Subroutines and variables in Pompyt

User routines

pomini.f -- SUBROUTINE POMINI(BEAM1,BEAM2,PBEAM1,PBEAM2) Initialize MC generation procedure. BEAM1,BEAM2 -- incomming particles PBEAM1,PBEAM2 -- momenta of incomming particles
pompyt.f -- SUBROUTINE POMPYT Generate an event
pomend.f -- SUBROUTINE POMEND Print a summary of the simulation.

Matrix element, parton shower and hadronisation

Done with Pythia and Jetset.

Kinematics

pomlim.f -- SUBROUTINE POMLIM
To calculate effective limits for the diffractive variables.
pomkin.f -- SUBROUTINE POMKIN(DX1,DX2,DY1,DY2,IFLAG)
Diffractive kinematics: For two input variables (DX1,DX2) calculate two others (DY1,DY2).
IFLAG=1 -- DX1=Sqrt(Sepom) and DX2=T ---> DY1=xF and DY2=Pt**2.
IFLAG=2 -- DX1=xF and DX2=T ---> DY1=Sepom and DY2=Pt**2.
IFLAG=3 -- DX1=Sqrt(Sepom) and DX2=Pt ---> DY1=xF and DY2=T.
IFLAG=4 -- DX1=xF and DX2=Pt ---> DY1=Sepom and DY2=T.
IFLAG=5 -- DX1=xF and DX2=Sqrt(Sepom) ---> DY1=Pt**2 and DY2=T.
IFLAG=6 -- DX1=Pt and DX2=T ---> DY1=xF and DY2=Sepom.
dpomli.f -- FUNCTION DPOMLI(DX,IFLAG)
Some constraint on diffractive variables.
IFLAG=1 -- T[min]=T(xF[max]).
IFLAG=2 -- T[min]=T(Sep[min]).
IFLAG=3 -- T[max]=T(Sep[max]).
IFLAG=4 -- Sep[max]=Sep(T[min]).
IFLAG=5 -- T[min]=T(Pt[min]).
IFLAG=6 -- Pt[max]=Pt(T[max]).
IFLAG=7 -- xF[max]=xF(Pt[min]).
IFLAG=8 -- Pt[max]=Pt(xF[max]).
pomtlo.f -- FUNCTION POMTLO(XXO)
Lower limit of T, fixed Xpom/Xf.
pomtup.f -- FUNCTION POMTUP(XXO)
Upper limit of T, fixed Xpom/Xf.

Flux factors

pomflx.f -- SUBROUTINE POMFLX(ICASE)
Pomeron flux facor.
ICASE=0 -- integrate flux factor
ICASE!=0 -- Choose xp and t according to flux. Kinematics found in COMMON/POMIN3/
pomedl.f -- SUBROUTINE POMEDL(ERRT,ERRF,FDLINT)
Pomeron flux factor in the Donnachie-Landshof model.
pomfdl.f -- FUNCTION POMFDL(DDXP,DDT)
DL flux factor.
pomfdt.f -- FUNCTION POMFDT(DDT)
DL flux factor, fixed xp
pomeft.f -- FUNCTION POMEFT(DDT)
To evaluate F(T) form factor.
pomft2.f -- SUBROUTINE POMFT2(DTL,DTU,DA,DB,DC,DD,T0)
Integral of |F(t)|**2 between DTL and DTU, used for pomeron flux factor.
pomreg.f -- FUNCTION POMREG(DDT)
To evaluate pomeron trajectory (positive T).
pomfd3.f -- FUNCTION POMFD3(DDXP,DDT)
Delta flux factor
pomfd2.f -- FUNCTION POMFD2(DDT)
Delta flux factor, fixed xf
pomfd1.f -- FUNCTION POMFD1(DDXP)
Delta flux factor, fixed t
pomfp3.f -- FUNCTION POMFP3(DDXX,DDT)
Pion flux factor
pomfp2.f -- FUNCTION POMFP2(DDT)
Pion flux factor, fixed xf/xp
pomfp1.f -- Pion flux factor, fixed t
pomfl1.f -- SUBROUTINE POMFL1(ICASE)
Pion flux factor for N --> pi N'.
pomfl2.f -- SUBROUTINE POMFL2(ICASE)
Pion flux factor for N --> pi Delta.

Parton densities

pystfu.f -- SUBROUTINE PYSTFU(KF,X,Q2,XPQ)
Taken from Pythia. Parton densities for pomeron, pion, proton etc.
KF -- KF code for particle (Pomeron=29, Pion= 211)
X,Q2 -- Kinematics
XPQ(-6,6) -- Parton density at X,Q2
pompdf.f -- SUBROUTINE POMPDF(X,Q2,XPPO)
Parton densities of the pomeron. Called from PYSTFU.
X,Q2 -- Kinematics
XPPO(-6,6) -- Parton density at X,Q2
parton.f -- Gehrman-Sterling parton densities for the pomeron.

subroutine gsinit Initiate grid.
subroutine pomp1(z,q2,sing,glue,f2li,f2c,f2t)
Get the PDF for GS model I.
subroutine pomp2(z,q2,sing,glue,f2lir,f2cr,f2lid,f2cd,f2t)
Get the PDF for GS model II.
subroutine rdarry(z,q2,aux,mflag)
The grid.
real*8 function dsing(z,q2)
real*8 function dcharm(z,q2)

Internal programs

pomove.f -- SUBROUTINE POMOVE(NSTART,NSHIFT)
Shift line numbers NSTART to N in event record NSHIFT lines forward, keeping line pointer information intact.
pomtim.f -- SUBROUTINE POMTIM(TIME)
Interface to routine giving cpu-time since job started. Nice, but not necessary information. Can be called by user.

Common blocks

pomdat.f -- Block data with default values for parameters.
COMMON/POMPAR/MPOM(20),PARPOM(40)
Contains input switches and parameters to control physics models and performance of the program. Overwriting default values should be made before calling POMINI.

MPOM(1) -- choice of flux factor $f(x,t)$ for exchanged object
MPOM(2) -- choice of parametrization for the pomeron parton density functions
MPOM(3) -- choice to generate complete events or only diffractive variables.
MPOM(4) -- status of scattered beam particle (emitting the pomeron/pion) in the event record.
MPOM(5) -- use of event weight in {\sc Pythia}, through MSTP(173)=MPOM(5) regulating use of PARP(173).
PARPOM(1) -- pomeron-proton total cross-section = 2.3 mb
PARPOM(2) -- power $p$ in $1/x_{\Pma}^p$ dependence =1
PARPOM(3),PARPOM(4),PARPOM(5) -- coefficients $a_1,a_2,a_3$ in exponential $t$-dependence used for MPOM(1)=1
PARPOM(6),PARPOM(7),PARPOM(8) -- exponential slopes $b_1,b_2,b_3$ in exponential $t$-dependence used for MPOM(1)=1;
PARPOM(9) -- overall normalization $C$ for the pomeron flux factor in eq.~(\ref{MIXFLUX}) used for MPOM(1)=2.
PARPOM(10) --
PARPOM(11) --
PARPOM(12) --
PARPOM(13) --
PARPOM(14) --
PARPOM(15) --
PARPOM(16) --
PARPOM(17) --
PARPOM(18) --
PARPOM(19) --
PARPOM(20) --
PARPOM(21) --
PARPOM(22) --
PARPOM(23) --
PARPOM(24) --
PARPOM(25) --
PARPOM(26) --
PARPOM(27) --
PARPOM(28) --
PARPOM(29) --
PARPOM(30) --
PARPOM(31) --
PARPOM(32) --
PARPOM(33) --
PARPOM(34) --
PARPOM(35) --
PARPOM(36) --
PARPOM(37) --
PARPOM(38) --
PARPOM(39) --
PARPOM(40) --

COMMON/POMCUT/UCUT(20),GCUT(20)
For the user to set limits (UCUT) on the diffractive variables

UCUT(1),UCUT(2) -- lower, upper limit of $x_F$
UCUT(3),UCUT(4) -- lower, upper limit of $M_X$
UCUT(5),UCUT(6) -- lower, upper limit of $t$
UCUT(7),UCUT(8) -- lower, upper limit of lab fram $p_{\perp}$
To store effective limits (GCUT) for the generation.
GCUT(1),GCUT(2) -- effective lower, upper limit of $x_F$
GCUT(3),GCUT(4) -- effective lower, upper limit of $M_X$
GCUT(5),GCUT(6) -- effective lower, upper limit of $t$
GCUT(7),GCUT(8) -- effective lower, upper limit of $p_{\perp}$
GCUT(9),GCUT(10) -- effective lower, upper limit of $W_{had}$, calculated

COMMON/POMEVT/KIN(4,5),PIN(4,5),ROOTS,XMASS,XF,XPOM,T,PT,WHAD
Give access to information about the latest generated event.

KIN(4,5),PIN(4,5) --
Information on incoming beam particles (I=1,2), scattered beam particle (I=3) and exchanged pomeron (pion) (I=4) with notation as for the K- and P-arrays in LUJETS.
ROOTS -- $\sqrt{s}$, i.e. overall cms energy of user-defined beam particles.
XMASS -- $M_X$, i.e. cms energy of pomeron-particle system. XF -- $x_F$, i.e. momentum fraction of quasi-elastically scattered beam hadron.
XPOM -- $x_{\Pma}=1-x_F$, i.e. momentum fraction of exchanged pomeron (pion).
T -- $t=(p_i-p_f)^2$, i.e. squared diffractive momentum transfer (equals mass squared of exchanged pomeron/pion).
PT -- $p_\bot$ of quasi-elastically scattered hadron (and exchanged pomeron/pion) in lab frame.
WHAD -- invariant mass of the hadronic final state (i.e. excluding the scattered lepton in lepton-nucleon scattering).

COMMON/POMSIG/NEVT,SIGTOT
Gives overall number of events and cross-section.

NEVT -- number of (accepted) events generated.
SIGTOT -- total cross-section for the generated event sample (updated for each event), normally equal to PARI(1) in {\sc Pythia} (but see MPOM(5)). The subprocess cross-sections XSEC(ISUB,3) in {\sc Pythia} can also be used.

COMMON/POMIN1/NTRY,FLUXI,CPUTIM(3)

NTRY -- number of calls to PYEVNT.
FLUXI -- integral of pomeron flux factor, used for normalisation of cross-section
CPUTIM(3) -- cpu time at start, end of initialization and after latest generated event.

COMMON/POMIN2/DCOEF(10),DPIN(4,5)
Effective coefficients for handling the flux factor

DCOEF(1) --
DCOEF(2) --
DCOEF(3) --
DCOEF(4) --
DCOEF(5) --
DCOEF(6) --
DCOEF(7) --
DCOEF(8) --
DCOEF(9) --
DCOEF(10) --
DPIN(4,5) -- four-momenta of the incoming particles in double precision, cf. PIN in POMEVT.

COMMON/POMIN3/DMASS,DXF,DT,DPT,DROOTS,DXFL,DXFU,DXML,DXMU,DTL, & DTU,DPTL,DPTU,DXPL,DXPU,DXXL,DXXU
Double precision variables mainly for internal use.

DMASS -- diffractive variable $M_X$
DXF -- diffractive variable $x_F$,
DT -- diffractive variable $t$
DPT -- diffractive variable $p_\bot$
DROOTS - overall cms energy $\sqrt{s}$ of user-defined beam particles.
DXFL -- effective lower limit of $x_F$.
DXFU -- effective upper limit of $x_F$.
DXML -- effective lower limit of $M_X$
DXMU -- effective upper limit of $M_X$
DTL -- effective lower limit of $t$.
DTU -- effective upper limit of $t$.
DPTL -- effective lower limit of $p_{\perp}$.
DPTU -- effective upper limit of $p_{\perp}$.
DXPL -- effective lower limit of $x_{\Pma}$($x_{\pi}$).
DXPU -- effective upper limit of $x_{\Pma}$($x_{\pi}$).
DXXL -- internally used lower limit of $x_{\Pma}$($x_{\pi}$).
DXXU -- internally used upper limit of $x_{\Pma}$($x_{\pi}$).

COMMON/POMIN4/WH(4),GENVAR(20)
to calculate internally $W_{had}$.

WH(1) --
WH(2) --
WH(3) --
WH(4) --
To store the current min and max of diffractive variables and of the mass of the resulting hadronic final state.
GENVAR(1) --
GENVAR(2) --
GENVAR(3) --
GENVAR(4) --
GENVAR(5) --
GENVAR(6) --
GENVAR(7) --
GENVAR(8) --
GENVAR(9) --
GENVAR(10) --
GENVAR(11) --
GENVAR(12) --
GENVAR(13) --
GENVAR(14) --
GENVAR(15) --
GENVAR(16) --
GENVAR(17) --
GENVAR(18) --
GENVAR(19) --
GENVAR(20) --

COMMON/POMIN5/NREJ1
To store number of rejections.

NREJ1 --

COMMON/POMLIS/CHFRAM,CHBEAM,CHTARG,CHEXCH,CHSCAT CHARACTER*8 CHFRAM,CHBEAM,CHTARG,CHEXCH,CHSCAT

CHFRAM -- frame in which to generate events.
CHBEAM -- beam particle.
CHTARG -- target particle.
CHEXCH -- exchanged particle.

CHSCAT -- quasi-elastically scattered hadron.

Integration

gadap.f --
gadap2.f --
gadapf.f --