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da0e9ce3 | 1 | C-------------------------------------------------------------------------- |
2 | C | |
3 | C Environment: | |
4 | C This software is part of the EvtGen package developed jointly | |
5 | C for the BaBar and CLEO collaborations. If you use all or part | |
6 | C of it, please give an appropriate acknowledgement. | |
7 | C | |
8 | C Copyright Information: See EvtGen/COPYRIGHT | |
9 | C Copyright (C) 1998 Caltech, UCSB | |
10 | C | |
11 | C Module: EvtBTo3piP00.F | |
12 | C | |
13 | C Description: | |
14 | C | |
15 | C Modification history: | |
16 | C | |
17 | C DJL/RYD August 11, 1998 Module created | |
18 | C | |
19 | C------------------------------------------------------------------------ | |
20 | C=================================================================== | |
21 | C This package is providing a B -->-- 3pions decay generator | |
22 | C Its is composed of the following subroutines: | |
23 | C | |
24 | C [*] HowToUse | |
25 | C This is an How To Use routine where one may find the | |
26 | C implementation of the time dependance: That is to | |
27 | C say that it shows how the output of the routine is | |
28 | C supposed to be used in the mind of the authors. | |
29 | C | |
30 | C=================================================================== | |
31 | C [0] EVT3pions | |
32 | C The routine to be called. Note that on the first call | |
33 | C some initialization will be made, in particular the | |
34 | C computation of a normalization factor designed to help | |
35 | C the subsequent time-dependent generation of events. | |
36 | C The normalisation done inside EVT3pions is such that | |
37 | C at the level of the time implementation, the maximum | |
38 | C time-dependant weight is unity : nothing is to be | |
39 | C computed to generate unity-weight events. The exact | |
40 | C meaning of the above is made explicit in the HowToUse | |
41 | C routine. | |
42 | C [1] first_step_P00 | |
43 | C Generation of the kinematics of the 3 pions | |
44 | C It uses the function ranf which is a random number | |
45 | C generator providing an uniform distribution | |
46 | C of Real*4 random number between 0 and 1 | |
47 | C [2] compute | |
48 | C return the amplitudes of the B0 -->-- 3pions | |
49 | C and of the B0_bar -->-- 3pions | |
50 | C corrected for the generation mechanism | |
51 | C The notations used are the ones of the paper of | |
52 | C A. Snyder and H. Quinn [Phys.Rev.D48 (1993) 2139] | |
53 | C [3] BreitWigner | |
54 | C compute the Breit-Wigner of the contributing rho s | |
55 | C taking into account the cosine term linked to the | |
56 | C zero-helicity of the rho s. There is three forms of | |
57 | C Breit-Wigners available. The first one is the simple | |
58 | C non-relativistic form, while the second and third | |
59 | C ones are more involved relativistic expressions which | |
60 | C in addition incorporate the contributions of three | |
61 | C rho resonances [rho(770:1450:1700)]. The parameters | |
62 | C used are the ones resulting from the ALEPH analysis | |
63 | C which might be found in CERN-PPE:97013 (submitted to | |
64 |