28/2/2006s. rosati - mc workshop1 muon identification and reconstruction stefano rosati infn –...

28/2/2006 S. Rosati - MC Workshop 1

Muon Identification and Reconstruction

Stefano RosatiINFN – Roma 1


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


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:


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


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


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


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


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


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


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


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


ATLAS - Muon Isolation

• Mean value of the

transverse EM energy

vs cone size

• Low and High

Luminosity Pileup


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:


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


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


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


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


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


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


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


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)


CMS - pT Resolution• q/pT) for various momenta

Standalone reconstruction Combined reconstruction


CMS pT Resolution• p/p resolution in barrel and endcap


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


CMS - Performance


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


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

28/2/2006s. rosati - mc workshop1 muon identification and reconstruction stefano rosati infn –...

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