Como, ICATPP 2009 R.Crupi 1 Roberto Crupi INFN Lecce & Physics Department, University of Salento - Italy on behalf of the ATLAS Collaboration 11 th ICATPP Conference on Astroparticle, Particle, Space Physics, Detectors and Medical Physics Applications Villa Olmo, Como 5-9 October 2009 Muon reconstruction and selection at the last trigger level of the ATLAS experiment

Como, ICATPP 2009 R.Crupi 2 Outline Overview on the ATLAS Trigger System The Muon Event Filter The Muon Event Filter Performance Studies Performance Studies

Como, ICATPP 2009 R.Crupi 3 ATLAS (A Toroidal LHC ApparatuS)

Como, ICATPP 2009 R.Crupi 4 MDT RPC TGC CSC The ATLAS Muon Spectrometer Trigger Chambers Trigger Chambers: RPC RPC (Resistive Plate Chambers) |  |<1.05 TGC TGC (Thin Gap Chambers ) 1.05<|  |<2.4 Tracking Chambers Tracking Chambers: MDT MDT (Monitored Drift Tubes) |  |<2 CSC CSC (Cathode Strip Chambers) 2<|  |<2.7 Technologies deployed in the muon system: A magnetic field allows muon momentum measurements The Muon Spectrometer has the standalone capability of measuring muon momenta  p T /p T < 10% up to 1 TeV Δp T /p T of few % up to 100 GeV

Como, ICATPP 2009 R.Crupi 5 To obtain the required event rate reduction, the trigger is structured in three levels: Level-1 40MHz initial 75 kHz2.5  sRoI Level-1 : hardware based, with coarse granularity from calorimeters and muon systems. It reduces the ~40MHz initial rate to 75 kHz in a maximum latency of 2.5  s. It looks for regions of activity in the detector (Regions of Interest, RoIs) Event Filter Event Filter : software based. It uses the same algorithms as in the offline and runs after event building, then it can access the complete event data. It reduces Level-2 output rate to 200 Hz4s ~200 Hz with a 4s mean processing time. It accesses the full granularity data inside a Level-2 RoI. Level-2 & EF are together referred as High Level Trigger (HLT) Level-2 3 kHz Level-2 : software based, algorithms optimized for fast rejection. It reduces Level-1 output rate to ~3 kHz with a 40 ms mean processing time. It accesses the full granularity data inside a Level-1 RoI. The ATLAS Trigger ~75 kHz ~3 kHz ~200 Hz 2.5 s 40 ms 4 s 40 MHz BUNCH CROSSING RATE

Como, ICATPP 2009 R.Crupi 6 The Muon Spectrometer is a powerful tool for precise measurements of high p T muons and identification of low p T muons The longer lever arm improves charge determination for high energy muons Extrapolation to the Interaction Point (IP) can better discriminate from secondary muons and the ones coming from the in-flight decay of π/K mesons. Inner Detector The Inner Detector (ID) performs precise track reconstruction with high efficiency for low p T muons Muon Identification is achieved by combining ID measurements with the ones provided by MS The final momentum resolution takes advantage of both ID and MS Isolation criteria applied to muons before reaching the MS allows a good muons discrimination from the ones deriving from jets Reconstruction and identification in the muon system

Como, ICATPP 2009 R.Crupi 7 The Muon Trigger Level-1result Region of Interest selected By Level-1 Event Filter (EF) Event Filter (EF) performs muon Identification and Reconstruction thanks to dedicated offline packages developed in the ATHENA framework Refines Level-2 estimates Confirms/Discards Level-2 Hypothesis For debug purposes EF could directly receive a seed from Level-1 RoIs Level-2: muFast muFast: standalone MS muon reconstruction, fast muon p T estimation via LUT muComb muComb: combined ID/MS muon reconstruction; improvement of p T resolution wrt μFast muIso muIso: Calorimeter and ID isolation muTile muTile: Muon Tagging in Tile Calorimeter Level-2 tasks: rejection of low p T muons rejection of secondary muons deriving from the decay in flight of π/k rejection of fake muon tracks generated by hits due to cavern background

Como, ICATPP 2009 R.Crupi 8 Two algorithms have been implemented in muon EF: TrigMuonEF and TrigMuGirl TrigMuonEF and TrigMuGirl. Both are wrappers of muon offline reconstruction tools. They have an opposite strategy in muon reconstruction/identification: TrigMuonEF MS extrapolation to the IPtrack combination in the inner detector TrigMuonEF starts from the reconstruction in the MS and performs a backward extrapolation to the IP and track combination in the inner detector. TrigMuGirl muon reconstruction ID extrapolates tracks MS. TrigMuGirl starts muon reconstruction from the ID and extrapolates tracks to MS. Muon Event Filter

Como, ICATPP 2009 R.Crupi 9 TrigMuGirl are structured in TrigMuonEF and TrigMuGirl are structured in : FEX) look for feature Feature EXtraction (FEX) algorithms: normally RoI seeded, retrieve detector data inside RoI and look for feature in this data. HYPOcompare features by FEXs against some hypothesis HYPOthesis (HYPO) algorithms: compare features provided by the FEXs against some hypothesis and validate or reject the TE output according to the success or failure of the hypothesis Trigger selection strategy is based on the definition of: TEs) : abstract objects representing the state of the reconstructions Trigger Elements (TEs) : abstract objects representing the state of the reconstructions. Chains: sequences of several TEs For each chain, the trigger steering runs the sequence of algorithms configured to produce all the output TEs at each step of the chain For each chain, the trigger steering runs the sequence of algorithms configured to produce all the output TEs at each step of the chain. TE FEX HYPO Updated TE Muon Event Filter

Como, ICATPP 2009 R.Crupi 10 TrigMuonEF Implementation TrigMuonEF is a TrigMuonEF is a wrapper of offline packages developed for the purpose of muon reconstruction and identification: TrigMuonEF is composed of: fourFEX A sequence of four FEX algorithms which compute physics quantities. HYPOalgorithms Four HYPO algorithms after each FEX. Possible configurations: –Seed from Level 2 (standard) –Seed from Level 1 (for debug) –Unseeded (full event reconstruction)

Como, ICATPP 2009 R.Crupi 11 Segment Finder Segment Finder : selects MDT precision hits to found a segment. Track Builder Track Builder: Reconstructs muon tracks inside the MS taking advantage of its high precision tracking system and provides a precise measurement of the track parameter outside the calorimeter. TrackExtrapolator TrackExtrapolator: performs a backward extrapolation to the interaction region through the calorimeters. It takes into account the magnetic field and corrections for energy loss and multiple scattering effects from all crossed material TrackCombiner TrackCombiner: Extrapolated tracks are combined with the corresponding matching tracks, if they exist, in the ID. MS and ID tracks are matched by forming a  2 built with the parameters of both tracks use a global fit of all the hits collected in both ID and MS TrigMuonEF Implementation

Como, ICATPP 2009 R.Crupi 12 Muon candidate starts from an ID track Muon candidate starts from an ID track inside a Level-2 RoI, provided by EF ID algorithms. Tracks are extrapolated to the MS chambers. A roadaround the extrapolated coordinates. A road in eta and phi is created around the extrapolated coordinates. looks for hits extrapolated track The algorithm looks for hits around the extrapolated track to fit segments. The best fittedsegmentto refine estimated track coordinates The best fitted segment is used to refine the estimated track coordinates and road in the current station. TrigMuGirl Implementation TrigMuGirl HypoAlg CandidateTool GlobalFitTool ANNSelectionTool EF ID Tracks In Muon RoI Hits and segments improve extrapolation Hits and segments collected in the various stations of the MS chambers allow TrigMuGirl to improve extrapolation and the to identify muon-like candidate. Muon-like candidatesprecalibrated ANN functions. Muon-like candidates are selected using precalibrated ANN functions. global fit further improvement of the momentum estimate A global fit, icluding ID and MS hits is applied to tracks belonging to identified muons for a further improvement of the momentum estimate.

Como, ICATPP 2009 R.Crupi 13 TrigMuGirl includes a dedicated tool to trigger Stable Massive Particles (SMP, e.g. in Susy R-parity violating scenario). Reconstruction efficiency takes advantage of hits collected from both the previous and the following Bunch Crossing.  and mass reconstruction using RPC and MDT technologies. Specific R-Hadrons selection for candidates that don’t have an ID track. Seed search in the MS from a Level-2 trigger element. Source10 34 rate (Hz)10 31 rate(Hz) L2_mu40Slow c-cbar b-bbar Wmunu t-tbar0.2small zmumusmall SMP trigger runs in a separate chain (Slow) in the trigger Menu for L1: mu10 L2: beta/mass reco in the barrel L2: beta/mass reco in the barrel EF: TrigMuGirl beta/mass reco EF: TrigMuGirl beta/mass reco Estimated beta resolution and reconstructed mass for single stau Background Rates M=110 GeV M truth =110 GeV M = ± 9.7 GeV TrigMuGirl: Slow Particle Mode

Como, ICATPP 2009 R.Crupi 14 Simulated t-tbar sample Association to true muon in a cone of DR<0.002 for muon EF combined algorithms. No p T thresholds have been applied for TrigMuonEF while the requirement of a 10GeV p T muon in the event is applied for TrigMuGirl. The p T resolution as a function of transverse momentum is shown forExtrapolatorCombinerTrigMuGirl with respect to Level-2 muComb p T resolution vs p T Muon EF Performance EF efficiencies wrt Level-2 ATLAS Preliminary

Como, ICATPP 2009 R.Crupi 15 TrigMuGirl TrigMuonEF Zμμ MC sample Efficiency wrt MC Truth eta resolution vs p T phi resolution vs p T TrigMuonEF and TrigMuGirl: improve significantly trigger rejection power due to better p T resolution wrt Level-2 improve significantly trigger rejection power due to better p T resolution wrt Level-2 have similar performance in efficiency and resolutions have similar performance in efficiency and resolutions Muon EF Performance Level-2:muFastmuComb

Como, ICATPP 2009 R.Crupi 16 Results on 2008 cosmic data TrigMuonEF TrackBuilder algorithm: comparison of eta (  ) and phi (Φ) wrt to offline algorithm   =0.007,   =17mrad Solenoidal and toroidal field on

Como, ICATPP 2009 R.Crupi 17 Conclusions The Muon Event Filter has been designed and implemented to cope with the demanding requirements of the ATLAS trigger system in the high luminosity and background enviroment at LHC TrigMuonEF and TrigMuGirl have been successfully integrated in the Muon EF and constantly tested and validated TrigMuonEF and TrigMuGirl have been successfully integrated in the Muon EF and constantly tested and validated TrigMuonEF and TrigMuGirl show very good and similar performance TrigMuonEF and TrigMuGirl show very good and similar performance At the startup muon selection will take advantage of both algorithms running At the startup muon selection will take advantage of both algorithms running

Como, ICATPP 2009 R.Crupi 18 BACK UP SLIDES

Como, ICATPP 2009 R.Crupi 19 LHC Center of Mass Energy (p-p) –14 TeV (design) –10 TeV (start-up) Instantaneous Luminosity: –L = cm -2 s -1 –L = cm -2 s -1 Integrated Luminosity / year ) –  Ldt  100 fb -1 The cross sections of interesting physics processes are highly suppressed w.r.t.  tot –Calibrations and precision physics Leptonic W decay –New Physics Higgs boson production Event rate at LHC design lumi) ~1 GHz –40 MHz (BC frequency) x 23 interactions per BC Max allowed acquisition rate ~200 Hz –Bandwidth ~ 300 MByte/s –Event Size ~ 1.5 MByte

Como, ICATPP 2009 R.Crupi Muon menu and rates Total of muons: 1.7k -220 ~40

Como, ICATPP 2009 R.Crupi 21 Slow Particle Trigger

Como, ICATPP 2009 R.Crupi 22 StauHypo: p T > 40GeV,  40 GeV At Level-2; StauHypo: p T > 40GeV,  40 GeV TrigMuGirl for Slow Particles Enables to select candidates when segment reconstruction is imperfect Efficiency for low  is improved using TGC hits form next BC  estimation using RPC- as in Level-2  estimation using MDT Loop over possible  Change TOF according to  –MDT radii change accordingly Create MDT segments from the re-time radii Minimize segment  2 wrt  → estimate Determine  and Mass

Como, ICATPP 2009 R.Crupi 23  New mu20_slow is in trigger menu for  L1 mu10   L2 stau (B) | mu20 (EC)   TrigMuGirlSlow  Estimated background rates

Como, ICATPP 2009 R.Crupi 24