Hardeep Bansil (University of Birmingham) on behalf of L1Calo collaboration ATLAS UK Meeting, Royal Holloway January 2011 Argonne Birmingham Cambridge Heidelberg (KIP) Mainz Michigan State Queen Mary, London RAL (PPD, ID) Stockholm (EPP, S&I)

Contents System Overview Calibration Rates Efficiencies Plans for the future Level-1 Calorimeter Trigger: Commissioning and Performance - ATLAS UK Meeting 2

Trigger Overview Level-1 Custom built HW Fixed latency < 2.5 μs, L1A ~75 kHz Level-2 Software based Full granularity for areas of activity marked by L1 (RoI) Latency ~40 ms, L2A ~3.5kHz Event Filter Software based Offline algorithms on full event Latency ~1s, EFA ~200Hz Level-1 trigger: L1-Calorimeter (L1Calo) L1-Muon (L1Muon) Central Trigger Processor Level-1 Calorimeter Trigger: Commissioning and Performance - ATLAS UK Meeting 3

L1Calo HW implementation Pipelined, synchronous system with fixed latency Many parallel processing stages using custom electronics: ~300 VME modules of 10 types housed in 17 crates Level-1 Calorimeter Trigger: Commissioning and Performance - ATLAS UK Meeting 4 Main parts: Preprocessor: Conditioning and calibration of analogue signals, digitization, bunch cross identification Cluster processor: Electrons/photons, taus Jet / Energy Sum processor: jets, E T, Missing E T

Selection of interesting events Hard final state objects in an event: e/γ and τ/h objects: EM and HAD cluster > E T threshold local E T maximum compared to neighbour windows Jet candidates: coarser granularity, digital summation EM+HAD look for local maximum Global event properties: Total E T Missing E T Sum E T Sends to Central trigger processor: Multiplicity of electrons/photons, taus and jets passing thresholds Thresholds passed by Total and Missing E T Sends to Level 2 trigger: positions and signatures of RoIs Level-1 Calorimeter Trigger: Commissioning and Performance - ATLAS UK Meeting 5 CP Algorithm JEP Algorithm

Calibration Many types of calibration are required when dealing with a complex trigger system Timing Energy calibration Look Up Table filling schemes EM overlap region FCAL complexities FIR filter settings Noise cut optimizations Anything else Will focus on timing and energy calibration Level-1 Calorimeter Trigger: Commissioning and Performance - ATLAS UK Meeting 6

Timing Calibration Calorimeter signals are associated to correct BC Iterations of pulser runs, splash events & collision data Most precise results from energy deposits (> 10GeV) to within 2ns 2010 corrections loaded in for HI & good into 2011 Level-1 Calorimeter Trigger: Commissioning and Performance - ATLAS UK Meeting 7 Latest timing corrections for individual towers in ns

Energy Calibration Trigger towers initially calibrated based on analysis of calorimeter pulser runs Collisions - use precise energies to compare to L1Calo 2010 provided data to calibrate most towers In particular FCAL calibration greatly improved Level-1 Calorimeter Trigger: Commissioning and Performance - ATLAS UK Meeting 8 EMB Typical energy correlations for good towers Tile

Hardware stability & Rates Commissioning with cosmics fixed most hardware problems Ran stably with L1Calo working well  negligible data losses Majority of trigger items scale linearly with luminosity Global quantities like E T Miss and Total E T do not due to pile-up Level-1 Calorimeter Trigger: Commissioning and Performance - ATLAS UK Meeting 9 Trigger rates V Instantaneous LumiTrigger rates for run

Efficiencies – EM objects Data taken using independent triggers (MBTS) Checking efficiency (#triggered/#all) of all electromagnetic L1Calo triggers for reconstructed offline clusters Example L1 threshold EM5: Energy of cluster as seen by L1 should be larger than 5 counts (~ 5 GeV) Where efficiency curve starts to rise (trigger uses E T > threshold) Full efficiency reached at 9 GeV Aim to make curves sharper in 2011 Level-1 Calorimeter Trigger: Commissioning and Performance - ATLAS UK Meeting 10 EM2, EM3, EM5 EM10, EM14

Efficiencies – EM Objects η-φ efficiency map for EM3 for offline reconstructed clusters with E T raw > 5 GeV Each entry corresponds to an individual EM trigger tower White regions are from faulty LAr OTXs (independent of L1Calo) Areas with reduced efficiency are identified and causes understood Level-1 Calorimeter Trigger: Commissioning and Performance - ATLAS UK Meeting 11

Efficiencies – Taus and Jets Efficiencies (#triggered/#all) for reconstructed offline taus and jets L1 thresholds set to 5 (LUT) counts (~ 5 GeV) L1 uses “raw” EM energy scale without dead material corrections Part of tau/jet energy may not be contained in L1 objects Full efficiency around 35 GeV Level-1 Calorimeter Trigger: Commissioning and Performance - ATLAS UK Meeting 12 Jets, J5Taus, TAU5

Plans for the future Hardware and firmware in excellent condition but improvements still in the works… Calibrations still developing Feedback from physics working groups welcome! Level-1 Calorimeter Trigger: Commissioning and Performance - ATLAS UK Meeting 13 Selection of events with large missing energy Use E T Miss significance XS = MET/√(SUMET) triggers instead of existing MET as more robust to pile-up Will require updates to firmware and software