# Presentation: 856102

## TriggerPeter Jacobs, LBNL

- 0: 10 Hz  pT~20 GeV/c
- Inclusive jets:
- 10 Hz  ET~50 GeV/c

- Pb+Pb interaction rate ~ 4-8 kHz
- Hard process trigger ~ 10 Hz
- need rejection factor 400-800

- An EMC for ALICE

## EMCal trigger: enhancement factor relative tominbias trigger + TPC

- Live time:
-  DAQ dynamic scaledown of common triggers (“central”, “minbias”)
-  Pierre v.d.Vyvre: reasonable to expect 90% livetime

- s=0: 0 vs p±

- An EMC for ALICE

## 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

## PHOS L1 Trigger 

- PHOS L1 Trigger

- L1 (6 s): 2x2 tower analog sum  TRU  4x4 tower peak finder
- EMCal: 12 FEE/GTL bus  12*32=384 towers/TRU
- 						(x ~0.24 x 0.36)

- An EMC for ALICE

## Charged jets (HLT study)

- ETcharged>m

- Charged jets: poor energy resolution, slow turn-on above trigger threshold, highly biased

- C. Loizides, FfM

- An EMC for ALICE

## 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

## Jet patch trigger in p+p

- 0.21x0.21

- Strong biases for ETmax>10 GeV

- PYTHIA

- An EMC for ALICE

## Jet Patch Trigger Simulations

- Andre Mischke (Utrecht)

-  Pythia jet (ET~50 GeV) + HIJING background
-  square candidate jet patches x s x s
-  sweep patch quasi-continuously over detector, find maximum ETmax

- An EMC for ALICE

## Why a large-ish trigger patch in A+A?

- Leading particle (0) 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

## Jet patch trigger in Pb+Pb

-  Centrality dependent pedestal (no surprise)
-  Background and fragmentation fluctuations of similar magnitude

- Weighted by Nch  data volume

- PYTHIA+HIJING

- 0.21x0.21

- ET cut for 80% trigger efficiency @ 50 GeV

- An EMC for ALICE

## 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

## Trigger efficiency I

- PYTHIA+HIJING

- Good efficiency at 100 GeV
- Background dependencies at 50 GeV

- An EMC for ALICE

## Trigger efficiency II: patch size dependence

- 0.3 x 0.3 apparently larger than optimal

- An EMC for ALICE

## 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

## PHOS trigger: Trigger Regional Unit

-  each TRU: x~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

## Candidate implementation: TRU hierarchy

- 13K towers ~ 30 TRUs

*Max aggregate input bandwidth= 3 Gbit/s*

- Jet patch trigger

- latency 1-2 s

- < 100 Mbit/s

- ~100 bits/evt

- An EMC for ALICE

## 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

## V0 response to Pb+Pb

- Large generation of secondaries in beampipe but response is nicely linear

- Forward detector TRD fig 3.6

- An EMC for ALICE

## V0 bits in jet patch summary TRU?

- latency 1-2 s

- < 100 Mbit/s

- V0

-  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...

- few bits

- Significant problem: no L1 cross-correlation in Central Trigger Processor (Orlando V-B)

- technically feasible (H. Muller, F. Fomenti, Y. Zoccarato)

- Centrality-dependent threshold?

- An EMC for ALICE

## V0 Interface between CTP, LTU, EMCal and FEE

**V0 Interface between CTP, LTU, EMCal and FEE**

- An EMC for ALICE

## 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