1. RAL Summer School September, 2004 Efstathios (Stathis) Stefanidis sstef@hep.ucl.ac.uk http://www.hep.ucl.ac.uk/~sstef High Level Trigger Studies for the ATLAS Detector Efstathios (Stathis) Stefanidis University College London

2. RAL Summer School September, 2004 Efstathios (Stathis) Stefanidis sstef@hep.ucl.ac.uk http://www.hep.ucl.ac.uk/~sstef OUTLINE  The ATLAS Detector : Overview.  The Trigger System. i.Overview. ii.High Level Trigger.  Performance Studies. i.IDScan. ii.e/γ vertical slice. iii.RoI size.  Future Plans.

3. RAL Summer School September, 2004 Efstathios (Stathis) Stefanidis sstef@hep.ucl.ac.uk http://www.hep.ucl.ac.uk/~sstef The ATLAS Detector: Overview. 1.pp colliding beams 14 TeV c.m. energy. 2.Design Luminosity: L =10 34 cm -2 s -1. 3.Three Parts: a)Inner Detector b)Calorimeter (EM – HAD) c)Muon Spectrometer 4.Magnet System: a)Solenoid:  2 T b)Toroid:  0.4 T

4. RAL Summer School September, 2004 Efstathios (Stathis) Stefanidis sstef@hep.ucl.ac.uk http://www.hep.ucl.ac.uk/~sstef The Trigger System: Overview. 1.LVL1: 40 MHz  75 kHz < 2.5 μs Hardware trigger Reduced granularity information 2.LVL2: 75 kHz  2 kHz 10 ms Full granularity information from both ID and Calorimeter RoI mechanism 3.Event Filter (EF): 2 kHz  100 Hz  2s Sophisticated algorithms Alignment data available High Level Trigger (HLT)

5. RAL Summer School September, 2004 Efstathios (Stathis) Stefanidis sstef@hep.ucl.ac.uk http://www.hep.ucl.ac.uk/~sstef The Trigger System: HLT. RoI mechanism (i) Defines the area where HLT will start from. (ii) Seeded by LVL1 (iii) Only the data needed are transferred  MINIMISE THE PROCESSING TIME AND NETWORK TRAFFIC ObjectsSelection Signatures Physics Coverage Electrone25i, 2e25iHiggs (SM, MSSM), new gauge bosons etc Jetj400, 3j150SUSY, compositeness, resonances etc. 1.Event Selection Strategy: Signature validation Checks for signatures coming from interesting physics events  REJECT UNINTERESTING EVENTS VERY EARLY

6. RAL Summer School September, 2004 Efstathios (Stathis) Stefanidis sstef@hep.ucl.ac.uk http://www.hep.ucl.ac.uk/~sstef The Trigger System: HLT. 2.Event Selection Software: ATHENA (i)Written using GAUDI architecture (ii)Provides common services (Transient Data Store, Histograms, Auditing etc) (iii)Well-defined interface not only to developers but also to the end-users  IMPROVE COHERENCY OF THE DIFFERENT SOFTWARE DOMAINS IDScan (i)LVL2 track reconstruction algorithm (ii)SPACE POINTS as input – Track parameters as output (iii)Runs several times per event and once per RoI

7. RAL Summer School September, 2004 Efstathios (Stathis) Stefanidis sstef@hep.ucl.ac.uk http://www.hep.ucl.ac.uk/~sstef Performance Studies: IDScan. Pattern Recognition AlgorithmsLow Luminosity High Luminosity IDScan (89.0 ± 0.4) %(82.9 ± 0.5) % xKalman (88.9 ± 0.4) %(84.0 ± 0.5) % iPatRec (87.2 ± 0.4) %(82.2 ± 0.5) %  |p T gen – p T rec |<15 GeV  |η gen – η rec |<0.01  |φ gen – φ rec |<0.01 rads

8. RAL Summer School September, 2004 Efstathios (Stathis) Stefanidis sstef@hep.ucl.ac.uk http://www.hep.ucl.ac.uk/~sstef Performance Studies: e/γ slice. Determine selection efficiencies and rates at each Trigger Level. Apply isolation, energy, tracking matching etc cuts. Trigger Level % Efficiency w.r.t LVL1 Rate LVL1 1007.9 kHz LVL2Calo 95.71.9 kHz LVL2ID 88.4359.1 Hz LV2IDCalo 86.3136.1 Hz EFCalo 84.892.3 Hz EFID 80.064.1 Hz EFIDCalo 73.431.1 Hz Electron selection W  eν e sample 22.5 GeV

9. RAL Summer School September, 2004 Efstathios (Stathis) Stefanidis sstef@hep.ucl.ac.uk http://www.hep.ucl.ac.uk/~sstef Performance Studies: RoI size. How is the RoI constructed? Take the information from LVL1 Calo : (η,φ) of the active region. The η coordinate is calculated w.r.t to z=0 Construct the shape of the RoI: z=0 ± 168 mm (  3  of the beam spread) η ± 0.1 φ ± 0.1 rad Motivation? Optimize the size of the RoI.  Less Space Points.  Less Combinatories.  Quicker Algorithms.  Improve efficiency. Implementation? Use the shower position at the 1st and 2nd EM sampling.

10. RAL Summer School September, 2004 Efstathios (Stathis) Stefanidis sstef@hep.ucl.ac.uk http://www.hep.ucl.ac.uk/~sstef Performance Studies: RoI size. Z vertex resolutionPhi vertex resolution Theta vertex resolution σ_low = 3.626 cm σ_high = 3.593 cm σ_low = 1.719 mrad σ_high = 1.692 mrad σ_low = 14.26 mrad σ_high = 14.11 mrad

11. RAL Summer School September, 2004 Efstathios (Stathis) Stefanidis sstef@hep.ucl.ac.uk http://www.hep.ucl.ac.uk/~sstef Future Plans. Performance Studies  IDScan : Optimize the size the RoI  e/γ analysis : Improve, validate, optimize the cuts Physics Studies  Low Mass Higgs (m H <150 GeV)  H  γγ  H  bb  Study the full production/simulation/reconstruction chain.