Charybdis

Charybdis is designed to simulate the production and decay of black holes in hadron collider experiments, according to theories with TeV-scale gravity and extra spatial dimensions. The production of the black hole is assumed to take place with a basically geometrical cross section. The decay then takes place via Hawking radiation using the D-dimensional grey-body factors.

If you use the code please reference

C.M. Harris, P. Richardson and B.R. Webber, CHARYBDIS: A Black Hole Event Generator, JHEP 0308:033, hep-ph/0307305, 2003;
C.M. Harris, P. Kanti, Hawking radiation from a (4+n)-dimensional black hole: Exact results for the Schwarzschild phase, JHEP 0310:014, hep-ph/0309054, 2003.

The first of these is available here as either postscript or html.

The generator itself only performs the production and decay of the black hole. It is interfaced, via the Les Houches accord, to either HERWIG or PYTHIA to perform the parton shower evolution of the partons produced in the decay and their hadronization.

The most recent version of the code is 1.003, which includes the Yoshino-Rychkov cross section enhancement factors, an optional new "boiling remnant" model, relabeling of the hard process as a black hole (in HERWIG only), compatibility with a range of Fortran 77 and 90 compilers, and changes so that the parameters can be reset in the main HERWIG or PYTHIA program.

• Version 1.003 is available here as a gzipped tar file.

• Version 1.002 fixed a problem with using the internal PYTHIA PDFs.
• Version 1.001 fixed a bug due to converting the variable D to TOTDIM in the code.
• First version of the code.

As the code is designed to run with either HERWIG or PYTHIA there are a few things which need to be set up.

You should have the following code:

• charybdis1003.F the code for the black hole generator;
• dummy.F the dummy routines needed if you are not using PDFLIB;
• mainpythia.f example main program for PYTHIA;
• mainherwig.f example main program for HERWIG;
• charybdis1003.inc include file for the black hole event generator.

In addition to this you will also need a Les Houches accord compliant version of either HERWIG or PYTHIA with both the dummy Les Houches routines UPINIT and UPEVNT and the dummy PDFLIB subroutines PDFSET and STRUCTM deleted. For HERWIG the first Les Houches compliant version is HERWIG6.500, for PYTHIA you will need a version above 6.220.

In the Les Houches routines the beams are specified as follows:

• IDBMUP(1),IDBMUP(2) PDG codes for the beam particles (only protons and antiprotons allowed) [2212,2212]
  
• EBMUP(1),EBMUP(2) energies of the beam particles [7000.,7000.]

The CHARYBDIS parameters available to the user are as follows. Their default values are set in charybdis1003.F; any of them can be changed in the main program, as shown in the samples mainpythia.f and mainherwig.f.

• MPLNCK the Planck Mass [1000.]

• MSSDEF shows whose definition of the Planck Mass you are using - see Appendix A of hep-ph/0110127 for a comparison [2]

• GTSCA sets momentum scale for calling PDFs (.TRUE. is using the inverse Schwarzschild radius and .FALSE. is using sqrt(s) - see discussion on p.12 of hep-ph/0106219 but note that the cross sections in this paper were NOT calculated with GTSCA=.TRUE. even though it suggests they were) [F]

• TOTDIM the total number of dimensions (i.e. 4+extra) [6]

• MINMSS the minimum mass of the black holes to be produced [5000.]

• MAXMSS the maximum mass of the black holes to be produced [14000.]

• NBODY the number of particles produced in the decay of the black hole remnant [2]

• TIMVAR time variation of the black hole's Hawking temperature (.TRUE. is on, .FALSE. is off) [T]

• MSSDEC the type of particles to produce in the decay, 1= only light SM particles, 2= light SM particles + top W/Z and 3= all SM particles [3]

• GRYBDY controls the use of the grey-body factors, for GRYBDY=.TRUE. the correct D-dimensional grey-body factors are used whereas for GRYBDY=.FALSE. the black-body spectrum is used [T]

• KINCUT Controls the termination of the Schwarzschild phase. For KINCUT=.TRUE. the Schwarzschild phase terminates when an emission is selected with energy greater than the black hole mass whereas for KINCUT=.FALSE. the Schwarzschild phase is terminated when the mass of the black hole remnant is less than the Planck mass [F]

• YRCSEC controls whether the Yoshino-Rychkov enhancement factors are used in computing the cross section (see Phys.Rev.D71:104028, 2005 [hep-th/0503171]) [F]

• THWMAX maximum value of the Hawking temperature (GeV). If a larger value is generated during decay, it is reset to this [1000.]

• RMBOIL controls whether to use the "boiling remnant" model, in which the black hole decay continues below the Planck scale, with temperature limited by THWMAX. (This option is inconsistent with the use of KINCUT=.TRUE.) [F]

• RMMINM minimum remnant mass. If the "boiling remnant" model is used, this should be less than MPLNCK, otherwise it is set equal to MPLNCK if smaller [1000.]

• IBHPRN print out option 0=no printout, 1=errors only, 2=errors+info. [1]

In the Makefile you must specify which general purpose event generator, i.e.

• GENERATOR = HERWIG for HERWIG

• GENERATOR = PYTHIA for PYTHIA

• PDFLIB = PDFLIB for PDFLIB

• PDFLIB =                      otherwise.

If you extract the code to run it separately then the following should be taken into account.

• charybdis1003.F will produce the HERWIG version by default when compiled the flag -DPYTHIA should be added if the PYTHIA version is required.

• dummy.F will by default produce the version for use without PDFLIB the flag -DPDFLIB should be added if PDFLIB is being used.

In the HERWIG version the black hole entry in the event record has been assigned the provisional PDG code IDHEP=40 with name 'BlacHole'. However this has not been implemented in the PYTHIA version.