Cosmic and Beam-Halo Muon Reconstruction Algorithms

Complete:

Goal of the page

This page is intended to familiarize you with the modules in the RecoMuon/CosmicMuonProducer package, which is dedicated to the reconstruction of muons originating outside of the detector, i.e., cosmic and beam-halo muons, using the muon system alone and the combination of the muon system and the silicon tracker.

Contacts

Chang Liu (Chang.Liu@cernNOSPAMPLEASE.ch)

Introduction

The cosmic muon reconstruction package is designed to reconstruct muon trajectories that originate from outside of the CMS detector, i.e. cosmic muons and beam-halo muons. It is different from the standard muon reconstruction (aimed at reconstructing muons produced in pp collisions) in that it uses different assumptions on the origin of the muons and has more flexibilities. The package is released as a part of official CMSSW and is used in official data processing of cosmic runs starting with MTCC in 2006.

It consists of 3 parts: 1) muon seed generator (in RecoMuon/CMS.MuonSeedGenerator package), which generates TrajectorySeed for further reconstruction; 2) cosmic muon reconstructor, which builds muon trajectories within the muon system alone; and 3) global cosmic muon reconstructor, which builds muon trajectories using both the muon and the tracker systems.

Definitions

The cosmic muons may traverse the whole detector, so usual definitions of "innermost" and "outermost" states do not have much meaning. Therefore, we use a more general definition. The innermost state is defined as the point where the muon enters the detector. The outermost state is defined as the point where the muon leaves the detector. For cosmic muons, the innermost states are typically located above the outermost states (a vast majority of muons is downward-going).

The parameters of tracks (e.g. Track::pt(), Track::eta(), ...) are usually defined according to the states closest to interaction point. Again, this state does not have much meaning for cosmic muons, so one should be careful in using these parameters. To compare reconstructed and generated cosmic muons, it is better to compare the parameters at the innermost state instead of the parameters in reco::Track objects.

Usage of the algorithm

• One can use the cosmic-muon reconstruction algorithm to build cosmic and beam-halo muons after the local muon reconstruction.
• The cosmicMuons modules require the result of muon local reconstruction. The globalCosmicMuons require the result of cosmicMuons and the reconstruction of tracker tracks, e.g., cosmictrackfinder.

Parameters of CosmicMuonSeed

• Enable[DT,CSC]Measurement are the flags to choose different muon subsystems.

Parameters of cosmicMuons

• Enable[DT,CSC,RPC]Measurement in TrajectoryBuilderParameters are the flags to choose different muon subsystems.
• BuildTraversingMuon in TrajectoryBuilderParameters is the flag to allow building trajectories crossing 2 halves of the detector, e.g., from top to bottom, or from left to right. Usually the option of BuildTraversingMuon with true is called 1-leg option, while 2-leg option means it's false, thus the trajectories on different halves are built separately.

Parameters of globalCosmicMuons

• TkTrackCollectionLabel in TrajectoryBuilderParameters is the flag to choose corresponding reconstruction algorithm of tracker tracks.

Other configuration parameters are intended to be used by experts only.

Some widely-used notations:

Notation	Description
BarrelOnly	Switch off all CSC and RPC in endcap
EndcapsOnly	Switch off all DT and RPC in barrel
Traversing	Muon track appears in two hemispheres of the detector
1Leg	Allow building traversing muons

Documentation

• The description of algorithm is documented in CMS Note 2008/001 and Euro. Phys. J. C.
• A presentation on the subject is here (a little bit old, but including all aspects): talk about cosmic muon reconstruction at the muon POG meeting Feb. 27 2007.
• A few illustrations of the work of cosmic-muon reconstructor can be found on this TWiki page.

Cosmic and Beam-Halo Muon Reconstruction Algorithms in CRUZET, beam test, and CRAFT

Detailed description of available data sets, skims, etc. can be found here.

Muon collections available prior to CMSSW_2_2_4

This section describes muon collections produced in the official processing of cosmic data performed with CMSSW versions prior to CMSSW_2_2_4. This includes prompt reconstruction and 1st reprocessing of 2008 CRAFT data. For recent reprocessing of CRAFT data, refer to the next section.

The cosmic muon producer produces the following reco::TrackCollections:

reco::TrackCollection; Muon and Tracker System	reco::TrackCollection; Muon System alone	Description	Input
globalCosmicMuons	cosmicMuons	Enable all detectors and using 2-leg option	CosmicMuonSeed, Segments, Hits
globalCosmicMuons1LegBarrelOnly	cosmicMuons1LegBarrelOnly	Enable barrel-only detectors and using 1-leg option	CosmicMuonSeed, DT Segments, Hits
globalCosmicMuonsNoDriftBarrelOnly	cosmicMuonsNoDriftBarrelOnly	Enable barrel-only detectors (with "No-Drift" option of the DT local reco algorithm) and using 1-leg option	CosmicMuonSeed, DT Segments, Hits
globalCosmicMuonsBarrelOnly	cosmicMuonsBarrelOnly	Enable barrel-only detectors and using 2-leg option	CosmicMuonSeed, DT Segments, Hits
globalCosmicMuonsEndCapsOnly	cosmicMuonsEndCapsOnly	Enable endcap-only detectors and using 2-leg option	CosmicMuonSeed, CSC Segments, Hits

For 2-leg option globalCosmicMuons, the tracks share the same tracker track, but use different standalone-muon tracks on opposite halves of the detector. For 1-leg option globalCosmicMuons1LegBarrelOnly, the tracker track is sandwiched in the middle between the 2 halves of the 1-leg cosmicMuons1LegBarrelOnly and a global refit is done outside-in and inside-out.

The following collections of muon candidates built using information in the muon system alone (i.e., standalone muons) are available:

reco::MuonCollection	reco::TrackCollection	Description
STAMuons	cosmicMuons	Enable all detectors and using 2-leg option
STAMuons1LegBarrelOnly	cosmicMuons1LegBarrelOnly	Enable barrel-only detectors and using 1-leg option
STAMuonsNoDriftBarrelOnly	cosmicMuonsNoDriftBarrelOnly	Enable barrel-only detectors (with "No-Drift" option of the DT local reco algorithm) and using 1-leg option
STAMuonsBarrelOnly	cosmicMuonsBarrelOnly	Enable barrel-only detectors and using 2-leg option
STAMuonsEndCapsOnly	cosmicMuonsEndCapsOnly	Enable endcap-only detectors and using 2-leg option

In order to facilitate access to the muon candidates, standalone muons reconstructed by each of the above 5 versions of the cosmic muon reconstructor are available both as reco::MuonCollections (1st column) and reco::TrackCollections (2nd column). Muons stored as reco::Muon objects (names starting with "STAMuons") contain references to the corresponding reco::Track objects (names starting with "cosmicMuons").

These collections of standalone muons are used to reconstruct muon candidates combining information in the silicon tracker with that in the muon system (i.e., global muons). The following collections of global muons are available:

reco::MuonCollection	reco::TrackCollection	Description
GLBMuons	globalCosmicMuons	Enable all detectors and using 2-leg option
GLBMuons1LegBarrelOnly	globalCosmicMuons1LegBarrelOnly	Enable barrel-only detectors and using 1-leg option
GLBMuonsNoDriftBarrelOnly	globalCosmicMuonsNoDriftBarrelOnly	Enable barrel-only detectors (with "No-Drift" option of the DT local reco algorithm) and using 1-leg option
GLBMuonsBarrelOnly	globalCosmicMuonsBarrelOnly	Enable barrel-only detectors and using 2-leg option
GLBMuonsEndCapsOnly	globalCosmicMuonsEndCapsOnly	Enable endcap-only detectors and using 2-leg option

Similarly to the standalone muons, global muons reconstructed by each of the above 5 versions of the global cosmic muon reconstructor are available both as reco::MuonCollections (1st column) and reco::TrackCollections (2nd column). Muons stored as reco::Muon objects (names starting with "GLBMuons") contain references to the corresponding reco::Track objects (names starting with "globalCosmicMuons").

For each version of the cosmic muon reconstructor, references to the tracker tracks, standalone muon tracks and global muon tracks are also assembled into one single collection of reco::Muon objects:

reco::MuonCollection	reco::TrackCollections	Description
muons	globalCosmicMuons, cosmicMuons, ctfWithMaterialTracksP5	Enable all detectors and using 2-leg option
muons1LegBarrelOnly	globalCosmicMuons1LegBarrelOnly, cosmicMuons1LegBarrelOnly, ctfWithMaterialTracksP5	Enable barrel-only detectors and using 1-leg option
muonsNoDriftBarrelOnly	globalCosmicMuonsNoDriftBarrelOnly, cosmicMuonsNoDriftBarrelOnly, ctfWithMaterialTracksP5	Enable barrel-only detectors (with "No-Drift" option of the DT local reco algorithm) and using 1-leg option
muonsBarrelOnly	globalCosmicMuonsBarrelOnly, cosmicMuonsBarrelOnly, ctfWithMaterialTracksP5	Enable barrel-only detectors and using 2-leg option
muonsEndCapsOnly	globalCosmicMuonsEndCapsOnly, cosmicMuonsEndCapsOnly, ctfWithMaterialTracksP5	Enable endcap-only detectors and using 2-leg option

Muon candidates stored in these 3-in-1 reco::MuonCollections (1st column; names starting with "muons") have links to reco::Track objects containing a standalone-muon track (cosmicMuons* collections), tracker-only track (ctfWithMaterialTracksP5 collection), and to a combined global-muon track (globalCosmicMuons* collections). These "summary" collections of reco::Muons are similar to muon collections used in Monte Carlo prodictions of various physics samples, whereas reco::Muons collections outlined in the previous tables are more limited in scope (GLBMuons have one single link to a global muon, and STAMuons have one single link to a standalone muon).

Finally, there are two reco::Muon collections with tracks reconstructed by the standard "collision-like" reconstruction of standalone muons. They have names beginning with lhc: lhcStandAloneMuonsBarrelOnly and lhcStandAloneMuonsEndCapsOnly. So far, standard global-muon reconstruction algorithms have not been used in the processings of CRAFT and CRUZET data.

More information can be found from a presentation on the muon reconstruction performance during CRUZET and a study of reconstruction performance and analysis of CRAFT data.

Muon collections available starting with CMSSW_2_2_4

The following collections are produced in the reprocessing of CRAFT data with CMSSW_2_2_4:

reco::MuonCollection	Tracker-only reco::TrackCollection	Standalone-muon reco::TrackCollection	Global-muon reco::TrackCollection	Description
muons	ctfWithMaterialTracksP5LHCNavigation	cosmicMuons	globalCosmicMuons	Enable all detectors and use 2-leg option. The 2 legs of globalCosmicMuons do not share tracker hits (tracker reco uses LHC-like navigation). Warning: the 2-leg BarrelOnly and EndCapsOnly collections below do share tracker hits, as they use the ctfWithMaterialTracksP5 tracker collection (for alignment)
muons1Leg	ctfWithMaterialTracksP5	cosmicMuons1Leg	globalCosmicMuons1Leg	Enable all detectors and use 1-leg option
muonsBarrelOnly	ctfWithMaterialTracksP5	cosmicMuonsBarrelOnly	globalCosmicMuonsBarrelOnly	Enable barrel-only detectors and use 2-leg option
muonsEndCapsOnly	ctfWithMaterialTracksP5	cosmicMuonsEndCapsOnly	globalCosmicMuonsEndCapsOnly	Enable endcap-only detectors and use 2-leg option
muonsBeamHaloEndCapsOnly	ctfWithMaterialTracksBeamHaloMuon	cosmicMuonsEndCapsOnly	globalBeamHaloMuonEndCapsOnly	Enable endcap-only detectors and use 2-leg option; for studies of beam-halo muons
muonsNoRPC	ctfWithMaterialTracksP5	cosmicMuonsNoRPC	globalCosmicMuonsNoRPC	Enable all detectors and use 2-leg option but no RPC; for performance study of reconstruction
splitMuons	splittedTracksP5	cosmicMuons	globalCosmicSplitMuons	Enable all detectors and use 2-leg option. The 2 legs of globalCosmicSplitMuons do not share tracker hits (tracker ctfWithMaterialTracksP5 collection split in two)

Muon candidates stored in the reco::MuonCollections (1st column) contain links to reco::TrackCollections of reco::Track objects: tracker-only track (2nd column), standalone-muon track (3rd column), and a combined global-muon track (4th column).

STAMuons and GLBMuons no longer exist -- only the combined muons* and splitMuons muon collections remain. The lhc* sequences remain the same as in previous rounds of CRAFT data processing.

Silicon track collections

Tracker-only reco::TrackCollection	Description
ctfWithMaterialTracksP5LHCNavigation	using default ctfWithMaterialTracks algorithm and default LHC-like algorithm (LHCNavigation) to find compatible layers (no traversing allowed)
ctfWithMaterialTracksP5	using default ctfWithMaterialTracks algorithm and cosmic-adapted algorithm to find compatible layers (traversing allowed)
splittedTracksP5	split the ctfWithMaterialTracksP5 TrackCollection into two collections of tracks reconstructed in two halves of the tracker
ctfWithMaterialTracksBeamHaloMuon	allow Tracks to cross 2 tracker endcaps

For a typical "Good" muon, one would expect 2 cosmicMuons, 1 cosmicMuons1Leg, 1 ctfWithMaterialTracksP5, 2 splittedTracksP5, 2 globalCosmicMuons, 1 globalCosmicMuons1Leg, 2 splitMuons, ..., etc.

Release-specific instruction

The GREN data can be access from, for example, /castor/cern.ch/cms/store/data/GlobalNov07/A/000/030/333/RAW/0000. The data themselves are already processed with cosmicMuons in HLT path. However, one can reprocess with CMSSW_1_7_5 and V00-06-03 tag of RecoMuon/CosmicMuonProducer, which has been greatly improved. If you want to build trajectory crossing the whole detector, keep BuildTraversingMuons as true, otherwise make it false, then it will stop in the first hemisphere (usually the top one). Please see attached cosmicGREN.cfg for an example.

Review status

Reviewer/Editor and Date (copy from screen)	Comments
ChangLiu - 14 Feb 2008	created page
ChangLiu - 13 Oct 2008	add information for CRUZET
ChangLiu - Feb 2009	Updated CRAFT collections

Responsible: CMS.ChangLiu
Last reviewed by: SlavaValuev - 04 Mar 2009