1. ALICE – First paper

2. ALICE Set-up TOF TRD HMPID ITS PMD Muon Arm PHOS TPC
Size: 16 x 26 meters
Weight: 10,000 tons
TOF
TRD
HMPID
ITS
PMD
Muon Arm
PHOS
ALICE Set-up
TPC

3. ALICE TPC Large volume gas detector
Drift volume and MPWC at the end caps
3-dim. “continuous” tracking device for charged particles
x,y of pad
z derived from drift time
Designed to record up to tracks
Event rate: about 1 kHz
Typical event size for a central Pb+Pb collision: about 75 MByte 3

4. ALICE TPC: 5 years of construction

6. Trigger system Minimal requirements High level requirements
Detect collisions
Initialise readout of detectors
Initialise data transfer to data acquisition (DAQ)
Protection against pile-up
High level requirements
Select interesting events
Needs real-time processing of raw data and extraction of physics observables
trigger detector
trigger system
Detectors
Why?
interaction rate (e.g. 8 kHz for Pb+Pb) >
detector readout rate (e.g. 1 kHz for TPC) >
DAQ archiving rate ( Hz)
Readout electronics
raw data
high-level
trigger
trigger
DAQ
processed data

7. What to trigger on? trigger
Every central Pb+Pb collisions produces a QGP - no need for a QGP-trigger
But hard probes are (still) rare at high momentum
In addition, the reconstruction efficiency of heavy quark probes is very low
E.g. Detection of hadronic charm decays: D0  K– + +
about 1 D0 per event (central Pb-Pb) in ALICE acceptance
after cuts
signal/event = 0.001
background/event = 0.01
trigger

8. PHOS L0 trigger
PbO4W- crystal calorimeter for photons, neutral mesons, 1 to > 100 GeV
Array of crystals APD preamp trigger logic readout
DAQ
L0 trigger
tasks
shower finder
energy sum
implementation
FPGA
VHDL firmware
L0/L1 trigger 8

9. PHOS – muon tracks

10. D0 trigger
Detection of hadronic charm decays: D0  K– + + (6.75%), c = 124 m
HLT code
D0 finder: cut on d0(K)*d0()
TPC tracker
TPC+ITS track fitter
displaced decay vertex finder
ITS
TPC
Preliminary result:
invariant mass resolution is within a factor of two compared to offline

11. Introducing the High Level Trigger
ALICE data rates (example TPC)
TPC is the largest
data source with
channels,
512 timebins and
10 bit ADC value.
Central Pb+Pb collisions
event rates: ~200 Hz (past/future protected)
event sizes: ~75 Mbyte (after zero-suppression)
data rates: ~ 15 Gbyte/sec
TPC data rate alone exceeds by far the total DAQ bandwidth of 1.25 Gbyte/sec
HLT tasks
Event selection based on software trigger
Efficient data compression

12. HLT requirements Full event reconstruction in real-time Event analysis
Main task: reconstruction of up to charged particle trajectories
Method: Pattern recognition in the TPC
Cluster finder
Track finder
Track fit
Global track fit ITS-TPC-TRD Vertex finder
Event analysis
Trigger decision

13. HLT architecture HLT is a generic high performance cluster Detectors
DAQ
HLT
Mass storage

14. HLT building blocks (1) Hardware Nodes Network Infrastructure
Sufficient computing power for p+p
121 Front-End PCs: 968 CPU cores, TB RAM, equipped with custom PCI card for receiving detector data
51 Computing PCs: 408 CPU cores,1.104 TB RAM
Network
Infiniband backbone, GigaBit ethernet
Infrastructure
20 redundant servers for all critical systems

15. HLT building blocks (2) Software Cluster management and monitoring
Data transport and process synchronisation framework
Interfaces to online systems: Experiement control system, Detector control system, Offline DB,...
Event reconstruction and trigger applications

16. First paper

17. First paper

18. First paper

19. First paper

20. First paper

21. Planning pp run November 200 collision @ 900 GeV
December 106 collisions @ 900 GeV
Some collisions @ 2.4 TeV
February-> collisions @ 7 TeV