GENXICC: A generator for hadronic production of the double heavy baryons ΞccΞcc, ΞbcΞbc and ΞbbΞbb

We write down a generator program for the hadronic production of the double-heavy baryons ΞccΞcc, ΞbcΞbc and ΞbbΞbb according to relevant publications. We name it as GENXICC and we test it by comparing its numerical results with those in references. It is written in a PYTHIA-compatible format and it can be easily implemented into PYTHIA. GENXICC is also written in modularization manner, with make, a GNU C compiler, one may apply the generator to various situations or experimental environments very conveniently.Program summaryProgram title:GENXICCCatalogue identifier:ADZJ_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADZJ_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions:Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.:99 252No. of bytes in distributed program, including test data, etc.:1 432 846Distribution format:tar.gzProgramming language:FORTRAN77/90Computer:Any LINUX based on PC with FORTRAN77 or FORTRAN90 and GNU C compiler installedOperating systems:LINUXRAM:About 2.0 MBClassification:11.2Nature of problem:  Hadronic production of a double-heavy baryons: ΞccΞcc, ΞbcΞbc and ΞbbΞbb.Solution method:  The production of the double-heavy baryons is realized by producing a binding double-heavy diquark either (QQ′)[S13]3¯,6 (Q,Q′=b,cQ,Q′=b,c) or (QQ′)[S01]3¯,6, which is in color anti-triplet 3¯ 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 ΞccΞcc, ΞbcΞbc1 and ΞbbΞbb, 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 ΞccΞcc (Ξcc+ or Ξcc++) 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 unweighted events accordingly as user's wish. Moreover, an interface to PYTHIA is provided to meet ones' needs to generate the ‘complete events’ of ΞQQ′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.Restrictions:  In GENXICC, the approach to the hadronic production in terms of a ‘complete αs4 calculation’ via the production of a binding diquark state either (QQ)[S13]3¯ or (QQ)[S01]6 (Q=c,bQ=c,b) for ΞccΞcc and ΞbbΞbb production, and via that of a binding diquark state of (bc)[S13]3¯ or (bc)[S01]3¯ or (bc)[S13]6 or (bc)[S01]6 for ΞbcΞbc 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 ΞccΞcc are available. But for most purposes and applications to the baryons ΞbbΞbb and ΞbcΞbc, 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 unpolarized 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)[S13]3¯ and (cc)[S01]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.