B0tracker basics

benchmarks/b0_tracker/scripts/gen_forward_protons.cxx

+#include "HepMC3/GenEvent.h"
+#include "HepMC3/ReaderAscii.h"
+#include "HepMC3/WriterAscii.h"
+#include "HepMC3/Print.h"
+
+#include <iostream>
+#include <random>
+#include <cmath>
+#include <math.h>
+
+#include "TMath.h"
+
+#include "common_bench/particles.h"
+
+using namespace HepMC3;
+
+/** Generate electrons in the central region.
+ *  This is for testing detectors in the "barrel" region.
+ */
+void gen_forward_protons(int n_events = 100, 
+                     const char* out_fname = "forward_protons.hepmc")
+{
+  double cos_theta_min = std::cos( 140.0*(M_PI/180.0));
+  double cos_theta_max = std::cos(170.0*(M_PI/180.0));
+
+  const double M_p = common_bench::particleMap.at(2212).mass;
+
+  WriterAscii hepmc_output(out_fname);
+  int events_parsed = 0;
+  GenEvent evt(Units::GEV, Units::MM);
+
+  // Random number generator
+  TRandom *r1 = new TRandom();
+
+  for (events_parsed = 0; events_parsed < n_events; events_parsed++) {
+    // FourVector(px,py,pz,e,pdgid,status)
+    // type 4 is beam
+    // pdgid 11 - electron
+    // pdgid 111 - pi0
+    // pdgid 2212 - proton
+    GenParticlePtr p1 =
+        std::make_shared<GenParticle>(FourVector(0.0, 0.0, 10.0, 10.0), 2212, 4);
+    GenParticlePtr p2 = std::make_shared<GenParticle>(
+        FourVector(0.0, 0.0, 0.0, M_p), 2212, 4);
+
+    // Define momentum
+    Double_t p     = r1->Uniform(1.0, 10.0);
+    Double_t phi   = r1->Uniform(0.0, 2.0 * M_PI);
+    Double_t costh = r1->Uniform(cos_theta_min, cos_theta_max);
+    Double_t th    = std::acos(costh);
+    Double_t px    = p * std::cos(phi) * std::sin(th);
+    Double_t py    = p * std::sin(phi) * std::sin(th);
+    Double_t pz    = p * std::cos(th);
+    // Generates random vectors, uniformly distributed over the surface of a
+    // sphere of given radius, in this case momentum.
+    // r1->Sphere(px, py, pz, p);
+
+    //std::cout << std::sqrt(px*px + py*py + pz*pz) - p << " is zero? \n";
+
+    // type 1 is final state
+    // pdgid 11 - electron 0.510 MeV/c^2
+    GenParticlePtr p3 = std::make_shared<GenParticle>(
+        FourVector(px, py, pz, sqrt(p * p + (M_p * M_p))), 2212, 1);
+
+    GenVertexPtr v1 = std::make_shared<GenVertex>();
+    v1->add_particle_in(p1);
+    v1->add_particle_in(p2);
+
+    v1->add_particle_out(p3);
+    evt.add_vertex(v1);
+
+    if (events_parsed == 0) {
+      std::cout << "First event: " << std::endl;
+      Print::listing(evt);
+    }
+
+    hepmc_output.write_event(evt);
+    if (events_parsed % 10000 == 0) {
+      std::cout << "Event: " << events_parsed << std::endl;
+    }
+    evt.clear();
+  }
+  hepmc_output.close();
+  std::cout << "Events parsed and written: " << events_parsed << std::endl;
+}