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fix: epsilon and gamma calculations in KinematicsFactory #1580

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fix: epsilon and gamma calculations in KinematicsFactory #1580

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15 changes: 6 additions & 9 deletions common-tools/clas-physics/src/main/java/org/jlab/physics/process/DVCSProcess.java
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Original file line number Diff line number Diff line change
Expand Up @@ -39,8 +39,8 @@ public PhysicsEvent getEvent(PhaseSpace kinematics) {
double t = kinematics.getDimension("t").getValue();
double phi = kinematics.getDimension("phi").getValue();

double min_t = this.t_min(q2, xb);
double max_t = this.t_max(q2, xb);
double min_t = this.t_min(E, q2, xb);
double max_t = this.t_max(E, q2, xb);
double xmin = q2/(2.0*MP*E);
/*System.out.println(" t = " + t + " t-min = "
+ this.t_min(q2, xb) + " t-max = " + this.t_max(q2, xb) +
Expand Down Expand Up @@ -148,15 +148,15 @@ public double getProperty(String key, PhysicsEvent event){
return 0.0;
}

public double t_min(double q2, double xb){
double eps = KinematicsFactory.getEpsilon(q2, xb);
public double t_min(double e, double q2, double xb){
double eps = KinematicsFactory.getEpsilon(e, q2, xb);
double nomin = 2.0*(1.0-xb)*(1.0-Math.sqrt(1+eps*eps)) + eps*eps;
double denom = 4.0*xb*(1.0-xb) + eps*eps;
return q2*(nomin/denom);
}

public double t_max(double q2, double xb){
double eps = KinematicsFactory.getEpsilon(q2, xb);
public double t_max(double e, double q2, double xb){
double eps = KinematicsFactory.getEpsilon(e, q2, xb);
double nomin = 2.0*(1.0-xb)*(1.0+Math.sqrt(1+eps*eps)) + eps*eps;
double denom = 4.0*xb*(1.0-xb) + eps*eps;
return q2*(nomin/denom);
Expand All @@ -167,9 +167,6 @@ public Particle getProton(PhysicsEvent event, double q2, double xb,double t){
LorentzVector cm = new LorentzVector(q2p.vector());
LorentzVector pr = new LorentzVector(0.0,0.0,0.0,0.938);
cm.add(pr);
double min_t = this.t_min(q2, xb);
double max_t = this.t_max(q2, xb);
double scale = (max_t - min_t)/Math.PI;
return new Particle(2212,0.0,0.0,0.0,0.0,0.0,0.0);
//return 1.0;
}
Expand Down
24 changes: 16 additions & 8 deletions common-tools/clas-physics/src/main/java/org/jlab/physics/process/KinematicsFactory.java
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Expand Up @@ -5,7 +5,6 @@
*/
package org.jlab.physics.process;

import org.jlab.clas.pdg.PDGDatabase;
import org.jlab.clas.physics.Particle;
import org.jlab.clas.physics.Vector3;

Expand All @@ -17,13 +16,12 @@ public class KinematicsFactory {

public static double MP = 0.93827;
/**
* returns mu for given kinematics variables
* returns nu for given kinematics variables
* @param q2 transferred momentum
* @param xb Bjorken x
* @return
*/
public static double getMu(double q2, double xb){
//double pmass = PDGDatabase.getParticleMass(2212);
public static double getNu(double q2, double xb){
return q2/(2.0*0.93827*xb);
}
/**
Expand All @@ -34,7 +32,7 @@ public static double getMu(double q2, double xb){
* @return
*/
public static double getEprime(double E, double q2, double xb){
return E - KinematicsFactory.getMu(q2, xb);
return E - KinematicsFactory.getNu(q2, xb);
}
/**
* returns scattered electron angle for given kinematics
Expand All @@ -50,8 +48,17 @@ public static double getTheta(double E, double q2, double xb){
return 2.0*Math.asin(value);
}

public static double getEpsilon(double q2, double xb){
return 2.0*xb*0.93827/q2;
public static double getEpsilon(double e, double q2, double xb){
double nu = KinematicsFactory.getNu(q2, xb);
double gamma = KinematicsFactory.getGamma(q2, xb);
double y = nu/e;
double epsilon_1 = 1 - y - 0.25*y*y*gamma*gamma;
double epsilon_2 = 1 - y + 0.5*y*y + 0.25*y*y*gamma*gamma;
return epsilon_1/epsilon_2;
}

public static double getGamma(double q2, double xb){
return 2.0*xb*0.93827/Math.sqrt(q2);
}

public static double getQ2(double E, double x, double y){
Expand All @@ -68,9 +75,10 @@ public static double getQ2(double E, double x, double y){
public static Particle getElectron(double E, double q2, double xb){
double eprime = KinematicsFactory.getEprime( E, q2, xb);
double theta = KinematicsFactory.getTheta( E, q2, xb);
double pprime = Math.sqrt(eprime*eprime-0.0005*0.0005);
//System.out.println("E-prime = " + eprime + " theta = " + Math.toDegrees(theta));
Vector3 vec = new Vector3();
vec.setMagThetaPhi(eprime, theta, 0.0);
vec.setMagThetaPhi(pprime, theta, 0.0);
return new Particle(11,vec.x(),vec.y(),vec.z(),0.0,0.0,0.0);
}
/**
Expand Down
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