ABSTRACT
The fourth version of the Ariadne program for generating QCD
cascades in the Colour Dipole Approximation is presented. A manual
for using the program is given together with a few sample programs.
1 Introduction
The Colour Dipole Model (CDM) [2-5] as implemented in the Ariadne pro-
gram has had considerable success in describing data from both e+e- [6] and
lepto-production [7] experiments.
The CDM differs from other QCD cascade models in that it in a natural
way correctly treats most QCD coherence effects by describing the gluon
bremsstrahlung in terms of radiation from colour dipoles between partons,
instead of treating partons as independent emitters.
Ariadne is one of the "Lund family of Monte Carlo programs" and is
not a complete event generator. It only generates the QCD cascade process
and has to be interfaced to other programs which handles hard interactions,
hadronization and particle decays. Standard interfaces to the JETSET [8-
10], LEPTO [11] and PYTHIA [8,9,12] programs are included in the version
presented in this paper.
1.1 Update history
The first version of Ariadne [13] only handled gluon radiation from primary
quarks in e+e- collisions. Since then the program has evolved as follows
o version 2 [14]: Included gluon emission from extended emitters to
describe the QCD showers in lepto-production.
o version 3 [15]: Included also production of QQ^bar pairs from gluon
splitting.
o version 3.1: Adopted the new event record of JETSET version 7.1.
o version 3.2: Included preliminary facilities for generating dipole show-
ers in hadron-hadron collisions.
o version 3.3: Included a preliminary treatment of electro-magnetic dipole
radiation of photons.
o version 4.01: Completely rewritten, built around a new internal dipole
oriented event record. The preliminary features of sub-versions 3.2
and 3.3 are properly included. Streamlined interfaces to the JETSET,
LEPTO and PYTHIA are introduced as well as a new jet clustering
routine, inspired by the CDM.
o version 4.02: Fixed bugs in connection with phase space restrictions
(in 4.01 the switch MSTA(11) was inactive and effectively set to 4 - see
section ??). Also a bug related to the option MSTA(20) = 2, and to
the quark masses and charges in QED emissions was fixed.
o version 4.03: Added options for emissions from extended dipoles (see
description of MSTA(18), MSTA(25) and PARA(25) in section ??). Also
introduced two new sets of tuned parameters ('ALEPH' and 'EMC')
in subroutine ARTUNE. Please note that, in connection with this, a
few parameters and switches were given new default values. Note
especially that the default is to automatically call ARTUNE('EMC)' in
subroutine ARINIT, hence the switch MSTA(3) must be set to 0 before
the call to ARINIT if the user wants to modify any parameters or
switches.
In previous releases, increased precision could be obtained by removing
the comment of an implicit double precision statement. From this
release on, increased precision will be the default (see appendix A).
o version 4.04: Fixed minor bug in ARCLUS and speeded up the clus-
tering algorithm. Added minor features to ARCLUS to make it more
compatible with the LUCLUS routine.
o version 4.05: Fixed bug in matrix element for the final state g->q-
qbar process (see MSTA(23)) and added a new option for this process
(MSTA(28)).
Introduced matching to the exact O(alpha_S) matrix elements for the
first emission in DIS (see MSTA(32) and MSTA(33)).
Introduced pomeron-like scattering procedure for remnant handling in
DIS and in hadron-hadron collisions (see MSTA(34)).
Introduced a preliminary (and un-documented) treatment of Drell-
Yan-like processes in hadron-hadron collisions (see MSTA(22)).
Revised the PYTHIA interface. All PYTHIA sub-processes are now
possible (although no guarantee is given for the physical relevance of
adding a dipole shower to a given sub-process).
Changed default parameters and switches to reflect the new features.
In particular the default call to ARTUNE('EMC') has changed, and to
retain the behavior of version 4.04 a call to ARTUNE('4.04') should
be made instead.
When run with LEPTO or PYTHIA, the subroutines dealing with
structure functions in these programs are called from within Ariadne.
This complicates the installation procedure somewhat (see section
A.2).
o version 4.06: Fixed bug in the O(alpha_S) matrix element for boson-
gluon fusion diagram in DIS.
Introduced initial state g->q-qbar splitting into the cascade (with first
emission correced for the O(alpha_S) matrix element in case of DIS).
Changed default parameters and switches to reflect the new features.
In particular the default call to ARTUNE('EMC') has changed, and to
retain the behavior of version 4.05 (except for the bug above) a call to
ARTUNE('4.05') should be made instead.
o version 4.07: Included correction for O(alpha_S) matrix elements and
improved the treatment of Drell-Yan production.
Introduced a colour reconnection scheme governed by MSTA(35) and
PARA(26) (switched off by default). This feature is so far not docu-
mented here.
Changed default treatment of extendedness. For remnants, mu is given
by the intrinsic p_T, which is now generated inside of Ariadne (see
MSTA(36), MSTA(37) and PARA(27)). By default the struck quark in
DIS is now extended with mu= Q.
Changed default parameters and switches to reflect the new features.
In particular, the default call to ARTUNE('EMC') has changed, and to
retain the behavior of version 4.06 a call to ARTUNE('4.06') should
be made instead.
o version 4.08: Fixed bug in orientation of emissions from qq^bar dipoles.
This mainly affects the general orientation of e+e- events i.e. the
thrust-axis distribution, but may also affect prompt photon production
in e+e-.
1.2 Programming philosophy
The program is a library of FORTRAN 77 subroutines to be called from
a user supplied main program. Although there exist over fifty subroutines,
only a handful are meant to be explicitly called by the user.
The interface to the main program as well as to other programs are
handled through the event record in JETSET's LUJETS common block. The
communication between different Ariadne routines is however handled by
an internal dipole oriented event record in the ARSTRS, ARDIPS and ARPART
common blocks, where the dipoles and partons are linked together to form
"Lund-type" strings.
1.3 About this manual
This paper is divided into three parts. The first part, section ??, explain
the underlying physics processes modeled in Ariadne. Section ?? describes
the actual program components and in section ?? a couple of sample main
programs are given to illustrate how Ariadne is used. In the appendix in-
formation on how to obtain, install and test the program is given.
2 The Colour Dipole Model
This section has been left out as contains a lot of figures and equations which
are not possible to reproduce in this ASCII file.
3 Program Components
inputcomponents
References
[1]L. L"onnblad, Comput. Phys. Commun. 71 (1992) 15.
[2]G. Gustafson, Phys. Lett. B 175 (1986) 453.
[3]G. Gustafson, U. Pettersson, Nucl. Phys. B 306 (1988) 746.
[4]B. Andersson et al., Z. Phys. C 43 (1989) 625.
[5]B Andersson, G. Gustafson, L. L"onnblad, Nucl. Phys. B 339
(1990) 393.
[6]OPAL Coll., M.Z. Akrawy et al., Z. Phys. C 47 (1990) 505.
[7]N. Magnussen et al., Generators for Deep Inelastic Scattering, in
Physics at HERA, edited by W. Buchm"uller, G. Ingelman, vol-
ume 3, p. 1167, DESY, 1991.
[8]T. Sj"ostrand, Comput. Phys. Commun. 82 (1994) 74.
[9]T. Sj"ostrand, PYTHIA 5.7 and JETSET 7.4 physics and manual,
CERN-TH.7112/93, Dec. 1993, (revised Aug. 1994).
[10]T. Sj"ostrand, Comput. Phys. Commun. 39 (1986) 347.
[11]G. Ingelman, LEPTO version 6.1, in Physics at HERA, edited by
W. Buchm"uller, G. Ingelman, volume 3, p. 1366, DESY, 1991.
[12]H-U. Bengtsson, T. Sj"ostrand, Comput. Phys. Commun. 46
(1987) 43.
[13]U. Pettersson, ARIADNE - A Monte Carlo for QCD Cascades in
the Colour Dipole Formulation, Lund Preprint LU-TP 88-5, 1988.
[14]ARIADNE 2, Lund Preprint LU-TP 88-15, 1988.
[15]ARIADNE 3, Lund Preprint LU TP 89-10, 1989.
A Appendix: Technical Information
The Ariadne program is written according to the FORTRAN 77 standard
and should work on any platform with a FORTRAN 77 compiler.
To avoid name clashes when run together with other programs, all exter-
nal names in Ariadne begins with the two character AR. All internal identi-
fiers conforms to the standard FORTRAN 77 implicit declarations except for
double precision and logical variables which are declared in all subroutines
as
IMPLICIT DOUBLE PRECISION (D)
IMPLICIT LOGICAL (Q)
Ariadne performs a large amount of boost to and from the center of mass
frames of the radiating dipoles which may give rise to precision problem when
the program is used for simulations at very high energies. To avoid these
Ariadne has an additional declaration of double precision variables
IMPLICIT DOUBLE PRECISION (B)
On some machines double precision arithmetic is much slower than single
precision, and if you feel that speed is more important than precision this
latter double precision declaration may be commented out (in every routine).
Note that possible warnings about non-conservation of four-momentum may
be avoided by adjusting MSTA(9) and PARA(39) (see section ??).
The internal event record of Ariadne has a maximum number of partons,
dipoles and strings which it can handle. These number are defined in the
parameter statement in each routine and are by default set to:
PARAMETER(MAXDIP=500,MAXPAR=500,MAXSTR=100)
These limits can of course be changed by the user, but it should be noted
that generation of more than 500 partons in Ariadne most probably is an
indication that an error has occurred.
Ariadne contains a block data routine ARDATA for setting the default
values of the parameters and switches used. When compiling Ariadne in
separate modules, this block data routine should be compiled in the same
module as ARINIT. Otherwise, since ARDATA is never actually referenced, it
will not be linked and Ariadne will not be properly initialized.
Ariadne has to be loaded together with version 7.4 or later of the JET-
SET program. In addition, when run in 'LEPTO' mode, it should be loaded
together with version 6.3 or later of the LEPTO program and, when run in
'PYTHIA' mode, together with version 5.7 or later of the PYTHIA program.
A.1 Availability
The program is available via anonymous ftp to freehep.scri.fsu.edu.
Here the program resides in the directory freehep/event_generators/ariadne
as the compressed tar-archive file ariadne-4.08.tar.Z (Forthcoming revi-
sions will be numbered 4.09, 4.10 etc.).
The program is also available on E-mail request from the author (Leif.Lonnbl*
*ad@cern.ch).
The program will then be sent as an E-mail message containing the latest
revision of the code together with the latest revision of this manual in ASCII
format.
A.2 Installation
If the program has been obtained through E-mail correspondence it should
simply be extracted into a file and be compiled.
To install the program obtained via anonymous ftp, the compressed tar-
file should be "un-compressed" and "un-tarred" which will create a directory
called ariadne-4.08. This directory will contain, besides the actual code, a
file called README containing all instructions needed to install the program.
In addition there will be the files ariadne.man and ariadne.ps containing
the latest revision of this manual in ASCII and Postscript format respec-
tively.
Note that the distribution contains two dummy subroutines PYSTFU and
LNSTRF. These are needed to avoid linking problems when not running with
PYTHIA or LEPTO, and should be removed when running with PYTHIA
or LEPTO respectively.
A.3 Test Programs
Ariadne contains a subroutine called ARTEST intended to be used for con-
firming that the installation has been successful. To use it, write a small
program calling the routine (this program is included in the tar-distribution
as the file atest.f):
PROGRAM TEST
CALL ARTEST(0)
END
When run, ARTEST will generate 10000 events randomly distributed in
center of mass energy and check their consistency w.r.t. momentum conser-
vation and colour flow. If Ariadne was successfully installed, a message
No errors experienced by Ariadne.
will be printed. If anything else is printed, such as
2 errors occurred in Ariadne.
please consult the author.
In the tar-distribution the sample programs described in section ?? are
also included as the files jtest.f, ltest.f and ptest.f including dummy
routines for parameter settings and analysis.
B Appendix: Description of Subroutines and Com-
mon Blocks
This is a (no longer) complete list of the subroutines in Ariadne.
o SUBROUTINE ARRADG(ID)
Administers the emission of a gluon from dipole ID.
o REAL FUNCTION ARANGL(I1,I2)
Returns the angle between partons I1 and I2 in radians.
o SUBROUTINE ARBOCM(ID)
Boosts the partons in dipole ID to their center of mass frame.
o SUBROUTINE ARBOLE(THEL,PHI1,PHI2,
DBXL,DBYL,DBZL)
Boost partons to the hadronic c.m.s. of a LEPTO event. The reverse
transform is given by first rotation PHI2 around the z-axis, then THEL
around the y-axis, PHI1 around the x-axis and last boosting with DBXL,
DBYL and DBZL.
o SUBROUTINE ARBOPY(THEPY,PHIPY,
DBXPY,DBYPY,DBZPY)
Boost partons to the total c.m.s. of a PYTHIA event. The reversed
transformation is achieved by calling LUDBRB(1,N,THEPY,PHIPY,DBXPY,DBYPY,D*
*BZPY).
o SUBROUTINE ARCASC
Contains the main loop over dipole emissions.
o SUBROUTINE ARCHEM(IMOD)
Checks that energy and momentum is conserved in Ariadne.
o SUBROUTINE ARCHKI(ID)
Checks that the emission generated for dipole ID is kinematically al-
lowed.
o SUBROUTINE ARCLUS(NJET)
Jet-clustering routine implementing the "inverse dipole radiation" al-
gorithm.
o SUBROUTINE ARCONT
Continues a dipole cascade peviously started with ARCASC.
o SUBROUTINE ARCOPA(IJ,IP,ITYP)
Copies a parton from position IJ in /LUJETS/ to position IP in /ARPART/.
o SUBROUTINE ARCOPJ
Copies particles to be considered jet-initiators to the end of /LUJETS/.
o SUBROUTINE ARCRDI(ID,IPA1,IPA3,IS,QED)
Creates a dipole entry in ID /ARDIPS/ from the partons at position
IPA1 and IPA3 in /ARPART/.
o SUBROUTINE ARDBRB(DTHE,DPHI,
DBEX,DBEY,DBEZ,NI,I)
Same as ARROBO below but with double precision arguments also for
the rotation angles.
o SUBROUTINE ARDUMP
Copies a partonic state from the internal event record to /LUJETS/.
o SUBROUTINE ARDUPH
Copies a photon radiated by Ariadne to /LUJETS/.
o REAL FUNCTION ARDYRE(IDE,BW,QRG1,QRG3)
Transfers the recoil of an emission to a Drell-Yan produced particle
if the emission and the particle are in the same phase space region.
Returns a negative number if no transfer was possible. IDE is the
position of the emitting dipole, BW the total invariant mass, and QRG1
and QRG3 are .TRUE. if the corresponding dipole ends are recoil gluons.
o REAL FUNCTION ARECOI(BE0,DE1,DE2,DE3,
BP0,DP1,DP2,DP3,BALP,PT12)
Calculates the recoil angle in the strategy of MSTA(17) = 3. BE0, BE1,
BE2, BE3, BP0, BP1, BP2 and BP3 are the energy and momentum of the
incolved partons, BALP is the angle between partons 1 and 3 and PT12
is the invarioant p_T of the emission.
o SUBROUTINE AREMIT
Administers the actual emission from dipole ID.
o SUBROUTINE ARERRM
Prints out an error message and optionally stops the execution. If the
execution is allowed to continue the value of MSTA(13) will be set to
a value corresponding to the warning produced:
3 /LUJETS/ event record was not properly formatted.
9 Total four-momentum was not conserved in Ariadne.
10 A particle was found to have inconsistent four-momentum.
13 A dipole was found to have inconsistent invariant mass.
20 Selected sub-process in PYTHIA is not supported by Ariadne.
21 ARCLUS was not performed due to too many jet-initiators.
o SUBROUTINE AREVOL(PTMAX,PTMIN)
Perform a dipole shower evolution allowing emissions between PTMAX
and PTMIN.
o SUBROUTINE AREVST(ISIN)
Reverse the colour flow of string entry ISIN.
o SUBROUTINE AREXEC
This is the main routine in Ariadne. Given a partonic state in /LUJETS/
it administers the dipole radiation according to the options and pa-
rameters set in /ARDAT1/.
o SUBROUTINE AREXMA(I1,I3)
Makes partons I1 and I3 mass-less if extended.
o SUBROUTINE ARFIDY(NSAVE) Fix up event record after dipole shower
in Drell-Yan events.
o SUBROUTINE ARGDIG(ID)
Calculates the p_T^2 of a possible gluon emission from the colour dipole
ID assuming it is the first emission of a DIS event.
o SUBROUTINE ARGDIS(ID)
Prepare for the calculation of the p_T^2 of a possible gluon emission in
ARGDIG.
o REAL FUNCTION ARGPT2(ID)
Returns the generated p_T^2 for a possible emission from dipole ID. If
necessary it calls the relevant procedure to generate this p_T^2.
o SUBROUTINE ARGQCD(ID)
Calculates the p_T^2 of a possible emission from the colour dipole ID.
o SUBROUTINE ARGQCG(ID)
The gluon emission part of ARGQCD.
o SUBROUTINE ARGQCQ(ID)
The gluon splitting part of ARGQCD.
o SUBROUTINE ARGQED(ID)
Calculates the p_T^2 of a possible emission from the electro-magnetic
dipole ID.
o SUBROUTINE ARGTYP(I,ITYP)
Determines the colour state of a particle in /LUJETS/.
o SUBROUTINE ARINIT(MODE)
Initializes the Ariadne program. The argument is a character string
indicating which program Ariadne is used with; 'JETSET', 'LEPTO',
'PYTHIA' or by itself - 'ARIADNE'.
o SUBROUTINE ARINQQ(IT,KQ,IRP,
PT2,ZQ,PHI,QFAIL)
Try to perform an initial-state g->q-qbar splitting given which tar-
get side IT, the flavour of the struck quark KQ, the position of the
chopped-off remnant particle, the p_T^2 (PT2), momentum fraction ZQ
and azimuthal angle PHI of the struck quark. If the emission fails
QFAIL is set to .TRUE.
o REAL FUNCTION ARIPSF(A,N,X)
Return the integral from X to 1 of the function xA(1 - x)N.
o REAL FUNCTION ARIPT2(I1,I2,I3)
Returns the invariant p_T^2 of parton I2 w.r.t. the partons I1 and I3.
o SUBROUTINE ARJOIN(J1,J2,J3)
Clusters the three jet-entries J1, J2 and J3 in /LUJETS/ into two
according to a "reversed" dipole emission scenario.
o SUBROUTINE ARJOQQ(IQ1,IQ2)
Join the quark and anti-quark entries IQ1 and IQ2 into a gluon entry
located at MIN(IQ1,IQ2).
o SUBROUTINE ARJOST(IS1,IS2,IPA1,IPA2)
Join the string entries IS1 and IS2 in the ends IP1 and IP2.
o SUBROUTINE ARLEPT
The interface to LEPTO used by AREXEC for MSTA(32) = 1.
o SUBROUTINE ARMADE
Determined some mass-dependent factors for use in the veto-algorithm.
o REAL FUNCTION ARMASS(N,I)
Returns the square of the invariant mass of the N partons pointed to
in the vector I(N).
o SUBROUTINE ARMCDI(ARRNDX,ARRNDY,ARVETO)
Implements the veto-algorithm for generating a p_T^2 for any dipole
given the functions ARRNDX, ARRNDY and ARVETO.
o REAL FUNCTION ARMIPT(IF,IL)
Returns the minimum invariant p_T^2 of the partons between positions
IF and IL in /ARPART/.
o REAL FUNCTION ARNOFL(W,MNOFW)
Returns the number of flavors to be used to calculate alpha_s at a scale
W.
o SUBROUTINE ARORDJ
Orders the jet entries in /LUJETS/ according to their energy.
o SUBROUTINE ARORIE(I1,I2,I3,
BS,B1,B3,QR1,QR3,PT21,PT23)
Orients the partons I1, I2 and I3 in their center of mass frame, given
their energy fractions and their total invariant mass.
o SUBROUTINE ARPARS(NSTART,NEND)
Parses the /LUJETS/ common block between positions NSTART and
NEND, copying partons to be cascaded into the internal event record.
o REAL FUNCTION ARPCMS(S,SM1,SM2)
Returns the positive light-cone component of a particle momentum
when placed in the c.m.s. system of itself and an other particle, given
the two particle masses SM1 and SM2 and the total energy squared S.
o SUBROUTINE ARPHAS(IFIRST) Rotate event begining from entry IFIRST
to correctly take into account azimuthal asymmetries in gluon emission
in DIS.
o SUBROUTINE ARPOKI(IT,IQR,IDR,IRP,IDIR,
KFTF,KFPR,XPOM,TPOM,QFAIL)
Redistribute remnants assuming an incoming hadron IT, outgoing
hadron KFTF with a pomeron (or other colourless sub-object) with mo-
mentum fraction XPOM and viruality -TPOM giving a remnant of flavour
KFPR. IQR, IDR and IRP as in subroutine ARREMN.
o SUBROUTINE ARPOSF(KFT,KFSTR,X,XQ2,
XPOM,TPOM,KFTF,KFPR,XFP,XFPOM)
Returns some information about possible pomeron interaction. The
arguments are the same as for ARUPOM in section ??.
o SUBROUTINE ARPRDA
Prints out the values of the parameters and switches used by Ariadne.
o SUBROUTINE ARPRDY
Make special preparations of the output from PYTHIA in case of a
Drell-Yan event.
o ARPTQQ(KF,KQ,PT2MAX,PT2MIN,
X,XQ2,XY,XP,ZQ,PHI)
Generate kinematical variables describing an initial state g->q-qbar
splitting. KF is the target code, KQ the flavour of the struck quark,
PT2MAX and PT2MIN limits the possible p_T^2 of the emission, X, XQ2
and XY are the usual DIS parameters x, Q^2 and y. XP is the ratio
between x and the momentum fraction of the incoming gluon, ZQ is
the momentum fraction and PHI the azimuthal angle of the struck
quark.
o SUBROUTINE ARPYTH
The interface to PYTHIA used by ARECEX.
o SUBROUTINE ARRADG(ID,NREM,SNR)
Performs the emission of a gluon from dipole ID.
o SUBROUTINE ARRADP(ID)
Performs the emission of a photon from dipole ID.
o SUBROUTINE ARRADQ(ID)
Performs the splitting of a gluon into a qq^bar pair in dipole ID.
o SUBROUTINE ARRECA(ID,IDS,IS1,IS3)
Recalls a full dipole entry to the internal event record, previously
stored away by ARSTOR.
o SUBROUTINE ARREMD(IREM)
Remove dipole entry IREM.
o SUBROUTINE ARREMG(IGI)
Remove gluon entry IGI.
o SUBROUTINE ARREMN(IT,IQR,IDR,IRP,IDIR)
Redistribute remnants on side IT given a single quark remnant in posi-
tion IQR and/or a di-quark remnant in position IDR and/or a chopped
off particle remnant in position IPR. IDIR indicates the direction along
the z-axis of the incomming parton.
o SUBROUTINE ARREMP(IREM)
Remove parton entry IREM.
o REAL FUNCTION ARNDX1(), ARNDX2() etc.
Different functions for generating a p_T^2 according to a Sudakov-
suppressed suppression, to be used by ARMCDI.
o REAL FUNCTION ARNDY1(), ARNDY2() etc.
Different functions for generating a rapidity according to a flat distri-
bution, to be used by ARMCDI.
o SUBROUTINE ARROBO(THE,PHI,
DBEX,DBEY,DBEZ,N,I)
Rotates and boost the N partons pointed to by the vector I(N). The
polar rotation is performed first (THE) followed by the azimuth rotation
(PHI) and the boost.
o SUBROUTINE ARSCAN(NSTART,NEND,NR,IR)
Same as ARPARS above but don't perfom any cascade. Instead put a
special marker any of the entries copied which are listed in the array
IR(NR).
o SUBROUTINE ARSPLG(IG,IFLAV)
Splits the gluon entry IG into a quark and an anti-quark entry with
flavors determined by IFLAV.
o SUBROUTINE ARSTOR(ID,IDS,IS1,IS3)
Stores away a full dipole entry in the internal event record for later
use.
o REAL FUNCTION ARSTRA(KF,KQ,X,XP,XQ2) Return the ratio of the struc-
ture function of flavour KQ in target KF evaluated at X/XP and XQ2 and
at X and XQ2.
o SUBROUTINE ARSUME(NULL,BSX,BSY,BSZ,BSE,BSM,NI,I)
Sum up energy and momentum of all entries listed in the array I(NI).
BSE, BSX, BSY and BSZ are the sum of the energy and momentum and
are set to zero befor summation if NULL = 0. BSM is the total invariant
mass.
o SUBROUTINE ARTEST(IPRINT)
A test program to check that Ariadne has been installed properly,
disguised as a subroutine.
o REAL FUNCTION ARTPT2(ID,SN,BX1IN,BX3IN,
Y1IN,Y2IN,Y3IN)
Calculate the minimum p_T of a radiated particle w.r.t. any of the
original dipole ends for a given dipole ID. If ID is zero, use total in-
variant mass squared in SN, x1 and x3 in BX1IN and BX3IN together
with the scaled mass ssquared of the partons Y1IN, Y2IN and Y3IN.
o SUBROUTINE ARTUNE(SET)
Sets the parameters in Ariadne as described in section ??.
o SUBROUTINE ARUPDJ(I2,I1,I3)
Calculates the minimum invariant p_T^2 of a jet entry in /LUJETS/
with respect to any other pair of jet-entries.
o SUBROUTINE ARUPOM(KFT,KFSTR,X,XQ2,
XPOM,TPOM,KFTF,KFPR,XFP,XFPOM)
This is a dummy routine which can be used to implement a user de-
fined pomeron distribution and structure function. See section ?? for
details.
o REAL FUNCTION ARVET1(), ARVET2() etc.
Different routines for calculating the veto factor to be used by ARMCDI.
o REAL FUNCTION ARZCMS(S,SM1,SM2)
Returns the z component of a particle momentum when placed in the
c.m.s. system of itself and an other particle given the two particle
masses SM1 and SM2 and the total energy squared S.
The following common blocks are used in Ariadne:
COMMON /ARDAT1/ PARA(40),MSTA(40)
The parameters and switches used in Ariadne as explained in section ??.
COMMON /ARDAT2/ PQMAS(10)
The quark masses used in Ariadne as described in section ??.
COMMON /ARDAT3/ IWRN(40)
The number of errors and warnings of each kind experienced by Ariadne.
COMMON /ARPART/ BP(MAXPAR,5),IFL(MAXPAR),QEX(MAXPAR),
$ QQ(MAXPAR),IDI(MAXPAR),IDO(MAXPAR),
$ INO(MAXPAR),INQ(MAXPAR),XPMU(MAXPAR),
$ XPA(MAXPAR),PT2GG(MAXPAR),IPART
The internal representation of partons in Ariadne:
o BP(I,1) x-component of the momentum of parton I.
o BP(I,2) y-component of the momentum of parton I.
o BP(I,3) z-component of the momentum of parton I.
o BP(I,4) energy of parton I.
o BP(I,5) mass of parton I.
o IFL(I) flavor code of parton I.
o QEX(i) is .TRUE. if parton I is extended
o QQ(I) is .TRUE. if parton I is in a colour-3 or 3^bar state.
o IDI(I) position of "incoming" dipole in /ARDIPS/.
o IDO(I) position of "outgoing" dipole in /ARDIPS/.
o INO(I) The number of the emission in which parton I was produced.
o INQ(I) For a quark produced in gluon splitting, the position of the
corresponding anti quark, otherwisw zero.
o XPMU(I) Soft suppression parameter mu for parton I.
o XPA(I) Power in soft suppression - alpha - for parton I.
o IPART The number of partons presently in /ARPART/.
COMMON /ARDIPS/ BX1(MAXDIP),BX3(MAXDIP),
$ PT2IN(MAXDIP),SDIP(MAXDIP),IP1(MAXDIP),
$ IP3(MAXDIP),AEX1(MAXDIP),AEX3(MAXDIP),
$ QDONE(MAXDIP),QEM(MAXDIP),IRAD(MAXDIP),
$ ISTR(MAXDIP),ICOLI(MAXDIP),IDIPS
The internal representation of dipoles in Ariadne.
o BX1(ID) value of x1 generated for dipole ID.
o BX3(ID) value of x3 generated for dipole ID.
o PT2IN(ID) invariant p_T^2 generated for dipole ID.
o SDIP(ID) invariant mass squared of dipole ID.
o IP1(ID) position of parton 1 in /ARPART/.
o IP3(ID) position of parton 3 in /ARPART/.
o AEX1(ID) value of a=(mu/p_T)^alpha for parton 1.
o AEX3(ID) value of a=(mu/p_T)^alpha for parton 3.
o QDONE(ID) is .TRUE. if a p_Thas been generated for dipole ID.
o QEM(ID) is .TRUE. if ID corresponds to an EM-dipole.
o IRAD(ID) the type of emission generated for dipole ID. 0: gluon radi-
ation (or photon radiation for EM dipole). (-)n: qq^bar radiation of
flavor n splitting gluon 1 (3).
o ISTR(ID) The string entry in common block /ARSTRS/ to which dipole
ID belongs.
o ICOLI(ID) The colour index of dipole ID.
o IDIPS The number of dipoles currently in /ARDIPS/.
COMMON /ARSTRS/ IPF(MAXSTR),IPL(MAXSTR),
$ IFLOW(MAXSTR),PT2LST,IMF,IML,IO,QDUMP,ISTRS
The internal representation of strings in Ariadne
o IPF(IS) position of the first parton in /ARPART/.
o IPL(IS) position of the last parton in /ARPART/.
o IFLOW(IS) the direction of colour flow in string IS. A positive value
corresponds to IPF(ID) being a colour-3 parton.
o PT2LST p_T^2 of the last emission in Ariadne
o IMF The position of the first parton in the parent string in /LUJETS/.
o IML The position of the first parton in the parent string in /LUJETS/.
o IO The number of emissions performed for the parent string.
o QDUMP is .TRUE. if current event information has been copied into the
/LUJETS/ common block.
o ISTRS The number of strings currently in /ARSTRS/.
COMMON /ARINT1/ BC1,BC3,BZM,BZP,BP1,BM1,BP3,BM3,
$ B1,B2,B3,XT2,XT,Y,QQ1,QQ3,NE1,NE3,
$ S,W,C,CN,ALPHA0,XLAM2,IFLG,
$ XT2MP,XT2ME,XT2M,XT2C,XTS,XT3,XT1,
$ YINT,YMAX,YMIN,
$ Y1,Y2,Y3,SY1,SY2,SY3,SSY,
$ AE1,AE3,NXP1,NXP3,FQ1,FQ3
The common variables needed for the veto-algorithm in subroutine ARMCDI.
COMMON /ARINT2/ DBEX,DBEY,DBEZ,PHI,THE
Information of the boost vector and rotation angles for transformation
of the radiating dipole back to the original Lorenz-frame.
COMMON /ARINT3/ DPTOT(5)
The total energy and momentum of the parton state being considered
by Ariadne.
COMMON /ARINT4/ BASS(5),BASSX1,BASSX3,IFLASS
Information to fix azimuthal asymmetry for the first gluon emission in
DIS. BASS(5) is the four-momentum an mass of the emitted gluon, BASSX1
and BASSX3 are the x1 and x3 of the corresponding emission and IFLASS is
the flavour of the gluon or zero if a foson-gluon fusion event.
COMMON /ARSTRF/ KFSAVE(2),XSAVE(2),XQ2SAV(2),XPQSAV(2,-6:6)
Structure function information in the current PYTHIA event. KFSAVE(IT)
is the code for the target on side IT. XSAVE(IT) and XQ2SAV(IT) is the x
and Q^2 of the incoming partons to the hard interaction on the corresponding
sides and XPQSAV(IT,IFL) is x times the structure function of flavour IFL.
Entered into the system by
M.G. (30 November 1995)