Pocket User Guide for Level 3 Muon Tools & Filters

 

version 2.1 – Nov 15, 2001

Contents

Introduction

Unpacking – L3TMuoUnpack

Local tracking – L3TMuoLocal

Fast scintillator tracking – L3TMuoScint

Time-of-flight – L3TMuoTOF

General subdetector matching

Central track matching – L3TMuoCentralMatch and L3TTracker

Calorimeter matching – L3TMuoCalMatch and L3TCalTrack

Global Muon Tool – L3TMuon

L3 Muon Filters – L3FMuon

Introduction

This document is a quick reference guide for the Level 3 Muon Tools and Filters. It is a document in development, and in some cases contains only stubs for parts of the software that are not yet available. This guide informs users of Level 3 Muon software of the different tools and filters available. For each tool, the purpose is given, there is a brief description of the algorithm, and the parameters are explained. One parameter will not be explained, which is the tooltype parameter. Every tool has this parameter. Its value is either “unpack”, which means that this tool is allowed to read raw data from the event, or “data”, which means the tool is allowed to store results in the event. Finally, some explanation about how to use the available filters will be given.

For a general introduction to the Level 3 system, specifically targeted at the muon system, see http://www-d0.fnal.gov/~balm/muon/DocumentationLevel3.htm

 

Paul Balm

 

Unpacking of the muon system – L3TMuoUnpack

Goal

Generally, unpacking is the reformatting of data, from the front-end format, to a more physical representation. In the case of the muon system at L3, unpacking goes all the way from ADC counts at an electronical address (representing for instance a drift-time) through the hit reconstruction, which provides the hits in a format that allows for reconstruction of the physics object. In the case of all muon hits, this is a format that has the position of the hit in D0 coordinates and a MuoIndex, pointing to the detector element that contains the hit.

For wirehits, there is also drift- and axial-time information (axial time is the time it takes the signal to run along the wire). For scintillatorhits, there is the time of the hit arrival, which is measured relative to the arrival of a speed-of-light particle, hitting the center of the scintillator.

The tool L3TMuoUnpack can be found in the package l3fmuo_unpack.

Algorithm

The algorithms are not Level 3 specific, but are implemented in other packages. The raw data, as it comes from the muon read-out cards (MRCs), is arranged in modules. From a software point of view, modules are sets of channels, each channel containing a wire or a scintillator. A channel can contain multiple hits per event. The different channels are defined in the package unpack_muo_fe. Channels are unpacked to multiple hits by the ChannelAdaptors in the package muon_raw. Hits themselves are defined in the package muo_hit. The basic algorithms used, and the definitions of the hits are identical to those used in the offline muon reconstruction.

Tool parameters

parameter

type

description

regional

bool

Switch for regional unpacking on or off

(not implemented)

tooltype

string

unpack

Local tracking in the muon system – L3TMuoLocal

Goal

Local tracking is tracking in the muon system only. The goal of this tool is to find muons, in a stand-alone mode of operation, based on muon hits only. The muon candidates that are found, are thought to be used by other tools as starting points, or seeds, for their measurement.

Algorithm

Muon tracking is implemented in two phases, segment reconstruction and track reconstruction and takes muon hits as input. For the input of hits, it requires the existence of a muon unpacking tool. Segment reconstruction starts from hits, and finds the separate parts of one muon track in different muon chambers. Segments are composed of both wire hits and scintillator hits. Track reconstruction is the combination of segments, and it includes the momentum measurement from the bending angle of the track.

The tool does not implement the algorithms itself. It uses the segment finding and track reconstruction algorithms that have been developed for both offline reconstruction and Level 3. These algorithms will be moved to the packages muo_segment and muo_track, but they are currently in the packages muo_segmentreco and muo_trackreco.

Tool parameters

parameter

type

description

segmentrcp

string

Filename of the RCP file containing parameters to the segment finding algorithm.

trackRCP

string

Filename of the RCP file containing parameters to the track reconstruction algorithm.

unpacktoolname

string

Name of the refset of the unpacking tool. The trigger list may define different muon unpacking tools- this parameter selects one.

tooltype

string

data

Fast scintillator tracking - L3TMuoScint

Goal

The purpose of the tool L3TMuoScint is to do tracking in the muon system, based on hit-information from the scintillators in the forward system (pixels). By ignoring the drift chambers, very little time has to be spent on pattern recognition, thereby making this tool very fast compared to L3TMuoLocal.

Currently this tool only works for the forward system. It should be extended to also find tracks in the central system.

Note that this tool will not work for A-stubs.

Algorithm

Connect B- and C-layer pixels. Extrapolate to A-layer to find matching pixel. If found, create track.

Tool parameters

parameter

type

description

Scintrcp

string

Filename of the RCP file containing parameters to the algorithm.

unpacktoolname

string

Name of the refset of the unpacking tool. The trigger list may define different muon unpacking tools- this parameter selects one.

tooltype

string

data

 

Time-of-flight - L3TMuoTOF

Goal

Scintillatorhits have very good timing resolution. The resolution is good enough to measure the time difference of a muon in different layers of the muon system (time differences of the order of 3 ns). The time-of-flight tool exploits this ability, by calculating the velocity of the passing muon. This gives rejection against cosmics, which have inverted velocity (inward), and slower punch-through particles can also be rejected.

Algorithm

The tool has not been implemented yet, but in short the tool will calculate the velocity of the muon, using the segments on the track. A segment has, apart from wirehits, scintillatorhits associated with it, and therefore the time of the segment is defined. Also, a segment has a position in the detector, and these two values allow for calculation of the velocity of the track.

Tool parameters

Not implemented.

General subdetector matching

Subdetector matching in the context of L3 Muon, is the search for confirmation of a muon in another subdetector. The currently there are two examples implemented. The central track matching tool, which attempts to confirm a muon seed in the muon system with a central track, and the calorimeter matching tool, which tries to match a given local muon seed to a MIP (hopefully a muon) in the calorimeter. These two tools are set up following one global design, that will be described in this section.

A set of tools responsible for subdetector consists of a “tracking tool” and a higher level “seed tool”. The seed tool will provide the starting point of the seed and interfaces with the tool providing that seed. In the currently implemented examples the tool providing the seed is the local muon tracking tool. When the seed tool has the seed, it calls the “tracking tool”, to perform the actual confirmation. This can be a tool doing tracking in the central tracker, or a tool performing a search in the calorimeter.

Central track matching – L3TMuoCentralMatch and L3TTracker

Goal

Confirmation of a muon seed, found by the local tracking tool, with a track in the central tracker.

Algorithm

The tool L3TMuoCentralMatch figures as the “seed tool” that has been described in the section “General subdetector matching”. It gets the seeds or candidates from the local tracking tool, and calls the tool for central tracking for confirmation. The central tracking tool will perform regional tracking in the region of interest only. To specify this region, L3TMuoCentralMatch obtains the local muon tracks from the local tracking tool, builds L3MuoTracks with those, and calls getL3PZRegion() method from L3MuoTrack. The method getL3PZRegion() provides a rectangle on the outer surface of the CFT, specified by a phi and a z-range. It also provides a pT , which allows the central tracking tool to be tuned towards high pT or low pT  tracks. However, this feature is not implemented yet.

The central tracking tool L3TTracker is an abstract base class, that doesn't implement an algorithm, but it defines an interface. The actual tools can be L3TGlobalTracker, for tracking in the SMT and CFT combined, or L3TCFTTrack, for CFT tracking only. These tools are described by their respective user guides (follow the links).

Note that this tool requires the existence of the local tracking tool and the central tracking tool, that are specified by the tool parameters.

Tool parameters (L3TMuoCentralMatch)

parameter

type

description

muontrackrefset

string

Name of the refset of the local tracking tool. The trigger list may define different muon unpacking tools- this parameter selects one.

trackerrefset

string

Name of the refset of the central tracking tool.

tooltype

string

data

Calorimeter matching – L3TMuoCalMatch and L3TMuoCalTrack

Goal

Confirmation of a muon seed, found by the local tracking tool, with a track in the calorimeter.

Algorithm

The tool L3TMuoCalMatch figures as the “seed tool” that has been described in the section “General subdetector matching”. It gets the seeds or candidates from the local tracking tool, and calls the tool for calorimeter tracking for confirmation. The calorimeter tracking tool will perform tracking in the region of interest only. To specify this region, L3TMuoCalMatch obtains the local muon tracks from the local tracking tool, and uses the A-layer segment of the track as a first guess of the location of the muon in the calorimeter. This tool is not implemented yet, but the code will live in the package l3fmuo_calmatch. Note that this tool requires the existence of the local tracking tool.

The calorimeter tracking tool L3TCalTrack uses algorithms developed during Run I. These algorithms were then implemented in the MTC package. Documentation exists on the MTC homepage, and a ‘pocket user guide’ can be found at Charles Legget's homepage. The algorithm basically propagates the seed track through the calorimeter, and tries to find a MIP in the cells crossed. The energy of the seed track may be corrected, in the case of a muon seed, by the energy lost in the calorimeter. The code exists in the package l3fmuo_caltrack.

L3TCalTrack tool parameters

parameter

type

description

enethrsh

float

Energy threshold for seed cells in calorimeter

roadrad

int

Radius of road in calorimeter - 1 = 3x3, 2=5x5, etc

tooltype

string

data

Global Muon Tool – L3TMuon

Goal

The Global Muon Tool will provide muons in the event, using all information from the detector available. It will do this by combining the information from all lower-level tools available.

Algorithm

The tool functionality is determined by the lower-level tools it relies on. The current implementation only calls the local tracking tool, and returns the tracks found. The way it is foreseen, is that L3TMuon will call the local tracking tool for seeds, the different subdetector matching tools for confirmation and for example also the timing tool to give more rejection against cosmics and punchthrough. Other tools that may be implemented will be added.

The code for the tool exists in the package l3fMuonTools.

Tool parameters

parameter

type

description

localtrackrefset

string

Name of the refset of the local tracking tool. The trigger list may define different muon unpacking tools- this parameter selects one.

 

L3 Muon Filters (L3FMuon)

In the level 3 trigger, the Filters make the trigger decisions, based on information obtained from tool. A filter may obtain all tracks, and decide to pass the event if one of the tracks is over some pT threshold. There is currently a number of filters implemented, namely L3FMuoUnpack, L3FMuoLocal an L3FMuon.

The first two only have the purpose of testing the underlying tool, being L3TMuoUnpack and L3TMuoLocal respectively. The filter L3FMuon on the other hand actually has some meaningful filtering capabilities. This filter will be explained below.

Algorithm

The filter L3FMuon runs L3TMuon and examines the L3MuonPhysicsResults it returns, to make its trigger decision. This examination currenly mainly consists of counting the number of segments on a track, and looking at the pT of the tracks found. So at this point, only local muon tracks are being considered.

The filter passes if there is any track over any threshold, so if there's any track with more segments than min_nsegs OR there is any track with a pT>min_pT, the filter will pass the event. However, if a threshold  is 0, it'll be ignored, and if they're both 0, all events will pass. For example, if you want:

The muon system obviously cannot measure the momentum of A-stubs, all we know is that they don't penetrate the toroid, but they did make it through the

calorimeter. That’s why the reconstruction sets the pT of those muons to 1.99 GeV.

Filter parameters

parameter

type

description

min_nseg

float

Minimum number of segments on a track

min_pT

float

Minimum pT of a track

 


Home
Paul Balm, July 2001
URL of this page is http://www-d0.fnal.gov/~balm/muon/PocketUserGuideLevel3MuonTools.htm