1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
|
// -*- C++ -*-
//
// TwoOffShellCalculator.h is a part of Herwig++ - A multi-purpose Monte Carlo event generator
// Copyright (C) 2002-2011 The Herwig Collaboration
//
// Herwig++ is licenced under version 2 of the GPL, see COPYING for details.
// Please respect the MCnet academic guidelines, see GUIDELINES for details.
//
#ifndef HERWIG_TwoOffShellCalculator_H
#define HERWIG_TwoOffShellCalculator_H
//
// This is the declaration of the TwoOffShellCalculator class.
//
#include "WidthCalculatorBase.h"
#include "GenericMassGenerator.h"
#include "TwoOffShellCalculator.fh"
#include "OneOffShellCalculator.fh"
#include "Herwig++/Utilities/GSLIntegrator.h"
namespace Herwig {
using namespace ThePEG;
struct TwoOffShellIntegrand;
/** \ingroup PDT
*
* Use <code>WidthCalculatorBase</code> objects to integrate over the mass of two
* external particles which can be off-shell for running width calculations.
*
* @see WidthCalculatorBase
* @see TwoOffShellIntegrand
*/
class TwoOffShellCalculator: public WidthCalculatorBase {
/**
* The TwoOffShellIntegrand class is a friend to allow access to the private
* members for the integration.
*/
friend struct TwoOffShellIntegrand;
public:
/**
* Constructor which should be used setting all the required members.
* @param inloc The mass which is off-shell and to be integrated over.
* @param inwidth Pointer to the WidthGeneratorBase object which calculates
* the partial width for a given mass of the off-shell particle. This
* should be a OneOffShellCalculator instance.
* @param inmass Pointer to the GenericMassGenerator for the off-shell particle.
* @param inmin1 The minimum mass for the first off-shell particle.
* @param inmin2 The minimum mass for the second off-shell particle.
*/
TwoOffShellCalculator(int inloc, WidthCalculatorBasePtr inwidth,
GenericMassGeneratorPtr inmass,
Energy inmin2,Energy inmin1)
: _themass(inloc),_minmass(inmin2),_mother(inmin1),_oneoffwidth(inwidth),
_massptr(inmass)
{}
/**
* member to calculate the partial width.
* @param scale The mass squared for the decaying particle.
* @return The partial width.
*/
Energy partialWidth(Energy2 scale) const;
/**
* Get the mass of one of the decay products. This must be
* implemented in classes inheriting from this one.
* @param imass The mass required.
* @param mass The new value.
* @return The mass required.
*/
void resetMass(int imass,Energy mass) {
_oneoffwidth->resetMass(imass,mass);
}
/**
* Get the mass of one of the decay products. This must be
* implemented in classes inheriting from this one.
* @param imass The mass required.
* @return The mass required.
*/
Energy getMass(const int imass) const {
return _oneoffwidth->getMass(imass);
}
/**
* Get the masses of all bar the one specified. Used to get the limits
* for integration.
* @param imass The particle not needed
* @return The sum of the other masses.
*/
Energy otherMass(const int imass) const {
return _oneoffwidth->otherMass(imass);
}
protected:
/**
* The integrand.
* @param mass The mass of the second off-shell particle,
* @return The differential rate.
*/
Energy dGamma(Energy mass) const {
_oneoffwidth->resetMass(_themass,mass);
Energy wgt = (_oneoffwidth->partialWidth(_scale));
wgt*=(_massptr->weight(mass));
return wgt;
}
private:
/**
* Private and non-existent assignment operator.
*/
TwoOffShellCalculator & operator=(const TwoOffShellCalculator &);
private:
/**
* The second mass which is offshell
*/
int _themass;
/**
* the minimum allowed mass
*/
Energy _minmass;
/**
* sum of the masses of the other decay products
*/
Energy _mother;
/**
* pointer to object calculating the width for one-off shell particle.
*/
WidthCalculatorBasePtr _oneoffwidth;
/**
* pointer to object calculating the mass of the particle
*/
GenericMassGeneratorPtr _massptr;
/**
* integrator
*/
GSLIntegrator _integrator;
/**
* the mass squared of the decaying particle
*/
mutable Energy2 _scale;
};
/** \ingroup PDT
* Class for the integrand of a matrix element where two of the outgoing
* particles is off-shell. This class is used by the TwoOffShellCalculator class
* to perform the integral.
*/
struct TwoOffShellIntegrand {
/**
* Constructor.
* @param in Pointer to the OneOffShellCalculator class this is doing the
* integration for.
* @param m2 The mass squared of the off-shell particle for the Jacobian
* transform.
* @param mw The mass times width of the off-shell particle for the Jacobian
* transform.
*/
TwoOffShellIntegrand(tcTwoOffShellCalculatorPtr in,Energy2 m2,Energy2 mw)
: _integrand(in),_mass2(m2),_mwidth(mw)
{}
/**
* Retreive function value
*/
Energy operator ()(double x) const {
return _integrand->dGamma(sqrt(_mass2+_mwidth*tan(x)));
}
/** Argument type for the GSLIntegrator */
typedef double ArgType;
/** Return type for the GSLIntegrator */
typedef Energy ValType;
private:
/**
* pointer to the decay integrator
*/
cTwoOffShellCalculatorPtr _integrand;
/**
* The mass squared for the off-shell particle for the Jacobian transform.
*/
Energy2 _mass2;
/**
* The mass times width for the off-shell particle for the Jacobian transform.
*/
Energy2 _mwidth;
};
}
#endif /* HERWIG_TwoOffShellCalculator_H */
|
