Status of tracking Thijs Cornelissen, Genova Thanks to Claudia Gemme and Andrea Coccaro

Tracking algorithms Default `NewTracking’ runs several different algorithms: Inside-out tracking: start from spacepoint seeds in pixels & SCT Backtracking and TRT tracking: start from TRT segments, use only hits that were not already used by inside-out LowPt tracking: use remaining silicon hits to find tracks with 100 MeV < pT < 500 MeV Standard set of tracking cuts designed to give best trade-off between efficiency and fake rates in busy events (e.g. ttbar) Commissioning settings much more loose: Allow more holes on track Allow worse track fit quality (20 instead of 7), loose cuts on ‘outlier’ hits Use conservative measurement errors (cluster width/√12) Further increased by error scaling where needed

First collisions First collisions on Nov. 23. Challenging for tracking: Pixels off SCT at 20V (only 50% efficient) Momentum unknown (solenoid off), therefore cannot correct for material effects (scattering) Limits quality of reconstructed tracks Tracking ran with very loose cuts Accept tracks with large impact parameters and/or large number of holes (i.e. sensors without a hit)

Pixel and SCT hits Number of pixel and SCT hits on combined tracks, very good agreement between data and simulation Can distinguish SCT endcap disks Smooth variation in number of pixel hits due to disabled modules (up to 4%)

Tracking efficiencies Reconstruct ‘tracklets’ in each subdetector, check efficiency relative to combined track Pixel tracking most efficient, TRT least efficient Due to problems with TRT tracking algorithm, see next slide

TRT tracking CTB xK Compare standard TRT tracking for collisions (‘xK’) with modified cosmics tracking (‘CTB’) Higher efficiencies and lower fake rates with CTB Modified version of cosmics TRT extension also under study

TRT tracking (cont’d) Rtrack (mm) TRT simulation does not reproduce data well: less hits on track, worse resolutions (especially tails) Default cuts in tracking are rather tight, gets rid of most of the tail Commissioning settings much more loose, caused bad fit qualities in simulation (average c2/ndf around 2)

Silicon tracking efficiency Check silicon tracking efficiency by using pixel tracklets to probe combined track collection (`SCT extension’) Very good agreement between data and MC up to |h| ~ 2.2 Discrepancy at large |h| not yet understood

dE/dx per le tracce La dE/dx si calcola come media troncata del rilascio di energia di tutti I cluster appartenenti alla traccia. Troncata perche’ si escude il cluster con rilascio di carica maggiore (in modo da tagliare le code della Landau). dE/dx accesibile in InnerDetector/InDetRecTools/PixelToTPIDTool Puo’ essere usato per studiare risonanze come il L, f e, piu` tardi, l’identificazione di esotici (low b) Clusters cuts: Barrel and EndCap Residuals: abs(pullPhi)<5, abs(pullEta)<5 Spatial Incidence angle a : cos(a)>0.1 (i.e. a<1.47) Cut on Incident Angle in rf plane: none Tracks cuts: Tracks: Good clusters >=3

PID Runs 141811, 142165 Per adesso solo una rozza identificazione per poter fare I primi plot. p k p p k Positive: 9800 (p), 3000 (k) Negative: 2800 (p), 1800 (k) 10

Online tracking: pT spectrum In 2009 run, HLT including SiTrack was run in pass-through mode pT spectrum of reconstructed online tracks (red) and offline tracks (black) Good agreement (online tracking cuts at |pT| > 1 GeV)

Online tracking: z0 spectrum Vertex shifted along z during the run, due to LHC adjustments Shift detected both by SiTrack and IDScan

Online tracking: efficiencies Efficiencies of SiTrack (red) and IDScan (blue) relative to offline tracking (black) Inefficiencies in SiTrack thought to be due to initial misalignments, to be checked with upcoming trigger reprocessing Trigger reprocessing uses improved alignment (esp. endcaps)

Conclusions Tracking worked quite well from beginning Items to be understood/improved: TRT tracking efficiencies and fake rates Silicon tracking efficiency near |h| = 2.5 Need to work towards removing commissioning settings Would benefit from improved resolution (esp. pixels) Better rejection against fake tracks Online tracking works Need to study performance with updated alignment Will soon be needed to select events dE/dx tool now available Need to study efficiencies and fake rates of PID using data and MC

Backup

Tracking efficiency in MB analysis