GENXICC2.1: An improved version of GENXICC for hadronic production of doubly heavy baryons

We present an improved version of GENXICC, which is a generator for hadronic production of the doubly heavy baryons Ξ_cc, Ξ_bc and Ξ_bb and has been introduced by C.H. Chang, J.X. Wang and X.G. Wu [Comput. Phys. Commun. 177 (2007) 467; Comput. Phys. Commun. 181 (2010) 1144]. In comparison with the previous GENXICC versions, we update the program in order to generate the unweighted baryon events more effectively under various simulation environments, whose distributions are now generated according to the probability proportional to the integrand. One Les Houches Event (LHE) common block has been added to produce a standard LHE data file that contains useful information of the doubly heavy baryon and its accompanying partons. Such LHE data can be conveniently imported into PYTHIA to do further hadronization and decay simulation, especially, the color-flow problem can be solved with PYTHIA8.0.

NEW VERSION PROGRAM SUMMARYTitle of program: GENXICC2.1

Program obtained from: CPC Program Library

Reference to original program: GENXICC

Reference in CPC: Comput. Phys. Commun. 177, 467 (2007); Comput. Phys. Commun. 181, 1144 (2010)

Does the new version supersede the old program: No

Computer: Any LINUX based on PC with FORTRAN 77 or FORTRAN 90 and GNU C compiler as well

Operating systems: LINUX

Programming language used: FORTRAN 77/90

Memory required to execute with typical data: About 2.0 MB

No. of bytes in distributed program: About 2 MB, including PYTHIA6.4

Distribution format: .tar.gz

Nature of physical problem: Hadronic production of doubly heavy baryons Ξ_cc, Ξ_bc and Ξ_bb.

Method of solution: The upgraded version with a proper interface to PYTHIA can generate full production and decay events, either weighted or unweighted, conveniently and effectively. Especially, the unweighted events are generated by using an improved hit-and-miss approach.

Reasons for new version: Responding to the feedback from users of CMS and LHCb groups at the Large Hadron Collider, and based on the recent improvements of PYTHIA on the color-flow problem, we improve the efficiency for generating the unweighted events, and also improve the color-flow part for further hadronization. Especially, an interface has been added to import the output production events into a suitable form for PYTHIA8.0 simulation, in which the color-flow during the simulation can be correctly set.

Typical running time: It depends on which option is chosen to match PYTHIA when generating the full events and also on which mechanism is chosen to generate the events. Typically, for the dominant gluon-gluon fusion mechanism to generate the mixed events via the intermediate diquarks in (cc)[3S₁]_3¯ and (cc)[1S₀]₆ states, setting IDWTUP=3 and unwght =.true., it takes 30 min to generate 10⁵ unweighted events on a 2.27 GHz Intel Xeon E5520 processor machine; setting IDWTUP=3 and unwght =.false. or IDWTUP=1 and IGENERATE=0, it only needs 2 min to generate the 10⁵ baryon events (the fastest way, for theoretical purposes only). As a comparison, for previous GENXICC versions, if setting IDWTUP=1 and IGENERATE=1, it takes about 22 hours to generate 1000 unweighted events.

Keywords: Event generator; Doubly heavy baryons; Hadronic production.

Summary of the changes (improvements): (1) The scheme for generating unweighted events has been improved; (2) One Les Houches Event (LHE) common block has been added to record the standard LHE data in order to be the correct input for PYTHIA8.0 for later simulation; (3) We present the code for connecting GENXICC to PYTHIA8.0, where three color-flows have to be correctly set for later simulation. More specifically, we present the changes together with their detailed explanations in the following: