Update on LHCb Level-1 trigger 4 February 2019 Federica Legger

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 4 February 2019

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 February 2019

TDR L1 code L1 Generic (B meson decay products) 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 Courtesy of Thomas Schietinger 4 February 2019

Advantages: Disadvantages: 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 4 February 2019

Post TDR Redesign of L1 code 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 4 February 2019

DC04 L1 code Parallel (and overlapping) subtriggers 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 4 February 2019

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 4 February 2019

Overlaps are absorbed in this direction Bandwidth division Massive improvements in generic algorithm (multiple PVs!) result in larger bandwidth for other triggers (in particular dimuons) Before: Bandwidth (kHz) Photon Electron Dimuon, J/Psi Dimuon, general Single-muon Adjusted for overlap Generic 29.4 (74.1%) 6.8 (17.1%) 1.5 ( 3.8%) 1.8 ( 4.6%) 3.7 ( 9.4%) 4.3 (10.8%) 3.2 ( 8.0%) 1.2 ( 3.1%) 1.2 ( 2.9%) 2.2 ( 5.5%) 2.5 ( 6.4%) Now: Overlaps are absorbed in this direction 4 February 2019 Courtesy of Thomas Schietinger

L1 efficiencies Offline selected Reconstructible 4 February 2019

4-prong give best generic efficiency! 10-20% improvement!!! L1 efficiencies Offline selected Reconstructible why different? Hadrons trigger e and g! 4 February 2019 4-prong give best generic efficiency!

Implementation: DaVinci (LHCb analysis program) Trg/L1Decision 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 4 February 2019

To check L1 performances… summary Min Bias fit Efficiency vs. Retention plots for each subtrigger 4 February 2019

More complicated case… Choose second cut first: Electron Photon 4 February 2019

4 February 2019

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. 4 February 2019

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? 4 February 2019

Control channels: Bd  p+ p- 2 high PT tracks Bs  Ds K 1 high PT track Bd  D0(Kp)K* no high PT track 4 February 2019

Multiple PVs No big differences # PVs > 2 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? 4 February 2019

TDR L1 Generic D Signal Min Bias Log IPS1 + Log IPS2 Signal Min Bias D Log PT1 + Log PT2 L1 Variable = D (2d distance from L1 line) 4 February 2019

DC04 L1 Generic Improved vertexing Simpler cut: No need for IPS; Log PT1 + Log PT2 4 February 2019

Do we need a weighted PT2? NOW NOW 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 4 February 2019

Default PT for tracks with no measured PT NOW 4 February 2019

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 4 February 2019

Status and plans L1 shows good (and unexpected) performances; Still some open issues; Start thinking about systematics (high luminosity, beam background) and online issues 4 February 2019