= Trigger Element

1. LVL1 Selection Comb Isol Toroid Fast RPC MOORE Comb CTPI CTP TGC MuId SA TrigDiMuon Low pT (6 GeV) Fast rate (kHz) Comb rate (kHz) MuId COMB Tile K/ decays 3.18 1.1 b decays 0.91 0.68 75 KHz c decays 0.41 0.35 ~2 kHz ~ 200 Hz Fake L1 <10-3 <10-3 Total 4.5 2.13  No RPC hit Low-pT plane missing High-pT plane missing Seeding and Guidance of Algorithms Region-of-Interest Selection and Raw Data Conversion Algorithms to extract Features from event data 1 10-1 10-2 10-3 efficiency Common “Language” within and between Algorithms: Event Data Objects (e.g., Clusters, SpacePoints, Tracks) Hardware (PCs) running Selection Software pT GeV Importation of Offline Software Framework and Object Store  pT, h, f Minimum pT MUONROI MU6 MU6’ MOORE muFast Vtx close to IP MuIdSA MU6’’’’ MuIdCB MU6’’ MU6’’’ m production point MuId StandAlone (top) and Muid Combined (down) pT resolutions for 7GeV muons simulated with cavern background (safety factor: left x1, right x5) and pile-up for a luminosity of 1033cm-2s-1. Sergio Grancagnolo (INFN & University of Lecce - Italy) on behalf of the ATLAS Muon HLT group 10th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD06) 1 - 5 October 2006   Siena, Italy Implementation and performance of the ATLAS Trigger Muon “Vertical Slice” The ATLAS trigger system is designed to keep high efficiency for interesting events, while rejecting low pT events with a suppression of the order of 107, reaching the ~200 Hz data storage capability of the DAQ system. Level 1 Trigger Level 2 Trigger Core algorithm is muFast, that confirm/reject LVL1 result and refine muon pT evaluation, using MDT precision measurements. LVL1 selects active detector regions in each events: Region of Interest (RoI) High pT muons are important for many known processes, that can be used for monitoring and calibration (Zmm) and for several new phenomena predicted at the LHC energy (Higgs, SUSY), therefore the muon trigger system is of primary importance. • Following steps are to be achieved within the 10 sec latency time: • “Global Pattern Recognition” involving trigger chambers and positions of MDT tubes (no use of drift time); • “Track fit” involving drift time measurements, performed for each MDT chamber; • Fast “pT estimate” via a Look-up-table (LUT) with no use of time consuming fit methods. The Muon Spectrometer (MS) is the detector dedicated to the identification of muons. It consists of RPC and TGC trigger chambers and MDT and CSC precision chambers. The Muon Vertical Slice consists of three main trigger steps, one hardware, level 1 (LVL1) and two software, level 2 (LVL2) and event filter (EF). Last two compose the High Level Trigger (HLT). LVL1 trigger use RPC |h|<1 and TGC 1<|h|<2.4 LVL2 Selection EF Selection Total latency time 2 s 10 ms 2.5 s TrigMoore barrel muFast efficiencies in the barrel for low pT and high pT muons To refine the muFast pT, muCombuse Inner Detector (ID) data, allowing to sharpen the threshold at low pT. endcap B Physics processor LVL2 algorithm rates in the barrel. Full bandwidth 30% of all inefficiencies are due to feet and elevator sector Decision on each event is based on reduced-granularity detector data for interesting region at LVL1, full-granularity and precision, but only for same LVL1 regions, at LVL2, and full event data, as in offline, at EF. Larger pi/K rejection with respect to prompt muon (barrel only) The HLT software schema. Example of LVL2 trigger for B-Physics J/ψ particles are widely produced in B decays. After muFast, a specific J/ψselection is done by TrigDiMuon requiring: J/ψμ(pT>6GeV)μ(pT>3GeV) events • One μ with pT>6 from LVL1 Trigger • Two opposite sign tracks in ID • one points to the LVL1 RoI • the other is extrapolated to MS • Invariant mass for the di-muon m()>2.8 GeV Overall LVL1 Efficiency is 83% Low-pT, 79% High-pT. Rates (lumi): low pT ~11 kHz (1033cm-2s-1), high pT ~2 kHz (1034cm-2s-1) Estimated physics performance Event Filter Muons pT=8 GeV/c ~ 66% - 78% of events can be identified at LVL2 with output rate ~260-380 Hz The Muon Event Filter consists of three algorithms: MOORE, MuId StandAlone and MuId Combined. MOORE and MuId are two object oriented offline packages written in C++, already integrated in the ATLAS software framework: ATHENA. Imported in the trigger environment, they became TrigMOORE. The role of MuId StandAlone is to extrapolate MS tracks to the production point. Muon momenta are measured with a resolution pT/pT < 10% up to 1 TeV. MuId StandAlone MOORE ||<0.9   Efficiencies vs h for MOORE (up) and MuId StandAlone (down). TrigMOORE can work in two different modes, wrapped, scanning full detector data, and seeded, starting from RoI seeded by LVL2 (full trigger chain) or alternatively by LVL1 (for trigger studies). Tracks are reconstructed also in the ID by one dedicated software (iPatRec). MuId Combined uses these informations, thus enhancing momentum resolution for pT up to 50 GeV and allowing good discrimination of muons in jets. 1/pT resolution for EF algorithms. Single µ, pT=100GeV L=1034cm-2s-1 + nominal cavern background Background studies Combination Pentium 4 XEON 2.4GHz, 1 GB RAM Extrapolation The radiation generated by p-p collisions interact with the detector and the collider activating their material. Particles released by the materials, mainly neutrons, produce secondaries time-uncorrelated neutral and charged particles, that diffuse in the apparatus like a gas. This cavern backgroundcauses counting rates expected at design luminosity of the order of 10-100 Hz/cm2 in the barrel and ~1 kHz/cm2 in the endcap, slightly depending on pseudorapidity. Outer stations are less affected. To be conservative simulations are done with background levels multiplied by safety factors. Tracks Roads RZSegment PhiSegment Total EF timings, mean and RMS, latency of data access included. A trigger chain example = Trigger Element Trigger software works with objects called Trigger Elements (TE). Feature Extraction Algorithms (FEX) are activated by input TE produced by previous trigger levels. FEX are able to access the detector data and compute physical quantities, Features, that are then attached to the output TE. Selection is done in Hypothesis Algorithms, that can validate or reject TE that do not satisfy trigger requirements. = Feature Extraction Algorithm = Hypothesis Algorithm pT = 6 GeV threshold pT = 20 GeV threshold = Feature In-flight decays of pions and kaons are the main source of LVL1 trigger rate at low pT. One goal of the muon HLT is to reject such fake muons while having high selection efficiency on prompt muons. Trigger menus like the one on the left can be used for this purpose. ||<0.9 MuId COMB efficiency wrt LVL2 No pT threshold applied Rates for all trigger levels in the barrel. Further rate reduction is expected when cuts dedicated to K/p rejection, will be applied. Efficiencies vs pT for MuId combined