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

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

3. Johannes HallerThe First Level Trigger of ATLAS 3 ~ 10 ms ATLAS Trigger System software hardware 2.5  s ~ sec. 3-Level Trigger System: this talk : LVL1 : Calorimeter Trigger Muon Trigger Central Trigger 1)LVL1 decision based on data from calorimeters and muon trigger chambers; synchronous at 40 MHz; bunch crossing identification 2)LVL2 uses Regions of Interest (identified by LVL1) data (ca. 2%) with full granularity from all detectors 3)Event Filter has access to full event and can perform more refined event reconstruction 1)LVL1 decision based on data from calorimeters and muon trigger chambers; synchronous at 40 MHz; bunch crossing identification 2)LVL2 uses Regions of Interest (identified by LVL1) data (ca. 2%) with full granularity from all detectors 3)Event Filter has access to full event and can perform more refined event reconstruction

4. Johannes HallerThe First Level Trigger of ATLAS 4 Analogue tower sums 0.1 x 0.1 (~7200) LVL1 Calorimeter Trigger to LVL2 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/  and  had. cluster finding 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/  and  had. cluster finding output: at 40 MHz: multiplicities for e/ , jets,  /had and flags for energy sums to Central Trigger (CTP) accepted events: position of objects (RoIs) to LVL2 and additional information to DAQ output: at 40 MHz: multiplicities for e/ , jets,  /had and flags for energy sums to Central Trigger (CTP) accepted events: position of objects (RoIs) to LVL2 and additional information to DAQ feature types/ positions DAQ RODs Input/output data to DAQ e/ ,  /had Clusters (CP) 0.2 x 0.2 Jet /  E T (JEP) 0.1 x 0.1 Pre- Processor (PPr) RoI RODs to CTP 8 PPr crates 2 JEP crates 2 ROD crates to CTP example: e/  algorithm : goal: good discrimination e/  ↔ jets identify 2x2 RoI with local E T maximum cluster/ isolation cuts on various E T sums example: e/  algorithm : goal: good discrimination e/  ↔ jets identify 2x2 RoI with local E T maximum cluster/ isolation cuts on various E T sums

5. Johannes HallerThe First Level Trigger of ATLAS 5 LVL1 Muon Trigger 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) 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 p T threshold looking for coincidences in chamber layers programmable widths of 6 coincidence windows determines p T threshold algorithm:

6. Johannes HallerThe First Level Trigger of ATLAS 6 LVL1 Central Trigger Central Trigger Processor (CTP) multiplicities of e/ ,  /h, jet for 8 p T thresholds each; flags for  E T,  E T j, E T miss over thresholds multiplicities of  for 6 p T thresholds Calorimeter trigger Muon trigger Cluster Processor (e/ ,  /h) Pre-Processor (analogue  E T ) Jet / Energy-sum Processor Muon-CTP Interface (MuCTPI) Muon Barrel Trigger (RPC) Muon End-cap Trigger (TGC) 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 LVL1 Menu2x10 33 cm -2 s -1 MU200.8 2MU60.2 EM25i12.0 2EM15i4.0 J2000.2 3J900.2 4J650.2 J60+xE600.4 TAU25+xE302.0 MU10+EM15i0.1 Others5.0 Total rate (kHz)~ 25 big uncertainties on predicted rates example trigger menu:

7. Johannes HallerThe First Level Trigger of ATLAS 7 ATLAS Combined Test Beam setup at CERN’s SPS H8 beam-line: (2004) beam (π, μ, e, p,  E beam = (1 to 360) GeV 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 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 L1Muon setup end-cap chambers barrel chambers

8. Johannes HallerThe First Level Trigger of ATLAS 8 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 latency projected to ATLAS: 2.13 μs  LVL1 triggered the readout of all sub-detectors CTP latency: 95 ns at test-beam ~125 ns (not optimized) signal distribution at test-beam: Muon Trigger Calo Triggerall sub- detec- tors

9. Johannes HallerThe First Level Trigger of ATLAS 9 Test-Beam Results: Muon Trigger position in precision muon chambers vs. position in RPCs Triggered Bunch  Next Bunch Previous Bunch total efficiency p T threshold 6  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%  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% barrel (RPCs): end-caps (TGCs): efficiency and BCID threshold efficiency after chamber shifting  p T threshold 5  p T threshold 4  chamber was shifted to emulate the effect of deflection in magnetic field  coincidence algorithm works  big timing margin where  (correct bunch) high and  (bunches before and after) tiny  chamber was shifted to emulate the effect of deflection in magnetic field  coincidence algorithm works  big timing margin where  (correct bunch) high and  (bunches before and after) tiny

10. Johannes HallerThe First Level Trigger of ATLAS 10 Test-Beam Results: Calorimeter Trigger Correlation of energy in LAr calo. and CPM ROD PreProcessor Receivers CPMs/JEMs L1Calo setup  a full slice of the calorimeter trigger system was installed: ~1% of final capacity  checks of data consistency very successful  a full slice of the calorimeter trigger system was installed: ~1% of final capacity  checks of data consistency very successful counting room reality:  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  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

11. Johannes HallerThe First Level Trigger of ATLAS 11 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 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