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da0e9ce3 | 1 | #include "EvtGenBase/EvtPatches.hh" |
2 | /******************************************************************************* | |
3 | * Project: BaBar detector at the SLAC PEP-II B-factory | |
4 | * Package: EvtGenBase | |
5 | * Author: Denis Dujmic, ddujmic@slac.stanford.edu | |
6 | * | |
7 | * Copyright (C) 2005 SLAC | |
8 | *******************************************************************************/ | |
9 | ||
10 | #include <assert.h> | |
11 | #include <math.h> | |
12 | #include <iostream> | |
13 | #include "EvtGenBase/EvtComplex.hh" | |
14 | #include "EvtGenBase/EvtLASSAmp.hh" | |
15 | #include "EvtGenBase/EvtDalitzCoord.hh" | |
16 | #include "EvtGenBase/EvtdFunction.hh" | |
17 | #include "EvtGenBase/EvtCyclic3.hh" | |
18 | using std::endl; | |
19 | using EvtCyclic3::Index; | |
20 | using EvtCyclic3::Pair; | |
21 | ||
22 | ||
23 | EvtLASSAmp::EvtLASSAmp(EvtDalitzPlot *dp, | |
24 | EvtCyclic3::Pair pair, | |
25 | double m0, double g0, | |
26 | double a, double r, double cutoff) : | |
27 | EvtAmplitude<EvtDalitzPoint>(), | |
28 | _pair(pair), | |
29 | _m0(m0), | |
30 | _g0(g0), | |
31 | _r(r), | |
32 | _a(a), | |
33 | _cutoff(cutoff) | |
34 | { | |
35 | _dalitzSpace = dp; | |
36 | double ma = dp->m( first(pair) ); | |
37 | double mb = dp->m( second(pair) ); | |
38 | double E0a = 0.5 * (_m0*_m0 + ma*ma - mb*mb) / _m0; | |
39 | _q0 = E0a*E0a - ma*ma; | |
40 | assert(_q0>0); | |
41 | _q0 = sqrt(_q0); | |
42 | } | |
43 | ||
44 | ||
45 | ||
46 | EvtLASSAmp::EvtLASSAmp(const EvtLASSAmp& other) : | |
47 | EvtAmplitude<EvtDalitzPoint>(other), | |
48 | _pair(other._pair), | |
49 | _m0(other._m0), | |
50 | _g0(other._g0), | |
51 | _q0(other._q0), | |
52 | _r(other._r), | |
53 | _a(other._a), | |
54 | _cutoff(other._cutoff) | |
55 | { | |
56 | _dalitzSpace = other._dalitzSpace; | |
57 | } | |
58 | ||
59 | ||
60 | EvtLASSAmp::~EvtLASSAmp() {} | |
61 | ||
62 | ||
63 | ||
64 | EvtComplex | |
65 | EvtLASSAmp::amplitude(const EvtDalitzPoint &dalitzPoint) const { | |
66 | ||
67 | /* | |
68 | ||
69 | Parameterization of Kpi S-wave using LASS scattering data. | |
70 | - Nucl.Phys.B296, 493 (1988) | |
71 | - W.Dunwoodie,http://www.slac.stanford.edu/~wmd/kpi_swave/kpi_swave_fit.note | |
72 | ||
73 | m m0^2*Gamma0/q0 | |
74 | ----------------- + exp(2*i*delta) * -------------------------------- | |
75 | q*cot(delta)-i*q m0^2-m^2 - i*m0*Gamma0*q/m*m0/q0 | |
76 | ||
77 | ||
78 | where q = momentum of K or pi in Kpi system | |
79 | ||
80 | q*cot(delta) = 1/ a + 1/2 * [ r * q**2 ] | |
81 | ||
82 | a = scattering length | |
83 | ||
84 | r = effective range | |
85 | ||
86 | */ | |
87 | ||
88 | double s = dalitzPoint.q(_pair); | |
89 | double m = sqrt(s); | |
90 | double q = dalitzPoint.p(first(_pair), _pair); | |
91 | ||
92 | // elastic scattering | |
93 | double qcotd = 1./_a + 0.5*_r*q*q; | |
94 | EvtComplex lass_elastic = m<_cutoff ? m / ( qcotd - EvtComplex(0,q) ) : 0; | |
95 | ||
96 | // relative phase | |
97 | double cosd=1; | |
98 | double sind=0; | |
99 | if (q>0) { | |
100 | cosd = qcotd*qcotd/(q*q); | |
101 | cosd = sqrt( cosd/(1+cosd) ); | |
102 | sind = sqrt( 1-cosd*cosd ); | |
103 | } | |
104 | EvtComplex lass_phase( cosd, sind); | |
105 | lass_phase *= lass_phase; | |
106 | ||
107 | // K*(1430) | |
108 | double gamma = _g0 * q/m * _m0/_q0; | |
109 | EvtComplex lass_Kstar = (_m0*_m0)*(_g0/_q0)/(_m0*_m0-m*m-EvtComplex(0.,_m0*gamma)); | |
110 | ||
111 | return lass_elastic + lass_phase * lass_Kstar; | |
112 | } |