1. High Level Trigger – Applications Open Charm physics Quarkonium spectroscopy Dielectrons Dimuons Jets

2. Assumptions Detector readout rate (i.e. TPC) >> DAQ bandwidth  mass storage bandwidth Physics motivation for a high level trigger Need for an online rudimentary event reconstruction for monitoring

3. Data volume and event rate TPC detector data volume = 300 Mbyte/event, data rate = 200 Hz front-end electronics DAQ – event building realtime data compression & pattern recognition PC farm = 1000 clustered SMP permanent storage system bandwidth 60 Gbyte/sec 15 Gbyte/sec < 1.2 Gbyte/sec < 2 Gbyte/sec parallel processing

4. Data rate reduction Volume reduction –regions-of-interest and partial readout pile-up removal in p+p –data compression entropy coder vector quantization TPC-data modeling Rate reduction –(sub)-event reconstruction and (sub)-event rejection before event building

5. Fast pattern recognition Essential part of Level-3 system –crude complete event reconstruction  monitoring –redundant local tracklet finder for cluster evaluation  efficient data compression –selection of ( , ,p T )-slices  ROI –high precision tracking for selected track candidates  dielectrons,...

6. Level-3 system structure TPC : fast cluster finder + fast tracker Hough transform + cluster evaluator Kalman fitter TRD trigger Dimuon trigger Trigger detectors Pattern Recognition Dimuon arm tracking PHOS trigger Extrapolate to ITS Extrapolate to TOF Extrapolate to TRD... Level-1 Level-3 (Sub)-event Reconstruction

7. TPC Rate limitations Pb+Pbp+p L [cm -2 s -1 ] 5  10 26 2  10 30 event rate4 kHz140 kHz pile-up10%20 clean min. bias / central rate1 kHz / 200 Hz event size (10 bit zero-suppressed & Huffman coded) 80 MByte 50 Mbyte (central) 1.5 MByte 1 MByte TPC readout rate1 kHz / 200 Hz1 kHz front-end data rate / DDL47 MByte/s (central) 5.5 MByte/s Level-3 input event rate200 Hz (central)1 kHz Level-3 output event rate (full TPC events) 10 Hz (central) 1 kHz pile-up removal Level-3 output data rate0.5 GByte/s<0.2 GByte/s

8. Open Charm Physics (1) Hadronic charm decays –D 0  K – +  + –B.R. = 3.86% –c  = 124  m –high p T of the decay products: 75% of decay pions have p T > 0.8 GeV/c

9. Open Charm Physics (2) Charm Filter HLT momentum filter –subevent rejection –subevent = low- p T tracks –11% of charged particles have p T > 0.8 GeV/c

10. Open Charm Physics (3) Charm Filter Trigger strategy –find high-p T tracks in outer sector of TPC (based on seeds from TRD) –extrapolate track back to vertex –record raw data along trajectory Problem of overlapping clusters –for deconvolution of high-p T track clusters the knowledge of track parameters of crossing tracks is necessary Solution – reconstruction of all tracks in the neighborhood (same/neighboring sector and  )

11. Open Charm Physics (4) Charm Filter Trigger efficiency –signal loss: <25% –data volume reduction to 7 Mbyte/event (factor 10) –p T > 0.8 GeV/c vs. all p T

12. Open Charm Physics (5) Charm Filter Trigger efficiency –signal loss: <35% –data volume reduction to 10 Mbyte/event (factor 5)

13. Open Charm Physics (5) Event Abortion Level-3 trigger: event abortion –Trigger strategy high-precision reconstruction of high- p T tracks (Kalman + PID) extrapolation to ITS cuts on impact parameters, invariant mass etc. –Trigger efficiency signal/event = 0.0027 * background/event = 0.15 * event rejection rate of 85% (new result incl. PID and pt-cut: factor 10 higher) * A. Dainese, ALICE-PR-2001-04

14. TPC tracking

15. Tracking in the ITS: PbPb central event,  slice 83 o -87 o - primary vertex - secondary vertices => for Hyperons => for Charm and Beauty - dE/dx for particle identification (@low momenta) - improve TPC momentum resolution - stand-alone tracking for low-P t particles

16. Heavy Quark Physics Detectors involved: –TRD, TPC, ITS –Dimuon arm, ITS Quarkonium spectroscopy –J/ ,  D, B

17. Quarkonium spectroscopy - dielectrons (1) Trigger rates pt single > 1 GeV/c pt single > 0.8 GeV/c pt pair > 3 GeV/c J/  /event 0.0070.0006 background/event0.390.15 TRD @ 1kHzTPC @ 150 Hz Online track reconstruction: 1) selection of e + e — pairs (ROI) 2) analysis of e + e — pairs (event rejection) HLT system

18. Quarkonium spectroscopy - dielectrons (2) Trigger strategy –precise tracking of dielectron candidates in TPC –additional PID by dE/dx –rejection of background tracks (mainly misidentified pions) by combined (TRD+TPC) PID –rejection factor 5 (singles) 25 (pairs) –HLT output rate: 1- 40 Hz(full events or ROIs)

19. Quarkonium spectroscopy - dielectrons (3): event flow

20. Quarkonium spectroscopy - dimuons Sharpening of pt- cut Trigger rate reduction: >4