The First-Level Trigger of ATLAS International Europhysics Conference on High Energy Physics, July 21st-27th 2005, Lisbon, Portugal The First-Level Trigger of ATLAS Johannes Haller (CERN) on behalf of the ATLAS First-Level Trigger Groups

The First Level Trigger of ATLAS Triggering at the LHC σ rate bunch crossing rate: 40 MHz total interaction rate:~ 1 GHz event size: ~ 1.5 MB total interaction rate affordable: ~ 300 MB/s storage rate: ~ 200 Hz → online rejection: 99.9995% e.g.: Higgs → ZZ → 2e+2m 23 min. bias events: ~ 1725 particles/BC storage rate discoveries powerful trigger needed enormous rate reduction retaining the rare events in the very tough LHC environment ET Johannes Haller The First Level Trigger of ATLAS

The First Level Trigger of ATLAS ATLAS Trigger System 3-Level Trigger System: hardware LVL1 decision based on data from calorimeters and muon trigger chambers; synchronous at 40 MHz; bunch crossing identification LVL2 uses Regions of Interest (identified by LVL1) data (ca. 2%) with full granularity from all detectors Event Filter has access to full event and can perform more refined event reconstruction 2.5 ms software ~ 10 ms ~ sec. this talk: LVL1: Calorimeter Trigger Muon Trigger Central Trigger Johannes Haller The First Level Trigger of ATLAS

LVL1 Calorimeter Trigger to DAQ Input/output data DAQ RODs example: e/g algorithm: goal: good discrimination e/g ↔ jets identify 2x2 RoI with local ET maximum cluster/ isolation cuts on various ET sums 2 ROD crates Jet / ET (JEP) 2 JEP crates to LVL2 RoI RODs 0.2 x 0.2 Analogue tower sums 0.1 x 0.1 (~7200) to CTP Pre- Processor (PPr) feature types/ positions e/, /had Clusters (CP) to CTP 8 PPr crates 0.1 x 0.1 4 CP crates electronic components (installed in counting room heavily FPGA based  flexibility): PPr: digitisation of analogue signals from calorimeters and bunch crossing ID JEP: jet finding and energy sums CP: e/g and t/ had. cluster finding output: at 40 MHz: multiplicities for e/g, jets, t/had and flags for energy sums to Central Trigger (CTP) accepted events: position of objects (RoIs) to LVL2 and additional information to DAQ Johannes Haller The First Level Trigger of ATLAS

The First Level Trigger of ATLAS LVL1 Muon Trigger algorithm: dedicated muon chambers with good timing resolution for trigger: Barrel |η|<1.0 : Resistive Plate Chambers (RPCs) End-caps 1.0<|η|<2.4 : Thin Gap Chambers (TGCs) local track finding for LVL1 done on- detector (ASICs) looking for coincidences in chamber layers programmable widths of 6 coincidence windows determines pT threshold Johannes Haller The First Level Trigger of ATLAS

LVL1 Central Trigger CTP: (one 9U VME64x crate, FPGA based) Calorimeter trigger Muon trigger Cluster Processor (e/g, t/h) Pre-Processor (analogue  ET) Jet / Energy-sum Processor Muon-CTP Interface (MuCTPI) Muon Barrel Trigger (RPC) Muon End-cap Trigger (TGC) multiplicities of e/g, t/h, jet for 8 pT thresholds each; flags for SET, SET j, ETmiss over thresholds multiplicities of m for 6 pT thresholds Central Trigger Processor (CTP) example trigger menu: LVL1 Menu 2x1033cm-2s-1 MU20 0.8 2MU6 0.2 EM25i 12.0 2EM15i 4.0 J200 3J90 4J65 J60+xE60 0.4 TAU25+xE30 2.0 MU10+EM15i 0.1 Others 5.0 Total rate (kHz) ~ 25 CTP: (one 9U VME64x crate, FPGA based) central part of LVL1 trigger system combination of up to 160 input bits (plus internal bits) to 256 triggers (with prescale factors) calculation of trigger decision based on inputs from L1Calo and L1Muon according to trigger menu ATLAS LVL1 trigger strategy is as inclusive as possible to reduce bias and be open for new physics big uncertainties on predicted rates Johannes Haller The First Level Trigger of ATLAS

ATLAS Combined Test Beam setup at CERN’s SPS H8 beam-line: (2004) beam (π, μ, e, p, g) Ebeam = (1 to 360) GeV L1Muon setup full scale ATLAS slice, all sub- detectors test of prototypes and final modules periods of 25ns structured beam (like LHC) aim to establish full trigger and data acquisition chain end-cap chambers barrel chambers Johannes Haller The First Level Trigger of ATLAS

LVL1 Trigger at the Test-Beam all trigger, timing, control and readout paths successfully established: full LVL1 trigger chain established for the first time ATLAS run control LVL1 triggered the readout of all sub-detectors LVL1 latency projected to ATLAS: 2.13 μs signal distribution at test-beam: Muon Trigger Calo Trigger all sub- detec- tors CTP latency: 95 ns at test-beam ~125 ns (not optimized) Johannes Haller The First Level Trigger of ATLAS

Test-Beam Results: Muon Trigger end-caps (TGCs): barrel (RPCs): threshold efficiency after chamber shifting position in precision muon chambers vs. position in RPCs efficiency and BCID Triggered Bunch Next Bunch Previous Bunch total efficiency pT threshold 6  pT threshold 5  pT threshold 4 nice correlation between RPC and MDT position measurement trigger efficiency at test-beam (3/4, phi): 99.4% efficiency for correct identification of bunch crossing: 99.5% chamber was shifted to emulate the effect of deflection in magnetic field coincidence algorithm works big timing margin where e(correct bunch) high and e(bunches before and after) tiny Johannes Haller The First Level Trigger of ATLAS

Test-Beam Results: Calorimeter Trigger a full slice of the calorimeter trigger system was installed: ~1% of final capacity checks of data consistency very successful Correlation of energy in LAr calo. and CPM counting room reality: ROD PreProcessor Receivers CPMs/JEMs L1Calo setup good correlation of energy values measured in calorimeter and received in CP module no event below e.m. trigger threshold of 20 GeV  calorimeter trigger did work Johannes Haller The First Level Trigger of ATLAS

The First Level Trigger of ATLAS Summary The trigger and its performance are of paramount importance at the LHC The First Level Trigger of ATLAS is based on calorimeters and dedicated muon chambers and reduces the event rate to ~75 kHz Successful test of the First Level Trigger system at the ATLAS Combined Test Beam Status: Prototypes of all types of modules and all ASICs validated; mass production started Road to data-taking at the LHC: muon trigger chamber integration already started CTP installation: September 2005 calorimeter trigger installation starts in September 2005 first cosmic ray runs with a subset of detectors early 2006 ATLAS expects to be ready for first pp collisions in 2007 Johannes Haller The First Level Trigger of ATLAS