Post on 19-Dec-2015
28/2/2006 S. Rosati - MC Workshop 1
Muon Identification and Reconstruction
Stefano RosatiINFN – Roma 1
28/2/2006 S. Rosati - MC Workshop 2
Muon Detectors for LHCAspects 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 cleaner environment of the muon system
– Combination with inner tracking detectors to improve resolution
28/2/2006 S. Rosati - MC Workshop 3
ATLAS and CMS Experiements
• 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 ( and )
– 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 GeV pT
– Combined reconstruction needed to achieve optimal resolution– Less stringent requirements on muon tracking detectors resolution,
and on their calibration and alignment
Two approaches for the two experiments:
28/2/2006 S. Rosati - MC Workshop 4
ATLAS Muon Trigger – LVL1
• 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 and ) and time within geometrical windows in different trigger detector layers
Barrel Trigger
28/2/2006 S. Rosati - MC Workshop 5
ATLAS – Level 1 Trigger • Endcap Efficiency vs pT Threshold – acceptance up to ||<2.4
• Example trigger menus and final rates, after also LVL2 and Event Filter (for L=2•1033 cm-2s-1):1 20 GeV, 2 10 GeV (40 Hz)2 6 GeV (25 Hz)• Valid for both Barrel and Endcap
28/2/2006 S. Rosati - MC Workshop 6
3 points
angle-point
Ribs
sometimesangle-angle
3 points 3 points
angle-point
1TeV 5GeV
B
B
B~0
3 points 3 points
angle-point
1TeV 5GeV
B
B
B~0
Ribs
B~0
B
B
Initial layout angle-angle
Muon Reconstruction in ATLAS
28/2/2006 S. Rosati - MC Workshop 7
ATLAS - Combined Reconstruction• Tracks are back-extrapolated to
the IP
• Parameters corrected for energy
losses and multiple scattering
• Energy loss ~3 GeV at =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.
Detector acceptance
Initial layout
Combined reco efficiency
28/2/2006 S. Rosati - MC Workshop 8
ATLAS – pT Resolution
• -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 % (||<1.9)
~200%*pT 3% (||=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)
Resolution vs pT
28/2/2006 S. Rosati - MC Workshop 9
ATLAS – pT Resolution• Muon Standalone reconstruction in brief: - 10% resolution up to 1 TeV requires 50 m sagitta resolution
- Single point resolution ~80m (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 m alignment precision obtained during TB of a full-scale slice
Contributions to the standalone resolution
28/2/2006 S. Rosati - MC Workshop 10
Low pT Muon Reconstruction• Low pT muons (pT5 GeV) do not reach the outer muon stations
• Extrapolate ID tracks and
match with patterns of hits in
the muon chambers
pT (MeV)
=40 MeVEfficiency
28/2/2006 S. Rosati - MC Workshop 11
GeV
ATLAS - Muon IsolationGeV
GeV
HZZ*4lZbbtt
Calorimeter Isolation - transverse energy ID Isolation, pT
• Isolation energies in a R = 0.2 cone• Correlation between Inner Detector and Calo isolation
ID vs Calo isolation
28/2/2006 S. Rosati - MC Workshop 12
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 13
Impact Parameter
SignalZbbttHighest significance
2nd Highest
• d0 significance in HZZ*4l event selection• Reject Zbb and tt backgrounds• d0 w.r.t. primary interaction vertex fitted
s=13 mExample:
28/2/2006 S. Rosati - MC Workshop 14
ATLAS - Cavern Background• High background level expected in the ATLAS experimental hall• Background particles originating from p+phadrons + 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)
neutrons 53.94%
photons 43.15%
electrons 1.88%
protons 0.54%
positrons 0.21%
anti-neutrons 0.17%
muons (+-) 0.06%
Cavern background composition
Rates
28/2/2006 S. Rosati - MC Workshop 15
Cavern Background
10 keV
Energy distribution• 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 and n
28/2/2006 S. Rosati - MC Workshop 16
ATLAS - Performance
HZZ*4(M=130 GeV)=1.9 GeV
ZMuon Standalone=3.0 GeV
ZMuonCombined
=2.5 GeV
• Mass resolutions for benchmark physics processes• Zfundamental to determine the detector mass scale with the first data, MS and MS-ID data
MuonCombined
28/2/2006 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
||=1.6
28/2/2006 S. Rosati - MC Workshop 18
CMS LVL1 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 ||=2.1
• RPC Trigger will cover up to ||=1.6 at the startup
28/2/2006 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
28/2/2006 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/purityCalorimeter Match Muon Detectors Match
28/2/2006 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)
28/2/2006 S. Rosati - MC Workshop 22
CMS - pT Resolution• q/pT) for various momenta
Standalone reconstruction Combined reconstruction
28/2/2006 S. Rosati - MC Workshop 24
CMS Muon Isolation
• b-jet muon rejection
vs efficiency for W 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 26
CMS - Performance• Z , reconstructed mass - 1 day of data taking at L=2•1033 cm-2s-1
- QCD background and pileup included
• Z’(1 TeV) in three scenarios: - Ideal geometry - First data misalignment - Long term misalignment
• Alignment exploiting inclusive single muons with pT>40 GeV and Z
28/2/2006 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, HZZ*4l, A/hSusy 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 (HWW22, HZZ2e2, h, WW scattering)
• Grazie a Ugo Gasparini per tutta la documentazione su CMS