Accessing Event Data

1
Accessing Event Data
2
Objectives

• After completing this lesson, you should be able
  to
• Understand how objects are delivered to user
  algorithms.
• Retrieve objects from the event data store within
  an algorithm.
• Use relationships between objects.
• Specify event data input.

3
Event Data Reside In Data Store

• Tree - similar to file system
• Identification by path/Event/MCEvent/MCEcalHit
• Objects or
• Containers of objectsObjectVectorltTypegt

4
Containers ObjectVectorltTgt

• Templated class
• What you fill in are pointers to T
• Iteration like STL vector

ObjectVectorltMCParticlegt p...ObjectVectorltMCPa
rticlegtiterator ifor( ip-gtbegin() i !
p-gtend() i ) log ltlt MSGINFO ltlt
(i)-gtparticleID().id()
5
Understanding Data Stores Loading
Try to accessan object data
6
Caveats

• Consider Objects on the store asREAD-ONLY
• Do not modify existing objects!
• Do not destroy existing objects!
• Never, never delete an object which is registered
  to the store
• Its not yours!
• It will only screw up others!

7
Data Access In Algorithms

• Objects can be accessed using a
  SmartDataPtrltclass-typegt
• Usage similar to a normal pointer

• SmartDataPtrltEventgt evt(eventSvc(),/Event)
• if ( !evt ) !error!

Do not forget to check validity
8
SmartDataPtr Ingredients

• SmartDataPtrltEventgt evt( eventSvc(), /Event )

• Template class type

• Data store manager Pointer to service

• Item identifier location of the object

9
SmartDataPtr Usage

• SmartDataPtrltEventgt evt(eventSvc(),/Event)
• if ( evt )
• MsgStream log(msgSvc(), name())
• log ltlt MSGINFO ltlt Run ltlt evt-gtrun()
• ltlt endreq

This will trigger some action
this as well

• If invalid the evt-gtrun() will cause access
  violation (core dump)

10
Relationships Between Objects

• Objects have relationships between each other

• Vertices are also connected to particles, but
  this we neglect here...

11
Implementing Relationships

• 0..1 Relationships can be implemented using a
  SmartRefltclass-typegt
• Usage similar to a normal pointer
• 0..n Relationships are implemented using a
  SmartRefVectorltclass-typegtan array of
  SmartRefltclass-typegt
• Allow for late data loading

12
Using These Relationships
class MCParticle ... SmartRefltMCVertexgt
m_originVertex ... MCVertex
originMCVertex() return m_originMCVertex

See Doxygen code documentation
load data and trigger conversion
13
Using SmartReflttypegt
MCParticle p new MCParticle() SmartRefltMCParti
clegt ref
Assignment from raw pointer
ref p
p ref
Assignment to raw pointer
Usage
HepLorentzVector mom4 p-gtfourMomentum() HepLo
rentzVector mom4_2 ref-gtfourMomentum()
14
Specify Event Data Input
EventSelector.Input FILEsicbmc.dat
Spec-1, ... ,Spec-n

• Event data input is specified in the job options
• Spec is an array of qualified
  stringsKEY1VALUE1 KEYnVALUEn

15
Specify SICB Event Input
Input Type KEY VALUE SICB data file FILE
/afs//myfile.dat SICB data from
JOBID JOBID 16835

• Retrieve JobIDs from the bookkeeping web page.
• Our main data source is SICB output.

16
Specify Other Event Input
KEY VALUE EXAMPLE DATAFIL
E ltfile-namegt /afs//myfile.dat TYPE
lttechnologygt ROOT COLLECTIO
N lttuple-namegt MyCollection SELECTION
ltSQL-preselectiongt NTRACKgt50 FUNCTION
ltnamegt MySelector

17
Hands On Print B0 Decays

• Use particle property service
• See User Guide chapter 12.5
• Retrieve MCParticles from event store
• /Event/MC/MCParticles
• Filter out the B0 particles
• Part. member particleID().id() is Geant 3
  particle code
• For each B0 Loop over all decay vertices and
  print the decay particles
• recursion ?

18
DecayTreeAlgorithm.cpp Add Headers
include "CLHEP/Units/PhysicalConstants.h" includ
e "GaudiKernel/IParticlePropertySvc.h" include
"GaudiKernel/ParticleProperty.h" include
"GaudiKernel/SmartDataPtr.h" include
"LHCbEvent/MCParticle.h" include
"LHCbEvent/MCVertex.h"
19
Using IParticlePropertySvc
...DecayTreeAlgorithm.h... IParticleProperySvc
m_ppSvc stdstring m_partName
long m_partID ...DecayTreeAlgorit
hminitialize()... m_ppSvc 0 StatusCode
sc service("ParticlePropertySvc", m_ppSvc )
if( !sc.isSuccess() ) // You have to handle
the error! ParticleProperty partProp
m_ppSvc-gtfind( m_partName ) if ( 0 partProp
) // You have to handle the error!
m_partID partProp-gtgeantID()
20
Hands On Retrieve MCParticles
include GaudiKernel/SmartDataPtr.h
SmartDataPtrltMCParticleVectorgt
parts(eventSvc(), /Event/MC/MCParticles) if (
parts ) loop over particles
21
Hands On Loop Over MCParticles
MCParticleVectorconst_iterator
i for(iparts-gtbegin()i ! parts-gtend() i )
if ( (i)-gtparticleID().id() m_partID )
printDecayTree( i )
New member function
22
Hands On Print Decays

• For each selected particle
• Loop over decay vertices
• Print all daughters
• If daughters have decay vertices
• recurse
• If you run out of time, just print someparticle
  property

23
Loop Over Decay Vertices
const SmartRefVectorltMCVertexgt decays
mother-gtdecayMCVertices() SmartRefVectorltMCVert
exgtconst_iterator iv for (iv
decays.begin() iv ! decays.end() iv )
const SmartRefVectorltMCParticlegt daughters

(iv)-gtdaughterMCParticles()
SmartRefVectorltMCParticlegtconst_iterator idau
for (idaudaughters.begin()
idau!daughters.end() idau )
printDecayTree( 0, " ", idau )
24
printDecayTree
void DecayTreeAlgorithmprintDecayTree(long
depth,
const stdstring prefix,
const MCParticle mother)
MsgStream log(msgSvc(), name()) const
SmartRefVectorltMCVertexgt decays
mother-gtdecayMCVertices() ParticleProperty p
m_ppSvc-gtfind( mother-gtparticleID().id() )
log ltlt MSGINFO ltlt depth ltlt prefix.substr(0,
prefix.length()-1) ltlt "---gt" ltlt
p-gtparticle() ltlt endreq if ( depth lt m_depth )
SmartRefVectorltMCVertexgtconst_iterator
iv for ( iv decays.begin() iv !
decays.end() iv ) const
SmartRefVectorltMCParticlegt daughters
(iv)-gtdaughterMCParticles()
SmartRefVectorltMCParticlegtconst_iterator idau
for ( idau daughters.begin() idau !
daughters.end() idau )
printDecayTree( depth1, prefix" ", idau )