Trigger in ATLAS (and CMS)
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NICA/SPD workshop, PRAGA, 12.02.2014
V.Kukhtin, JINR, Dubna
Outline
- LHC, CMS and ATLAS
- the main parameters important for design of the trigger system
- multi-level trigger,
- 1st, 2nd and 3d level triggers
- conclusions
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8 intersection points
4 experiments
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2 general purpose detector - CMS and ATLAS on the floor 4 NICA/SPD workshop, PRAGA, 12.02.2014
CMS detector
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ATLAS detector
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Calorimeters
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Muon spectrometer
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The main boundary conditions
for the trigger system design:
bunch crossing frequency( information appearance frequency )
rates of PP-interactions, energy -> variety of interesting physical processes
event size
mass storage capacity
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Clock is distributed from P4 to the detectors
LHC
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One wants to record all physics -common objects
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The table of different trigger rates
Какие же триггеры и какие их пороги выбраны в
первом уровне
Отметить, что пороги загружаемы
Светимость уменьшается – частоту записи на
носители оставляем постоянной – снижаются
требования
Live time of the beams ->
luminosity, rates goes down ->
change thresholds setting to keep output rate constant
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The conditions shown above determine the basic features of the trigger
and data acquisition system:
a multi-level trigger with pipelined front-end readout and
hierarchical data acquisition architecture.
The functional scheme reflects the nature of the expected event selection
chain:
a level-1 trigger with negligible dead time and with the shortest possible
latency , making an identification of the bunch crossing containing the event
of interest;
a level-2 trigger with programmable algorithms based on local data;
a level-3 trigger for which the full detector information will be used.
Trigger logic
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L1 receives its input from the Calo. and Muon
detector signals stored to front-end pipelines,
pending L1 decision
designed to provide latency < 2.5 mks and
output rate 75 kHz(->100 kHz
If L1=“TRUE”, data from each detector -> ROB
and made available for HLT for further analysis
HLT = L2 + EF, farms of commodity processors,
connected by fast dedicated network
L2 is based on fast custom algorithm,
processing data within RoI provided by L1.
designed output rate ~ 3 kHz,
processing time – 40 ms/ev
EF is based on mostly offline algorithms to
reconstruct the data with greater precision
than L2.
designed to reduce the rate to ~ 400 Hz,
processing time ~ 4s/ev
Schematic of ATLAS trigger
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Trigger L1
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Some details of the L1 trigger - Calorimeter
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Some details of the L1 trigger - Muon spectrometer
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Thresholds are changed within the beam life-time to keep
event output rate ~ constant
L1 – thresholds setting
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High level trigger
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Trigger performance
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Encore un fois
The ATLAS trigger scheme
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Conclusions
The multilevel trigger approach
takes into account all physics processes of interest;
permits to realize fast reconstruction algorithms with
the dedicated electronics;
permits to apply offline algorithms for events reconstruction;
permits to get reasonable output rate for data storage without
loosing data quality.
HIGGS boson was found with this trigger logic !!!!!!!!!!!!!!!
Such approach to the trigger construction for the NICA detectors seems to be
very reasonable
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Backup slides
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