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Trigger Peter Jacobs, LBNL

10 Hz. Trigger Peter Jacobs, LBNL. Pb+Pb interaction rate ~ 4-8 kHz Hard process trigger ~ 10 Hz  need rejection factor 400-800. p 0 : 10 Hz  p T ~20 GeV/c Inclusive jets: 10 Hz  E T ~50 GeV/c. EMCal trigger: enhancement factor relative to minbias trigger + TPC. s=0: p 0 vs p ±.

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Trigger Peter Jacobs, LBNL

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  1. 10 Hz TriggerPeter Jacobs, LBNL Pb+Pb interaction rate ~ 4-8 kHz Hard process trigger ~ 10 Hz need rejection factor 400-800 p0: 10 Hz  pT~20 GeV/c Inclusive jets: 10 Hz  ET~50 GeV/c An EMC for ALICE

  2. EMCal trigger: enhancement factor relative tominbias trigger + TPC s=0: p0 vs p± • Live time: • DAQ dynamic scaledown of common triggers (“central”, “minbias”) • Pierre v.d.Vyvre: reasonable to expect 90% livetime An EMC for ALICE

  3. Why bother with jets in p+p? • Is ALICE irrelevant for jet studies in p+p? Maybe not. • p+p at top luminosity: 1034/cm2/s x 100 mb ~ 109 Hz • 20 ns bunch spacing  20 minbias interactions per bunch crossing • ALICE runs at L~1031  much cleaner environment in low to intermediate pT region • ALICE may have a unique niche in p+p: detailed studies of jet fragmentation down to low z  important reference for A+A program An EMC for ALICE

  4. PHOS L1 Trigger L1 (6 ms): 2x2 tower analog sum  TRU  4x4 tower peak finder EMCal: 12 FEE/GTL bus  12*32=384 towers/TRU (Dh x df~0.24 x 0.36) An EMC for ALICE

  5. Charged jets (HLT study) C. Loizides, FfM ETcharged>m Charged jets: poor energy resolution, slow turn-on above trigger threshold, highly biased An EMC for ALICE

  6. Conjecture: better solution is Level 1 EMCal + HLT TPC+EMCal • Some rough numbers: • Minbias data rate ~ 20 MB/evt*4 KHz ~ 80 GB/s • HLT input bandwidth ~ 15 GB/s • Least-biased efficient trigger algorithm: • EMCAL@L1: mildly biased jet patch trigger to cut minbias rate by factor 10 ~ 8 GB/s • do the rest in HLT incorporating charged tracks, neutral energy from emcal, dijet topologies (?), etc An EMC for ALICE

  7. Jet patch trigger in p+p PYTHIA 0.21x0.21 Strong biases for ETmax>10 GeV An EMC for ALICE

  8. Jet Patch Trigger Simulations Andre Mischke (Utrecht) • Pythia jet (ET~50 GeV) + HIJING background • square candidate jet patches Dh x Df = s x s • sweep patch quasi-continuously over detector, find maximum ETmax An EMC for ALICE

  9. Why a large-ish trigger patch in A+A? • Leading particle (p0) trigger strongly biased • Fragmentation bias (prefer low ET jets fragmenting hard) • Geometric bias (prefer lower than average energy loss surface emission) • PYTHIA fragmentation requires relatively small patches (0.1 x 0.1) for efficient triggering (Bill, Chris) • fragmentation fluctuations primarily in distribution of few hardest (colinear) hadrons But the physics we are after is the modification of the fragmentation, including potentially large jet broadening effects (and correspondingly smaller background fluctuations?) no really solid theory guidance  prudent experimental design requires flexible patch trigger  also for lighter systems than Pb+Pb An EMC for ALICE

  10. bkgd jet (ET~50 GeV) Jet patch trigger in Pb+Pb PYTHIA+HIJING 0.21x0.21 ET cut for 80% trigger efficiency @ 50 GeV Weighted by Nch  data volume • Centrality dependent pedestal (no surprise) • Background and fragmentation fluctuations of similar magnitude An EMC for ALICE

  11. input rate Output rate L1 output data rate for 80% jet efficiency @ 50 GeV • Details strongly dependent on models of signal + background • Qualitative conclusion nevertheless: required L1 rejection achievable with reasonable efficiency for ~50 GeV jets • requires centrality-dependent threshold An EMC for ALICE

  12. Trigger efficiency I PYTHIA+HIJING Good efficiency at 100 GeV Background dependencies at 50 GeV An EMC for ALICE

  13. Trigger efficiency II: patch size dependence 0.3 x 0.3 apparently larger than optimal An EMC for ALICE

  14. Trigger efficiency III: quenching models Strong model dependencies But models are only first guesses  prudent experimental design requires flexible patch trigger An EMC for ALICE

  15. PHOS trigger: Trigger Regional Unit • each TRU: DhxDf~0.24x0.36 (depends on how we cable) • no inter-TRU communication large acceptance hit for jet patch, limited maximum patch size An EMC for ALICE

  16. Summary TRU Low-latency serial pass-through Low-latency serial pass-through Low-latency serial pass-through …………… TRU ~400 towers TRU ~400 towers TRU ~400 towers TRU ~400 towers TRU ~400 towers TRU ~400 towers Candidate implementation: TRU hierarchy Jet patch trigger Max aggregate input bandwidth= 3 Gbit/s latency 1-2 ms < 100 Mbit/s ~100 bits/evt 13K towers ~ 30 TRUs An EMC for ALICE

  17. Centrality-dependent trigger threshold? V0 Uniform jet trigger efficiency across centralities: need to account for centrality-correlated pedestal fluctuations V0 is only fast (L1) detector with sufficient coverage An EMC for ALICE

  18. V0 response to Pb+Pb Forward detector TRD fig 3.6 • Large generation of secondaries in beampipe but response is nicely linear An EMC for ALICE

  19. Summary TRU Low-latency serial pass-through Low-latency serial pass-through Low-latency serial pass-through …………… TRU ~500 towers TRU ~500 towers TRU ~500 towers TRU ~500 towers TRU ~500 towers TRU ~500 towers V0 bits in jet patch summary TRU? Centrality-dependent threshold? Significant problem: no L1 cross-correlation in Central Trigger Processor (Orlando V-B) few bits V0 technically feasible (H. Muller, F. Fomenti, Y. Zoccarato) latency 1-2 ms < 100 Mbit/s • System design issues: non-locality of trigger logic (i.e. not in CTP), scalars,… • PHOS TRU: Hans Muller has added 3 optical Gigabit ports for interconnectivity… An EMC for ALICE

  20. V0 Interface between CTP, LTU, EMCal and FEE An EMC for ALICE

  21. General trigger issues Interface with ALICE CTP for issuing and receiving L0/L1 Decisions being made now, we need to be involved … An EMC for ALICE

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