BCVEGPY2.0: An upgraded version of the generator BCVEGPY with the addition of hadroproduction of the P -wave BcBc states

The generator BCVEGPY is upgraded by improving some of its features and by adding the hadroproduction of the P  -wave excited BcBc states (denoted by BcJ,L=1∗ or by hBchBc and χBcχBc). In order to make the generator more efficient, we manipulate the amplitude as compact as possible with special effort. The correctness of the program is tested by various checks. We denote it as BCVEGPY2.0. As for the added part of the P  -wave production, only the dominant gluon–gluon fusion mechanism (gg→BcJ,L=1∗+c¯+b) is taken into account. Moreover, in the program, not only the ability to compute the contributions from the color-singlet components (cb¯)1 to the P  -wave production but also the ability to compute the contributions from the color-octet components (cb¯)8 are available. With BCVEGPY2.0 the contributions from the two ‘color components’ to the production of each of the P-wave states may be computed separately by an option, furthermore, besides individually the event samples of the S-wave and P  -wave (cb¯)-heavy-quarkonium in various correct (realistic) mixtures can be generated by relevant options too.Program summaryTitle of program: BCVEGPYVersion: 2.0 (December, 2004)Catalogue identifier: ADWQProgram summary URL:http://cpc.cs.qub.ac.uk/summaries/ADWQProgram obtained from: CPC Program Library, Queen's University of Belfast, N. IrelandReference to original program: ADTJ (BCVEGPY1.0)Reference in CPC: Comput. Phys. Comm. 159 (2004) 192Does the new version supersede the old program: yesComputer: Any computer with FORTRAN 77 or 90 compiler. The program has been tested on HP-SC45 Sigma-X parallel computer, Linux PCs and Windows PCs with Visual FortranOperating systems: UNIX, Linux and WindowsProgramming language used: FORTRAN 77/90Memory required to execute with typical data: About 2.0 MBNo. of lines in distributed program, including test data, etc.: 124 297No. of bytes in distributed program, including test data, etc.: 1 137 177Distribution format: tar.g2Nature of physical problem:   Hadronic production of BcBc meson itself and its excited states.Method of solution: The code with option can generate weighted and unweighted events. For jet hadronization, an interface to PYTHIA is provided.Reason for the new version: There are two reasons. One is to provide additional codes for the hadronic production of P  -wave excited BcBc states: the four via color-singlet P-wave state directly and the two via color-octet S-wave state accordingly. The other one is to decompose the color-flow factor for the amplitude by an approximate way, that is adopted in PYTHIA.Summary of Revisions:   (1) The integration efficiency over the momentum fractions of the initial partons x1x1 and x2x2 are improved; (2) The amplitudes for the hadronic production of the color-singlet components corresponding to the four P  -wave states, BcJ,L=1∗ or P11 and PJ3 (J=0,1,2J=0,1,2), are included; (3) The amplitudes for P  -wave production via the two color-octet components |(cb¯)8(S01)g〉 and |(cb¯)8(S13)g〉 are included; (4) For comparison, the S  -wave (S01 and S13) hadronic production via the light quark–antiquark annihilation mechanism is also included; (5) For convenience, 24 data files to record the information of the generated events in one run are added; (6) An additional file, parameter.for, is added to set the initial values of the parameters; (7) Two new parameters ‘IMIX’ (IMIX = 0 or 1) and ‘IMIXTYPE’ (IMIXTYPE = 1,  = 2 or  = 3) are added to meet the needs of generating the events for simulating ‘mixing’ or ‘separate’ event samples for various BcBc and its excited states correctly; (8) One switch, ‘IVEGGRADE’, is added to determine whether to use the existed importance sampling function to generate a more precise importance sampling function or not; (9) Two parameters, ‘IOUTPDF’ and ‘IPDFNUM’, are added to determine which type of PDFs to use; (10) The color-flow decomposition for the amplitudes is rewritten by an approximate way, that is adopted in PYTHIA.Restrictions on the complexity of the problem:   The hadronic production of (cb¯)-quarkonium in S-wave and P-wave states via the mechanism of gluon–gluon fusion are given by the ‘complete calculation’ approach of the leading order QCD. The contributions from the other mechanisms for P-wave production which are small comparatively are not included.Typical running time:   Generally speaking, it depends on which option is used to drive PYTHIA when generating the BcBc events. Typically, for the hadronic production of the S  -wave (cb¯)-quarkonium, if the PYTHIA parameter IDWTUP = 1, then it takes about 20 hours on a 1.8 GHz Intel P4-processor machine to generate 1000 events; however if IDWTUP = 3, to generate 106 events, it takes only about 40 minutes. For the hadronic production of the P  -wave (cb¯)-quarkonium, the necessary time will be almost two times longer than the S-wave quarkonium production.