Gabriele Cosmo
295 lines
9.9 KiB
C++
295 lines
9.9 KiB
C++
//
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// ********************************************************************
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// * License and Disclaimer *
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// * *
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// * The Geant4 software is copyright of the Copyright Holders of *
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// * the Geant4 Collaboration. It is provided under the terms and *
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// * conditions of the Geant4 Software License, included in the file *
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// * LICENSE and available at http://cern.ch/geant4/license . These *
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// * include a list of copyright holders. *
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// * *
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// * Neither the authors of this software system, nor their employing *
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// * institutes,nor the agencies providing financial support for this *
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// * work make any representation or warranty, express or implied, *
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// * regarding this software system or assume any liability for its *
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// * use. Please see the license in the file LICENSE and URL above *
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// * for the full disclaimer and the limitation of liability. *
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// * *
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// * This code implementation is the result of the scientific and *
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// * technical work of the GEANT4 collaboration. *
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// * By using, copying, modifying or distributing the software (or *
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// * any work based on the software) you agree to acknowledge its *
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// * use in resulting scientific publications, and indicate your *
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// * acceptance of all terms of the Geant4 Software license. *
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// ********************************************************************
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//
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// G4MuonDecayChannelWithSpin class implementation
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//
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// References:
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// - Florian Scheck "Muon Physics", in Physics Reports
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// (Review Section of Physics Letters) 44, No. 4 (1978)
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// 187-248. North-Holland Publishing Company, Amsterdam at page 210 cc.
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// - W.E. Fisher and F. Scheck, Nucl. Phys. B83 (1974) 25.
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// Authors: P.Gumplinger and T.MacPhail, 17 August 2004
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// --------------------------------------------------------------------
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#include "G4MuonDecayChannelWithSpin.hh"
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#include "G4DecayProducts.hh"
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#include "G4LorentzVector.hh"
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#include "G4PhysicalConstants.hh"
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#include "G4SystemOfUnits.hh"
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#include "Randomize.hh"
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G4MuonDecayChannelWithSpin::G4MuonDecayChannelWithSpin(const G4String& theParentName,
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G4double theBR)
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: G4MuonDecayChannel(theParentName, theBR)
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{}
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G4MuonDecayChannelWithSpin&
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G4MuonDecayChannelWithSpin::operator=(const G4MuonDecayChannelWithSpin& right)
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{
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if (this != &right) {
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kinematics_name = right.kinematics_name;
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verboseLevel = right.verboseLevel;
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rbranch = right.rbranch;
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// copy parent name
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delete parent_name;
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parent_name = new G4String(*right.parent_name);
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// clear daughters_name array
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ClearDaughtersName();
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// recreate array
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numberOfDaughters = right.numberOfDaughters;
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if (numberOfDaughters > 0) {
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daughters_name = new G4String*[numberOfDaughters];
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// copy daughters name
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for (G4int index = 0; index < numberOfDaughters; ++index) {
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daughters_name[index] = new G4String(*right.daughters_name[index]);
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}
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}
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}
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return *this;
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}
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G4DecayProducts* G4MuonDecayChannelWithSpin::DecayIt(G4double)
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{
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// This version assumes V-A coupling with 1st order radiative correctons,
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// the standard model Michel parameter values, but
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// gives incorrect energy spectrum for neutrinos
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#ifdef G4VERBOSE
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if (GetVerboseLevel() > 1) G4cout << "G4MuonDecayChannelWithSpin::DecayIt ";
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#endif
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CheckAndFillParent();
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CheckAndFillDaughters();
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// parent mass
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G4double parentmass = G4MT_parent->GetPDGMass();
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G4double EMMU = parentmass;
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// daughters'mass
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G4double daughtermass[3];
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// G4double sumofdaughtermass = 0.0;
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for (G4int index = 0; index < 3; ++index) {
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daughtermass[index] = G4MT_daughters[index]->GetPDGMass();
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// sumofdaughtermass += daughtermass[index];
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}
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G4double EMASS = daughtermass[0];
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// create parent G4DynamicParticle at rest
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G4ThreeVector dummy;
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auto parentparticle = new G4DynamicParticle(G4MT_parent, dummy, 0.0);
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// create G4Decayproducts
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auto products = new G4DecayProducts(*parentparticle);
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delete parentparticle;
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// calculate electron energy
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G4double michel_rho = 0.75; // Standard Model Michel rho
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G4double michel_delta = 0.75; // Standard Model Michel delta
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G4double michel_xsi = 1.00; // Standard Model Michel xsi
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G4double michel_eta = 0.00; // Standard Model eta
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G4double rndm, x, ctheta;
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G4double FG;
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G4double FG_max = 2.00;
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G4double W_mue = (EMMU * EMMU + EMASS * EMASS) / (2. * EMMU);
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G4double x0 = EMASS / W_mue;
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G4double x0_squared = x0 * x0;
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// ***************************************************
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// x0 <= x <= 1. and -1 <= y <= 1
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//
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// F(x,y) = f(x)*g(x,y); g(x,y) = 1.+g(x)*y
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// ***************************************************
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// ***** sampling F(x,y) directly (brute force) *****
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const std::size_t MAX_LOOP = 10000;
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for (std::size_t loop_count = 0; loop_count < MAX_LOOP; ++loop_count) {
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// Sample the positron energy by sampling from F
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rndm = G4UniformRand();
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x = x0 + rndm * (1. - x0);
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G4double x_squared = x * x;
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G4double F_IS, F_AS, G_IS, G_AS;
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F_IS = 1. / 6. * (-2. * x_squared + 3. * x - x0_squared);
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F_AS = 1. / 6. * std::sqrt(x_squared - x0_squared) * (2. * x - 2. + std::sqrt(1. - x0_squared));
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G_IS = 2. / 9. * (michel_rho - 0.75) * (4. * x_squared - 3. * x - x0_squared);
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G_IS = G_IS + michel_eta * (1. - x) * x0;
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G_AS = 3. * (michel_xsi - 1.) * (1. - x);
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G_AS =
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G_AS + 2. * (michel_xsi * michel_delta - 0.75) * (4. * x - 4. + std::sqrt(1. - x0_squared));
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G_AS = 1. / 9. * std::sqrt(x_squared - x0_squared) * G_AS;
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F_IS = F_IS + G_IS;
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F_AS = F_AS + G_AS;
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// *** Radiative Corrections ***
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const G4double omega = std::log(EMMU / EMASS);
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G4double R_IS = F_c(x, x0, omega);
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G4double F = 6. * F_IS + R_IS / std::sqrt(x_squared - x0_squared);
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// *** Radiative Corrections ***
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G4double R_AS = F_theta(x, x0, omega);
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rndm = G4UniformRand();
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ctheta = 2. * rndm - 1.;
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G4double G = 6. * F_AS - R_AS / std::sqrt(x_squared - x0_squared);
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FG = std::sqrt(x_squared - x0_squared) * F * (1. + (G / F) * ctheta);
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if (FG > FG_max) {
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G4Exception("G4MuonDecayChannelWithSpin::DecayIt()", "PART113", JustWarning,
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"Problem in Muon Decay: FG > FG_max");
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FG_max = FG;
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}
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rndm = G4UniformRand();
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if (FG >= rndm * FG_max) break;
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}
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G4double energy = x * W_mue;
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rndm = G4UniformRand();
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G4double phi = twopi * rndm;
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if (energy < EMASS) energy = EMASS;
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// Calculate daughter momentum
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G4double daughtermomentum[3];
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daughtermomentum[0] = std::sqrt(energy * energy - EMASS * EMASS);
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G4double stheta = std::sqrt(1. - ctheta * ctheta);
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G4double cphi = std::cos(phi);
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G4double sphi = std::sin(phi);
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// Coordinates of the decay positron with respect to the muon spin
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G4double px = stheta * cphi;
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G4double py = stheta * sphi;
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G4double pz = ctheta;
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G4ThreeVector direction0(px, py, pz);
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direction0.rotateUz(parent_polarization);
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auto daughterparticle0 =
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new G4DynamicParticle(G4MT_daughters[0], daughtermomentum[0] * direction0);
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products->PushProducts(daughterparticle0);
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// daughter 1 ,2 (neutrinos)
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// create neutrinos in the C.M frame of two neutrinos
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G4double energy2 = parentmass - energy;
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G4double vmass = std::sqrt((energy2 - daughtermomentum[0]) * (energy2 + daughtermomentum[0]));
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G4double beta = -1.0 * daughtermomentum[0] / energy2;
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G4double costhetan = 2. * G4UniformRand() - 1.0;
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G4double sinthetan = std::sqrt((1.0 - costhetan) * (1.0 + costhetan));
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G4double phin = twopi * G4UniformRand() * rad;
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G4double sinphin = std::sin(phin);
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G4double cosphin = std::cos(phin);
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G4ThreeVector direction1(sinthetan * cosphin, sinthetan * sinphin, costhetan);
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auto daughterparticle1 = new G4DynamicParticle(G4MT_daughters[1], direction1 * (vmass / 2.));
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auto daughterparticle2 =
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new G4DynamicParticle(G4MT_daughters[2], direction1 * (-1.0 * vmass / 2.));
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// boost to the muon rest frame
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G4LorentzVector p4;
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p4 = daughterparticle1->Get4Momentum();
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p4.boost(direction0.x() * beta, direction0.y() * beta, direction0.z() * beta);
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daughterparticle1->Set4Momentum(p4);
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p4 = daughterparticle2->Get4Momentum();
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p4.boost(direction0.x() * beta, direction0.y() * beta, direction0.z() * beta);
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daughterparticle2->Set4Momentum(p4);
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products->PushProducts(daughterparticle1);
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products->PushProducts(daughterparticle2);
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daughtermomentum[1] = daughterparticle1->GetTotalMomentum();
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daughtermomentum[2] = daughterparticle2->GetTotalMomentum();
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// output message
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#ifdef G4VERBOSE
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if (GetVerboseLevel() > 1) {
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G4cout << "G4MuonDecayChannelWithSpin::DecayIt ";
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G4cout << " create decay products in rest frame " << G4endl;
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G4double TT = daughterparticle0->GetTotalEnergy() + daughterparticle1->GetTotalEnergy()
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+ daughterparticle2->GetTotalEnergy();
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G4cout << "e " << daughterparticle0->GetTotalEnergy() / MeV << G4endl;
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G4cout << "nu1" << daughterparticle1->GetTotalEnergy() / MeV << G4endl;
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G4cout << "nu2" << daughterparticle2->GetTotalEnergy() / MeV << G4endl;
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G4cout << "total" << (TT - parentmass) / keV << G4endl;
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if (GetVerboseLevel() > 2) {
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products->DumpInfo();
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}
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}
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#endif
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return products;
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}
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G4double G4MuonDecayChannelWithSpin::R_c(G4double x, G4double omega)
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{
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auto n_max = (G4int)(100. * x);
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if (n_max < 10) n_max = 10;
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G4double L2 = 0.0;
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for (G4int n = 1; n <= n_max; ++n) {
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L2 += std::pow(x, n) / (n * n);
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}
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G4double r_c;
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r_c = 2. * L2 - (pi * pi / 3.) - 2.;
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r_c = r_c + omega * (1.5 + 2. * std::log((1. - x) / x));
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r_c = r_c - std::log(x) * (2. * std::log(x) - 1.);
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r_c = r_c + (3. * std::log(x) - 1. - 1. / x) * std::log(1. - x);
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return r_c;
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}
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