1. 27 th June 2008Johannes Albrecht, BEACH 2008 Johannes Albrecht Physikalisches Institut Universität Heidelberg on behalf of the LHCb Collaboration The LHCb Trigger System

2. 2 / 1927 th June 2008Johannes Albrecht, BEACH 2008 LHCb Environment B-physics at LHC: –pp collisions at 14 TeV   = 0.5 mb for b-bbar –bunch crossing rate: 40 MHz –L=2*10 32 cm -2 s -1 @ LHCb  12 MHz visible interaction rate Visible B decays: 15kHz  10 11 fully contained B’s / 2 fb -1 Interesting B decays: BR~ 10 -4 -10 -9  10 2 -10 7 events / 2 fb -1 ( per channel) Interactions / bunch crossing

3. 3 / 1927 th June 2008Johannes Albrecht, BEACH 2008 B Event in LHCb Signature of B-decays: –pt ( B-daughter) > pt ( inelastic pp)  trigger: need high bandwidth –decay length L ~7 mm  trigger: CPU intense to calculate IP 15 kHz of B-decays  save only relevant decays  primary vertex (PV)  (PV)~40-60  m ++ -- K-K- K+K+ Bs0Bs0 J/  L b-hadron D+D+ ++

4. 4 / 1927 th June 2008Johannes Albrecht, BEACH 2008 B Event in LHCb B decay & underlying event 1 cm secondary vertex

5. 5 / 1927 th June 2008Johannes Albrecht, BEACH 2008 The LHCb Experiment Magnet OT RICH-1 TT IT Tracker PSSPD VELO Muon Stations M2-M5 Calorimeters RICH-2 M1 HCalECal

6. 6 / 1927 th June 2008Johannes Albrecht, BEACH 2008 Trigger Overview Hardware Trigger (L0) –“high pt” calorimeter & muon objects –rejects busy events Software Trigger (High Level Trigger) –HLT first level: trigger on B decay products –HLT second level: trigger fully reconstructed B decays on tape 2 kHz L0 HLT visible collisions 12 MHz detector readout 1 MHz

7. 7 / 1927 th June 2008Johannes Albrecht, BEACH 2008 Muons: –with constraint to (0,0,0):  p/p ~ 20% –single-  (pt >1.3 GeV) –di-muon (  pt > 1.5 GeV) Calorimeter: –“high Et” hadrons, e ±,  and  0 (threshold: 2.3 - 4.5 GeV) –particle identification from ECal / HCal energy PS and SPD information –reject busy events Hardware Trigger Strategy Scintillating Pad Detector (SPD) Pre-Shower Detector (PS) ECal HCal (0,0,0) M1M2M3 B 

8. 8 / 1927 th June 2008Johannes Albrecht, BEACH 2008 Hardware Trigger Performance threshold pt / Et (GeV) rate / kHz 3.5 700 h 1.3 200   > 1.5  2.6 200 e±e± 2.3  4-4.5 00 combined 1 MHz Bandwidth share: B  Ds  45%5%10%50% B  J/  20%90%5%90% B  K*  30%10%60%70% L0 trigger performance: efficiencies corrected for acceptance and selection

9. 9 / 1927 th June 2008Johannes Albrecht, BEACH 2008 Trigger & DAQ System Front-end –detector read out –performs zero suppression Readout network –gigabit Ethernet –total throughput: ~50 GB/s Event Filter Farm –1000 – 2000 nodes (~16.000 CPU cores) –organized in ~50 sub farms Front-end VeloCaloMuon L0 Trigger Trigger and Fast control Readout network Event Filter Farm 1000-2000 nodes CPU RICHTrackers trigger data fast control full data Y/N

10. 10 / 1927 th June 2008Johannes Albrecht, BEACH 2008 HLT: Software Trigger I HLT first level (HLT1): –confirm L0 decision using tracking system –reconstruction in region of interest –trigger on simple signatures (pt, IP,..)  increase fraction of bbar HLT second level (HLT2): –exclusive signal selections full B analysis (relaxed offline cuts) –inclusive streams trigger on clear signatures gives unbiased B sample  selection of interesting B-decays exclusive 200 Hz HLT 2 detector data: 1 MHz full event reconstruction: ~30 kHz inclusive 1800 Hz HLT 1

11. 11 / 1927 th June 2008Johannes Albrecht, BEACH 2008 HLT: Software Trigger II Independent alleys: follow L0 triggered candidate –hadron, muon, ECal Confirmation: via Tracker or via Velo –important to reduce rate fast –example: hadron alley via main tracker L0 HLT 1 st levelHLT 2 nd level hadron muon ECal

12. 12 / 1927 th June 2008Johannes Albrecht, BEACH 2008 HLT1: Confirmation with Tracker HCal tracker two charge assumptions  two R.o.I.

13. 13 / 1927 th June 2008Johannes Albrecht, BEACH 2008 HLT1: Confirmation with Tracker HCal tracker In RoI: ~160 hits (~4000 in total)  CPU time: ~1.5ms / event (~1.3 L0 candidates) Track finding efficiency: 98% (normalized to offline tracks)  pt/pt ~3% Pt resolution (hadrons) L0:  Et/Et ~30% online track:  pt/pt ~3% pt / Et resolution events / a.u.

14. 14 / 1927 th June 2008Johannes Albrecht, BEACH 2008 HLT1 Example: Hadron Alley Retention from pt and IP cut Confirmation: –first confirm with tracker, then match Velo track –require high pt and IP  rate 700kHz  30 kHz Additional signature trigger: –make two track vertex HLT1 hadron trigger: –single:pt>5 GeV, IP>100  m –di-h:IP>100  m, pt1>2.5GeV, pt2 > 1GeV, vertex pointing to PV  rate ~11 kHz Overall signal efficiency: ~70-85% signal (Bd  K  ) inelastic pp IP>0, pt > 0 IP>100  m, pt > 2.5 GeV IP>50  m, pt > 1.5 GeV IP>75  m, pt > 2 GeV

15. 15 / 1927 th June 2008Johannes Albrecht, BEACH 2008 HLT1: Trigger on Simple Signatures 700 kHz 30 kHz hadron L0 Confirmation 11 kHz additional signature trigger ECal 200 kHz 80kHz muon 17 kHz Combination of all Hlt first level steps 30-40 kHz Rate allows full event reconstruction work in progress 200 kHz Preliminary numbers!

16. 16 / 1927 th June 2008Johannes Albrecht, BEACH 2008 HLT2: Exclusive Selections HLT second level: ~30 kHz fully reconstructed events –select interesting signals exclusively –select inclusive channels for calibration, physics Exclusive selections: –~100 core physics channels (control channels included) –full reconstruction and analysis 200 Hz offline Bd    = 15 MeV  = 32 MeV B mass / MeV/c 2 signal MC online Bd  

17. 17 / 1927 th June 2008Johannes Albrecht, BEACH 2008 HLT2: Inclusive Streams charm physics, PID calibration partly  -unbiased B decays, lifetime calibration trigger-unbiased B, calibration of tagging physics D* Di-  (J/  ) Generic B (single  ) Line 300 Hz 900 Hz 600 Hz The generic B sample: –900 Hz of B   X, 550 Hz true –from the accompanying B meson: ~ 1.5  10 9 fully contained, decay-unbiased B mesons / 2fb-1 unbiased B PV trigger  rate

18. 18 / 1927 th June 2008Johannes Albrecht, BEACH 2008 Trigger Performance muonic hadronic radiative Type 90% 50% 70% L0 80% 60% Hlt Total efficiency: 70% 40% total efficiency efficiencies corrected for acceptance and selection Bs  J/   B  hh B  K*  Example Timing: –profiling run of Event Filter Farm end 2007  full HLT1 + HLT2: ~1600 events /s / box (16 single CPU cores)  we can run the HLT at 1 MHz

19. 19 / 1927 th June 2008Johannes Albrecht, BEACH 2008 Summary L0 (hardware): –high pt calorimeter & muon –efficiency: hadron: 50% muon: 90% HLT (software): –confirmation step –full B-candidate reconstruction and analysis in Trigger exclusive selections of B decays (200 Hz) inclusive streams (1800 Hz) –efficiency: 50-80% permanent storage: 2 kHz L0: high pt particles (calorimeter & Muon) HLT: confirmation step selection step visible collisions: 12 MHz full detector readout: 1 MHz

20. 20 / 1927 th June 2008Johannes Albrecht, BEACH 2008 Backup slides

21. 21 / 1927 th June 2008Johannes Albrecht, BEACH 2008 L0 Pile-Up System Detector components: –2 silicon planes upstream of nominal IP, part of the Velo Strategy: Identify multi PV events –calculate z of vertices for all combinations of A and B –find highest peak in histogram of z –remove hits that contribute to that peak –find second highest peak two interactions / bunch crossing identified with ~60% efficiency and 95% purity Vertex Locator (Velo) Vertex z Position

22. 22 / 1927 th June 2008Johannes Albrecht, BEACH 2008 Confirmation With Vertex Detector For trigger, VELO R-sensors allow for a fast search of high IP tracks in 2-D: R z IP ~ 14  m ± 35  m/p T offline !

23. 23 / 1927 th June 2008Johannes Albrecht, BEACH 2008 Detailed HLT Performance L0 HLT L0  HLT

24. 24 / 1927 th June 2008Johannes Albrecht, BEACH 2008 Trigger Monitoring General monitoring approach: –TOS: Trigger on Signal –TIS: Trigger independent of Signal –Efficiency: (TIS ∩ TOS ) / TIS