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Muon Identification and Reconstruction

Muon Identification and Reconstruction. Stefano Rosati INFN – Roma 1. Muon Detectors for LHC. Aspects of central relevance: Trigger: reduce the event rate from the initial 40 MHz to the ~200 Hz affordable by the event storage system

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Muon Identification and Reconstruction

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  1. Muon Identification and Reconstruction Stefano Rosati INFN – Roma 1 S. Rosati - MC Workshop

  2. Muon Detectors for LHC Aspects of central relevance: • Trigger: reduce the event rate from the initial 40 MHz to the ~200 Hz affordable by the event storage system • Organized over more levels, the first one has to operate a fast (<10 ns) choice and identification of the Region of Interest • Following levels process a limited subset of data (only from the RoI) with higher resolution and detail • Final level very close to offline reconstruction, running online on RoI data. • Offline reconstruction: provide optimal muon identification and momentum resolution over the pT range 5-1000 GeV • Standalone reconstruction can exploit the cleanerenvironment of the muon system • Combination with inner tracking detectors to improve resolution S. Rosati - MC Workshop

  3. ATLAS and CMS Experiements Two approaches for the two experiments: • ATLAS: • 3 Air-core Toroids (one barrel, two endcaps), mean field 0.6 T with excellent standalone capabilities – complemented by a 2T Central Solenoid) • Different bending planes for Inner Detector and Muon Spectrometer (f and h) • Stringent requirements on tracking detectors resolution, calibration and alignment • Combined reconstruction gives optimal resolution in a certain momentum range • CMS: • Muon Detectors in the return yoke of the 4 T inner solenoidal field • Resolution dominated by Multiple Scatteringup to ~200 GeV pT • Combined reconstruction neededto achieve optimal resolution • Less stringent requirements on muon tracking detectors resolution, and on their calibration and alignment S. Rosati - MC Workshop

  4. ATLAS Muon Trigger – LVL1 Barrel Trigger Uses dedicated detector system based on RPCs and TGCs Selection of events with muons above a given pT threshold (up to six programmable thresholds) Coincidence of hits in space (both h and f) and time within geometrical windows in different trigger detector layers S. Rosati - MC Workshop

  5. ATLAS – Level 1 Trigger Endcap Efficiency vs pT Threshold – acceptance up to |h|<2.4 Example trigger menus and final rates, after also LVL2 and Event Filter (for L=2•1033 cm-2s-1):1m 20 GeV, 2m 10 GeV (40 Hz)2m 6 GeV (25 Hz) Valid for both Barrel and Endcap S. Rosati - MC Workshop

  6. 3 points Initial layout angle-angle B~0 B angle-point B sometimes angle-angle Ribs Ribs Muon Reconstruction in ATLAS S. Rosati - MC Workshop

  7. Initial layout Detector acceptance ATLAS - Combined Reconstruction • Tracks are back-extrapolated to the IP • Parameters corrected for energy losses and multiple scattering • Energy loss ~3 GeV at h=0 • Look for match with tracks reconstructed in the ID • Combined refit of the two tracks • or: statistical combination oftrack parameters • Inner Detector in a Solenoidal Field of 2 T. Combined reco efficiency S. Rosati - MC Workshop

  8. ATLAS – pT Resolution Resolution vs pT • m-Spectrometer Standalone:~10%*pT 2 to 3% (pT in TeV) 150 X0 Calo Material:non-gaussian tails when back-extrapolated • Inner Detector Standalone:~40%*pT 1.5 % (|h|<1.9)~200%*pT 3% (|h|=2.5)(pT in TeV) • Combination dominated by the Inner Detector below the cross-over point~40 to 80 GeV (20 GeV in forward region) S. Rosati - MC Workshop

  9. ATLAS – pT Resolution • Muon Standalone reconstruction in brief: - 10% resolution up to 1 TeV requires 50 mm sagitta resolution - Single point resolution ~80mm(MDT tracker – r-t calibration needed) - ~25 measurement points over the 3 stations • Alignment and calibration contribution becomes relevant above ~200 GeV • Alignment through optical system + alignment with tracks(e.g. data with field off/on) required ~20 mm alignment precision obtained during TB of a full-scale slice Contributions to the standalone resolution S. Rosati - MC Workshop

  10. pT (MeV) Low pT MuonReconstruction Low pT muons (pT5 GeV) do not reach the outer muon stations Extrapolate ID tracks and match with patterns of hits in the muon chambers s=40 MeV Efficiency S. Rosati - MC Workshop

  11. HZZ*4l Zbb tt GeV GeV GeV ATLAS - Muon Isolation Calorimeter Isolation - transverse energy ID Isolation, SpT • Isolation energies in a DR = 0.2 cone • Correlation between Inner Detector and Calo isolation ID vs Calo isolation S. Rosati - MC Workshop

  12. ATLAS - Muon Isolation Mean value of the transverse EM energy vs cone size Low and High Luminosity Pileup S. Rosati - MC Workshop

  13. Signal Zbb tt Impact Parameter Example: d0 significance in HZZ*4l event selection Reject Zbb and tt backgrounds d0 w.r.t. primary interaction vertex fitted s=13 mm Highest significance 2nd Highest S. Rosati - MC Workshop

  14. ATLAS - Cavern Background • High background level expected in the ATLAS experimental hall • Background particles originating from p+phadrons + interactions in: • ATLAS shielding, forward detectors, machine elements • Relevant for trigger (fake coincidences), reconstruction (pattern recognition), detectors ageing (~0.7 C/cm after 10 years LHC on MDT wires) Cavern background composition Rates S. Rosati - MC Workshop

  15. 10 keV Cavern Background Tracking detectors sensitivities to neutral particles- photons ~1% - neutrons ~0.1% Safety factors included in simulations to account for model uncertainties High rates of uncorrelated hits:e.g. at L=1034cm-2s-1, safety factor 5,30K hits in MDT chambers(~10% occupancy) Forward processes critical for the correct estimation of background production Propagation of low-energy g and n Energy distribution S. Rosati - MC Workshop

  16. Zmm Muon Standalones=3.0 GeV ATLAS - Performance Mass resolutions for benchmark physics processes Zmm fundamental to determine the detector mass scale with the first data, MS and MS-ID data HZZ*4m(M=130 GeV)s=1.9 GeV MuonCombined Zmm MuonCombined s=2.5 GeV S. Rosati - MC Workshop

  17. CMS Muon System 4 measurement stations interleaved with the iron yoke slabs 4T field in the Solenoid Drift Tubes and RPC in the Barrel CSC and RPC in endcap, RPC coverage up to |h|=1.6 S. Rosati - MC Workshop

  18. CMS LVL1 Trigger Two independent and redundant systemsDT+CSC or RPC, can be combined, together with calorimeters in a global trigger (GMT) Trigger coverage for single muons up to |h|=2.1 RPC Trigger will cover up to |h|=1.6 at the startup S. Rosati - MC Workshop

  19. CMS Muon Reconstruction Tracks are reconstructed in the muon spectrometer and back-extrapolated to the inner silicon tracker GEANE package for the propagation through calo and coil material Combined refit with vertex constraint S. Rosati - MC Workshop

  20. CMS Muon Identification • Muon Compatibility Values for two algs: • matching tracks with deposits in outer hadron calo • matching tracks with patterns in the inner muon chambers, not used for a standalone track fit • Cuts on discriminating values tunable for efficiency/purity Calorimeter Match Muon Detectors Match S. Rosati - MC Workshop

  21. CMS Muon Identification Reconstruction+identification efficiency for muons in b-jets (pT>5 GeV) Outside-in approach Inside-out approach(track in Inner Detectormatched with muon hits) S. Rosati - MC Workshop

  22. CMS - pT Resolution s(q/pT) for various momenta Combined reconstruction Standalone reconstruction S. Rosati - MC Workshop

  23. CMS pT Resolution Dp/p resolution in barrel and endcap S. Rosati - MC Workshop

  24. CMS Muon Isolation b-jet muon rejection vs efficiency for Wmn identification Three independent isolation criteria:- Energy deposits in calorimeters- Hits in pixel detector- Tracks reconstructed in inner tracker S. Rosati - MC Workshop

  25. CMS - Performance S. Rosati - MC Workshop

  26. CMS - Performance Zmm , reconstructed mass - 1 day of data taking at L=2•1033 cm-2s-1 - QCD background and pileup included Z’(1 TeV)mmin three scenarios: - Ideal geometry - First data misalignment - Long term misalignment Alignment exploiting inclusive single muons with pT>40 GeV and Zmm S. Rosati - MC Workshop

  27. In conclusione: competenze italiane • ATLAS-Muon (Bologna, Cosenza, Frascati, Lecce, Napoli, Pavia, Roma 1, Roma 2, Roma 3) • Trigger (Livello 1 barrel, Livello 2, Event Filter) • Calibrazione ed allineamento MDT • Simulazione del rivelatore, studi sul fondo di caverna • Ricostruzione standalone e combinata, online e offline, Analysis Software Framework • Analisi (Z+jets, HZZ*4l, A/hmm, Susy searches ) • CMS-Muon (Bari, Bologna, Napoli, Padova, Torino) • Trigger di Livello 1 con I DT • Simulazione/digitizzazione, trigger RPC • Ricostruzione, High Level Trigger, Analysis Software Framework • Analisi (HWW2m2n, HZZ2e2m, hmm, WW scattering) • Grazie a Ugo Gasparini per tutta la documentazione su CMS S. Rosati - MC Workshop

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