Alignment Studies in Muon Software for LHCb: Insights and Future Directions

1. Recent studies on Muon System software alignment Stefania Vecchi (INFN Bologna) Wander Baldini - Simone Brusa - Antonio Falabella (INFN Ferrara) Muon Software meeting Oct 26th, 2006

2. Outline • Studies on RTTC data. • Studies on DC06 data started (S.Brusa) • Definition of the alignment stratergy (Diploma Thesis A.Falabella) • The idea/implementation (fast MonteCarlo) • The validation with full simulation in LHCb • Conclusions / To be done: • Define alignment requirements • Integrate in LHCb software/study realistic scenarios. • On DC06 Full simulation: repeat the studies on L0MuonTrigger (updated) Muon Software meeting

3. Studies on RTTC data • Limited analysis due to the impossibility of changing Muon detector geomety. • We could only study the effects of Muon misalignment on L0MuonTrigger performances in a limited way • change Pt calculation including a misalignment by hand • No possibility of studying effects on FOI • We shifted M1&M2 full (half) station • Main conclusions: • deviations from expected performances shows up for misaligments >=10 mm. • Charge asymmetry: +-<10% with 10 mm displaced M1 (M2) • The statistics was also limited, so it was not possible to define how precisely the efficiency has to be known to see and limit misalignment effects. • Studies on RTTC data halted. Muon Software meeting

4. Studies on DC06 data • New Event Model allows playing “easily” with alignment constant during simulation/reconstruction • More quantitative results can be obtained analyzing this data. • Studies on DC06 data started (Simone Brusa) • Need time to get practice with LHCb simulation software. • Generate, Digitize and Reconstruct some data. • Need to learn how to play with XML file in order to introduce misalignments in the detector • ParticleGun: muons generated in LHCb acceptance with 0<p<100GeV/c Muon Software meeting

5. Particle gun: single muons 0<p<100 GeV in LHCb acceptance Angular deviation [mrad] due to MultipleScattering at each muon station Absolute coordinate [mm] deviation P<20 GeV P<40 GeVP<60 GeVP<80 GeVP<100 GeV Muon Software meeting

6. Future studies on DC06 data • Need to learn how to play with XML file in order to introduce misalignments in the detector at Simulation or Reconstruction level. • Prove that misalignment effects can be well described by misaligning the detector at reconstruction level (to save time) • Repeat the studies on L0MuonTrigger efficiency quantitatively (effects on FOI, pt cut) • Define efficiency accuracies/limits requirements Muon Software meeting

7. Study on the alignment procedure • The Muon detector can be aligned stand-alone first, by using “straight” muon tracks crossing the stations, then globally aligned to LHCb reference, by matching the muon tracks with the tracks measured by the tracking system (aligned). • During the Pilot Run data with B field=0 will be taken. They will be useful for a first software alignment (constraint the muon to come from the IP) • The idea: simply apply a linear fit in x-z (y-z) plane of the measured coordinates (preselected muon candidates) • Study the residual distribution on each station Mi (divided in half station or region or….): • RMi=(XfitMi-XMi) (hp: no ZMi displacement) • If residual’s mean deviates from Zero, use it to correct position of Mi, then iterate until convergence. Muon Software meeting

8. experience….from litherature…. If all data are used in the fit….iteration converges to a wrong solution (in this example we have 10 tracking planes) From Blobel talk “Software alignment for tracking detectors” Hamburg 17th Jan 2005 Muon Software meeting

9. The reason for non-convergence is that two degrees of freedom are undefined: a simultaneous shift and a rotation of all planes! • Possible improvements: • Fix the displacement (i.e. displacement = 0) of two planes, (assumed to be carefully aligned externally) • Use only two fixed planes in the fit, and determine the residuals of other planes; • To determine the displacement of a certain plane use all other planes in the fit. Muon Software meeting

10. Alignment algorithm..…starting from simple • Study alignment of M1-M5 (+IntPoint) in x-z plane (should be conceptually the same in y-z) • Simulate “straight” tracks through a simplified LHCb detector (IntPoint, T3, M1-M5) with “home made” generator • Calculate coordinates x-z on each plane taking into account for: • multiple scattering (assuming homogeneous media in between detector planes) • detector pad size and position • Validation of the Toy Generator with the full simulation by using muons generated with the ParticleGun (DC06 data) • Linear Fit of “muon hits” / check residuals & iterate to align muon stations. Muon Software meeting

11. Simple Mcarlo generation: muons 0<p<100 GeV in LHCb acceptance Angular deviation [mrad] due to MultipleScattering at each muon station Absolute coordinate [mm] deviation Muon Software meeting

12. simple MonteCarlo LHCb MonteCarlo (Gauss) M1 M2 M3 M4M5 SigmaX a bit understimated Even with a rough description of material the simple simulation describes well enough the muons properties…… Maybe a just a correction on NX0 can account for differences. Muon Software meeting

13. One example: Stand-alone fit: fit all M1-M5 data, no SHIFTs Error on residual mean should define alignment reach (out systematic effects) Muon Software meeting

14. To do…/..Conclusion • Define alignment requirements: • Precision on alignment constant with the residual method (Muon Station/Region/Chamber). • Statistics: how much to get the Muon detector aligned in all its parts? • Find the best stratergy. (which stations to fix) • Improve alignment by using high momenta muons? • Integrate in LHCb software/study realistic scenarios. • On DC06 Full simulation: do quantitative studies on L0MuonTrigger performances (updated) Muon Software meeting

15. spares Muon Software meeting

16. Detector misaligned M1 M2 M3 M4 M5 L0/reconstruction response misaligned L0/reconstruction @ nominal position Real situation Detector @ nominal position Simulated situation Muon Software meeting

17. Detector Granularity and readout Pad Dimension (cm2) Chamber readout Muon Software meeting