# Presentation: 304138

## ATLAS muon system performance

- David Adams
- Brookhaven National Laboratory
- May 29, 2006

- ATLAS Trigger and Physics Workshop
- Muon Trigger and Combined Performance Session

*Updated 19:00 May 29, 2006*

## Contents

- Goals
- AOD muons
- Selecting muons
- Performance evaluation
- Monte Carlo muons
- Matching
- Performance parameters
- Example results
- Summary results
- Efficiency
- Fakes/event
- Fakes/reals

- Type contributions to efficiency and fakes
- Misreconstructed fraction
- Type contributions to good efficiency and misrecos
- Resolutions
- PTsum tail
- Summary comments
- Issues
- Conclusions

- Event Data History           David Adams   BNL

- December 2001

## Goals

- Assess the performance of the muon reconstruction software
- Release 11.0.X
- CSC production samples
- Examine the view presented for physics analysis
- Two AOD collections
- MuidMuonCollection
- StacoMuonCollection
- Learn how to select a sensible set of muons from these collections
- Kinematic and quality cuts
- Establish metrics for evaluating performance
- Efficiency, fake rate, resolutions, ...
- For different selections
- As functions of kinematic variables

- Event Data History           David Adams   BNL

- December 2001

## AOD muons

- AOD has two muon containers
- StacoMuonCollection
- MuidMuonCollection
- Each muon has one or more of four track particles
- inDetTrackParticle
- Inner detector track, e.g. from low-pT algorithm
- muonSpectrometerTrackParticle
- From standalone muon finding
- Parameters at entrance to the muon system
- muonExtrapolatedTrackParticle
- Previous extrapolated to the beamline DCA
- combinedMuonTrackParticle
- Combination of inner and standalone muon tracks

- Event Data History           David Adams   BNL

- December 2001

## AOD muons

- I divide these into four categories
- Combined (0100)
- Have  a combined inner detector and muon spectrometer track,
- are “best match” and
- have good fit and match chi-squares
- Split (1000)
- Combined with bad fit or match chi-square
- Inner detector track is used
- Standalone (0010)
- Tracks which have an muon spectrometer track propagated to the beam line
- Excluding combined or split if enabled
- Inner (0001)
- Muons which have an inner detector track but do not have a muon spectrometer track

- Event Data History           David Adams   BNL

- December 2001

## AOD muons (cont )

- Quality parameters
- Needed to distinguish real from fake muons
- Fit and match chi-squares are present but don’t provide much discrimination
- Isolation helps but we don’t want to lose all non-isolated muons
- There are methods to return the number of hits for each detector type but they return incorrect values
- Associated digit counts are available only for Muid low-pT
- I use a crude cut to reduce the number of Muid low-pT fakes
- It would be very helpful to have information about misses, i.e. active detectors that were crossed with no hit or segment found
- Inner detector calls these “holes” and, for selected subdetectors, records the number of such layers
- Complicated muon geometry would probably be better handled with some sort of likelihood estimate for each miss and/or the whole track

- Event Data History           David Adams   BNL

- December 2001

## Selecting muons

- I use the following job options to select muons:
- Name of the muon container (Staco... or Muid...)
- Flags indicating which categories of muons to accept
- I consider three cases for each of the two containers:
- 0010 = standalone only
- 0100 = combined only
- 1111 = all four (combined, split, standalone and inner)
- Kinematic cuts
- pT above some threshold (3 GeV/c in the following)
- abs(z0) (z at the DCA) below some value (not used)
- Fit chi-square limit for all track types
- Fit chi-square/DOF (below 100.0)
- Loose to allow for kinks (brem); tighter cuts follow

- Event Data History           David Adams   BNL

- December 2001

## Selecting muons

- Chi-square limits to define good combined muons
- Fit chi-square/DOF below 5.0
- Match chi-square below 20.0
- Those above these values are “split”
- Isolation
- Muon is said to be isolated if it has an isolation energy less than 10 GeV (0.45. cone)
- Split, standalone and inner muons are required to be isolated
- Non-isolated, combined muons are subject to tight chi-square cuts
- Fit chi-square below 2.5
- Match chi-square below 10.0
- Associated digit counts
- Muid low-pT (inner) muons are required to have more than 10 digits (precision or trigger)
- To reduce the large number of fakes

- Event Data History           David Adams   BNL

- December 2001

## Selecting muons

- Overlaps
- Muons are said to have spatial overlap if they are within dR of 0.50
- The following are removed:
- Split, standalone and inner muons overlapping a combined muon
- Split and standalone muons overlapping an inner muon
- Inner muons overlapping an inner muon with smaller fit chi-square
- Shared tracks
- Muons may removed if they share tracks with another muon
- The following would be removed
- Combined muons sharing any track with a combined muon with larger match chi-square
- Split, standalone and inner sharing any track with a combined muon
- Split muons sharing an inner track with an inner muon.
- However, *shared track cuts were not applied because some muons in the Muid container have invalid track assignments*
- Expect that shared track filter is redundant with overlap filter
- Future studies will likely add shared filter and reduce the filtering in the overlap filter

- Event Data History           David Adams   BNL

- December 2001

## Selecting muons

- Cut summary
- Container: Muid or Staco
- Categories: standalone (0100), combined (0010) or all (1111)
- Kinematics: pT > 3 GeV/c, no cut on z0
- Chi-square/DOF (all muons): below 100.0
- Combined/split discrimination (split if either fails)
- Fit chi-square/DOF below 5.0
- Match chi-square below 20.0
- Isolation: 10 GeV/c in 0.45 cone
- Split, standalone and inner muons required to be isolated
- Chi-squares for non isolated combined muons:
- Fit chi-square/DOF below 2.5
- Match chi-square below 10.0
- Muid inner muons required to have more than 10 digits
- Overlaps removed if dR below 0.5
- Shared track filter disabled

- Event Data History           David Adams   BNL

- December 2001

## Performance evaluation

- For Monte Carlo samples, we can evaluate the performance of the muon reconstruction using truth information
- Select a collection of reconstructed muons (evaluation sample)
- Select a collection of Monte Carlo muons (reference sample)
- Match the two (one reco to one MC)
- Efficiency is (# matched MC)/(# MC)
- Fake rate is the (# unmatched reco)/event
- Compare matched reco and MC parameters to calculate resolutions and fraction of misreconstructed tracks
- Following sections describe
- Selection of MC muons
- Matching algorithm
- Precise definitions of efficiency, fake rate, ...
- Results for selected CSC samples

- Event Data History           David Adams   BNL

- December 2001

## Monte Carlo muons

- Monte Carlo muons are taken from the truth particle container
- Includes prompt muons and those produced in the tracking volume
- Assume all such muons (above our pT threshold) are recorded
- Monte Carlo selections:
- Loose selection to construct the reference sample for matching
- Use final state particles (ATLAS algorithm)
- pT above job option threshold (2 GeV/c in the following)
- PDG ID must correspond to muon (+/-13)
- Tight selection to evaluate efficiency (after matching)
- Increase pT threshold (4 Gev/c)
- Maximum value for eta (2.7)
- Maximum value for muon production radius (2 cm)
- All can be set with job options

- Event Data History           David Adams   BNL

- December 2001

## Matching

- Each reconstructed track is matched to the nearest MC track
- Using reco-to-MC distance DR = sqrt[(TR – TMC) WR (TR – TMC)]
- TR = reconstructed track vector
- WR = inverse of error matrix for track vector
- TMC = Monte Carlo value for the track vector
- If no MC track is found within some maximum distance DRmax, then the reconstructed track is left unmatched
- In the following, DRmax is set to 1000
- A MC-to-reco distance is calculated for each match: DMC =
- sqrt[((R-MC)/)2 + ((R-MC)/)2  + ((pTR-pTMC)/pTMC/pTrat)2 ]
- Matches with DMC > DMCmax are dropped
- DMCmax, ,andpTrat are all job options
- For this study: 100, 0.005, 0.005 and 0.03 were used

- Event Data History           David Adams   BNL

- December 2001

## Matching (cont)

- Only one reco track is allowed to match each MC track
- Matches with larger DMC are dropped
- Not DR because it favors tracks with large errors
- Tracks classified according to their match status
- Matched tracks are ***found***
- Unmatched MC tracks are ***lost***
- Unmatched reco tracks are ***fake**** *
- Found tracks are well-reconstructed (***good***) if
- DR < DRgood and DMC < DMCgood
- Limits are job options
- Both set to 10 for this study
- Good tracks are used to evaluate resolutions
- Tracks found but not good are called ***bad*** or ***misreconstructed***
- Efficiency and resolutions are calculated using tight MC cuts

- Event Data History           David Adams   BNL

- December 2001

## Matching (cont)

*Found*

*Lost*

*Fake*

*Matching example*

*Reco*

*MC*

- Event Data History           David Adams   BNL

- December 2001

## Matching (cont)

*Reco-to-MC distance*
*whbb, Muid combined*

- Event Data History           David Adams   BNL

- December 2001

## Matching (cont)

*MC-to-reco distance*
*whbb, Muid combined*

- Event Data History           David Adams   BNL

- December 2001

## Matching (cont)

- MC parameter summary
- Efficiency is presented for all MC muons with
- pT > 4 GeV/c
- eta < 2.7
- r0 < 2.0 cm
- Found muons are labeled as “good” if
- DMC < 10.0
- DR < 10.0
-  =  = 0.005
-  pTrat = 0.03

- Event Data History           David Adams   BNL

- December 2001

## Performance parameters

- The following are used to evaluate the performance
- Efficiency = (# found) / (# MC)
- Good fraction = (# good) / (# found)
- Misreco fraction = 1 – (good fraction)
- Good efficiency = (# good) / (# MC)
- Fakes/event = (# fake) / (# events)
- Fakes/reals = (# fake) / (# found)
- Resolution in X = RMS of (XR – XMC)
- X may be , , pT or any of the track parameters
- Evaluated for good (well-reconstructed) tracks
- In addition, pTsum tails are calculated
- Each event, vector sum over pT is calculated for both MC and reco muons
- The magnitude of the vector difference between these sums is calculated
- Fraction of events with this difference exceeding some threshold is the pTsum tail

- Event Data History           David Adams   BNL

- December 2001

## Example results

- Following slides show some example plots
- Efficiency
- Fakes
- pT sum

- Event Data History           David Adams   BNL

- December 2001

## Found

*Found*

*Lost*

- Event Data History           David Adams   BNL

- December 2001

## Fakes

*Fakes*

- Event Data History           David Adams   BNL

- December 2001

## MC

*MC*

*Found*

*Residual*

- Event Data History           David Adams   BNL

- December 2001

## Summary results

- Summary results are presented on the following pages
- Six sets of muons:
- Staco and Muid for three cases
- Standalone
- Combined
- All (combined, split, standalone and inner)
- Eleven datasets
- s050 - csc11.007231.singlepart_mu50.recon.AOD.v11004103
- s100 - csc11.007233.singlepart_mu100.recon.AOD.v11004103
- zmm - csc11.005151.McAtNloZmumu.recon.AOD.v11004103
- wmu - csc11.005101.JimmyWmunu.recon.AOD.v11004103
- whbb - csc11.005850.WH120bb_pythia.recon.AOD.v1100410
- h1304l - csc11.005300.PythiaH130zz4l.recon.AOD.v11004103_bnl
- h170wwll - csc11.005320.PythiaH170wwll.recon.AOD.v11004107
- G500mm - csc11.005621.Gmm_500_pythia_photos.recon.AOD.v11004103
- j1 - csc11.005010.J1_pythia_jetjet.recon.AOD.v11004103
- j3 - csc11.005012.J3_pythia_jetjet.recon.AOD.v11004103
- j6 - csc11.005015.J6_pythia_jetjet.recon.AOD.v11004103

- Event Data History           David Adams   BNL

- December 2001

## Efficiency

- Event Data History           David Adams   BNL

- December 2001

## Fakes/event

- Event Data History           David Adams   BNL

- December 2001

## Fakes/reals

- Event Data History           David Adams   BNL

- December 2001

## Type contributions to efficiency and fakes

- Event Data History           David Adams   BNL

- December 2001

## Misreconstructed fraction

- Event Data History           David Adams   BNL

- December 2001

## Type contributions to good efficiency and misrecos

- Event Data History           David Adams   BNL

- December 2001

## Resolutions

- Event Data History           David Adams   BNL

- December 2001

## Resolutions (cont)

- Event Data History           David Adams   BNL

- December 2001

## Resolutions (cont)

- Event Data History           David Adams   BNL

- December 2001

## Resolutions (cont)

- Event Data History           David Adams   BNL

- December 2001

## Resolutions (cont)

- Event Data History           David Adams   BNL

- December 2001

## Resolutions (cont)

- Event Data History           David Adams   BNL

- December 2001

## Resolutions (cont)

- Event Data History           David Adams   BNL

- December 2001

## Resolutions (cont)

- Event Data History           David Adams   BNL

- December 2001

## pT sum tail

- Event Data History           David Adams   BNL

- December 2001

## pT sum tail (cont)

- Event Data History           David Adams   BNL

- December 2001

## pT sum tail (cont)

- Event Data History           David Adams   BNL

- December 2001

## Summary comments

- Standalone
- Both Muid and Staco do a good job of finding isolated muons
- Efficiency: 95% in single muon, Z and W samples
- 80% in busier Higgs events
- Falls dramatically in high-pT jets
- Due to isolation cut required to reduce fakes
- Need some work here to improve crude isolation cut
- Probably best to calculate a likelihood during reconstruction that can be used to discriminate between reals and fakes
- Fakes are 2-5X worse in Muid
- In j6, Muid is 0.02/event, Staco is 0.007/event
- Resolutions and pT sum residuals are similar

- Event Data History           David Adams   BNL

- December 2001

## Summary comments (cont)

- Combined
- Staco efficiency is better
- 3-5% in single muons and high-pT samples
- 10-15% in jets
- Efficiencies flat around 88% for Staco
- Much of the decrease from standalone is due to the eta coverage of inner tracker
- Fakes, resolutions and pt sum residuals are similar for Staco and Muid
- Fakes up to 0.05/event in j6
- Muid has 3-8X fewer misreconstructed muons in high-pT samples
- But Staco and Muid are the same in the dijet events

- Event Data History           David Adams   BNL

- December 2001

## Summary comments (cont)

- All (combined, split, standalone and inner)
- Staco and Muid efficiencies similar in high pT events: 95%
- In jets, Staco performs better
- For j6, Staco is 86%, Muid is 73%
- Staco fakes range from comparable to 2X less than Muid
- Muid getting efficiency boost and fakes from inner muons
- Misreconstructed fractions and resolutions are similar
- Staco has slightly better pT resolution
- Muid is slightly better with eta and phi resolutions
- pT sum residual
- In both cases, combined does better than all
- Less fakes and misrecos more important than extra efficiency (mostly at high eta)
-  Staco tails are generally 2-3X lower than those for Muid
- But Staco and Mui jet results for combined muons are very similar

- Event Data History           David Adams   BNL

- December 2001

## Issues

- Hit counts are missing or wrong in the Muid AOD
- Could use this as a measure of track quality
- There are incorrect track assignments in the Muid AOD
- Cannot filter muons with shared tracks
- Poor fit quality at high eta
- Presumably due to CSC problems
- Need better AOD handles to discriminate against fakes for inner (low-pT) tracks
- E.g. likelihood that track would produce the observed signals (and absence of signals) in the muon detectors

- Event Data History           David Adams   BNL

- December 2001

## Issues (cont)

- Like to have track positions at muon spectrometer “entrance”
- To filter standalone overlaps
- Some common surface (cylinder for central, z-plane for endcaps)
- Or can (and should) we use the muon spectrometer track particle?
- Like to have truth muons produced outside tracking volume
- To identify “fakes” due to pi/K decays in calorimeter
- Like to make use of calorimeter information in finding
- Find muons where muon spectrometer is blind
- E.g. Wisconsin topo cluster method
- YATA (Yet Another Tracking Algorithm)

- Event Data History           David Adams   BNL

- December 2001

## Conclusions

- It is now (release 11.0.X) possible to analyze AOD muons from both Staco and Muid
- Very similar analysis algorithms
- Allows direct comparison
- Good performance for combined muons for either collection
- Efficiency 80-90%
- Fakes around 0.01/event approaching 0.1/event in high-pT jets
- Addition of split, standalone and inner muons improve performance
- Efficiency increases to 95% for high-pT muon
- Biggest gain at high eta
- Fakes kept at similar levels with isolation cuts
- Require all split, standalone and inner muons to be isolated
- Apply tighter cuts for non-isolated combined muons
- Need better discriminants (and more work) to simultaneously improve efficiency and fake rejection

- Event Data History           David Adams   BNL

- December 2001