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Manuscript Title: BCVEGPY2.0: An upgraded version of the generator BCVEGPY with the addition of hadroproduction of the P-wave B_c states
Authors: Chao-Hsi Chang, Jian-Xiong Wang, Xing-Gang Wu
Program title: BCVEGPY
Catalogue identifier: ADTJ_v2_0 Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 174(2006)241
Programming language: FORTRAN 77/90.
Computer: 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 Fortran.
Operating system: UNIX, Linux and Windows.
RAM: About 2.0 MB
Keywords: Event generator, hadronic production, B_c meson, S-wave and P-wave states.
PACS: 13.85.Ni, 12.38.Bx, 14.40.Nd, 14.40.Lb.
Classification: 11.5.
Nature of problem: Hadronic production of B_c meson itself and its excited states.
Solution method: The code with option can generate weighted and un-weighted events. For jet hadronization, an interface to PYTHIA is provided.
Reasons for new version: There are two reasons. One is to provide additional codes for the hadronic production of P-wave excited B_c 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: The integration efficiency over the momentum fractions of the initial partons x₁ and x₂ are improved; The amplitudes for the hadronic production of the color-singlet components corresponding to the four P-wave states, B^_cJ,L=1* or ¹P₁ and ³P_j (J=0,1,2), are included; The amplitudes for P-wave production via the two color-octet components \|(cbbar)₈(¹S₀)g⟩ and \|(cbbar)₈(³S₁)g⟩ are included; For comparison, the S-wave (¹S₀ and ³S₁) hadronic production via the light quark-antiquark annihilation mechanism is also included; For convenience, 24 data files to record the information of the generated events in one run are added; An additional file, parameter.for, is added to set the initial values of the parameters; 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 B_c and its excited states correctly; One switch, `IVEGGRADE', is added to determine whether to use the existing importance sampling function to generate a more precise importance sampling function or not; Two parameters, `IOUTPDF' and `IPDFNUM', are added to determine which type of PDFs to use; The color-flow decomposition for the amplitudes is rewritten by an approximate way, that is adopted in PYTHIA.
Restrictions: The hadronic production of (cbbar)-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.
Running time: Generally speaking, it depends on which option is used to drive PYTHIA when generating the B_c events. Typically, for the hadronic production of the S-wave (cbbar)-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 (cbbar)-quarkonium, the necessary time will be almost two times longer than the S-wave quarkonium production.