Status of Tracker Alignment

1. Status of Tracker Alignment b-tagging Workshop 29.10.08 Nhan Tran (JHU) On behalf of the Tracker Alignment Group

2. Outline • Misalignment and b-tagging • Standard CSA07/08 scenarios • Effect of APE • Overview of recent experience with Global Runs • CRUZET results and first CRAFT data • Towards APE and resolution • Outlook

3. Introduction:Misalignment and b-tagging • Track and vertex reconstruction (and thus b-tagging) is highly affected by misalignment • Standard CSA07/08 misalignment scenarios • SurveyLASOnly; SurveyLASCosmics(Startup);10 pb-1; 100 pb-1 • PXB Alignment vital • Alignment Position Errors (APE) - added to track errors to maintain track finding efficiency • Affects track impact parameter significances • For further studies, please refer to CMS NOTE 2008/029 & CMS AN 2007/047

4. CRUZET (B = 0T) • Alignment with nearly whole tracker - good turnaround of alignment constants • Two samples of selected tracks • July, 285k tracks • August, 345k tracks • No magnetic field, no momentum measurement • Running both HIP and MillePede algorithms - similar results • First experience with pixel detector - half barrel alignment • Improvement of track 2 and hit residuals pixel hit strip hit Distribution dependent on momentum assumption

5. CRUZET Results Effect of alignment on tracking: Idea to split cosmics tracks along impact parameter and compare track parameters of top and bottom halves Alignment shows improvement in bias and resolution of the track parameters dxy and  (also for dz and ) Cosmic splitting n.b. No pixels…Stay tuned to CRAFT!

6. First CRAFT Data (B = 3.8T) • Expect ~3 weeks of CRAFT running • After a “bumpy” start, results improving - data still coming in! • As of 10h CET, ~1.3 M events • Still many things to understand • Tracking variable distributions • Pixel hit efficiency • pT distributions • Cut optimization • Expecting pixel statistics for module level alignment • Observing 0.7% of tracks with at least one pixel hit • First attempt at ladder level • Pixel APEs under investigation • PXF appear underestimated

7. Towards Resolution and APE • Unique -dependent systematics for cosmics • Methods dependent on Cosmic MC (in production) - no definitive results yet • Distribution of the mean of the residuals, residuals from high-pT tracks, MC-tuning of residuals, APE-tuning • Preliminary results show better-than-expected resolution for strip barrel modules with good statistics • Focused alignment group efforts underway Distribution of the mean of residuals in CRUZET; Modules with > 100 modules preliminary preliminary Waiting for corresponding MC…

8. Outlook • First experiences with Global Runs positive from tracker alignment perspective - still many things to understand • PXB alignment and APE estimation vital for b-tagging • Expect statistics for alignemnt of PXB at module level • APE estimation under investigation - high priority • Standard CSA07/08 Scenarios affected • Unforeseen PXB alignment - unknown level of achievable alignment at this time • Strip Tracker resolution overestimated for modules with good statistics • Pixels still under investigation in CRAFT - PXF appear underestimated; PXB case less clear

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10. Status of Tracker Alignment • Alignment algorithms (HIP, MillePede) both running with good turnaround • Validation package including track 2, hit residuals, and geometry comparison standardized • Experience during both CSA08 and Global Runs positive Alignment Workflow