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genie::utils::bwfunc Namespace Reference

Breit Wigner functions. More...

Functions

double BreitWignerLGamma (double W, int L, double mass, double width0, double norm)
double BreitWignerL (double W, int L, double mass, double width0, double norm)
double BreitWigner (double W, double mass, double width, double norm)

Detailed Description

Breit Wigner functions.

Author
Costas Andreopoulos <c.andreopoulos \at cern.ch> University of Liverpool
Created:\n November 22, 2004
License:\n Copyright (c) 2003-2025, The GENIE Collaboration
For the full text of the license visit http://copyright.genie-mc.org

Function Documentation

◆ BreitWigner()

double genie::utils::bwfunc::BreitWigner ( double W,
double mass,
double width,
double norm )

Definition at line 141 of file BWFunc.cxx.

143{
144//Inputs:
145// - W: Invariant mass (GeV)
146// - mass: Resonance mass (GeV)
147// - width: Resonance width
148// - norm: Breit Wigner norm
149
150 //-- sanity checks
151 assert(mass > 0);
152 assert(width > 0);
153 assert(norm > 0);
154 assert(W > 0);
155
156 //-- auxiliary parameters
157 double width_2 = TMath::Power( width, 2);
158 double W_m_2 = TMath::Power( W-mass, 2);
159
160 //-- calculate the Breit Wigner function for the input W
161 double bw = (0.5/kPi) * (width/norm) / (W_m_2 + 0.25*width_2);
162 return bw;
163}

References genie::constants::kPi.

◆ BreitWignerL()

double genie::utils::bwfunc::BreitWignerL ( double W,
int L,
double mass,
double width0,
double norm )

Definition at line 99 of file BWFunc.cxx.

101{
102//Inputs:
103// - W: Invariant mass (GeV)
104// - L: Resonance orbital angular momentum
105// - mass: Resonance mass (GeV)
106// - width0: Resonance width
107// - norm: Breit Wigner norm
108
109 //-- sanity checks
110 assert(mass > 0);
111 assert(width0 > 0);
112 assert(norm > 0);
113 assert(W > 0);
114 assert(L >= 0);
115
116 //-- auxiliary parameters
117 double mN = kNucleonMass;
118 double mPi = kPi0Mass;
119 double m_2 = TMath::Power(mass, 2);
120 double mN_2 = TMath::Power(mN, 2);
121 double mPi_2 = TMath::Power(mPi, 2);
122 double W_2 = TMath::Power(W, 2);
123
124 //-- calculate the L-dependent resonance width
125 double qpW_2 = ( TMath::Power(W_2 - mN_2 - mPi_2, 2) - 4*mN_2*mPi_2 );
126 double qpM_2 = ( TMath::Power(m_2 - mN_2 - mPi_2, 2) - 4*mN_2*mPi_2 );
127 if(qpW_2 < 0) qpW_2 = 0;
128 if(qpM_2 < 0) qpM_2 = 0;
129 double qpW = TMath::Sqrt(qpW_2) / (2*W);
130 double qpM = TMath::Sqrt(qpM_2) / (2*mass);
131 double width = width0 * TMath::Power( qpW/qpM, 2*L+1 );
132
133 //-- calculate the Breit Wigner function for the input W
134 double width_2 = TMath::Power( width, 2);
135 double W_m_2 = TMath::Power( W-mass, 2);
136
137 double bw = (0.5/kPi) * (width/norm) / (W_m_2 + 0.25*width_2);
138 return bw;
139}

References genie::constants::kNucleonMass, genie::constants::kPi, and genie::constants::kPi0Mass.

Referenced by genie::utils::res::BWNorm(), main(), genie::BSKLNBaseRESPXSec2014::XSec(), and genie::ReinSehgalRESPXSec::XSec().

◆ BreitWignerLGamma()

double genie::utils::bwfunc::BreitWignerLGamma ( double W,
int L,
double mass,
double width0,
double norm )

Definition at line 22 of file BWFunc.cxx.

24{
25//Inputs:
26// - W: Invariant mass (GeV)
27// - L: Resonance orbital angular momentum
28// - mass: Resonance mass (GeV)
29// - width0: Resonance width
30// - norm: Breit Wigner norm
31
32 //-- sanity checks
33 assert(mass > 0);
34 assert(width0 > 0);
35 assert(norm > 0);
36 assert(W > 0);
37 assert(L >= 0);
38
39 //-- auxiliary parameters
40 double mN = kNucleonMass;
41 double mPi = kPi0Mass;
42 double m_2 = TMath::Power(mass, 2);
43 double mN_2 = TMath::Power(mN, 2);
44 double W_2 = TMath::Power(W, 2);
45
46 double m=mass;
47 //m_aux1 m_aux2
48 double m_aux1= TMath::Power(mN+mPi, 2);
49 double m_aux2= TMath::Power(mN-mPi, 2);
50
51 double BRPi0 = 0.994; //Npi Branching Ratio
52 double BRgamma0 = 0.006; //Ngamma Branching Ratio
53
54 double widPi0 = width0*BRPi0;
55 double widgamma0= width0*BRgamma0;
56
57 //-- calculate the L-dependent resonance width
58 double EgammaW= (W_2-mN_2)/(2*W);
59 double Egammam= (m_2-mN_2)/(2*m);
60
61
62 if(EgammaW<0) {
63// cout<< "Two small W!!! W is lower than one Nucleon Mass!!!!"<<endl;
64 return 0;
65 }
66 //pPiW pion momentum
67 double pPiW = 0;
68 //
69 if(W_2>m_aux1) pPiW = TMath::Sqrt((W_2-m_aux1)*(W_2-m_aux2))/(2*W);
70
71 double pPim = TMath::Sqrt((m_2-m_aux1)*(m_2-m_aux2))/(2*m);
72
73 //double TPiW = pPiW*TMath::Power(pPiW*rDelta, 2*L)/(1+TMath::Power(pPiW*rDelta, 2));
74 //double TPim = pPim*TMath::Power(pPim*rDelta, 2*L)/(1+TMath::Power(pPim*rDelta, 2));
75
76 // Form factors
77 //double fgammaW= 1/(TMath::Power(1+EgammaW*EgammaW/0.706, 2)*(1+EgammaW*EgammaW/3.519));
78 //double fgammam= 1/(TMath::Power(1+Egammam*Egammam/0.706, 2)*(1+Egammam*Egammam/3.519));
79 double fgammaW= 1/(TMath::Power(1+EgammaW*EgammaW/0.706, 2));
80 double fgammam= 1/(TMath::Power(1+Egammam*Egammam/0.706, 2));
81
82
83 double EgammaW_3=TMath::Power(EgammaW, 3);
84 double Egammam_3=TMath::Power(Egammam, 3);
85 double fgammaW_2=TMath::Power(fgammaW, 2);
86 double fgammam_2=TMath::Power(fgammam, 2);
87
88 //double width = widPi0*(TPiW/TPim)+widgamma0*(EgammaW_3*fgammaW_2/(Egammam_3*fgammam_2));
89 double width = widPi0*TMath::Power((pPiW/pPim),3)+widgamma0*(EgammaW_3*fgammaW_2/(Egammam_3*fgammam_2));
90 //-- calculate the Breit Wigner function for the input W
91 double width_2 = TMath::Power( width, 2);
92 double W_m_2 = TMath::Power( W-mass, 2);
93
94 double bw = (0.5/kPi) * (width/norm) / (W_m_2 + 0.25*width_2);
95
96 return bw;
97}

References genie::constants::kNucleonMass, genie::constants::kPi, and genie::constants::kPi0Mass.

Referenced by genie::ReinSehgalRESPXSec::XSec().

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