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Update on LHCb Level-1 trigger

This update covers the redesign and efficiency enhancements of LHCb Level-1 trigger system. It explores subtriggers, bandwidth division, efficiencies, and open questions regarding trigger decisions. The post-TDR improvements and plans for future enhancements are discussed in detail.

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Update on LHCb Level-1 trigger

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  1. Update on LHCb Level-1 trigger Federica Legger

  2. Summary • TDR L1 • Post TDR needs • L1 redesign • L1 bandwidth division • L1 efficiencies for some representative channels • Long-standing L1 open questions • Status and plans

  3. TDR times LHCb trigger TDR (September 2003) Aim for highest possible efficiencies for a list of benchmark channels (tagging not taken into consideration due to the lack of statistics…)

  4. TDR L1 code Massive  high Pt Long-lived high IP • L1 Generic (B meson decay products) • Selects events with two high PT tracks in IP window [0.15, 3.] mm.; • Bonus system (specific) • Dimuon • |mmm – mJ/| < 500 MeV • mmm > mB – 500 MeV • Electron • Etmax > 3 GeV • Photon • Etmax > 3 GeV Courtesy of Thomas Schietinger

  5. Advantages: • Bonus values are tunable for optimal efficiencies/bandwidth; • Good for TDR! • Trigger summary in just one variable: • Convenient for comparisons • Easy for users Disadvantages: • Correlation among various subtriggers; • Cut on PT depends on bonus values • Hard to understand why an event has triggered; • An event with some momentum, some dimuon mass, a little bit of photon and electron can trigger…(???) • Not easy to implement parallel subtriggers • example: Thomas’ single muon hack

  6. Post TDR • Some bug corrections and code improvements • tracking and multiple PVs • Need to better understand L1 behaviour & systematics • Unbiased data samples • trigger on tag • Indipendent trigger line Redesign of L1 code

  7. DC04 L1 code GENERIC SPECIFIC • Parallel (and overlapping) subtriggers • Generic • Single muon • Dimuon • Dimuon (J/Psi) • Electron • Photon • Final decision is OR of single subtrigger decisions Courtesy of Thomas Schietinger some PT cut still needed to reduce bandwidth

  8. Generic (pT):ln(PT1) + ln(PT2) > 13.925 • For tracks with IP > 0.15 mm • Pile-up veto (IP < 0.15 mm), up to 2 PVs • Single-muon:IP> 0.15 mm, PT > 2.32 GeV • Pile-up veto (IP < 0.1 mm), up to 3 PVs • Dimuon general:mmm> 500 MeV, IPmm > 0.05 • Dimuon J/: |mmm – mJ/|< 500 MeV OR • includes B, Z, H, X mm mmm> mB – 500 MeV • No IP cut • Electron:max. ET(e) > 3.6 GeV AND ln(PT1) + ln(PT2) > 13.0 • Photon: max. ET(g) > 3.1 GeV AND ln(PT1) + ln(PT2) > 13.0

  9. Bandwidth (kHz) Adjusted for overlap Generic 29.4 (74.1%) 29.4 (74.1%) Single-muon 6.8 (17.1%) 3.2 ( 8.0%) Dimuon, general 1.5 ( 3.8%) 1.2 ( 3.1%) Dimuon, J/Psi 1.8 ( 4.6%) 1.2 ( 2.9%) Electron 3.7 ( 9.4%) 2.2 ( 5.5%) Photon 4.3 (10.8%) 2.5 ( 6.4%) Bandwidth division Massive improvements in generic algorithm (multiple PVs!) result in larger bandwidth for other triggers (in particular dimuons) Before: Now: Overlaps are absorbed in this direction Courtesy of Thomas Schietinger

  10. L1 efficiencies Offline selected Reconstructible

  11. 10-20% improvement!!! L1 efficiencies Offline selected Reconstructible why different? Hadrons trigger e and g! 4-prong give best generic efficiency!

  12. Implementation: • DaVinci (LHCb analysis program) • v12r2; • Trg/L1Decision • v3r1; • Activating L1 decision via option file generates • N-tuple with L1 information • Root macro coming with L1 package creates all kinds of plots to analyze L1 performances

  13. To check L1 performances… L1 summary Min Bias fit Efficiency vs. Retention plots for each subtrigger

  14. More complicated case… Choose second cut first: • Electron • Photon

  15. Advantages of new L1 code: • Easy to impose bandwidth division • user-steerable; • Single trigger bits accessible to users • Easy to understand why an event triggered; • Allows clean implementation of new trigger lines.

  16. L1 open questions for generic subtrigger: • Multiple PVs treatment • Is current solution the best one? • L1 Generic decision function • S (log PT) • log (S PT) • Weighted PT2? • PT3? • Is 400 MeV/C a good value for tracks with no measured PT?

  17. Control channels: • Bdp+ p- 2 high PT tracks • Bs Ds K1 high PT track • Bd D0(Kp)K*no high PT track

  18. Multiple PVs • No big differences • current solution seems to be the best • # PVs > 2 • Not enough statistics at current luminosity • Higher number of PVS • Need some high luminosity data!! NOW Is PV1 = highest multiplicity vertex enough? Veto on # PVs?

  19. TDR L1 Generic Log IPS1 + Log IPS2 Signal Min Bias D Log PT1 + Log PT2 L1 Variable = D (2d distance from L1 line)

  20. DC04 L1 Generic • Improved vertexing • No need for IPS; • Simpler cut: • Log PT1 + Log PT2

  21. Log (PT1+PT2) • Log PT1 + Log PT2 = Log(PT1*PT2) • Do we need PT3? • Do we need a weighted PT2? GENERIC GENERIC NOW NOW Weight

  22. Default PT for tracks with no measured PT NOW

  23. Current solution is OK, but do we really understand it? • Are default Pt = 400 MeV/c and L1 = S log disentangled? • PT1, PT2 dependence not so clear • Try two separate thresholds for PT1 and PT2 and play with it

  24. Status and plans • L1 shows good (and unexpected) performances; • Still some open issues; • Start thinking about systematics (high luminosity, beam background) and online issues

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