1. The Silicon Track Trigger (STT) at DØ Beauty 2005 in Assisi, June 2005 Sascha Caron for the DØ collaboration Tag beauty fast …

2. page 1 page 1 The Silicon Track Trigger at DØ OUTLINE OUTLINE - D0 detector - - D0 trigger - - What is the STT? - - dataflow - - clustering and tracking - - B identification - - Performance - - Summary Sascha Caron Sascha Caron

3. page 2 page 2 The Silicon Track Trigger at DØ Sascha Caron Sascha Caron D0 in Run II The Silicon Track Trigger is based on information of the : Silicon Microstrip Tracker Central Fiber Tracker

4. page 3 page 3 The Silicon Track Trigger at DØ Sascha Caron Sascha Caron D0 in Run II The Silicon Track Trigger is based on information of the : Silicon Microstrip Tracker Central Fiber Tracker o 50 μm pitch strips (parallel to beam) o 800000 readout channels o Only axial strips used for STT tracks o Scintillating fibers o Coverage: |Rapidity| < 1.7

5. page 4 page 4 The Silicon Track Trigger at DØ Sascha Caron Sascha Caron Events for L=100 E30 cm -2 /s L=100 E30 cm -2 /s = about 8 pb -1 /day 10 1 0.1 0.01 0.001 Higgs->b bbar ZH-> bbvv, bH->bbb etc. Z-> b bbar QCD E T >30 GeV dijet production b-jets E T >30 GeV 0.0001 Eventspersecond Find b-events early to keep high efficiency at an acceptable rate Find b-events early to keep high efficiency at an acceptable rate Aim: High E T Z->bb, HZ->bbvv, H->bb, etc. Z->bb, HZ->bbvv, H->bb, etc. Hopefully B physics

6. page 5 page 5 The Silicon Track Trigger at DØ Sascha Caron Sascha Caron Principal Idea B decay length is mm Impact parameter (2d in x-y plane) B decay products o Silicon Improved Tracks with 2d impact parameter 2d impact parameter o Select events with large impact parameter tracks Interaction point is mean beam spot

7. page 6 page 6 The Silicon Track Trigger at DØ Sascha Caron Sascha Caron L1 Trigger decision time decision time about 4 μs (1500) 5000 Hz (700)1000Hz 50 Hz 2.5MHz L2 Trigger decision time decision time about 200 μs L3 Trigger decision time decision time about 50 ms Trigger System p p bunch crossing frequency ¯ o Hardware based o CTT tracks, calorimeter towers, muons o Hardware/Software o simple jets, electrons, muons, taus o Silicon Microvertex improved tracks (STT) o global processor to combine information (e.g. STT tracks for Bid) o Software based o partial event reconstruction

8. page 7 page 7 The Silicon Track Trigger at DØ Sascha Caron Sascha Caron SiliconMicroDetector CentralFiberTracker L2STT L1CTT L2CTT L2Global other L2 pre- processors Detector Level 1 Level 2 Level 1 Detector Data flow chart L2 tracks

9. page 8 page 8 The Silicon Track Trigger at DØ Sascha Caron Sascha Caron How is the tracking improved? o Tracks found at L1 with the Central Fiber Tracker are used to define roads into the Silicon o Silicon hits are clustered o Track is re-fit within the road

10. page 9 page 9 The Silicon Track Trigger at DØ Sascha Caron Sascha Caron Silicon Track Trigger cards Road data to Fiber Road Card SMT data to 9 Silicon Trigger Cards Cards Fitting done in Track Fit Card L2CTT Done in parallel for each of the 12 sectors 2 sectors in 1 crate -> 6 Crates with 1 Fiber Road Card 9 Silicon Trigger Cards 2 Track Fit Cards

11. page 9 page 9 The Silicon Track Trigger at DØ Sascha Caron Sascha Caron Silicon Track Trigger cards Road data to Fiber Road Card - Receives and distributes L1 tracks - Communicates with Trigger framework framework SMT data to Silicon Trigger Cards Cards - Perform clustering and cluster- road matching - Clusters SMT hits + pedestal correction - Axial clusters are matched to the roads Fitting done in Track Fit Card - receives road and axial clusters - convert to physics coordinates via LUT - perform track fit φ(r)= b/r+kr+φ 0 - beam spot correction - output tracks to L2CTT

12. page 10 page 10 The Silicon Track Trigger at DØ Sascha Caron Sascha Caron Performance studies STT tracks Impact Parameter resolution Correlation to RECO p T (GeV) Resolution in μ m Purity Including beam spot size 35 μm and 15 μm SMT resolution

13. page 11 page 11 The Silicon Track Trigger at DØ Sascha Caron Sascha Caron - Fast, simple and efficient technique - Time needed is 2 operations per track and goes linear with the number of tracks -> about 1-5 μs - Degrades bad tracks without cutting them Store 2d signal (b events) to background (light quarks) ratio into a lookup table B identification B identification Signal to Background ratio b/db b/db 1.5 mm RiRiRiRi

14. page 12 page 12 The Silicon Track Trigger at DØ Sascha Caron Sascha Caron Performance studies Very well separation of signal and background events Large background reduction with L2 b-ID algorithms efficiency Z->bb L2 B-id likelihood Red : Red : Simple Cut Blue/Green: B-id

15. page 13 page 13 The Silicon Track Trigger at DØ Sascha Caron Sascha Caron First studies using data Max IP Significance Likelihood L2 data well correlated with offline data -> proof of b-id principle -> Much more studies on their way Jet data Offline B-tagged data Likelihood shifted to higher values due to e.g. min bias effects DØ preliminary Using MC pdfs DØ preliminary

16. page 14 page 14 The Silicon Track Trigger at DØ Sascha Caron Sascha Caron Summary o The STT is operating routinely and smooth o High Impact Parameter resolution o Data is understood o Very fast L2 b-id is (almost) implemented o We expect a high potential for Z->bb and Higgs physics now and at L=200E30cm -2 /s Z->bb and Higgs physics now and at L=200E30cm -2 /s Outlook o Implementation of new Layer 0 (r=22mm) into STT -> further increase in precision and stability -> further increase in precision and stability