1. High Level Trigger (HLT) for ALICE Bergen Frankfurt Heidelberg Oslo

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 Level-3 system permanent storage system bandwidth 60 Gbyte/sec 15 Gbyte/sec < 1.2 Gbyte/sec < 2 Gbyte/sec

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 TR D trig ger Dimu on trigge r Trigge r detect ors Pattern Recognition Dimuon arm tracking PHO S trigge r Extrapolate to ITS Extrapolate to TOF Extrapolate to TRD... Level-1 Level -3 (Sub)-event Reconstruction

7. Hough transform (1) Data flow

8. Hough transform (2)  -slices

9. Hough transform (3)

10. Level-3 trigger: case studies Limitations Level-3 trigger applications –Open Charm physics –Quarkonium spectroscopy –B-physics –Jets

11. 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

12. 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

13. Open Charm Physics (2) Charm Filter Level-3 trigger: momentum filter –subevent rejection –subevent = low- p T tracks –11% of charged particles have p T > 0.8 GeV/c

14. 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  )

15. 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

16. 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

17. Heavy Quark Physics (1) Detectors involved: –TRD, TPC, ITS –Dimuon arm, ITS Quarkonium spectroscopy –J/ ,  D, B

18. Heavy Quark Physics (2) - electrons Trigger strategy –find high-p T tracks in TRD –identify electron-(pair) candidates –trigger TPC readout Level-3 –select ROIs in TPC based on TRD track seeds –high precision tracking and PID for selected track candidates –extrapolate to ITS –verify high-p T track(s) in TPC/ITS –abort eventbuilding or select ROIs for partial readout

19. Event flow Event sizes and number of links TPC only

20. 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) level-3 trigger system

21. 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)

22. Quarkonium spectroscopy dimuons (1) Franck Manso, ALICE week, Feb. 2001

23. Quarkonium spectroscopy dimuons (2) Franck Manso, ALICE week, Feb. 2001

24. Quarkonium spectroscopy dimuons (3) Background rejection GEANT Cuts 100 keV (e, photons), 200 events Hijing6000: Pb-Pb central coll. = 16000 hadrons 0° --20° Low pt cut L0 trigger 64 L3 trigger 8 L3 rejection factor 8 High pt cut L0 trigger 13 L3 trigger 0 L3 rejection factor - Hijing8000: Pb-Pb central coll. = 32000 hadrons 0 °--20° Low pt cut L0 trigger 137 L3 trigger 26 L3 rejection factor 5 High pt cut L0 trigger 42 L3 trigger 0 L3 rejection factor -

25. J/  low pt cuts high pt cuts low/high pt cuts Acceptance and 3/4 plans 1746 1898 1898 L0 Trigger 1313 (75%) 1623 (86%) 1835 (97%) L3 Filter 1312 (68%) 1623 (84%) 1635 (97%) L3 Trigger 1182 (68%)1592 (84%) 1800 (95%) Quarkonium spectroscopy dimuons (4) Signal

26. Quarkonium spectroscopy dimuons (5) Trigger rates –Low pt cut L0 ~ 1600Hz (unlike sign) ---> L3 ~ 400Hz L0 ~ 2000Hz (all sign) ---> L3 ~ 500Hz –High Pt cut L0 ~ 450Hz (unlike sign) ---> very low L3 rate L0 ~ 550Hz (all sign) ---> very low L3 rate (Event size - dimuon arm only: 110 kbyte)

27. Semileptonic D and B decays D , B  -> e  + X Trigger strategy –TRD candidate –TPC verification: precise tracking + PID by dE/de –combined PID (TRD+TPC) –extrapolate track to ITS –impact parameter cut > 150  m Trigger rates (Pb+Pb) * –B/event in acceptance, pt > 3 GeV/c: 0.02 –background/event: 0.43 –Level-3 rejection factor: > 5 * J. Stachel, PPR, this ALICE week

28. Jet Physics (1) p+p jet rates in ALICE * J. M. Castro, ALICE-PR-2001-05

29. Jet Physics (2) Detectors involved –TPC, TRD Trigger strategy –Level-1 trigger 3-5 high-p T ( > 3-5 GeV/c) tracks in TRD –Level-3 trigger reconstruct TPC tracks inside ROI given by TRD combine TRD, TPC information Select/reject event

30. Jet Physics (3) Jet rates Pb+Pbp+p L [cm -2 s -1 ] 5  10 26 2  10 30 event rate1 kHz140 kHz jets (  100 GeV/c) 2 Hz0.9 Hz jets (  100 GeV/c) central 1 Hz jets (  200 GeV/c)7  10 -2 Hz5  10 -2 Hz Triggered event rates (TRD) * Trigger background [Hz]signal [Hz] (Et > 100 GeV) min. bias1000 2 jet trigger (3 part, pt>3GeV/c) 311.8 jet trigger (3 part, pt>5GeV/c) 0.41.3 central (15%) 1501 jet trigger (3 part, pt>3GeV/c) 270.9 jet trigger (3 part, pt>5GeV/c) 0.350.7 Level-3 rejection factor: > 10 * P. Braun-Munzinger, PPR, this ALICE week

31. Jet Physics (4) Energy resolution (p T = 150 GeV/c) –charged particle tracking: about 25-30% Jet fragmentation Jet multiplicity Leading particle p T

32. Jet Physics (5) Calibration –Photon tagged jets –PHOS + TPC/TRD

33. Conclusion High level trigger applicable to hadronic open charm, J/ , , D, B, jets, etc. Event rate reduction by event rejection:> 10 Date volume reduction by subevent selection:  10