Include the charge in the energy loss computation (#1138)

* include the charge in the energy loss computation

* add java doc

Author: ftouchte

common-tools/clas-tracking/src/main/java/org/jlab/clas/tracking/kalmanfilter/Material.java

@@ -59,7 +59,14 @@ public Material clone(double newThickness) {
         return new Material(this.name, newThickness, this.density, this.ZoverA, this.X0, this.IeV, this.units);
     }
     // RDV make units a property of the material
-    public double getEloss(double p, double mass) {
+    /**
+     * Compute the energy loss.
+     * 
+     * @param p momentum of the particle crossing the material volume
+     * @param mass mass of the particle crossing the material volume
+     * @param charge charge (in unit of e) of the particle crossing the material volume
+     */
+    public double getEloss(double p, double mass, int charge) {
         if(mass==0) return 0;
         double beta = p / Math.sqrt(p * p + mass * mass);
         double s = PhysicsConstants.massElectron() / mass;
@@ -69,11 +76,21 @@ public double getEloss(double p, double mass) {
         double K = 0.000307075 * units.value() * units.value(); //  GeV mol-1 cm2
         double I = this.IeV * 1E-9;
         double logterm = 2. * PhysicsConstants.massElectron() * beta * beta * gamma * gamma * Wmax / (I * I);
-        double dE = this.thickness * this.density * K * this.ZoverA
+        double dE = this.thickness * this.density * K * charge * charge *this.ZoverA
                 * (0.5 * Math.log(logterm) - beta * beta) / beta / beta; //in GeV
         return dE;
     }
 
+    /**
+     * Compute the energy loss assuming the charge is 1. See {@link Material#getEloss(double, double, int)}.
+     * 
+     * @param p momentum of the particle crossing the material volume
+     * @param mass mass of the particle crossing the material volume
+     */
+    public double getEloss(double p, double mass) {
+        return getEloss(p, mass, 1);
+    }
+
     @Override
     public String toString() {
         String s = "Material: ";