Inefficiencies in the feet region

1. LVL1 Selection TrigMoore Comb Isol Toroid Fast RPC CTPI CTP TGC  No RPC hit Low-pT plane missing High-pT plane missing  Tag Probe (*) A typical Muon Trigger Menu for 1031 luminosity (LHC startup). (*) mu_4 is a totally open threshold used for cosmic data limited by cabling only. pT = 6 GeV threshold pT = 20 GeV threshold pT, h, f Minimum pT ||<1.05 MUONROI MU6 MU6’ MOORE muFast MuId COMB efficiency wrt LVL2 Vtx close to IP 6 GeV8 GeV 20 GeV40 GeV MuIdSA MU6’’’’ MuIdCB MU6’’ MU6’’’ m production point Barrel efficiencies vs pT for MuId combined Sergio Grancagnolo (University of Salento & INFN Lecce - Italy) on behalf of the ATLAS Muon HLT group 10th International Conference on Advanced Technology and Particle Physics (ICATPP) 8-12 October 2007 Villa Olmo, Como, 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 standard model physics low pT events, with a suppression factor 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 (Region of Interest, RoI), in each event. Coincidence windows are defined on the allowed geometrical roads with their center corresponding to the infinite momentum track. At pT=6 GeV threshold, barrel efficiency is 83%, rate ~11 kHz (lumi=1033cm-2s-1), at pT=20 GeV efficienc is 79% and the rate is ~2 kHz (lumi=1034cm-2s-1) 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 msec 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 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). LVL2 Selection EF Selection Total latency time 2 s 10 ms Barrel 2.5 s End Cap MOORE MS barrel Comb muFast resolutions in the barrel and in the endcap for low pT and high pT muons CALO MuId SA To refine the muFast pT, muCombuses Inner Detector (ID) data, allowing to sharpen the threshold at low pT. 3-station coincidence trigger efficiency of TGC TrigDiMuon endcap LVL1 trigger uses RPC in the barrel (|h|<1) and TGC in the endcaps (1<|h|<2.4) ID MuId COMB Tile 6 GeV 20 GeV Endcap B Physics processor Full bandwidth Event Filter 75 kHz ~2 kHz ~ 200 Hz 40 GeV muons selection efficiency The Muon Event Filter consists of three algorithms: MOORE, MuId StandAlone and MuId Combined. 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. 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 become TrigMOORE. Low pT rates: muons from pions and kaons h One of the main sources of muons at low pT are in flight decays of light mesons. Barrel – End Cap transition A track from such decays appears with a kink, and the c2 of the fit is worse than prompt muon tracks. All possible kinematic parameters and statistical techniques must be used in order to reject such tracks. 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). f Inefficiencies in the feet region Differential cross-section for production of muons from pions and kaons Efficiency from Zmm sample Trigger Menus The role of MuId StandAlone is to extrapolate MS tracks to the production point using calorimetric information. Muon momenta are measured with a resolution pT/pT < 10% up to 1 TeV. Different kinds of physic events need to share available bandwidth, that is limited. Flexible trigger menus allow to avoid saturation from few processes, and guarantee the possibility to organize the analysis depending from luminosity conditions. When the rates are too high, prescale factors can be applied to low pT thresholds at LVL1, and leave the HLT in pass through mode. The HLT capabilities are studied flagging the events without rejection. Express streams, not prescaled, at fixed thresholds, are used for calibration and monitoring purposes. Method to evaluate performance directly from data, using one m reconstructed in both ID and MS as a tag, and the other requiring only the ID as a probe. This method can be applied to extract MS trigger efficiency Single muons Tracks are reconstructed also in the ID by a dedicated software (newTracking). MuidStandAlone ||<2.5 TrigMoore MuidCombined Tag combined triggered muon ID+MS pT > 20 GeV |η| < 2.4 MuId Combined uses these informations, thus enhancing momentum resolution for pT up to 50 GeV and allowing good discrimination of muons in jets. ID improves resolution at low pT, MS at high pT. Probe ID track pT > TPcut |Mμμ - MZ| < 10 GeV Δφ > 0.3 1/pT resolution for EF algorithms. Muons are present in many standard model processess. Resolution and efficiencies are evaluated on single muon samples generated at different pT values. Rates are then estimated using the theoretical contribution from different sources, heavy and light mesons, top, W, etc. TPcut = 20 GeV trigger measurement over threshold TPcut = 1 GeV for integrated trigger efficiency Allows threshold trigger efficiency measurements with good precision wrt to MC generator. 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 = 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. EF trigger rates estimated with single muon sample.