Generation of a primary event Ruhani Khanna INFNLNS

Generation of a primary event Ruhani Khanna (INFN-LNS) XVI Seminar on Software for Nuclear, Sub-nuclear and Applied Physics Tuesday 28 th May, 2019 – Alghero, Italy softwareschool. infnlns@gmail. com 1

Lesson Outline 2 Introduction to some classes Primary Generation Action class Implementation Generators Further details/ examples Task softwareschool. infnlns@gmail. com

Classes Global - only exists in memory for 1 instance, shared by all threads At Initialisation: At Execution: Thread-local - instance of each action class exists for each thread G 4 User. Detector. Constructio n G 4 VUser. Primary. Generator. Act ion G 4 VUser. Physics. List G 4 User. Run. Action G 4 VUser. Action. Initialization G 4 User. Event. Action To define use G 4 Run. Manager: : Set. User. Initialization () Invoked at initialisation G A P Cirrone, Ph. D - INFN-LNS (Italy) - G 4 User. Stacking. Action G 4 User. Tracking. Actio G 4 User. Stepping. Action To define use G 4 Run. Manager: : Set. User. Action() Invoked during an event

Primary Generator Action At Execution: Mandatory user class G 4 VUser. Primary. Generator. Ac tion Doesn’t generate primaries Invokes Generate. Primary. Vertex() (method to make the primary) Sends the primary particles to G 4 Event object G A P Cirrone, Ph. D - INFN-LNS (Italy) - Primary vertex and the primary particle are added to a GEANT 4 Event

Implementation in the src file Ex. P 02 Primary. Generator. Action: : Ex. P 02 Primary. Generator. Action() G 4 VUser. Primary. Generator. Action(), Class constructor Initiation of primary generator -> f. Particle. Gun(0) { G 4 Particle. Gun() G 4 int n_particle = 1; f. Particle. Gun = new G 4 Particle. Gun(n_particle); G 4 Particle. Table* particle. Table = G 4 Particle. Table: : Get. Particle. Table(); G 4 String particle. Name; Setting of default f. Particle. Gun->Set. Particle. Definition(particle. Table>Find. Particle(particle. Name="geantino")); values f. Particle. Gun->Set. Particle. Energy(1. 0*Ge. V); f. Particle. Gun->Set. Particle. Position(G 4 Three. Vector(0. 0, 0. 0)); Generate. Primaries() } Ex. P 02 Primary. Generator. Action: : ~Ex. P 02 Primary. Generator. Action() - Randomises particle { delete f. Particle. Gun; -by-particle values Class destructor } - Sets values to void Ex. P 02 Primary. Generator. Action: : Generate. Primaries(G 4 Event* an. Event) { primary generator G 4 Three. Vector v(1. 0, 0. 1); f. Particle. Gun->Set. Particle. Momentum. Direction(v); f. Particle. Gun->Generate. Primary. Vertex(an. Event); } Invokes Generate. Primary. Vertex() -> method of primary generator softwareschool. infnlns@gmail. com

Generators 6

G 4 VPrimary. Generator 7 Introduction to some classes Generate. Primaries(G 4 Event*a. Event) (mandatory event) Geant 4 provides 3 G 4 VPrimary. Generators: (all concrete implementation G 4 Particle. G un G 4 HEPEvt. Interfa ce G 4 General. Particle. Sour ce softwareschool. infnlns@gmail. com

G 4 Particle. Gun Shoots one primary particle of a certain energy from a certain point at a certain time to a certain direction Various ‘Set’ methods available (/source/event/include/G 4 Particle. Gun. hh) - Void Set. Particle. Energy (G 4 Double a. Kinetic. Energy) - Void Set. Particle. Momentum (G 4 double a. Momentum) Methods can be repeated for generating more than onepprimary particle. Gun = G 4 Particle. Gun(); softwareschool. infnlns@gmail. com

Implementation example Can be repeated for generating more than one primary particles softwareschool. infnlns@gmail. com

G 4 HEPEvt. Interface GEANT 4 provides an ASCII file interface (unlike usual FORTRAN code) for event generators G 4 HEPEvt. Interface reads this ASCII file produced by an Event generator to reproduce the G 4 Primary. Particle objects (in particular the /HEPEVT/ fortran block) Does not place for the primary particle so the interaction point must be set by the User softwareschool. infnlns@gmail. com

G 4 General. Particle. Source Designed to replace G 4 Particle. Gun class Allows specification of multiple particle sources each with independent definition of particle type, position, direction and energy distribution Primary vertex can be chosen on the surface of a certain volume (randomly) Momentum, direction and kinetic energy can also be randomised Distribution defined by UI commands f. Generate. Particle. Source = new G 4 Generate. Particle. Source(); …/source/event/include/G 4 General. Particle. Source. hh softwareschool. infnlns@gmail. com

Implementation example Source: point like, 100 Me. V proton along z /gps/pos/type point /gps/particle proton /gps/energy 100 Me. V /gps/direction 0 0 1 Source: plane source(2 x 2), 100 Me. V proton along z /gps/pos/type/plane /gps/pos/shape square /gps/pos/centre x y z /gps/pos/Halfx /gps/pos/Halfy softwareschool. infnlns@gmail. com

Comparison Particle Gun General Particle Source HEP event interface Simple and native Powerful Shoots one track at a time Controlled by UI commands Doesn’t give place of primary particle Interaction point must be set by user Easy to handle Capability of shooting particles from a surface of a volume and of randomising kinetic energy, position, direction, following (complicated) user softwareschool. infnlns@gmail. com

Further details Online manual: (http: //reat. space. qinetiq. com/gps/) softwareschool. infnlns@gmail. com

Thank you softwareschool. infnlns@gmail. com

Tasks to do: Task 2 a: Particle Gun Task 2 b: General Particle Source http: //geant 4. lngs. infn. it/alghero 2019/task 2 softwareschool. infnlns@gmail. com