  In particular, a very good alignment is required (for trigger, particle ID, tracking,…)

  38. 1. Introduction 2. The alignment challenge 3. Conclusions LHC Startup S. Viret 34  LHCb alignment strategy has been presented (available in CERN-LHCb-2006-035).  It has to take into account LHCb unique specificities (RICH, moving VELO) and requirements (online vertex trigger)  Work is ongoing on many fronts, and some nice results have already been obtained (VELO testbeam alignment, RICH alignment,…). A common framework is taking shape.  We are now waiting the first beams (as we can’t play with cosmics)

  39. Backup Slides

  40.  Extensive use of specific types of tracks*(beam halo/ beam gas), mass resonances (e.g. J/y),… * No cosmics in LHCb. LHC Startup S. Viret A0  Align with what ? Alignment algorithm feeding has to be taken seriously !  First alignment will be determined using magnet OFF data (very important for tracking systems).  Then this first alignment will be updated with magnet ON data. Specific trigger scheme for those events necessary after 2008 (work ongoing).

  41. LHC Startup S. Viret A1  Methodology for the tests:  200 runs of 25000 events (5000 min.bias + 20000 pseudo-halo) were passed trough LHCb software with the following misalignments scales (all 6 degrees of freedom are taken into account at each level): Misalignment scales chosen using misalignment studies and hardware information  Misaligned events are produced via LHCb geometry framework.  No momentum cut applied for track selection (try to rely on VELO information only)

  42. … … kCkglobal Hk kwkxk D = 0 0 … … … … kwkak 0 0 dk Cklocal HkT 0 0 … … … … LHC Startup S. Viret A2  The huge matrix we had to invert is very sparse: Nglobal Nlocal xNtracks Inversion by partitioning (implemented in V.Blobel’s MILLEPEDE algorithm), reduces the problem to a Nglobal xNglobal matrix inversion !!!  AsNglobal 100 for the VELO, the problem could be solved in few sec. !!!

  43. R f  But R and f sensors are precisely bonded together within a module (~10mm precision), and also precisely surveyed (~ few mm precision). LHC Startup S. Viret A3  How to linearize the system ?  Millepede is interesting, but linearity is a key point. Obviously VELO sensors R/f geometry is not the most linear thing in the world… Could consider module as a rigid object and thus transform (R/f) into (X,Y) point. Module is then the basic detector element to align.

  44. LHC Startup S. Viret A4  VELO : MC results (STEP 2: boxes alignment)  Results obtained with limited statistic ( ~1500 PV’s and ~300 overlap tracks ) : PV soffset (PV) = 17mm stilt (PV) = 99mrad soffset (Overlap) = 13mm stilt (Overlap) = 40mrad  Results could still be improved but are already well within trigger requirements. Overlap

  45. 1. Introduction 2. The alignment challenge 3. Conclusions 1. Physics justification 2. The detector 3. LHCb startup program Momentum Resolution Impact Parameter Resolution Dp/p s(ip) s = 14.8m+30.4m/pt 1/pT p [GeV] LHC Startup S. Viret A5  Tracking performance:  Track fit: bi-directional Kalman fit  Tracking efficiency (p>5GeV) ~94% (ghost rate ~16%)  Proper time resolution ~ 40 fs  B Mass resolution ~ 15 MeV 125.6 mm

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