Muon Identification and Reconstruction Stefano Rosati INFN Roma

Muon Identification and Reconstruction Stefano Rosati INFN – Roma 1 28/2/2006 S. Rosati - MC Workshop 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 – 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 Ro. I) with higher resolution and detail – Final level very close to offline reconstruction, running online on Ro. I data. • Offline reconstruction: provide optimal muon identification and momentum resolution over the p. T range 5 -1000 Ge. V – Standalone reconstruction can exploit the cleaner environment of the muon system – Combination with inner tracking detectors to improve resolution 28/2/2006 S. Rosati - MC Workshop 2

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 2 T 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 Scattering up to ~200 Ge. V p. T Combined reconstruction needed to achieve optimal resolution Less stringent requirements on muon tracking detectors resolution, and on their calibration and alignment 28/2/2006 S. Rosati - MC Workshop 3

ATLAS Muon Trigger – LVL 1 Barrel Trigger • Uses dedicated detector system based on RPCs and TGCs • Selection of events with muons above a given p. T 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 28/2/2006 S. Rosati - MC Workshop 4

ATLAS – Level 1 Trigger • Endcap Efficiency vs p. T Threshold – acceptance up to |h|<2. 4 • Example trigger menus and final rates, after also LVL 2 and Event Filter (for L=2 • 1033 cm-2 s-1): 1 m 20 Ge. V, 2 m 10 Ge. V (40 Hz) 2 m 6 Ge. V (25 Hz) • Valid for both Barrel and Endcap 28/2/2006 S. Rosati - MC Workshop 5

Muon Reconstruction in ATLAS 3 points Initial layout angle-angle B~0 angle-point B B sometimes angle-angle Ribs 28/2/2006 S. Rosati - MC Workshop 6

ATLAS - Combined Reconstruction • Tracks are back-extrapolated to the IP Combined reco efficiency • Parameters corrected for energy losses and multiple scattering • Energy loss ~3 Ge. V at h=0 • Look for match with tracks reconstructed in the ID • Combined refit of the two tracks • or: statistical combination of track parameters • Inner Detector in a Solenoidal Field of 2 T. 28/2/2006 Initial layout Detector acceptance S. Rosati - MC Workshop 7

ATLAS – p. T Resolution • m-Spectrometer Standalone: ~10%*p. T 2 to 3% (p. T in Te. V) Resolution vs p. T 150 X 0 Calo Material: non-gaussian tails when back-extrapolated • Inner Detector Standalone: ~40%*p. T 1. 5 % (|h|<1. 9) ~200%*p. T 3% (|h|=2. 5) (p. T in Te. V) • Combination dominated by the Inner Detector below the cross-over point ~40 to 80 Ge. V (20 Ge. V in forward region) 28/2/2006 S. Rosati - MC Workshop 8

ATLAS – p. T Resolution • Muon Standalone reconstruction in brief: Contributions to the standalone resolution - 10% resolution up to 1 Te. V requires 50 mm sagitta resolution - Single point resolution ~80 mm (MDT tracker – r-t calibration needed) - ~25 measurement points over the 3 stations • Alignment and calibration contribution becomes relevant above ~200 Ge. V • 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 28/2/2006 S. Rosati - MC Workshop 9

Low p. T Muon Reconstruction • Low p. T muons (p. T 5 Ge. V) do not reach the outer muon stations • Extrapolate ID tracks and match with patterns of hits in the muon chambers Efficiency s=40 Me. V p. T (Me. V) 28/2/2006 S. Rosati - MC Workshop 10

ATLAS - Muon Isolation Calorimeter Isolation - transverse energy ID Isolation, Sp. T H ZZ* 4 l Zbb tt Ge. V ID vs Calo isolation 28/2/2006 • Isolation energies in a DR = 0. 2 cone • Correlation between Inner Detector and Calo isolation Ge. V- MC Workshop S. Rosati 11

ATLAS - Muon Isolation • Mean value of the transverse EM energy vs cone size • Low and High Luminosity Pileup 28/2/2006 S. Rosati - MC Workshop 12

Impact Parameter Example: • d 0 significance in H ZZ* 4 l event selection • Reject Zbb and tt backgrounds • d 0 w. r. t. primary interaction vertex fitted s=13 mm Signal Zbb tt Highest significance 28/2/2006 S. Rosati - MC Workshop 2 nd Highest 13

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 neutrons 53. 94% photons 43. 15% electrons 1. 88% protons 0. 54% positrons 0. 21% anti-neutrons 0. 17% muons (+-) 0. 06% 28/2/2006 S. Rosati - MC Workshop Rates 14

Cavern Background • Tracking detectors sensitivities to neutral particles - photons ~1% - neutrons ~0. 1% Energy distribution • Safety factors included in simulations to account for model uncertainties • High rates of uncorrelated hits: e. g. at L=1034 cm-2 s-1, safety factor 5, 30 K hits in MDT chambers (~10% occupancy) • Forward processes critical for the correct estimation of background production • Propagation of low-energy g and n 28/2/2006 10 ke. V S. Rosati - MC Workshop 15

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* 4 m (M=130 Ge. V) s=1. 9 Ge. V 28/2/2006 Muon Combined S. Rosati - MC Workshop Z mm Muon Standalone s=3. 0 Ge. V Z mm Muon Combined s=2. 5 Ge. V 16

CMS Muon System • 4 measurement stations interleaved with the iron yoke slabs • 4 T field in the Solenoid • Drift Tubes and RPC in the Barrel • CSC and RPC in endcap, RPC coverage up to |h|=1. 6 28/2/2006 S. Rosati - MC Workshop 17

CMS LVL 1 Trigger • Two independent and redundant systems DT+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 28/2/2006 S. Rosati - MC Workshop 18

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 28/2/2006 S. Rosati - MC Workshop 19

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 28/2/2006 Muon Detectors Match S. Rosati - MC Workshop 20

CMS Muon Identification • Reconstruction+identification efficiency for muons in b-jets (p. T>5 Ge. V) Outside-in approach Inside-out approach (track in Inner Detector matched with muon hits) 28/2/2006 S. Rosati - MC Workshop 21

CMS - p. T Resolution • s(q/p. T) for various momenta Standalone reconstruction 28/2/2006 Combined reconstruction S. Rosati - MC Workshop 22

CMS p. T Resolution • Dp/p resolution in barrel and endcap 28/2/2006 S. Rosati - MC Workshop 23

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 28/2/2006 S. Rosati - MC Workshop 24

CMS - Performance 28/2/2006 S. Rosati - MC Workshop 25

CMS - Performance • Z mm , reconstructed mass - 1 day of data taking at L=2 • 1033 cm-2 s-1 - QCD background and pileup included • Z’(1 Te. V) mm in three scenarios: - Ideal geometry - First data misalignment - Long term misalignment • Alignment exploiting inclusive single muons with p. T>40 Ge. V and Z mm 28/2/2006 S. Rosati - MC Workshop 26

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* 4 l, 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 2 m 2 n, H ZZ 2 e 2 m, h mm, WW scattering) • Grazie a Ugo Gasparini per tutta la documentazione su CMS 28/2/2006 S. Rosati - MC Workshop 27