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Manuscript Title: GENXICC: A Generator for Hadronic Production of the Double Heavy Baryons Ξcc, Ξbc and Ξbb
Authors: Chao-Hsi Chang, Jian-Xiong Wang, Xing-Gang Wu
Program title: GENXICC
Catalogue identifier: ADZJ_v1_0
Distribution format: tar.gz
Journal reference: Comput. Phys. Commun. 177(2007)467
Programming language: FORTRAN77/90.
Computer: Any LINUX based on PC with FORTRAN 77 or FORTRAN90 and GNU C compiler installed.
Operating system: LINUX.
RAM: About 2.0 MB
Keywords: Event generator, Hadronic production, Double-heavy baryon ( Ξcc, Ξbc, Ξbb).
PACS: 14.20.Lq, 12.38.Bx, 12.39.Jh.
Classification: 11.2.

Nature of problem:
Hadronic production of a double-heavy baryons: Ξcc, Ξbc and Ξbb.

Solution method:
The production of the double-heavy baryons is realized by producing a binding double-heavy diquark either (QQ′)[3S1]3bar,6 (Q,Q' = b, c) or (QQ′)[1S0]3bar,6, which is in color anti-triplet 3bar or color sextuplet 6 and in S-wave triplet or singlet configuration respectively, and then by absorbing a proper light quark non-perturbatively. For the production of the various double-heavy baryons Ξcc, Ξbc* and Ξbb, the 'gluon-gluon fusion' mechanism, being the most important, is written precisely in the generator, but two additional mechanisms, i.e. the 'gluon-charm collision' and the 'charm-charm collision' ones, only for Ξcc ( Ξ+cc or Ξ++cc) are written. Furthermore, all the mechanisms are treated consistently within the general-mass flavor-number (GM-VFN) scheme. Specially, to deal with the amplitude and in order to save CPU time as much as possible, the 'improved helicity-approach' is applied for the most complicated gluon-gluon fusion mechanism. The code with a proper option can generate weighted and un-weighted events accordingly as user's wish. Moreover, an interface to PYTHIA is provided to meet ones' needs to generate the 'complete events' of ΞQQ′, i.e. to do the 'showers' of the partons appearing in the initial and final states of the subprocess, and the hadronization for final obtained `showers' etc.

* In fact, there are two kinds of states for Ξbc i.e., one is that the inside b and c are symmetric in 'flavor space' and the other is that b and c are anti-symmetric in 'flavor space' similar to the case for the baryons Λ and Σ0. Let us call them as Ξ1bc for symmetric one and Ξ2bc for antisymmetric one when we need to distinguish them. Due to the electromagnetic interaction between the quarks for instance, the two kinds of states may have different masses (degeneracy broken).

Restrictions:
In GENXICC, the approach to the hadronic production in terms of a 'complete α4s calculation' via the production of a binding diquark state either (QQ)[3S1]3bar or (QQ)[1S0]6 (Q =c, b) for Ξcc and Ξbb production, and via that of a binding diquark state of (bc)[3S1]3bar or (bc)[1S0]3bar or (bc)[3S1]6 or (bc)[1S0]6 for Ξbc is available, but the contributions from the other higher Fock states of the diquark states are not involved. Considering the needs of comparisons and applications in most cases, three mechanisms and their consistent summation for the hadronic production of Ξcc are available. But for most purposes and applications to the baryons Ξbb and Ξbc, which contain b-quark(s) (much heavier than c-quark), only the 'gluon-gluon fusion' mechanism for the production is accurate enough, therefore, here only the 'gluon-gluon fusion' mechanism is available. Moreover, since the polarization of the double-heavy baryons is also strongly effected by hadronization of the double-heavy diquark produced via the mechanisms considered here, so in the present generator only the un-polarized production for the baryons are available.

Running time:
It depends on which option one chooses to match PYTHIA when generating the events and also on which mechanism is chosen for generating the events. Typically, for the most complicated case via gluon-gluon mechanism to generate the mixed events via the intermediate diquark in (cc)[3S1]3bar and (cc)[1S0]6 states, then on a 1.8 GHz Intel P4-processor PC-machine, if taking IDWTUP=1 for PYTHIA option (the meaning will be explained later on), it takes about 20 hours to generate 1000 events, whereas, if IDWTUP=3 (the meaning will be explained later on), it takes only about 40 minutes to generate 106 events.