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Tracking in TRD and on-line event selection

Tracking in TRD and on-line event selection. Maciej Krauze , Arkadiusz Bubak, Wiktor Zipper University of Silesia, Katowice. Outline. Standalone tracking in TRD The algorithm Comparison of results for new and old TRD geometry TRD J/ ψ e vent selection STS+TRD scenario

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Tracking in TRD and on-line event selection

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  1. Tracking in TRD and on-line event selection Maciej Krauze, Arkadiusz Bubak, Wiktor Zipper University of Silesia, Katowice

  2. Outline • Standalone tracking in TRD • The algorithm • Comparison of results for new and old TRD geometry TRD • J/ψ event selection • STS+TRD scenario • TRD Standalone scenario • Conclusions and next steps

  3. Standalone tracking in TRD • The Cellular Automaton algorithm overview (ESR*) *ESR – Extremally Short Reminder

  4. Tracking results (25AGeV) • Previous results using trd_12.geo (1st TRD at 4 m) • Currently using trd_standard.geo (1st TRD at 5m)

  5. Tools used for event selection • CBMROOT AUG07 • mbias UrQMD events: Au+Au@25AGeV • e+e- data from J/ψ decay generated by Pluto and processed by CBMROOT • patience...

  6. TRD+STS J/ψ event selection

  7. TRD+STS event selection • Fast (TRD and STS tracking done in parallel and independently) • sts_standard.geo and trd_standard.geo used • no MVD but additional fit to target used • High momentum resolution obtained from STS (~1%) σ=1.27% σ=1.08% without fit to zero vertex fit to zero vertex applied

  8. STS-TRD matching TRDtracks X STS track extrapolation OK 1st TRD target

  9. Stages of track matching • Matching efficiency STS to TRD tracks ~96% • Matching done in two stages: • Extrapolation of STS track to 1st TRD station and search for TRD tracks within a certain area (distance parameter) • each found TRD track is paired with extrapolated STS track • Comparison of slopes of STS and TRD track pairs • the comparison parameter is a final critterion to decide which tracks pair to choose • TRD track previously matched cannot be matched to anothet STS track!

  10. Some numbers... • Cuts applied: • Hadron identification: 99% • Transversal momentum Pt > 1 GeV/c • Invariant mass 2 < M < 4 GeV/c2 • Signal events accepted: 49% of detectable e+e- form J/ψ decay • detectable  event contains e+e- from J/ψ with 12 hits in TRD each • Background events (mbias) rejected: 99.8%

  11. TRD standalone scenario

  12. TRD standalone selection • New fitting strategy resulting in momentum resolution improvement • momentum resolution below 14% • hadron identification 99% • using reconstructed charge • 90.5% J/ψ track reconstruction efficiency • only 81% of detectable signal events left!

  13. TRD steps of selection • tracking efficiency leaves only 81% detectable J/ψ • detectable means: event contains e+e- with 12 hits in TRD • hadron identification 99% • cut on momentum estimation quality parameter χ < 3 (77.2% of signal survives) • cut on TRD fit quality parameter χ2< 10 (77.2% of signal still present) • Transversal momentum Pt > 1 (55% of signal left) • charge determination (does not affect signal)

  14. J/ψ invariant mass • invariant mass є (2.5 , 3.5) GeV/c2 (52% of signal left) • using the same conditions we remove 98% of mbias background events 1000 pure J/ψ events after selection

  15. Signal and background radius = 1  2.5 < M < 3.5 signal efficiency [%] 500 mbias events

  16. Summary • TRD standalone L1 selection suppresses 98% of background, while ~50% of the signal events are accepted • background reduction by a factor 50 gives more time for a possible L2 selection (more sophisticated and time-consuming algorithm) • TRD+STS scenario – more complicated but offering better results (49% signal events and 99.8% background rejection)

  17. Next steps • possible connection of TRD standalone selection with RICH for better hadron ID • adding second level (L2) event selection, which offers further background reduction • use also for other than J/ψ physics (?) • event selection procedures are ready to be merged with the current CBMROOT version

  18. And...

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