TRIGGERING IN THE ATLAS EXPERIMENT Thomas Schörner-Sadenius UHH (formerly CERN EP/ATR) UHH, SS06

TSS: Triggering in ATLAS2 OVERVIEW ¶ INTRODUCTION The Large Hadron Collider (LHC) – Why? Physics at the LHC The ATLAS Experiment The ATLAS Trigger ¶ THE LEVEL1 TRIGGER (L1) ¶ THE HIGH-LEVEL TRIGGER (HLT) ¶ TRIGGER PERFOMANCE STUDIES

UHH, SS06TSS: Triggering in ATLAS3 THE LHC - WHY? Standard-Model (SM) well confirmed, but incomplete ! LHC Higgs bosons (SM/MSSM) Supersymmetry Large Extra Dimensions, Compositeness, new heavy gauge bosons SM measurements, b physics LEP, HERA, Tevatron … + SM precision measurements (QED, QCD, electroweak) -- EW symmetry breaking? free parameters? -- Unification? -- Discrepancy at sin 2  eff etc? … but open questions:

UHH, SS06TSS: Triggering in ATLAS4 PHYSICS AT THE LHC I pp collisions with  s = 14 TeV, L = cm -2 s -1, f = 40 MHz SM Higgs: MSSM/SUSY: SM Physics: B 0 d  K 0* 

UHH, SS06TSS: Triggering in ATLAS5 PHYSICS AT THE LHC II Comparison of SM and ‘new physics’ processes Small cross- sections for ‘new physics’ processes Understanding of SM processes important Backgrounds for ‘discovery physics’: Wbb, ttbb, W/Z pairs… Calibration, energy scale: Z  e + e -,  +  -, J/   e + e -,  +  -, W  jj… At high luminosity ~23 events overlaid … for cm -2 s -1 usually only one event … and small branching ratios (e.g. H   ). SM processes dominate. Necessity of efficient trigger!

UHH, SS06TSS: Triggering in ATLAS6 ATLAS TRIGGER MENU COVERAGE Inclusive and di-lepton B physics H   SUSY, leptoquarks Resonances, compositeness Gauge boson pair production for study of anomalous couplings and behaviour of production at high energies single and pair top production direct Higgs production with H  ZZ*/WW*; associated SM Higgs production with WH, ZH, ttH MSSM Higgs decays Production of new gauge bosons with decays to leptons. SUSY and leptoquark searches specialised, more exclusive menus 2EM15I at L1, 2  20i at L2. Also MSSM. High p T jets with/without E Tmiss. High p T jets. Triggering mostly with inclusive / di-leptons.

UHH, SS06TSS: Triggering in ATLAS7 THE LHC pp at 14 TeV

UHH, SS06TSS: Triggering in ATLAS8 THE LHC pp at 14 TeV

UHH, SS06TSS: Triggering in ATLAS9 THE LHC pp at 14 TeV

UHH, SS06TSS: Triggering in ATLAS10 THE LHC pp at 14 TeV

UHH, SS06TSS: Triggering in ATLAS11 THE ATLAS EXPERIMENT - Length ~40 m - Diameter ~25 m - Weight ~7000 t channels (event ~2MB) - ‘Inner (tracking) Detector’ - calorimeters (energies) - muon detectors - Barrel: solenoid around ID and toroid fields in muon system - Endcaps: toroid fields

UHH, SS06TSS: Triggering in ATLAS12 THE ‘INNER DETECTOR’ Pixel Detector: - 3 barrel layers - 24 end-discs channels -  R  =12  m,  z,R =~70  m - |  | <2.5 Silicon Tracker: - 4 barrel layers, |  | < end-discs, 1.4 <  < Area 60 m channels -  R  =16  m,  z,R =580  m Transition Radiation Tracker channels -  =170  m per straw - |  | <2.5

UHH, SS06TSS: Triggering in ATLAS13 THE CALORIMETERS Hadronic Tile: scintillating tiles PMTs - Granularity  : <1.0, ( ) - L=11.4 m, R out =4.2 m Hadronic LAr Endcaps: - steel absorbers channels / EM LAr Accordeon: - lead absorbers channels  : <2.5, <3.2 Forward LAr: rods of 1mm - cell size 2-5cm 2 (4 rods) -  : <3.1, < copper, 2 tungsten LAr Pre-Sampler Against effects of energy losses in front of calorimeters

UHH, SS06TSS: Triggering in ATLAS14 THE MUON SYSTEM Monitored Drift Tubes - 3 cylinders at R=7, 7.5, 10m - 3 layers at z=7, 10, 14 m tubes, cm -  space =80  m,  t =300ps (24-bit FADCs) Cathode Strip Chambers wires - only for |  |>2 in first layer -  space =60  m,  t =7ns Thin Gap Chambers channels - ~MWPCs Resistive Plate Chambers channels -  space =1cm - trigger signals in 1ns

UHH, SS06TSS: Triggering in ATLAS15 THE ATLAS TRIGGER: OVERVIEW Multi-layer structure for rate reduction: 1 GHz  100 Hz. } EF - Full event - Best calibration - Offline algorithms - Latency ~seconds } L1 - Hardware-based (FPGAs and ASICs) - Coarse granularity from calo/muon - 2  s latency (pipelines) } L2 - ‘Regions-of-Interest’ - ‘Fast rejection’ - Spec. algorithms - Latency ~10ms

UHH, SS06TSS: Triggering in ATLAS16 OVERVIEW ¶ INTRODUCTION ¶ THE LEVEL1 TRIGGER (L1) Overview The Calorimeter and Muon Triggers The CTP and the L1 Event Decision Simulation (and Configuration) ¶ THE HIGH-LEVEL TRIGGER (HLT) ¶ TRIGGER PERFOMANCE STUDIES

UHH, SS06TSS: Triggering in ATLAS17 THE LEVEL1-TRIGGER Selection based on high-p T objects from calo and muon. Multiplicities Regions- of- Interest Event decision for L1 Interface to front-end Muon candidates above p T thresholds Interface to higher trigger levels/DAQ: objects with p T, ,  Candidates for electrons/photons, taus/hadrons,jets above p T thres- holds. Energy sums above thresholds

UHH, SS06TSS: Triggering in ATLAS18 THE CALORIMETER TRIGGER I Complex system with many modules to be developed. digitisation, presumming to jet elements with granularity analog sums of EM/HA cells  7200 trigger towers (granularity ) cluster processor: Find e/  and  /hadron candidates in 6400 trigger towers (|  |<2.5) jet/energy processor: - Find jet candidates in 3032 jet elements for |  |<3.2 - Build total E T sum up to |  |<4.9.

UHH, SS06TSS: Triggering in ATLAS19 THE CALORIMETER TRIGGER II Example: The  /hadron trigger Example: The jet/energy trigger 2·2 jet EM+HA cluster (RoI) in 2·2 or 3·3 or 4·4 region (gives E T ). 8 (4) (forward) jet E T thresholds. Total/missing E T from jets (sum of 0.2·0.2 jet elements to  ·  =0.4·0.2, conversion to E x,E y, then summation). Maximum of EM+HA E T in 2·2 ‘RoI’, isolation criteria (alternative core definitions?). Multiplicities for 8(8) e/  (  / hadron) E T thresholds. Builds candidate objects (RoIs): electrons/photons, taus/hadrons, jets. Ideas about core definitions, isolation criteria not really finalised.

UHH, SS06TSS: Triggering in ATLAS20 THE MUON TRIGGER ‘Roads’ can be defined for 6 different p T thresholds (for which multiplicity counts are delivered to the CTP).  BCID =1.5 ns. Trigger chambers: 3 RPC stations for |  |< TGC stations for 1.05<|  |< ,  layers per station (TGC 2/3) p T information from hit coincidences in successive detector layers. Procedure: Put predefined ‘roads’ through all stations (width in  ~ p T ). If hit coincidences in 2(3) stations  muon candidate for p T thres- hold corresponding to ‘road’. ATLAS quadrant in rz view trigger chambers precision chambers

UHH, SS06TSS: Triggering in ATLAS21 THE MUON-TO-CTP INTERFACE 208 RPC/TGC sectors deliver 1-2 RoIs  combined by 16 MIOCTs. MIBAK backplane builds RoI multiplicities for 6 p T thresholds.

UHH, SS06TSS: Triggering in ATLAS22 THE L1 DECISION Derived in the ‘Central Trigger Processor’ (CTP). Multiplicities of objects above p T thresholds ‘Conditions’: multiplicity requirements ‘Items’: logical combinations of ‘conditions’ L1 result as ‘OR’ of all ‘items’ Inputs to HLT: L1 result and objects with p T, , . CTP calorimeter, muon

UHH, SS06TSS: Triggering in ATLAS23 THE CENTRAL TRIGGER PROCESSOR existing prototype 1 9U VME module final design ~7 different modules Combines calorimeter and muon information to L1 decision. Lookup tables: ‘conditions’ Programmable devices: ‘items’ Dead time etc. Combination of ‘items’ One big FPGA Interfaces to detectors,LHC Input bits: multiplicities To Level2 Number of items?

UHH, SS06TSS: Triggering in ATLAS24 L1 SIMULATION: OVERVIEW Most developments originally for stand-alone applications.  Generation of MonteCarlo events for analysis purposes  Rate/efficiency estimates  Inputs for HLT tests  Tests of L1 trigger hardware (~done for some compo- nents; just starting ‘slices’, configuration problem!)

UHH, SS06TSS: Triggering in ATLAS25 L1 SIMULATION: ORGANISATION Organisation  Coordination: TSS  Calorimeter trigger: London  Muon trigger + MuCTPI: Tokyo, Rom, CERN  CTP, RoIB, interfaces, configuration: TSS Framework  C++ Code  LHCb framework Gaudi adapted to ATLAS-needs  Athena (ATLAS Offline environment) Status  Complete simulation chain for calo trigger ready. Currently working on muon trigger integration.  Also done: configuration code (sets up L1 trigger simulation software and hardware !)  Successfully used for simulation of L1 result as input to HLT tests (important for HLT TDR). Many contributors around the world. Storage concept Specific concept for run/event-wise data persistency:  StoreGate and DetectorStore for package communication: Objects are sent to predefined memory locations with ‘keys’.

UHH, SS06TSS: Triggering in ATLAS26 L1 CONFIGURATION Based on XML: Calo and muon need to know which multiplicity is to be delivered on which physical line. Simple definition of logical structures (better HTML). Simple ‘parsing’ into instances of C++ classes. Structure of L1 decision configures CTP. Prevent from configuring logical structure that exceeds CTP’s abilities (number of inputs etc.). Definition of objects to be triggered: Trigger Menu Def. of objects for which calo and muon deliver multi- plicity counts: thresholds Description of hardware

UHH, SS06TSS: Triggering in ATLAS27 L1 CONFIGURATION Implementation in C++ classes Logical tree structure of XML tags Definitions of trigger menu “Parsing”

UHH, SS06TSS: Triggering in ATLAS28 PROBLEM: HARDWARE CONFIGURATION Idea: Run simulation against L1 hardware  Tests of hardware and software systems.  Needs common input data.  Needs unified configuration for simulation software and hardware. Status  First lookup table files successfully loaded.  First (simple) VHDL code written. Translating and loading dangerous (damaging FPGA).  Have to generate  lookup table files  VHDL code for FPGAs.  Have to be generated ‘on the fly’, from running configuration code. Problem TBV[0] = MIO[0] & MIO[1] & !MIO[2] & maskff[0] & !LOCADT[0] & !GLOBDT1[0] & !GLOBDT2[0] & !VETO

UHH, SS06TSS: Triggering in ATLAS29 OVERVIEW ¶ INTRODUCTION ¶ THE LEVEL1 TRIGGER (L1) ¶ THE HIGH-LEVEL TRIGGER (HLT) Design of HLT and Selection Software Selection Principles and Step-wise Procedure HLT Decision HLT Configuration ¶ TRIGGER PERFOMANCE STUDIES

UHH, SS06TSS: Triggering in ATLAS30 THE HIGH-LEVEL TRIGGER (HLT) Good example for solid software process.

UHH, SS06TSS: Triggering in ATLAS31 HLT: DESIGN OVERVIEW EventFilter (EF) Classification Selection ~10 2 Hz Hardware Implementation LEVEL 2 (LVL2) ~1 kHz Level1 (L1) ~10 2 kHz Read-Out Subsystem Modules High-Level Trigger: Design HIGH-LEVEL TRIGGER (HLT) Offline Simplified subsystem view Event- Filter

UHH, SS06TSS: Triggering in ATLAS32 HLT: SELECTION SOFTWARE EventFilter Level2 PESA Core Software PESA Algorithms Offline Architecture & Core Software Offline Reconstruction Running in Level2 Processing Units (L2PU)+EF. Set-up by HLT configuration

UHH, SS06TSS: Triggering in ATLAS33 HLT: SELECTION PRINCIPLES ‘Regions-of- Interest’ (RoI) Step-wise process and ‘Fast rejection’ Flexible L2/ EF boundary Use of offline reconstruction algorithms PESA = ‘Physics- and Event Selection Architecture’ ¶ Selection/Rejection starts with localized L1 objects (‘Regions-of-Interest’)  limited data amount. ¶ Then step-wise more and more correlated data from muon/calo and other detectors (e.g. cluster shapes, tracks for e/  separation). ¶ After every step: Check whether selection criteria still fulfilled  optimal use of HLT processors. ¶ flexible distribution of load and use of resources. ¶ Use of common software architecture + algorithms  understanding of trigger rates/efficiencies. ¶ Use of common ‘event data model’ (should be trivial ;-) ).

UHH, SS06TSS: Triggering in ATLAS34 HLT DECISION (LEVEL2 AND EF) Overview of step-wise procedure with ‘dummy’ example Z  e + e - After every step: test + possibly rejection. ‘Physics Signature’: Z  e + e - with p T >30 GeV ‘Intermediate Signature’ L1 result: 2 EM clusters with p T >20 GeV ‘Intermediate Signature’ decision partalgorithmic part

UHH, SS06TSS: Triggering in ATLAS35 OVERVIEW ¶ INTRODUCTION ¶ THE LEVEL1 TRIGGER (L1) ¶ THE HIGH-LEVEL TRIGGER (HLT) ¶ TRIGGER PERFOMANCE STUDIES Selection Planning L1 Performance L2 / HLT / Combined Performance

UHH, SS06TSS: Triggering in ATLAS36 TRÍGGER STUDIES Mostly done using full GEANT simulation of ATLAS detector and of trigger logic. Usually not full events used, but only parts (QCD jets, H   processes etc.) Full dijet event ~1000s. For jets and E Tmiss studies only with fast parametrised simulation. Fast L1 trigger simulation for some purposes (large samples etc.). Most studies have large uncertainties: LO MCs, computing time per event, costs, classification. Should be reduced with new L1 simulation + HLT software for HLT technical design report (5/2003). Only rigidly done for L1+L2. EF should be ~100% efficient. Most studies from 1998 Trigger Performance Status Report.

UHH, SS06TSS: Triggering in ATLAS37 LEVEL1 SELECTION: PLANNING Selection2·10 33 cm -2 s cm -2 s -1 MU6(20?) (20)23 (3?)4.0 2MU6--- (1?)1.0 EM25i (30) EM15i (20)25.0 J200 (290)0.2 3J90 (130)0.2 4J65 (90)0.2 J60+xE60 (100) TAU25+xE MU10+EM15i others5.0 total~ 44 (25?)~ 40 Rates in kHz; thresholds define 95% efficiencies. No safety factors included (LO MonteCarlos etc.). Muon triggers contribute to (di)lepton signatures. Electron/photon triggers strong; large backgrounds. Low rate for jet triggers; difficult to control backgrounds New studies assume much reduced  rate (~kHz).

UHH, SS06TSS: Triggering in ATLAS38 HLT SELECTION: PLANNING Selection2·10 33 cm -2 s cm -2 s -1 Rates (Hz, low lumi) Electrone25i, 2e15ie30i, 2e20i~40 Photon  60i, 2  20i ~40 Muon  20, 2  10 ~40 Jetsj400, 3j165, 4j110j590, 3j260, 4j150~25 jet+E tmiss j70+xE70j100+xE100~20 tau+E tmiss  35+xE45  60+xE60 ~5 B physics 2  6 with m B /m J/  2  6 with m B ~20 Total~200 Optimization of efficiency/rejection and CPU load / data volume. Rate·Event size (1.6MB)  needed band widths / storage volume Rate·CPU time  number of processors (500?)

UHH, SS06TSS: Triggering in ATLAS39 threshold ~30 GeV Inclusive e/  trigger rate for high lumi with/without isolation. L1 e/  TRIGGER Selection Threshold [E T in GeV] Rate [kHz]  1 e/  17 / 2611 / 21.5  2 e/  12 / / 5.2 Total rate13 / 27 threshold ~20 GeV e/  pair trigger rate for high lumi with /without isolation. EM isolation for e/jets Tolerable rate dictates E T thresholds. Isolation criteria vital for rate control.

UHH, SS06TSS: Triggering in ATLAS40 L1  /hadron TRIGGER 25 GeV threshold, but no single tau / hadron trigger planned for (hadr. decays  HA calibration?). SelectionEM IsolationRate 20 GeV7 GeV16 kHz 40 GeV10 GeV2.1 kHz 25 GeV+E Tmiss 1-2 kHz L1 tau/hadron efficiency as function of tau p T. Problems: - Core definition (21,22,22+44 etc.) - isolation threshold definition. For Z  , W   with additional lepton or E Tmiss.

UHH, SS06TSS: Triggering in ATLAS41 L1 JET TRIGGER:  1,3,4 JETS Efficiency to flag a jet RoI at high lumi. How low can you go? TypeLow lumiHigh lumi 1 jetE T >180GeVE T >290GeV 3 jetsE T >75GeVE T >130GeV 4 jetsE T >55GeVE T >90GeV Rate assigment defines thresholds and jet windows. Performance depends on - window for E T determination, - jet element thresholds, - declustering procedure. N jet =1 N jet =4 180 GeV 55 GeV Jet trigger rates (low lumi), assign 200Hz for 1,3,4 jet processes

UHH, SS06TSS: Triggering in ATLAS42 L1 MUON TRIGGER PERFORMANCE TGC efficiency for different thresholds  sharp rise, good . TypeBarrelEndcapAllNon-pp 6 GeV > GeV >0.026 Mainly want to trigger W/Z  . Semilept.b,c   is background (L2). Fake rates from background particles about 10Hz/cm 2 ? New muon studies assume less rate. Muon trigger rates overview [kHz]

UHH, SS06TSS: Triggering in ATLAS43 HLT: CALORIMETER TRIGGERS Second sampling ( ): 24X 0 Back sampling ( ): 2-12X 0 Main backgrounds in L1 sample:  0   and narrow hadronic jets. Algorithms mainly based on E T, hadronic leakage, lateral shower shape and sub-structures in cluster (use of track veto possible). Variables: - EM-E T in 37 cells E=w gl (w ps *E ps +E 1 +E 2 +E 3 ) - HA-E T - lateral shape in 2. sampling: R = E 3*7 / E 7*7 >0.9 for e - lateral shape in 1. Sampling for narrow hadr. showers or jets with small E had - Cuts tuned for  >0.95 with large jet rejections First sampling with finer cell granularity for  0 rejection ( ): 6X 0

UHH, SS06TSS: Triggering in ATLAS44 HLT  TRIGGER:  40(60)i, 2  20i 2 peaks from  0   / narrow hadronic shower from jet BG (first sampling) 1 peak from real  Validation of L1 E T, ,  information (granularity, calibration)  sharper cuts on E T + cluster shape analysis. Efficiency for 20 GeV photons at high lumi. Single photon efficiency > 90% (diphoton triggers >80%; f(E T )). 100 (600) Hz on L2 for  triggers. Jet rejection of ~3000.

UHH, SS06TSS: Triggering in ATLAS45 HLT ELECTRON: e25(30)i, 2e15(20)i Similar to photons, but looser cuts. Track search in inner detector (reject neutrals, cuts on p T, shower shapes etc.). L2 e/  trigger efficiency for 30 GeV electrons, (high lumi). Electron triggers: rate of 100 (600) Hz after L2 selection. Service crack between barrel and endcap Efficiency after L1+L2 for single 30GeV electrons at high lumi. Crack between barrel halves

UHH, SS06TSS: Triggering in ATLAS46 HLT JET TRIGGER: 1,3,4 JETS L2 jet efficiency for 50,100,150 GeV as function of threshold (cone, threshold from trigger jet). L2/L1 reduction for low lumi at 90(95)% L2(L1) 1-jet efficiency (2 at 80 GeV). Hard to suppress BG without inv. Mass cuts. Sum cells to ; run jet algo on window around RoI. TypeL1 [kHz]L2 [kHz] J J J Rates for  =95(90)% L1(L2). Algorithms? Cell noise cut? Threshold definition? Window size? L1 TT cut 1 GeV

UHH, SS06TSS: Triggering in ATLAS47 Get p T (MDTs), extrapolate track Reduce L1 rate by ~100 (harder cuts or more subdetectors) Reduce BG from b-decays by factor 10 with high W/Z-  95%. HLT MUON TRIGGER:  20, 2  10 L2 trigger algorithm efficiency in barrel for two thresholds. Efficiency >95% with r.m.s momentum resolution of 1-2 GeV (7% for 6 GeV)). --- W,Z signal b,c BG Also E T criteria in calo cones 200(300) Hz L2 trigger rate for  signatures (without B triggers with exclusive requirements on masses). Calo discriminates W/Z vs. b,c.

UHH, SS06TSS: Triggering in ATLAS48 SUMMARY LHC/ATLAS Necessary to complete Standard Model and to find extensions (SUSY etc.). High event rates + small new physics cross-sections. Multi-layer structure: Reduction 1 GHz  100 Hz. L1 Trigger Hardware-based with calo/muon inputs. L1 decision in Central Trigger Processor (CTP). (Offline) configuration and simulation ~ready. HLT HLT: Two software levels (Level2 and EventFilter) HLT principles: Regions-of-Interest and step-wise decision procedure (‘fast rejection’). Performance Detailed studies for all trigger types based on old simulations (basically results from 1998, only L2). New studies to be done for HLT TDR (5/2003) with new HLT selection and L1 simulation SW. Large uncertainties (physics+computing)

UHH, SS06TSS: Triggering in ATLAS49 AN ATLAS EVENT H  ZZ*  e + e -  +  - (m H = 130 GeV) at high luminosity (10 34 cm -2 s -1 ) The ‘hard’ Higgs event is overlaid with ~23 ‘minimum-bias’ and background events.

UHH, SS06TSS: Triggering in ATLAS50 Backup Material

UHH, SS06TSS: Triggering in ATLAS51 L1 SIMULATION: SUBSYSTEMS Simulation procedure; simplified view (only one storage instance). Random Inputs Data Files Input zu HLT/ DataFlow Thresholds Triggermenu Hardware Geant3 cells, test vectors

UHH, SS06TSS: Triggering in ATLAS52 menu table of step N HLT CONFIGURATION PRINCIPLE Comps. C N-2 at step N-2 Signature S N at step N Signature S N-1 at step N-1 Comps. C N-1 at step N-1 Signature S N-2 at step N-2 Comps. C N at step N Signature s N at step N Comps. c N at step N Comps. c N-1 at step N-1 Signature s N-1 at step N-1 menu table of step N-1 menu table of step N-2 algo sequence table of step N sequence table of step N-1 sequence table of step N-2 Recursive algorithms derives all ‘lower-level’ signatures (=intermediate decisions) using top-level (physics) signatures (XML definition) and set of implemented sequences (algorithms+in/outputs). algo L1 RoIs

UHH, SS06TSS: Triggering in ATLAS53 HLT CONFIGURATION IMPLEMENTATION Status  Well-tested software, used in many HLT applications.  Currently: Development of ‘real-life’ algorithms which run on inputs of calo trigger simulation (HLT TDR!). Code  Recursive algorithm implemented in C++ code in Athena framework (more complex than shown).  Uses XML for definition of ‘Physics signatures und sequences.  Embedded in HLT selection software (PESA steering code). One signature and one sequence per step and ‘Physics Signatur’. One ‘Menu Table’ and one ‘Sequence Table’ per step.

UHH, SS06TSS: Triggering in ATLAS54 HLT: CONFIGURATION ‘Top-down’ approach: Input 1: Signature ‘2e30i’ Input 2: all known sequences (Algos+In/Outputs) List of all ‘Physics Signatures’ = Trigger Menu e30i  Algo -1  e30 3: Then next-lower signature clear: 2- times e30: 2e30 1: ‘Physics Signature’ and constituents (2-times e30i) 2: Sequence: Outputs, Algorithm, Inputs 4: Procedure recursively down to 2EM20i signature. One signature and one sequence per step. 5: Signatures of all ‘Physics Signatures’ in one step: Menu Table 6: Sequences of all ‘Physics Signatures’ in one step: Sequence Table