alice's dimuon high level 09/30/08 trigger...

09/30/08ALICE's Dimuon High Level Trigger (dHLT)

Artur Szostak, INFN Cagliari

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Artur Szostak <[email protected]> for CNFA Palau 2008

What was happening on the beach?

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What was happening on the beach?

Rugby!

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HLT and dHLT goals

• Process raw data online, applying partial event reconstruction to better identify interesting events.

– Event reconstruction online implies high performance parallel systems and algorithms.

• Deliver trigger decision to DAQ which can filter raw data based on this trigger. This is HLT mode C running.

• dHLT is HLT focused on dimuon spectrometer and has the following specific goals:

– Apply a pT cut to partially reconstructed tracks.– The cut should be sharper that L0.– The code must run at 1kHz.

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• 3rd level of triggering after L0, L1, L2 accept.• Delivers decision to DAQ over DDL just like any other detector.

Where does HLT fit in

ECS

DAQ DCSTrigger HLT

Detector

DAQ

HKT

MassStorage

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HLT architecture

HLT is a software trigger system, which implies great flexibility.

− We can and do run offline algorithms online. Software written as a hierarchy of processing stages where at each level

components run in parallel. Code runs on 81 front end nodes for the first processing stage of raw data

plus 50 compute nodes for secondary processing.− This is only 1/3 of full HLT machine. The rest will be needed for Pb+Pb.− Over 700 cores available for processing with ~2 Gbytes RAM per core.− Interconnected with 2*Gigabit per machine.− Yes, this machine will be used for offline reconstruction when there is no beam.

HLT sees all raw data from the whole detector (Only 50% used at the moment)

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Overview of dimuon HLT algorithm

• Apply fast 3 pad clusterfinding to tracking chambers.• Centre of gravity calculation used to reconstruct hit point.• Unpack L0 muon trigger information to use as track seeds.• Perform partial track reconstruction in stations 4 & 5 by tracking back through

muon filter wall.• Calculate momentum estimate from tracklet found in station 4 & 5.• Apply pT cut to tracks.

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Some results from extensive simulations: Hit reconstruction resolution.

• Resolutions on the order of 100 µm in bending and 1 mm in nonbending planes.

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Efficiency and fake tracks

• Using simulations of flat muons and assuming ideal L0 dimuon trigger.

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The pT cut

Black curves are for 1 (2) GeV/c effective cuts applied by L0 dimuon hardware trigger system.

Red curves are the dHLT cut resolutions.

Verification of dHLT pT cut resolutions for implemented dHLT system at CERN.

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Also looked at invariant mass:

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Speed of dHLT at CERN

• Only using about 50% of CPU and bandwidth.• Reached 2.1 kHz sustained rate in most recent tests.

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Results summary

Spatial resolution: ~100μm for bending and ~1mm nonbending planes.

Single muon detection efficiency ~ 97%, with fake track rate ~ 2% for p+p.

Pt resolutions are about 129 (182) MeV/c around the 1 (2) GeV/c cut.

Can sustain 2.2 kHz processing rate for p+p and 1kHz for Pb+Pb.

− Very interesting for the MUON CTP trigger configuration which was limited to 1kHz rate by design due to 500 MB/s limit to mass storage. Could increase sample of raw data with valuable signal.

− Looks like it may be possible to readout the dimuon spectrometer at ~2 kHz. Can the other detectors in the MUON configuration also do 2 kHz? will wait and see...

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Cosmics data

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Cosmics data

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Hardware cluster finder

• HLT HRORC cards contain an FPGA which stores control logic.– Most of the FPGA is empty, so why not use it for something useful?

• Implemented a cluster finding algorithm in firmware and synthesized to fit into the FPGA.

– This gives us an alternative high performance solution to process raw data at a high rate, if we need it.

Detector

HRORC

DDL DIU

DDL DIUFPGA

Full HLTchain

DAQ

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Hardware cluster finder

• HLT HRORC cards contain an FPGA which stores control logic.– Most of the FPGA is empty, so why not use it for something useful?

• Implemented a cluster finding algorithm in firmware and synthesized to fit into the FPGA.

– This gives us an alternative high performance solution to process raw data at a high rate, if we need it.

Detector

HRORC

DDL DIU

DDL DIU

Cluster Finderon FPGA

Rest of HLTchain

DAQ

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Current problems and work

• Commissioning not really completed. Why?– We need a dimuon spectrometer that has stations 4 & 5 working well.– Over the last few weeks we have started reading out with these stations.

• Some technical problems but not severe and already solved.

• Working on moving all analysis done over the last 2+ years to official analysis framework and performing the analyses again.

– Many things have changes in AliRoot and the real detector so it will be very worth while to redo these simulations

• HLT has been working hard to get things working and resolving all the technical issues, so physics with HLT has taken a bit of a back foot.

• Now with HLT commissioned the focus is back where it should be: physics with HLT. But facing some problems:

– ESD does not have a well defined location for the HLT trigger information– Still some technical issues to resolve with ESD filling and the analysis framework for

HLT.

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DDL decoders

• Lot of work done to improve common offline / online decoders to be– easy to use, robust and high performance

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Conclusions

• HLT is commissioned and ready.– dHLT is running well at the moment, but the real test is still with full stations 4 & 5 of

the dimuon spectrometer and p+p (then Pb+Pb).

• It is highly flexible,– ported and ran offline algorithms with little difficulty.– Some interesting opportunities for monitoring the detector which are complimentary

to MOOD and AMORE.

• dHLT is more or less ready to be studied within the analysis framework.– Though some problems with ESD to resolve to make it convenient for all.

• This will allow important studies to be done like:– spectrum X from analysis given HLT trigger.

alice's dimuon high level 09/30/08 trigger...

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