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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