Introduction to CMSSW

1
Introduction to CMSSW

• Framework Concepts
• Simulation Reconstruction

Liz Sexton-Kennedy January 10, 2008
2
Introduction

• CMS is now on its second generation of offline
  software. Use of the first generation software
  systems is long gone now, but much of the work
  that went into these projects (ORCA, OSCAR,
  COBRA, IGUANA) was reused by porting it
• to CMSSW.
• CMSSW is the full suite
• of offline software in the
• new architecture.
• Code for online data taking,
• Simulation, Primary
• reconstruction, and
• Physics analysis.

3
Introduction

• CMSSW is now a large software system

4
Code Organization

• The thousand (or so) packages that make up the
  project are organized into sub-systems with names
  that should be suggestive of their purpose

5
Glossary T(more/less)LA's

• CMSSW Compact Muon Solenoid SoftWare
• EDM Event Data Model
• FW Application Framework
• AOD Analysis Object Dataset
• TDR Technical Design Report
• DAQ Data Acquisition
• FED Front End Digitizer
• HLT High Level Trigger
• PAT Physics Analysis Toolkit software effort
• PADA Processing and Data Access computing
  effort
• CVS Code Versioning System also called the
  code repository
• CmsTC CMS Tag Collector integration tool

6
FW Architecture - Plugins

• Applications in CMSSW are built from special
  shared object libraries called plugins. In
  practice this means that there is only one
  command you need to know to run most CMS
  applications cmsRun ltsome-configuration-filegt
• Configurations are currently written in a
  specialized invented language, but we are in the
  process of moving to the python language. 2_0_X
  and earlier use the first, 2_1_X and later will
  use python.
• There are two types of plugins
• Module Plugins EDProducers, EDFilters,
  EDAnalyzers, (EDLoopers, etc.) and ESSources,
  ESProducers. These are the worker components of
  the FW. ED process event data, ES process
  event setup data.
• Data Object Plugins also known as root
  dictionaries because they can also be loaded
  directly into the root application. These are
  most of the products of the above work, and form
  the elements of the EDM.

7
Basic Concept of the EDM

• The data produced in the primary reconstruction
  farms (Tier 0 CERN), or reprocessing farms
  (Tier 1s) must be immediately useful for analysis
  (at least once we really understand the
  detector).
• We have designed the system so that the same
  pool/root data file can be used in three
  contexts
• Bare root.exe treat pool file as a root input
  file, allows browsing of simple objects (floats,
  ints, and composites of them) from the root
  TBrowser GUI.
• FWLight a small set of CMS defined loadable
  libraries added to root to allow more
  sophisticated use with root macro scripts. For
  the EDM this is a read-only application.
• cmsRun - input for a full framework
  application, could be used for a reprocessing
  pass or creation of more refined analysis objects
  stored into the AOD.

8
Basic Concepts of the FW

• A Software Bus Model
• Start from the raw-raw data
• Producers are scheduled to operate on the event
  data and produce their output which is written
  into the event
• At any point in the processing chain, the
  execution can be halted and the contents of the
  event can be examined outside of the context of
  the process that made it
• The schedule can be checked for correctness since
  the modules can declare their inputs (and outputs
  if they are EDProducers). This allows the FW to
  automatically track the provenance of what is
  produced.
• Several instances of the same module can be run
  in the same application and you will still be
  able to uniquely identify their products.
  Identified by C type, producer label, instance
  name, process name

9
Schematic Picture of Reconstruction

• A simplified example take from the calorimeter
  reconstruction

10
Where do I plug in ?

• As you can see from the previous slide each blue
  box must be defined by a reconstruction writer.
• The first step is to define what are the input
  and output objects needed for your algorithmic
  task.
• These need to be defined as C classes that
  follow the EDM rules gt define EDProduct classes
  in some DataFormat subsystem.
• Decide what services your algorithm needs
  (calibrations, geometry description) from
  EventSetup
• Start from templates or code generators for the 5
  types in FWCore/Skeletons/scripts (eg. mkedprod )
• Write the EDProducer that receives all of the
  information and passes it on to the algorithms.

11
More FW Concepts -EventSetup

• The EventSetup is the system which delivers all
  non-event data to EDProducers and other modules.
  Its component are activated on demand rather
  then scheduled in contrast to the event data
  components.

EventSetup
12
Simulation in CMSSW
Root data file (add SimHits)
Root data file (add Raw)
Root data file (HepMC)
Detector Simulation
Generation
Digitization
Reconstruction
Modeling of electronic signal (Digis)
Particle gun, physics generator (vertices,
particles)
Particle showers, EM Fields, based on Geant4
(SimHits)
Overlay in-time min-bias events from same
collision and out-of-time min-bias events from
neighboring collisions
Min-Bias Generator
Min-Bias SimHits
Event RawData
CPU
Signal Generator
Signal SimHits
13
Reconstruction in CMSSW
Simulation of Electronics
Low-level Reconstruction
Raw Data

• 20 interactions/ crossing
• 25 ns crossing time faster than detector
  response read out (simulate) crossings 53
• 200 pileup events per 1 signal event!

High-level Reconstruction and Analysis
HCAL
14
Summary

• CMSSW is a large scale software system for
  simulation, data acquisition, triggering,
  reconstruction and analysis of CMS data.
• A lot of work has been done over the past 3
  years, but there is a lot of work still to do. I
  expect the code base to be at least 2 to 3 times
  bigger (CDF for instance is). The work to
  understand the detector and capture that
  understanding in the software and databases is
  still to be done in the continued commissioning
  of the detector over the next year.
• Come and join the fun, become a CMSSW developer
  by attending the rest of the tutorials this week.