lcsim-contrib/src/main/java/org/lcsim/contrib/sATLAS

diff -N GenerateSingleParticles.java
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ GenerateSingleParticles.java	9 Sep 2009 04:20:18 -0000	1.1
@@ -0,0 +1,126 @@

+/*
+ * Simple java program to generate single particles of fixed momentum uniformly
+ * distributed in pseudorapidity.
+ */
+
+package org.lcsim.contrib.sATLAS;
+
+import hep.io.stdhep.StdhepEvent;
+import hep.io.stdhep.StdhepWriter;
+import hep.physics.particle.properties.ParticleType;
+import hep.physics.particle.properties.ParticlePropertyManager;
+import java.io.IOException;
+import java.util.Random;
+
+
+/**
+ *
+ * @author partridge
+ */
+public class GenerateSingleParticles{
+
+    //  Edit the following declarations to set desired paramters
+    static String dir = "c:\\";        // Output directory
+    static String file = "muon_pt100_eta2dot5_1000evt";  // File name
+    static String ext = "stdhep";      // File extension
+    static int nevt = 1000;            // Number of events to generate
+    static int pdgid = 13;             // PDG code for particle to generate (13 = muons)
+    static boolean flipsign = true;    // Set to false if you only want a specific charge
+    static double pmin = 100.;         // Minimum particle momentum at 90 degrees (GeV)
+    static double pmax = 100.;         // Maximum particle momentum at 90 degrees (GeV)
+    static boolean pfixed = true;      // Set to false for fixed pt
+    static double etamax = 2.5;        // Set to the maximum pseudorapidity
+    static double sigx = 0.012;        // Luminous region size in x (mm)
+    static double sigy = 0.012;        // Luminous region size in y (mm)
+    static double sigz = 53.4;         // Luminous region size in z (mm)
+
+    public static void main(String[] args) throws IOException {
+
+        //  Instantiate the random number generators
+        Random generator = new Random();
+
+        //  Decode the pdgid
+        ParticleType pid = ParticlePropertyManager.getParticlePropertyProvider().get(pdgid);
+        String pname = pid.getName();
+        
+        //  Open the output file
+        String fname = dir+file+"."+ext;
+        StdhepWriter sw = new StdhepWriter(fname, "Single particles",
+                "Single particles", nevt);
+        sw.setCompatibilityMode(false);
+
+        //  Loop over the events
+        for (int icross = 0; icross < nevt; icross++) {
+
+            //  Generate the momentum at 90 degrees
+            double p90 = pmin + (pmax - pmin) * generator.nextDouble();
+            
+            //  Generate the pseudorapidity and calculate the polar angle
+            double eta = etamax * (1 - 2 * generator.nextDouble());
+            double theta = 2. * Math.atan(Math.exp(-eta));
+
+            //  Figure out the transverse momentum and mass
+            double pt = p90;
+            if (pfixed) pt = p90 * Math.sin(theta);
+            double m = pid.getMass();
+
+            //  Generate the aximutha angle
+            double phi = 2. * Math.PI * generator.nextDouble();
+
+            //  Generate the IP
+            double x0 = sigx * generator.nextGaussian();
+            double y0 = sigy * generator.nextGaussian();
+            double z0 = sigz * generator.nextGaussian();
+            double t0 = 0.;
+
+            //  Fill the event record variables
+            //  Set the event number
+            int nevhep = icross;
+
+            //  Set the number of particles in the event
+            int nhep = 1;
+
+            //  Set the status code of the particle
+            int isthep[] = new int[2];
+            isthep[0] = 1;
+
+            //  Set the particle ID of the particle
+            int idhep[] = new int[2];
+            idhep[0] = pdgid;
+            if (flipsign && generator.nextDouble() > 0.5) idhep[0] = -pdgid;
+
+            //  Set the mother and daughter pointers
+            int jmohep[] = new int[2];
+            int jdahep[] = new int[2];
+            for (int i=0; i<2; i++) {
+                jmohep[i] = 0;
+                jdahep[i] = 0;
+            }
+
+            //  Set the momentum/energy/mass
+            double phep[] = new double[5];
+            phep[0] = pt * Math.cos(phi);
+            phep[1] = pt * Math.sin(phi);
+            phep[2] = pt / Math.tan(theta);
+            double p2 = pt*pt + phep[2]*phep[2];
+            phep[3] = Math.sqrt(p2 + m*m);
+            phep[4] = m;
+
+            //  Set the particle origin
+            double vhep[] = new double[4];
+            vhep[0] = x0;
+            vhep[1] = y0;
+            vhep[2] = z0;
+            vhep[3] = t0;
+
+            //  Create an event record
+            StdhepEvent ev = new StdhepEvent(nevhep, nhep, isthep, idhep, jmohep, jdahep, phep, vhep);
+
+            //  Write out the event record
+            sw.writeRecord(ev);
+        }
+
+        //  Done with generating particles - close the file
+        sw.close();
+    }
+}

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