Gabriele Cosmo
112 lines
5.0 KiB
C++
112 lines
5.0 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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//
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// -------------------------------------------------------------------
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//
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// GEANT4 Class header file
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//
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//
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// File name: G4LPMFunction
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//
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// Author: Mihaly Novak
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//
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// Creation date: 08 October 2025
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//
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// Modifications:
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//
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// Class Description:
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//
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// The `G(s)` and `\phi(s)` Landau Pomeranchuk Migdal (LPM) suppression
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// functions, utilised both in some bremsstrahlung and pair-production models
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// when computing the actual LPM suppression effect, are factored in this util.
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// The functions are pre-computed and interpolated over the `s \in [0,2)`
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// intervall while approximated at `s > 2` values when they converge to unity.
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//
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// `G(s)` and `\phi(s)` are the spin flip and no flip suppression functions of
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// Migdal (Migdal PR,1956) including some slowly converging series to which
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// approximate expressions were derived by Stanev (Stanev at al. PRD,1982).
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// (See e.g. `G4eBremsstrahlungRelModel::ComputeLPMGsPhis` at Geant4-v.11.3.0
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// on the details of the computation.)
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//
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// -------------------------------------------------------------------
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//
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#ifndef G4LPMFunction_h
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#define G4LPMFunction_h 1
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#include "G4Types.hh"
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namespace G4LPMFunction {
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// Precomputed G(s) and Phi(s) LPM functions.
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// Grid: s \in [0, 2.0], ds = 0.05 -> N = 41 points, interleaved (G(s),Phi(s))
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inline constexpr G4double kFuncLPM[] = {
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0.0000E+00, 0.0000E+00, 6.9163E-02, 2.5747E-01, 2.0597E-01, 4.4573E-01,
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3.5098E-01, 5.8373E-01, 4.8095E-01, 6.8530E-01, 5.8926E-01, 7.6040E-01,
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6.7626E-01, 8.1626E-01, 7.4479E-01, 8.5805E-01, 7.9826E-01, 8.8952E-01,
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8.4003E-01, 9.1338E-01, 8.7258E-01, 9.3159E-01, 8.9794E-01, 9.4558E-01,
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9.1776E-01, 9.5640E-01, 9.3332E-01, 9.6483E-01, 9.4560E-01, 9.7143E-01,
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9.5535E-01, 9.7664E-01, 9.6313E-01, 9.8078E-01, 9.6939E-01, 9.8408E-01,
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9.7444E-01, 9.8673E-01, 9.7855E-01, 9.8888E-01, 9.8191E-01, 9.9062E-01,
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9.8467E-01, 9.9204E-01, 9.8695E-01, 9.9321E-01, 9.8884E-01, 9.9417E-01,
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9.9042E-01, 9.9497E-01, 9.9174E-01, 9.9564E-01, 9.9285E-01, 9.9619E-01,
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9.9379E-01, 9.9666E-01, 9.9458E-01, 9.9706E-01, 9.9526E-01, 9.9739E-01,
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9.9583E-01, 9.9768E-01, 9.9632E-01, 9.9794E-01, 9.9674E-01, 9.9818E-01,
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9.9710E-01, 9.9839E-01, 9.9741E-01, 9.9857E-01, 9.9767E-01, 9.9873E-01,
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9.9790E-01, 9.9887E-01, 9.9809E-01, 9.9898E-01, 9.9826E-01, 9.9909E-01,
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9.9840E-01, 9.9918E-01, 9.9856E-01, 9.9926E-01
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};
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// Obtain the `G(s)` and `\phi(s)` LPM suppression functions at any `s >= 0`.
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inline void GetLPMFunctions(G4double& lpmFuncG, G4double& lpmFuncPhi, G4double sVar) {
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// sanity check (s should be >= 0)
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if (sVar < 0.0) {
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lpmFuncG = 0.0;
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lpmFuncPhi = 0.0;
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return;
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}
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// case of `s in [0, 2)` use the precomputed functions and interpolate
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const G4double lpmSLimit = 2.0; // max_s:=2
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const G4double lpmISDelt = 20.0; // deta_s:=0.05, 1/delta_s=20
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if (sVar < lpmSLimit) {
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G4double val = sVar*lpmISDelt;
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G4int ilow = static_cast<G4int>(val);
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val -= ilow;
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ilow *= 2;
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lpmFuncG = (kFuncLPM[ilow+2] - kFuncLPM[ilow] )*val + kFuncLPM[ilow];
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lpmFuncPhi = (kFuncLPM[ilow+3] - kFuncLPM[ilow+1])*val + kFuncLPM[ilow+1];
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return;
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}
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// asymptotic case: G(s), Phi(s) goes to 1.0
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G4double ss = 1.0/(sVar*sVar);
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ss *= ss;
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lpmFuncG = 1.0 - 0.0230655*ss;
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lpmFuncPhi = 1.0 - 0.01190476*ss;
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}
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};
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#endif // G4LPMFunction_h
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