# Presentation: 683958

## ATLAS muon system performance

- David Adams
- Brookhaven National Laboratory
- April 20, 2006

- BNL Analysis Meeting

*Updated 15:00 April 21, 2006*

## Contents

- Goals
- AOD muons
- Selecting muons
- Performance evaluation
- Monte Carlo muons
- Matching
- Performance parameters
- Datasets
- Results for whbb, Muid combined
- Summary results
- 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 (cont )

- Quality parameters
- Needed to distinguish real from fake muons
- Fit and match chi-squares are present but don’t provide much discrimination
- Still need to look at this jets
- 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, 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 track particle to accept:
- Combined, standalone (extrapolated), inner
- 010 = standalone
- 100 = combined
- 111 = combined, standalone and inner
- Muon is accepted if it has the track corresponding to a set flag
- If multiple track particles match, the first in the above order is used
- Kinematic cuts
- pT above some threshold (3 GeV/c in the following)
- abs(z0) (z at the DCA) below some value (20 cm in the following)
- Associated digit counts
- Minimum # precision digits (1 for “filtered” muons)
- Minimum # trigger digits (16 for “filtered” muons)
- These are only required for low-pT tracks in the Muid container

- 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 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
- DMC, ,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)

*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)

*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)

- 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 < DMCgood and DR < DMCgood
- Limits are job options
- Both set to 10 for this study
- Good tracks are used to evaluate resolutions
- Efficiency and resolutions are calculated using tight MC cuts

- 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)
- Good efficiency = (# good) / (# MC)
- Fake rate = (# fake) / (# events)
- 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
- For each event, the vector sum over pT is calculated for both MC and reco muons
- The magnitude of the vector difference between the reco and MC sums is calculated
- The fraction of events with this difference exceeding some threshold is the pTsum tail

- Event Data History           David Adams   BNL

- December 2001

## Datasets

- The following datasets were examined
- s050 - csc11.007231.singlepart_mu50.recon.AOD.v11004103
- s100 - csc11.007233.singlepart_mu100.recon.AOD.v11004103
- pyzmm - csc11.005145.PythiaZmumu.recon.AOD.v11004103
- mczmm - csc11.005151.McAtNloZmumu.recon.AOD.v11004103
- whbb - csc11.005850.WH120bb_pythia.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

## Results for whbb, Muid combined

*phi*

*eta*

*pT*

- Event Data History           David Adams   BNL

- December 2001

## Results for whbb, Muid combined (cont)

*phi*

*eta*

*pT*

- Event Data History           David Adams   BNL

- December 2001

## Results for whbb, Muid combined (cont)

*Resolutions*

*dpT/pT*

*eta*

*phi*

- Event Data History           David Adams   BNL

- December 2001

## Results for whbb, Muid combined (cont)

*Ptsum residual*

- Event Data History           David Adams   BNL

- December 2001

## Summary results

- Summary results are presented on the following pages
- Seven sets of muons
- Three Staco and four Muid
- Seven datasets

- Event Data History           David Adams   BNL

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## Conclusions

- To come...

- Event Data History           David Adams   BNL

- December 2001