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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. Outline. Studies on RTTC data. Studies on DC06 data started (S.Brusa)
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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
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
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
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
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
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
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
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
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
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
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
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
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
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
spares Muon Software meeting
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
Detector Granularity and readout Pad Dimension (cm2) Chamber readout Muon Software meeting