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http: //cern. ch/geant 4/ http: //www. ge. infn. it/geant 4/ through an application example Maria Grazia Pia INFN Genova Maria. Grazia. Pia@cern. ch INFN-LNS Laboratory, December 2002 Maria Grazia Pia

Capture User Requirements Define the scope of the software system to be built (“what it should do”) Maria Grazia Pia

The experimental set-up of our exercise A simple configuration, consisting of – – – a tracking detector an electromagnetic calorimeter a system of anti-coincidences What happens in our detectors – – – incident particles interact in the experimental set-up secondary particles may be generated and interact too detectors and their read-out electronics record the effects produced by primary and secondary particles Maria Grazia Pia

Maria Grazia Pia User Requirements

Outline This basic introduction is not meant to replace Geant 4 Application Developer Guide! Geant 4 user initialisation and action classes How to describe the experimental set-up – Basics of materials, geometry, hits&digits How to generate primary events – Basics of primary generators How to define the physics to be activated – – Basic concepts of how Geant 4 kernel works Particles and their physics interactions Physics processes, their management and how tracking deals with them Cuts How to control and monitor the execution – Basics of user interface, visualisation How to analyse the result of the simulation – Andreas Pfeiffer’s talk Maria Grazia Pia

Identify a candidate architecture Maria Grazia Pia

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The main program Geant 4 does not provide the main() In his/her main(), the user must – construct G 4 Run. Manager (or his/her own derived class) – notify the mandatory user classes to G 4 Run. Manager G 4 VUser. Detector. Construction G 4 VUser. Physics. List G 4 VUser. Primary. Generator. Action The user can define – Vis. Manager, (G)UI session, optional user action classes, one’s own persistency manager, an Analysis. Manager… in his/her main() Maria Grazia Pia

User classes Initialization classes Action classes Invoked at the initialization G 4 VUser. Detector. Construction G 4 VUser. Physics. List Invoked during the execution loop G 4 VUser. Primary. Generator. Action G 4 User. Run. Action G 4 User. Event. Action G 4 User. Stacking. Action G 4 User. Tracking. Action G 4 User. Stepping. Action Mandatory classes: Maria Grazia Pia G 4 VUser. Detector. Construction describe the experimental set-up G 4 VUser. Physics. List select the physics you want to activate G 4 VUser. Primary. Generator. Action generate primary events

Describe the experimental set-up Derive your own concrete class from the G 4 VUser. Detector. Construction abstract base class Implement the Construct() method (modularise it according to each detector component or sub-detector) – – – construct all necessary materials define shapes/solids required to describe the geometry shapes/solids construct and place volumes of your detector geometry volumes define sensitive detectors and identify detector volumes to associate sensitive detectors them to associate magnetic field to detector regions magnetic field define visualisation attributes for the detector elements attributes Maria Grazia Pia

Select physics processes Geant 4 does not have any default particles or processes – even for the particle transportation, one has to define it explicitly Derive your own concrete class from the G 4 VUser. Physics. List abstract base class – define all necessary particles – define all necessary processes and assign them to proper particles processes – define production thresholds (in terms of range) production thresholds Read the Physics Reference Manual first! The Advanced Examples offer a guidance for various typical experimental domains Maria Grazia Pia

Generate primary events Derive your concrete class from the G 4 VUser. Primary. Generator. Action abstract base class Pass a G 4 Event object to one or more primary generator concrete class objects, which generate primary vertices and primary particles The user can implement or interface his/her own generator – specific to a physics domain or to an experiment Maria Grazia Pia

Optional user action classes G 4 User. Run. Action Begin. Of. Run. Action(const G 4 Run*) Begin. Of. Run. Action – example: book histograms End. Of. Run. Action(const G 4 Run*) End. Of. Run. Action – example: store histograms G 4 User. Event. Action Begin. Of. Event. Action(const G 4 Event*) Begin. Of. Event. Action – example: event selection End. Of. Event. Action(const G 4 Event*) End. Of. Event. Action – example: analyse the event G 4 User. Tracking. Action Pre. User. Tracking. Action(const G 4 Track*) Pre. User. Tracking. Action G 4 User. Stepping. Action(const G 4 Step*) User. Stepping. Action – example: kill, suspend, postpone the track G 4 User. Stacking. Action Prepare. New. Event() Prepare. New. Event – Classify. New. Track(const G 4 Track*) Classify. New. Track – – Post. User. Tracking. Action(const G 4 Track*) Post. User. Tracking. Action – Maria Grazia Pia Invoked every time a new track is pushed Classify a new track (priority control) Urgent, Waiting, Postpone. To. Next. Event, Kill New. Stage() example: decide whether a trajectory should be stored or not – reset priority control invoked when the Urgent stack becomes empty change the classification criteria event filtering (event abortion)

Select (G)UI and visualisation In your main(), taking into account your computer environment, construct a G 4 UIsession concrete class provided by Geant 4 and invoke its session. Start() method Geant 4 provides: – G 4 UIterminal csh or tcsh like character terminal – G 4 GAG tcl/tk or Java PVM based GUI – G 4 Wo Opacs – G 4 UIBatch batch job with macro file – etc… Maria Grazia Pia Derive your own concrete class from G 4 VVis. Manager, according to your computer environment Geant 4 provides interfaces to various graphics drivers: – DAWN Fukui renderer – WIRED – Ray. Tracer ray tracing by Geant 4 tracking – OPACS – Open. GL – Open. Inventor – VRML

Physics Detector description Management Detector response Visualisation Primary event generation Analysis Maria Grazia Pia Architecture

Gamma. Ray. Tel main // Construct the default run manager G 4 Run. Manager* run. Manager = new G 4 Run. Manager; // Set mandatory user initialization classes Gamma. Ray. Tel. Detector. Construction* detector= new Gamma. Ray. Tel. Detector. Construction; run. Manager->Set. User. Initialization(detector); run. Manager->Set. User. Initialization(new Gamma. Ray. Tel. Physics. List); // Set mandatory user action classes run. Manager->Set. User. Action(new Gamma. Ray. Tel. Primary. Generator. Action); // Set optional user action classes Gamma. Ray. Tel. Event. Action* event. Action = new Gamma. Ray. Tel. Event. Action(); run. Manager->Set. User. Action(event. Action); Gamma. Ray. Tel. Run. Action* run. Action = new Gamma. Ray. Tel. Run. Action(); run. Manager->Set. User. Action(run. Action); Maria Grazia Pia

Gamma. Ray. Tel main (continued) // Creation of the analysis manager Gamma. Ray. Tel. Analysis* analysis = Gamma. Ray. Tel. Analysis: : get. Instance(); // Initialization of the User Interface Session G 4 UIsession* session = new G 4 UIterminal(); // Visualisation manager G 4 Vis. Manager* vis. Manager = new Gamma. Ray. Tel. Vis. Manager; vis. Manager->Initialize(); // Initialize G 4 kernel run. Manager->Initialize(); Maria Grazia Pia

Initialisation Describe a geometrical setup: a Si-W tracker, a Cs. I calorimeter and an anticoincidence system made out of plastic scintillators. Maria Grazia Pia Activate electromagnetic/hadronic processes appropriate to the energy range of the experiment

Beam On Generate primary events according to various distributions relevant to gamma astrophysics Maria Grazia Pia

Event processing Record the coordinates of impact of tracks in the tracker layers Record the energy deposited in each element of the calorimeter at every event Maria Grazia Pia

Describe the experimental set-up Maria Grazia Pia

Materials Different kinds of materials can be defined – – isotopes elements molecules compounds and mixtures Describe a geometrical setup: a Si-W tracker, a Cs. I calorimeter and an anticoincidence system made out of plastic Attributes associated: scintillators. – – temperature pressure state density Single element material double density = 1. 390*g/cm 3; double a = 39. 95*g/mole; G 4 Material* l. Ar = new G 4 Material("liquid. Argon", z=18. , a, density); Maria Grazia Pia

Definition of materials in Gamma. Ray. Tel // define elements G 4 double a = 1. 01*g/mole; G 4 Element* H = new G 4 Element(name="Hydrogen", symbol="H" , z= 1. , a); new G 4 Element a = 12. 01*g/mole; G 4 Element* C = new G 4 Element(name="Carbon" , symbol="C" , z= 6. , a); // define simple materials G 4 double density = 1. 032*g/cm 3; G 4 Material* Sci = new G 4 Material(name="Scintillator", density, ncomponents=2); G 4 Material Sci->Add. Element(C, natoms=9); Sci->Add. Element(H, natoms=10); Maria Grazia Pia

Define detector geometry Three conceptual layers – – – G 4 VSolid -- shape, size G 4 VSolid G 4 Logical. Volume -- daughter physical volumes, material, sensitivity, user G 4 Logical. Volume limits, etc. G 4 VPhysical. Volume -- position, rotation G 4 VPhysical. Volume A unique physical volume (the world volume), which represents the world experimental area, must exist and fully contain all other components G 4 VSolid G 4 Box G 4 Tubs Maria Grazia Pia G 4 Logical. Volume G 4 Material G 4 Vis. Attributes G 4 VSensitive. Detector G 4 VPhysical. Volume G 4 PVPlacement G 4 PVParameterised

G 4 VSolid Abstract class: all solids in Geant 4 derive from it Defines, but does not implement, all functions required to: – compute distances to/from the shape – check whether a point is inside the shape – compute the extent of the shape – compute the surface normal to the shape at a given point Maria Grazia Pia

Solids defined in Geant 4: CSG (Constructed Solid Geometry) solids – – G 4 Box, G 4 Tubs, G 4 Cons, G 4 Trd, … Analogous to simple GEANT 3 CSG solids Specific solids (CSG like) – G 4 Polycone, G 4 Polyhedra, G 4 Hype, … BREP (Boundary REPresented) solids – – G 4 BREPSolid. Polycone, G 4 BSpline. Surface, … Any order surface Boolean solids – G 4 Union. Solid, G 4 Subtraction. Solid, … STEP interface – to import BREP solid models from CAD systems - STEP compliant solid modeler Maria Grazia Pia

BREP Solids BREP = Boundary REPresented Solid Listing all the surfaces specifies a solid – e. g. 6 squares for a cube Surfaces can be – – planar, 2 nd or higher order (elementary BREPS) Splines, B-Splines, NURBS (Non-Uniform B-Splines) (advanced BREPS) Few elementary BREPS pre-defined – box, cons, tubs, sphere, torus, polycone, polyhedra Advanced BREPS built through CAD systems Maria Grazia Pia

Boolean Solids can be combined using boolean operations: – G 4 Union. Solid, G 4 Subtraction. Solid, G 4 Intersection. Solid Requires: – 2 solids, 1 boolean operation, and an (optional) transformation for the 2 nd solid Example: G 4 Box box(“Box", 20, 30, 40); G 4 Tubs cylinder(“Cylinder”, 0, 50, 0, 2*M_PI); G 4 Union. Solid union("Box+Cylinder", &box, &cylinder); G 4 Intersection. Solid intersect("Box Intersect Cylinder", &box, &cylinder); G 4 Subtraction. Solid subtract("Box-Cylinder", &box, &cylinder); Solids can be either CSG or other Boolean solids Note: tracking cost for the navigation in a complex Boolean solid is proportional to the number of constituent solids Maria Grazia Pia

G 4 Logical. Volume(G 4 VSolid *p. Solid, G 4 Material *p. Material, const G 4 String& name, G 4 Field. Manager *p. Field. Mgr=0, G 4 VSensitive. Detector *p. SDetector=0, G 4 User. Limits *p. ULimits=0); Contains all information of volume except position: – Shape and dimension (G 4 VSolid) – Material, sensitivity, visualization attributes – Position of daughter volumes – Magnetic field, User limits – Shower parameterization Physical volumes of same type can share a logical volume Maria Grazia Pia

Physical Volumes Placement: it is one positioned volume Placement Repeated: a volume placed many times Repeated – – can represent any number of volumes reduces use of memory Replica: simple repetition, similar to G 3 divisions Replica: Parameterised placement A mother volume can contain either – – many placement volumes OR one repeated volume Maria Grazia Pia repeated

G 4 VPhysical. Volume G 4 PVPlacement 1 Placement = One Volume – A volume instance positioned once in a mother volume G 4 PVParameterized 1 Parameterized = Many Volumes – Parameterized by the copy number Shape, size, material, position and rotation can be parameterized, by implementing a concrete class of G 4 PVParameterisation – Reduction of memory consumption Currently: parameterization can be used only for volumes that either a) have no further daughters or b) are identical in size and shape G 4 PVReplica 1 Replica = Many Volumes – Slicing a volume into smaller pieces (if it has a symmetry) Maria Grazia Pia

Replicated Physical Volumes The mother volume is sliced into replicas, all of the same size and dimensions Represents many touchable detector elements differing only in their positioning Replication may occur along: – Cartesian axes (X, Y, Z) – slices are considered perpendicular to the axis of replication Coordinate system at the center of each replica – Radial axis (r) – cons/tubs sections centered on the origin and un-rotated Coordinate system same as the mother – Phi axis (f) – phi sections or wedges, of cons/tubs form Coordinate system rotated such as that the X axis bisects the angle made by each wedge Maria Grazia Pia repeated

Grouping volumes To represent a regular pattern of positioned volumes, composing a more or less complex structure – structures which are hard to describe with simple replicas or parameterised volumes – structures which may consist of different shapes Assembly volume – – – acts as an envelope for its daughter volumes its role is over, once its logical volume has been placed daughter physical volumes become independent copies in the final structure

Detector. Construction // Calorimeter Structure (CALLayer. X + CALLayer. Y) // Solid solid. CALLayer. X = new G 4 Box("CALLayer. X", CALSize. XY/2, CALBar. Thickness/2); // Logical volume logic. CALLayer. X = new G 4 Logical. Volume(solid. CALLayer. X, CALMaterial, "CALLayer. X"); // Physical volume for (G 4 int i = 0; i < Nb. Of. CALLayers; i++) { physi. CALLayer. Y = new G 4 PVPlacement(…); physi. CALLayer. X = new G 4 PVPlacement(…); … } Maria Grazia Pia

How to identify a volume uniquely? Step p. PV 4 5 4 Later 4 4 5 1 2 3 Touchable 5 1 All generic touchables can reply to these queries: –positioning information (rotation, position): Get. Translation(, Specific types of touchable also know: –(solids) - their associated shape: Get. Solid() –(volumes) - their physical volume: Get. Volume() –(volumes) - their replication number: Get. Replica. Number() –(volumes hierarchy or touchable history) Maria Grazia Pia 2 Get. Rotation()

Interface to CAD systems Models imported from CAD systems can describe the solid geometry of detectors made by large number of elements with the greatest accuracy and detail – A solid model contains the purely geometrical data representing the solids and their position in a given reference frame Solid descriptions of detector models can be imported from CAD systems – e. g. Euclid & Pro/Engineer using STEP AP 203 compliant protocol Tracking in BREP solids created through CAD systems is supported

Visualisation of Detector Each logical volume can have a G 4 Vis. Attributes object associated – – – Visibility, visibility of daughter volumes Color, line style, line width Force flag to wire-frame or solid-style mode For parameterised volumes, attributes can be dynamically assigned to the logical volume Lifetime of visualisation attributes must be at least as long as the objects they’re assigned to

Debugging tools: DAVID is a graphical debugging tool for detecting potential intersections of volumes Accuracy of the graphical representation can be tuned to the exact geometrical description – – – physical-volume surfaces are automatically decomposed into 3 D polygons intersections of the generated polygons are parsed if a polygon intersects with another one, the physical volumes associated to these polygons are highlighted in colour (red is the default) DAVID can be downloaded from the web as an external tool for Geant 4

Detector response Record the coordinates of impact of tracks in the layers of the tracker. Record the energy deposited in each element of the calorimeter at every event. The user must provide his/her own implementation of the detector response Concepts: – Sensitive Detector – Readout Geometry – Hits – Digits Maria Grazia Pia

Detector sensitivity A logical volume becomes sensitive if it has a pointer to a concrete class derived from G 4 VSensitive. Detector A sensitive detector – either constructs one or more hit objects – or accumulates values to existing hits using information given in a G 4 Step object A sensitive detector creates hits using the information given by G 4 Step

Read-out Geometry Readout geometry is a virtual and artificial geometry it is associated to a sensitive detector can be defined in parallel to the real detector geometry helps optimising the performance Maria Grazia Pia

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Gamma. Ray. Tel Sensitive Detector and Readout Geometry // Sensitive Detector Manager G 4 SDManager* SDman = G 4 SDManager: : Get. SDMpointer(); // Sensitive Detectors - Tracker tracker. SD = new Gamma. Ray. Tel. Tracker. SD("Tracker. SD"); Gamma. Ray. Tel. Tracker. SD SDman->Add. New. Detector( tracker. SD ); // Readout geometry G 4 String ROgeometry. Name = "Tracker. ROGeom"; G 4 VRead. Out. Geometry* tracker. RO = new Gamma. Ray. Tel. Tracker. ROGeometry(ROgeometry. Name); Gamma. Ray. Tel. Tracker. ROGeometry tracker. RO->Build. ROGeometry(); tracker. SD->Set. ROgeometry(tracker. RO); logic. TKRActive. Tile. X->Set. Sensitive. Detector(tracker. SD); // Active. Tile. X logic. TKRActive. Tile. Y->Set. Sensitive. Detector(tracker. SD); // Active. Tile. Y Maria Grazia Pia

Hit is a user-defined class derived from G 4 VHit You can store various types information by implementing your own concrete Hit class: – – – position and time of the step momentum and energy of the track energy deposition of the step geometrical information etc. Hit objects of a concrete hit class must be stored in a dedicated collection, which is instantiated from G 4 THits. Collection template class The collection is associated to a G 4 Event object via G 4 HCof. This. Event Hit collections are accessible – through G 4 Event at the end of event – through G 4 SDManager during processing an event

Digitisation A Digi represents a detector output – e. g. ADC/TDC count, trigger signal A Digi is created with one or more hits and/or other digits The digitise() method of each G 4 VDigitizer. Module must be explicitly invoked by the user’s code – e. g. in the User. Event. Action

Hits and Digis Maria Grazia Pia

Hits in our example Each tracker hit contains the following information: ID of the event (this is important for multiple events run) Energy deposition of the particle in the strip Number of the plane Type of the plane Position of the hit (x, y, z) in the reference frame of the payload Maria Grazia Pia

public: Gamma. Ray. Tel. Tracker. Hit(); Gamma. Ray. Tel. Tracker. Hit ~Gamma. Ray. Tel. Tracker. Hit(); Gamma. Ray. Tel. Tracker. Hit(const Gamma. Ray. Tel. Tracker. Hit&); const Gamma. Ray. Tel. Tracker. Hit& operator=(const Gamma. Ray. Tel. Tracker. Hit&); int operator==(const Gamma. Ray. Tel. Tracker. Hit&) const; inline void* operator new(size_t); inline void operator delete(void*); void Draw(); void Print(); inline void Add. Sil(G 4 double de) inline void Set. NStrip(G 4 int i) inline void Set. NSil. Plane(G 4 int i) inline void Set. Plane. Type(G 4 int i) inline void Set. Pos(G 4 Three. Vector xyz) inline G 4 double Get. Edep. Sil() inline G 4 int Get. NStrip() inline G 4 int Get. NSil. Plane() inline G 4 int Get. Plane. Type() inline G 4 Three. Vector Get. Pos() Maria Grazia Pia {Edep. Sil += de; }; {NStrip = i; }; {NSil. Plane = i; }; {Is. XPlane = i; }; { pos = xyz; } { return Edep. Sil; }; { return NStrip; }; { return NSil. Plane; }; {return Is. XPlane; }; { return pos; };

Digits in our example A digi is generated when the hit energy deposit is greater than a threshold The Tracker digits contain: – ID of the event (this is important for multiple events run) – Number of the strip – Number of the plane – Type of the plane (1=X 0=Y) A concrete class Gamma. Ray. Tel. Digitizer, inheriting from G 4 VDigitizer. Module, implements the digitize() method – The digitize() method of each G 4 VDigitizer. Module must be explicitly invoked by the user code (e. g. at Event. Action) Maria Grazia Pia

public: Gamma. Ray. Tel. Digi(); ~Gamma. Ray. Tel. Digi(); Gamma. Ray. Tel. Digi(const Gamma. Ray. Tel. Digi&); const Gamma. Ray. Tel. Digi& operator=(const Gamma. Ray. Tel. Digi&); int operator==(const Gamma. Ray. Tel. Digi&) const; inline void* operator new(size_t); inline void operator delete(void*); void Draw(); void Print(); inline void Set. Plane. Number(G 4 int Plane. Num) {Plane. Number = Plane. Num; }; inline void Set. Plane. Type(G 4 int Plane. Typ) {Plane. Type = Plane. Typ; }; inline void Set. Strip. Number(G 4 int Strip. Num) {Strip. Number = Strip. Num; }; inline G 4 int Get. Plane. Number() inline G 4 int Get. Plane. Type() inline G 4 int Get. Strip. Number() Maria Grazia Pia {return Plane. Number; }; {return Plane. Type; }; {return Strip. Number; };

Gamma. Ray. Tel. Digitizer class Gamma. Ray. Tel. Digitizer : public G 4 VDigitizer. Module { public: Gamma. Ray. Tel. Digitizer(G 4 String name); ~Gamma. Ray. Tel. Digitizer(); void Digitize(); void Set. Threshold(G 4 double val) { Energy_Threshold = val; } private: Gamma. Ray. Tel. Digits. Collection* Digits. Collection; G 4 double Energy_Threshold; Gamma. Ray. Tel. Digitizer. Messenger* digi. Messenger; }; Maria Grazia Pia

Visualisation of Hits and Trajectories Each G 4 VHit concrete class must have an implementation of Draw() method – – – Colored marker Colored solid Change the color of detector element G 4 Trajectory class has a Draw() method – – – Blue : positive Green : neutral Red : negative You can implement alternatives by yourself

Generate primary events Maria Grazia Pia

Generating primary particles Generate primary events according to various distributions relevant to astrophysics Interface to Event Generators – Primary vertices and particles to be stored in G 4 Event before processing the event Various utilities provided within the Geant 4 Toolkit – Particle. Gun beam of selectable particle type, energy etc. – G 4 HEPEvt. Interface Suitable to /HEPEVT/ common block, which many of (FORTRAN) HEP physics generators are compliant to ASCII file input – General. Particle. Source provides sophisticated facilities to model a particle source used to model space radiation environments, sources of radioactivity in underground experiments etc. You can write your own, inheriting from G 4 VUser. Primary. Generator. Action Maria Grazia Pia

G 4 General. Particle. Source Maria Grazia Pia

Primary generator in our example Gamma. Ray. Tel. Particle. Generation. Action and its Messenger are responsible for the generation of primary particles and the related configuration through the UI Define the incident flux of particles: – – from a specific direction or from an isotropic background Choose also between two spectral options: – – monochromatic or with a power-law dependence The particle generator parameters are accessible through the UI – /gun/ tree Maria Grazia Pia

Gamma. Ray. Tel. Primary. Generator. Action void Gamma. Ray. Tel. Primary. Generator. Action: : Generate. Primaries(G 4 Event* an. Event) { // This function is called at the beginning of event G 4 double z 0 = 0. 5*(Gamma. Ray. Tel. Detector->Get. World. Size. Z()); G 4 double x 0 = 0. *cm, y 0 = 0. *cm; G 4 Three. Vector vertex 0 = G 4 Three. Vector(x 0, y 0, z 0); G 4 Three. Vector dir 0 = G 4 Three. Vector(0. , -1. ); particle. Gun->Set. Particle. Position(vertex 0); Set. Particle. Position particle. Gun->Set. Particle. Momentum. Direction(dir 0); Set. Particle. Momentum. Direction G 4 double p. Energy = G 4 Uniform. Rand() * 10. * Ge. V; particle. Gun->Set. Particle. Energy(p. Energy); Set. Particle. Energy particle. Gun->Generate. Primary. Vertex(an. Event); Generate. Primary. Vertex } Maria Grazia Pia

Activate physics processes Maria Grazia Pia

Physics processes in Geant 4 Present the concepts needed to understand how to build a Physics. List i. e. to set-up the physics to be activated in a simulation application A Physics. List is the class where the user defines which particles, processes and production thresholds are to be used in his/her application This is a mandatory and critical user’s task We will go through several aspects regarding the kernel of Geant 4 Maria Grazia Pia

Outline (it is quite complex…) What is tracked G 4 Particle. Definition G 4 Dynamic. Particle G 4 Track The process interface G 4 VProcess How processes are used in tracking The production cuts Why production cuts are needed The cuts scheme in Geant 4 Building the Physics. Lists G 4 VUser. Physics. List Concrete physics lists User-defined limits Maria Grazia Pia G 4 User. Limit G 4 User. Special. Cuts process

intrisic particle properties : mass, width, spin, lifetime… intrisic G 4 Particle. Definition sensitivity to physics sensitivity – This is realized by a G 4 Process. Manager attached to the G 4 Particle. Definition – The G 4 Process. Manager manages the list of processes the user wants the particle to be sensitive to – G 4 Particle. Definition does not know by itself its sensitivity to physics G 4 Particle. Definition G 4 VBoson G 4 Geantino G 4 VMeson G 4 Pion. Plus Maria Grazia Pia G 4 Process. Manager Process_1 Process_2 Process_3 G 4 Particle. With. Cuts G 4 VLepton G 4 Electron G 4 Particle. Definition G 4 VIon G 4 VShort. Lived. Particles G 4 VBaryon G 4 Alpha G 4 Proton G 4 Particle. Definition is the base class for defining concrete particles

More about particle design G 4 Dynamic. Particle Describes the purely dynamic part (i. e. no position, nor geometrical information…) of the particle state: – momentum, energy, polarization Holds a G 4 Particle. Definition pointer Retains eventual pre-assigned decay information – – decay products lifetime G 4 Track Defines the class of objects propagated by the Geant 4 tracking Represents a snapshot of the particle state Aggregates: – – – Maria Grazia Pia a G 4 Particle. Definition a G 4 Dynamic. Particle geometrical information: position, current volume … track ID, parent ID; process which created this G 4 Track weight, used for event biaising

Propagated by the tracking Snapshot of the particle state G 4 Track G 4 Dynamic. Particle Momentum, pre-assigned decay… G 4 Particle. Definition The particle type: G 4 Electron, G 4 Pion. Plus… G 4 Process. Manager Holds the physics sensitivity Process_1 Summary view Process_2 Process_3 The classes involved in building the Physics. List are: • the G 4 Particle. Definition concrete classes G 4 Particle. Definition • the G 4 Process. Manager • the processes Maria Grazia Pia The physics processes

G 4 VProcess Abstract class defining the common interface of all processes in Geant 4 Along. Step Define three kinds of actions: Post. Step – At. Rest actions: decay, annihilation … – Along. Step actions: continuous interactions occuring along the path, like ionisation – Post. Step actions: point-like interactions, like decay in flight, hard radiation… Post. Step A process can implement any combination of the three At. Rest, Along. Step and Post. Step actions: eg: decay = At. Rest + Post. Step Each action defines two methods: – Get. Physical. Interaction. Length() used to limit the step size – either because the process triggers an interaction or a decay – or in other cases, like fraction of energy loss, geometry boundary, user’s limit… – Do. It() • implements the actual action to be applied to the track • implements the related production of secondaries Maria Grazia Pia

Processes, Process. Manager and Stepping G 4 Process. Manager retains three vectors of actions: – – one for the At. Rest methods of the particle At. Rest one for the Along. Step ones one for the Post. Step actions Post. Step these are the vectors which the user sets up in the Physics. List and which are used by the tracking The stepping treats processes generically – it does not know which process it is handling The stepping lets the processes – – cooperate for Along. Step actions Along. Step compete for Post. Step and At. Rest actions Post. Step At. Rest Processes emit also signals to require particular treatment: – – – not. Forced: normal case forced: Post. Step. Do. It action applied anyway; forced: conditionally. Forced: Post. Step. Do. It applied if Along. Step has limited the step Maria Grazia Pia

Invocation sequence of processes: particle in flight At the beginning of the step, determine the step length – – consider all processes attached to the current G 4 Track define the step length as the smallest of the lengths among all Along. Step. Get. Physical. Interaction. Lenght() all Post. Step. Get. Physical. Interaction. Length() Apply all Along. Step. Do. It() actions at once () – – – changes computed from particle state at the beginning of the step accumulated in G 4 Step then applied to G 4 Track, by G 4 Step Apply Post. Step. Do. It() action(s) sequentially, () sequentially as long as the particle is alive – – apply Post. Step. Do. It() of the process which proposed the smallest step length apply forced and conditionnally forced actions Maria Grazia Pia

Invocation sequence of processes: particle at rest If the particle is at rest, is stable and cannot annihilate, it is killed by killed the tracking – more properly said: if a particle at rest has no At. Rest actions defined, it is killed Otherwise determine the lifetime – Take the smallest time among all At. Rest. Get. Physical. Interaction. Lenght() – Called physical interaction length, but it returns a time Apply the At. Rest. Do. It() action of the process which returned the () smallest time Maria Grazia Pia

Processes ordering Ordering of following processes is critical: – assuming n processes, the ordering of the Along. Get. Physical. Interaction. Length of the last processes should be: [n-2] … [n-1] multiple scattering [n] transportation Why ? – – – Processes return a true path length The multiple scattering virtually folds up this true path length into a shorter geometrical path length Based on this new length, the transportation can geometrically limit the step Other processes ordering usually do not matter Maria Grazia Pia

Cuts in Geant 4 In Geant 4 there are no tracking cuts – particles are tracked down to a zero range/kinetic energy Only production cuts exist production cuts – i. e. cuts allowing a particle to be born or not Why are production cuts needed ? Some electromagnetic processes involve infrared divergences – – – this leads to an infinity [huge number] of smaller and smaller energy photons/electrons (such as in Bremsstrahlung, d-ray production) production cuts limit this production to particles above threshold the remaining, divergent part is treated as a continuous effect (i. e. Along. Step action) Maria Grazia Pia

Range vs. energy production cuts The production of a secondary particle is relevant if it can generate visible effects in the detector – otherwise “local energy deposit” A range cut allows to easily define such visibility range cut – – “I want to produce particles able to travel at least 1 mm” criterion which can be applied uniformly across the detector The same energy cut leads to very different ranges energy cut – – for the same particle type, depending on the material for the same material, depending on particle type The user specifies a unique range cut in the Physics. List – – – this range cut is converted into energy cuts each particle (G 4 Particle. With. Cut) converts the range cut into an energy cut, for (G 4 Particle. With. Cut) each material processes then compute the cross-sections based on the energy cut Maria Grazia Pia

Effect of production thresholds In Geant 3 500 Me. V incident proton Pb Liquid Ar Threshold in range: 1. 5 mm 455 ke. V electron energy in liquid Ar 2 Me. V electron energy in Pb Maria Grazia Pia DCUTE = 455 ke. V one must set the cut for delta-rays (DCUTE) either to the Liquid Argon value, thus producing many small unnecessary d-rays in Pb, or to the Pb value, thus killing the drays production everywhere DCUTE = 2 Me. V

Violations of the production threshold In some cases particles are produced even if they are below the production threshold This is intended to let the processes do the best they can It happens typically for – decays – positron production: in order to simulate the resulting photons from the annihilation – hadronic processes: since no infrared divergences affect the cross-sections Note these are not “hard-coded” exceptions, but a sophisticated, generic mechanism of the tracking Maria Grazia Pia

G 4 VUser. Physics. List It is one of the mandatory user classes (abstract class) Pure virtual methods – – – Construct. Particles() Construct. Processes() Set. Cuts() () to be implemented by the user in his/her concrete derived class Maria Grazia Pia

Construct. Particles() To get particle G 4 xxx, you should invoke the static method xxx. Definition() in your Construct. Particles() method: – for example, to have electrons, positrons and photons: void My. Physics. List: : Construct. Particles() { G 4 Electron: : Electron. Definition(); G 4 Positron: : Positron. Definition(); G 4 Gamma: : Gamma. Definition(); } Alternatively, some helper classes are provided: – – – G 4 Boson. Constructor, G 4 Lepton. Constructor G 4 Meson. Constructor, G 4 Baryon. Constructor G 4 Ion. Constructor, G 4 Shortlived. Constructor G 4 Baryon. Constructor baryon. Constructor; baryon. Constructor. Construct. Particle(); Maria Grazia Pia

Construct. Processes() G 4 Process. Manager – – attaches processes to particles sets their ordering Several ways to add a process – – Add. Process Add. Rest. Process, Add. Discrete. Process, Add. Continuous. Process And to order At. Rest/Along. Step/Post. Step actions of processes Set. Process. Ordering – Set. Process. Ordering. To. First, Set. Process. Ordering. To. Last (This is the ordering for the Do. It() methods, the Get. Physical. Interaction. Length() ones have the reverse order) – Various examples available Maria Grazia Pia

Set. Cuts() This pure virtual method is used to define the range cut Recommended way of setting cuts: same cut for all particles – it is possible to set particle dependent cuts, but it requires some care The G 4 VUser. Physics. List base class has a protected member protected: G 4 double default. Cut. Value; (which is set to 1. 0*mm in the constructor) You may change this value in your implementation of Set. Cuts() void My. Physics. List: : Set. Cuts() { default. Cut. Value = 1. 0*mm; Set. Cuts. With. Default(); } Maria Grazia Pia

G 4 User. Limit This class allows the user to define the following limits in a given G 4 Logical. Volume: – Maximum step size – Maximum track length – Maximum track time – Minimum kinetic energy – Minimum range The user can inherit from G 4 User. Limit, or can instantiate the default implementation The object has then to be set to the G 4 Logical. Volume Maria Grazia Pia

G 4 User. Special. Cuts How to activate G 4 User. Limit ? The maximum step size is automatically taken into account by the stepping For the other limits, the G 4 User. Special. Cuts process (discrete G 4 User. Special. Cuts process) can be set in the physics list Maria Grazia Pia

Summary The Physics. List exposes, deliberately, the user to the choice deliberately choice of physics (particles + processes) relevant to his/her application This is a critical task, but guided by the framework Examples can be used as starting point Maria Grazia Pia

Gamma. Ray. Tel. Physics. List … if (particle. Name == "gamma") { // gamma p. Manager->Add. Discrete. Process(new G 4 Photo. Electric. Effect()); p. Manager->Add. Discrete. Process(new G 4 Compton. Scattering()); p. Manager->Add. Discrete. Process(new G 4 Gamma. Conversion()); } else if (particle. Name == "e-") { // electron p. Manager->Add. Process(new G 4 Multiple. Scattering(), -1, 1, 1); p. Manager->Add. Process(new G 4 e. Ionisation(), -1, 2, 2); p. Manager->Add. Process(new G 4 e. Bremsstrahlung(), -1, 3); } else if (particle. Name == "e+") { // positron p. Manager->Add. Process(new G 4 Multiple. Scattering(), -1, 1, 1); p. Manager->Add. Process(new G 4 e. Ionisation(), -1, 2, 2); p. Manager->Add. Process(new G 4 e. Bremsstrahlung(), -1, 3); p. Manager->Add. Process(new G 4 eplus. Annihilation(), 0, -1, 4); select physics processes to be activated for each particle type … Set. Cut. Value(cut. For. Gamma, "gamma"); Set. Cut. Value(cut. For. Electron, "e-"); Set. Cut. Value(cut. For. Electron, "e+"); Maria Grazia Pia set production thresholds

Now we can run our simulation, track particles, produce showers and record the effects in the detectors… …but our job is not limited to simulation only Maria Grazia Pia

Control, monitor and analyse the simulation Maria Grazia Pia

Maria Grazia Pia Detailing the design

Configure the tracker, by modifying the number of active planes, the pitch of the strips, the area of silicon tiles, the material of the converter Configure the calorimeter, by modifying the number of active elements, the Two phases of user actions number of layers – setup of simulation Configure the source – control of event generation and processing Configure digitisation by modifying the threshold Geant 4 provides interfaces for various (G)UI: Configure the histograms User Interface in Geant 4 – – – G 4 UIterminal: C-shell like character terminal G 4 UItcsh: tcsh-like character terminal with command completion, history, etc G 4 UIGAG: Java based GUI G 4 UIOPACS: OPACS-based GUI, command completion, etc G 4 UIBatch: Batch job with macro file G 4 UIXm: Motif-based GUI, command completion, etc Users can select and plug in (G)UI by setting environmental variables setenv G 4 UI_USE_TERMINAL 1 setenv G 4 UI_USE_GAG 1 setenv G 4 UI_USE_XM 1 – Note that Geant 4 library should be installed setting the corresponding environmental variable G 4 VIS_BUILD_GUINAME_SESSION to “ 1” beforehand Maria Grazia Pia

Geant 4 UI command A command consists of – command directory – command – parameter(s) Geant 4 UI command can be issued by – (G)UI interactive command submission – macro file – hard-coded implementation G 4 UImanager* UI = G 4 UImanager: : Get. UIpointer(); UI->Apply. Command("/run/verbose 1"); To get a list of available commands, including your custom ones: /control/manual [directory] (plain text format to standard output) /control/create. HTML [directory] (HTML file) List of built-in commands also in the Application Developers User's Guide Maria Grazia Pia

UI command messenger (G)UI 2. apply messenger 1. register 4. invoke 3. do it UImanager command parameter Maria Grazia Pia Target class

Messenger class To define user commands, one implements a concrete messenger class Constructor – Instantiate command objects, set guidance, parameter information, etc. , and register commands to UImanager Destructor – Delete commands (automatically unregistered) Set. New. Value method – – Convert parameter string to values Invoke appropriate method of target class object Get. Current. Value method – – Get current values from target class Convert to string Maria Grazia Pia

A Gamma. Ray. Tel user command Gamma. Ray. Tel. Detector. Messenger: : Gamma. Ray. Tel. Detector. Messenger (Gamma. Ray. Tel. Detector. Construction * Gamma. Ray. Tel. Det) : Gamma. Ray. Tel. Detector(Gamma. Ray. Tel. Det) { Gamma. Ray. Teldet. Dir = new G 4 UIdirectory("/payload/"); new G 4 UIdirectory Gamma. Ray. Teldet. Dir->Set. Guidance("Gamma. Ray. Tel payload control. "); Set. Guidance // converter material command Converter. Mater. Cmd = new G 4 UIcmd. With. AString("/payload/set. Conv. Mat", this); new G 4 UIcmd. With. AString Converter. Mater. Cmd->Set. Guidance("Select Material of the Converter. "); Set. Guidance Converter. Mater. Cmd->Set. Parameter. Name("choice", false); Set. Parameter. Name Converter. Mater. Cmd->Available. For. States(Idle); Available. For. States } void Gamma. Ray. Tel. Detector. Messenger: : Set. New. Value(G 4 UIcommand* command, G 4 String new. Value) { if (command == Converter. Mater. Cmd) Gamma. Ray. Tel. Detector->Set. Converter. Material(new. Value); } Maria Grazia Pia

Macro A macro is an ASCII file containing UI commands All commands must be given with their full-path directories /control/verbose 2 /control/save. History /run/verbose 2 /gun/particle gamma /gun/energy 1 Ge. V /gun/vertex. Radius 25. cm /gun/source. Type 2 A macro can be executed by – – – /control/execute /control/loop /control/foreach # you can modify the geometry of the telescope via a messenger /payload/set. Nb. Of. TKRLayers 10 /payload/update # run 10 events /run/beam. On 10 Maria Grazia Pia

Visualisation in Geant 4 Visualise the experimental set-up Visualise tracks in the experimental set-up Visualise hits Control of several kinds of visualisation – detector geometry – particle trajectories – hits in the detectors Using abstract G 4 Vis. Manager class – takes 3 -D data from geometry/track/hits – passes on to abstract visualization driver G 4 VGraphics. System (initialization) G 4 VScene. Handler (processing 3 -D data for visualisation) G 4 VViewer (rendering the processed 3 -D data) Maria Grazia Pia

Visualisable Objects You can visualise simulation data such as: detector components – a hierarchical structure of physical volumes – a piece of physical volume, logical volume, and solid – particle trajectories and tracking steps – hits of particles in detector components You can also visualise other user defined objects such as: – – a polyline, that is, a set of successive line segments (e. g. coordinate axes) a marker which marks an arbitrary 3 D position (e. g. eye guides) texts (i. e. character strings for description, comments, or titles) Visualisation is performed either with commands or by writing C++ source codes of user-action classes – various pre-defined commands available (see User Documentation)

Available Graphics Software By default, Geant 4 provides visualisation drivers, i. e. interfaces, for – – – DAWN : Technical high-quality Post. Script output DAWN OPACS: Interactivity, unified GUI OPACS Open. GL: Quick and flexible visualisation Open. GL Open. Inventor: Interactivity, virtual reality, etc. Open. Inventor Ray. Tracer : Photo-realistic rendering Ray. Tracer VRML: Interactivity, 3 D graphics on Web VRML

How to use visualisation drivers Users can select/use visualisation driver(s) by setting environmental variables before compilation: – setenv G 4 VIS_USE_DRIVERNAME 1 Example (DAWNFILE, Open. GLXlib, and VRMLFILE drivers): – – – setenv G 4 VIS_USE_DAWNFILE 1 setenv G 4 VIS_USE_OPENGLX 1 setenv G 4 VIS_USE_VRMLFILE 1 Note that Geant 4 libraries should be installed with setting the corresponding environmental variables G 4 VIS_BUILD_DRIVERNAME_DRIVER to “ 1” beforehand – setenv G 4 VIS_BUILD_DAWNFILE_DRIVER 1

The analysis framework Plot the x-y distribution of impact of the track Plot the energy distribution in the calorimeter. Store significant quantities in a ntuple (energy release in the strips, hit strips) for further analysis Plot histograms during the simulation execution. Talk by Andreas Pfeiffer Lizard Maria Grazia Pia

A simple traceability through User Requirements, Design, Implementation, Test Iterative and incremental process Every release cycle increments the functionality, until all requirements are satisfied Maria Grazia Pia

Geant 4 Gamma. Ray. Telescope advanced example Developed by Riccardo Giannitrapani, Francesco Longo, Giovanni Santin INFN Trieste - Udine Design and documentation in http: //www. ge. infn. it/geant 4/examples/gammaray_telescope/index. html Source code in geant 4/examples/advanced/gammaray_telescope/ Maria Grazia Pia

GLAST -ray telescope Credit: Hytec y r a in GLAST Maria Grazia Pia m i l e Pr Courtesy of F. Longo and R. Giannitrapani, GLAST

Exercise Retrieve the same concepts and functionalities in another advanced example Maria Grazia Pia

Geant 4 installation Installation manual as part of Geant 4 User Documentation Geant 4 User Forum: Installation script to guide the user – Asks questions, user provides answers Install on one of the supported platforms! RH version and other packages may be obtained from CERN distribution Maria Grazia Pia