1. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 1 The LHCb trigger strategy and performance Overview Level-0Detectors, algorithms, performance Level-1 Detectors, algorithms, performance Outlook Note: Higher Level triggers  Offline selection (not covered in this talk)

2. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 2 Overview of LHCb trigger L0: fully synchronous custom-made electronics fixed latency: 4  s reduce visible rate by ~ 1:10 L1 & HLT: flexible implementation (all software) share the same farm ~1000 CPUs asynchronous average L1 latency ~ 0.5 ms

3. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 3 PYTHIA VISIBLE  total  100 60 mb  beauty  0.6 0.2 mb To tape:  3  10 6 B d evts/yr  1  10 6 B s evts/yr Clock (40 MHz) Bd  +-Bd  +- Efficiency reconstructable events Event rates [Hz] B s  J/  (  +  - )  (K + K - ) B s  D s K Trigger rates: overview Effective reduction by L0 bunch crossing (30 MHz) with visible collisions (10 MHz) not PU-vetoed (9 MHz)

4. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 4 L0 & L1: General idea Looking for B s  D s K, J/ψ , Kπ, … B d  π π,  π, J/ψ K S, Κ * γ, … Use B-meson signatures: B mass or poor man’s B mass ~ high P T B lifetime ~ displaced vertices global variables to select cleanest B events and reduce fortuitous triggers: Veto pile-up events Cut on hit multiplicity + some channel-specific tricks: e.g. for dimuon (already at L0) (rec. in L1)

5. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 5 Electromagnetic Calorimeter: Shashlik type, 5952 cells, each 8-bit E T, 25X 0 Hadron Calorimeter: Fe & scint. tiles, 1468 cells, each 8-bit E T cells 5.6 I Scintillating Pad Detector and Preshower: (SPD/PS) both 5952 cells (each 1 bit) Pile-up Veto: 4 Si sensors Muon chambers: MWPCs, 26k pads, projective in y Detectors in L0 y z

6. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 6 Pile-Up Veto: Detector Purpose: give more bandwidth to pp crossings with single collision (good for B physics!) Use same sensors as in Vertex Locator 4 half-discs upstream of the interaction point Measure radius r (strip pitch 40 … 1XX  m) PU veto Hybrid Beetles Silicon Each disc: 2048 real strips ORed by groups of 4 in Beetle FE chip (discriminator mode, 80 MHz LVDS binary output) Covers –4.2 <  < -2.9 Beetles Diodes Routing lines 84 mm

7. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 7 Pile-Up Veto: principle R B (cm) Z PV (cm) R A (cm) R B (cm) peak P1 (peak size S1) peak P2 (peak size S2) ZBZB ZAZA RBRB RARA Z PV Silicon r-sensors B A  allows locating and counting visible pp collisions R A Z PV - Z A R B Z PV - Z B = k  Z A - k Z B 1 - k or Z PV = Tracks from same Z PV have the same ratio k k Z PV’ k’

8. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 8 Pile-Up Veto: Performance Rate of single-collision B-events as a function of luminosity Before level-0 After level-0: without and with Pile-up veto  gain factor of at least 1.4 in B-event rate at the same nominal luminosity (2  10 32 ) cm -2 s -1 Size of 2 nd Peak S2 200 100 0 200 100 0 Rate (a.u.) Bd  +-Bd  +- Min. bias

9. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 9 L0 Decision & Bandwidth Division L0 Decision Unit collects: From calorimeters: E T of all candidates (hadron, electron, , etc.)  E T (also of previous and next two crossings) SPD hit multiplicity From muon trigger: 4  2 largest P T From pile-up detector: number of tracks and z of 1 st and 2 nd vtx total hit multiplicity DU performs simple arithmetic, with adjustable thresholds, downscaling, etc. Bandwidth Division: L0 output rate fixed to 1 MHz (keep 100 kHz contingency). For every given off-line selected channel, scan over L0 thresholds and PU-Veto parameters to give best performance for this given channel. Then, minimise “combined” loss for all channels. Bandwidth Division: example

10. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 10 Detectors in L1: Vertex Locator  -sensors r-sensors Purpose: find displaced vertices VELO: 220  m thick Si, 170k binary channels for L1. Each station is a sandwich of an r- and  - sensor. 45 o sectors Sensitive area starts at ~8 mm from beam axis. VELO mounted on XY- table to center on beams. Roughly 1000 clusters per event. 10 o -20 o stereo angle

11. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 11 L1 vertexing Use r-z tracks (~70/evt) to get primary vtx Tracks with 0.2 < d/mm < 3 (~8/evt) are reconstructed in 3D using  -sensors (d = impact parameter to primvtx (2D or 3D ?) 91 cm 3.4 cm x,y rms = 30  m z rms = 75  m

12. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 12 e h  L1: matching L0 objects Re-use L0 candidates in L1 Combine E/HCAL energy+cell position and Muon tracks with VELO tracks 3D-reconstruct those with best match (~ 8/evt)??

13. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 13 Example: L0-  match wdce If m  > 2 GeV then L1-yes (  keep the rare decays!) Matched L0-  :  p /p ~ 5% p/pp/p 3D tracks Adds ~ 5 kHz L1 rate B s  J/  (  +  - )  Grabs about 60% of the L0-yes “Minimum bias” (offline selected)

14. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 14 Detectors in L1: Trigger Tracker Purpose: rough momentum measurement (  p /p~0.2) for L1. 0 o –5 o 5 o 0 o Stereo 4 silicon planes in fringe field of spectrometer magnet Measure x (bending) + stereo extrapolate VELO tracks to TT split in two stations ~400 clusters per event NEW!! LHC b light NEW!! LHC b light

15. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 15 L1 Algorithm and Decision Reconstruct r-z tracks and PV with VELO Match r-z tracks to L0-  3D-reconstruct r-z tracks if 0.2 < d/mm < 3, or (why 3 mm ??) belongs to the XX best L0-matched Determine P T with VELO+TT Take decision: Cut on  log(d/  d ) %  log(P T ) Overrule: if m  > 2 GeV then L1-yes

16. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 16 L1 Trigger performance Performance improved with addition of TT and L0- matching Further improvements with: IT/OT tracking ? Multiplicity cuts … VELO only

17. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 17 FIN

18. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 18 Trigger performance L0 (%)L1 HLT Tot µ µµ e γ h all(%)(%)(%) B d  π + π - 7 6 9 3 55 6151? 31 B s  D s K 8 7 5 2 37 4465? 29 B s  J/ψ(ee)  7 7 36 4 24 5243? 23 B s  J/ψ(µµ)  90 89 5 3 30 9373? 68 B d  Κ * γ 6 6 28 47 30 8233? 27 Trigger efficiencies for dimuon channels are ~30% higher Hadron trigger is central to LHCb physics goals Evenly spread selectivity = robustness and flexible

19. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 19 L0: Muon System High-P T Hardware: Muon System: MWPC, RPCs ?, y-projective, 120k physical channels, 26k, trigger channels, what bits ? Principle: Muon System: find track, assume origin=IP, use B-kick

20. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 20 L0: Calorimeter High-P T Detectors: HCAL / Hadron Calorimeter: Fe & Scint. Tiles, 1468 cells, each 8-bit E T PS / Preshower: 5952 cells (each 1 bit) SPD / Scintillating Pad Detector: 5952 cells (each 1 bit) ECAL / Electromag. Calorimeter: shashlik, 5952 cells, each 8-bit E T Principle: ignore B-field, assume origin = IP, use energy and cell position to determine E T (P T ) combine HCAL, ECAL, SPD, PS to produce high-P T candidates of type electron, gamma, hadron, local pi0, global pi0 polar angle Energy

21. 2 nd Workshop on CKM Unitarity Triangle – April 5-9, 2003, DurhamMassimiliano Ferro-Luzzi 21 L1 efficiency depends strongly on SPD cut egerfer