SUBROUTINE QIINIT - Initialize user parameters

This is an initialisation procedure designed to make the changing of default values as easy as possible. The parameters available to the user are listed in Tables 1-3 (for the kinematic variables see Fig. 1). In addition to these parameter settings, a name for the ``instanton particle'' is set by QIPARC(1)='INST'.

After setting the parameters, QIINIT calls the subroutine QIINIH to initialize the new instanton particle in the HERWIG event record. Finally, it sets the flag QIRCAL (calculate derived quantities and check limits) to .TRUE..

Table 1: Floating point parameters set in QIINIT.

Name	Default value	Description
QIUPAR(1)	0.75	Gluon mass (in GeV)
QIUPAR(2)	$1\cdot 10^{-3}$	Minimum allowed $x_{\rm Bj}$: $x_{\rm Bj\,min}$
QIUPAR(3)	1	Maximum momentum fraction $z$, $z_{\rm max}$,
		carried by the gluon
QIUPAR(4)	1	Maximum allowed $y_{\rm Bj}$: $y_{\rm Bj\,max}$
QIUPAR(5)	0.1	Minimum allowed $y_{\rm Bj}$: $y_{\rm Bj\,min}$
QIUPAR(6)	0.9	Maximum allowed $x^\prime$: $x^\prime_{\rm max}$
QIUPAR(7)	0.35	Minimum allowed $x^\prime$: $x^\prime_{\rm min}$
QIUPAR(8)	$(\sqrt{\rm QIUPAR(9)}+30)^2$	Maximum allowed $Q^{\prime 2}$: $Q^{\prime 2}_{\rm max}$ (in GeV$^2$)
QIUPAR(9)	$\left(8\,\frac{{\rm QIUPAR}(13)} {{\rm LAMNF}(3,0.15267)}\right)^2$	Minimum allowed $Q^{\prime 2}$: $Q^{\prime 2}_{\rm min}$ (in GeV$^2$)
QIUPAR(10)	QIUPAR(7)	Cut on $x^\prime$ below which
		const. matrix element is assumed
QIUPAR(11)	$-1\cdot 10^{-10}$	Minimum allowed weight for exit
		of main weight generation
QIUPAR(12)	0	Minimum allowed instanton CM energy:
		$W_{i\,{\rm min}}$ (in GeV)
QIUPAR(13)	LAMNF(QIPARI(4), 0.219)	QCD scale $\Lambda_{\rm\overline{MS}}^{(n_f)}$ (in GeV) for $n_f$ massless
		flavours; input value (3 loop):
		$\Lambda_{\rm\overline{MS}}^{(5)}=0.219^{+0.025}_{-0.023}$ GeV [1]
QIUPAR(15)	0	Minimum energy (in GeV) after mass
		subtraction from instanton
QIUPAR(16)	0.15	Choice of renormalization scale $\mu_r/Q^\prime\equiv \kappa$
QIUPAR(17)	QIUPAR(9)	Minimum allowed $Q^2$: $Q^2_{\rm min}$ (in GeV$^2$)
QIUPAR(18)	$\sqrt{{\rm QIUPAR(9)}}$	Factorization scale $\mu_f$ (in GeV)

Table 2: Integer parameters set in QIINIT.

Name	Default value	Description
QIPARI(1)	206	HERWIG [2] identity (IDHW) of instanton ``particle''
QIPARI(2)	100	Maximum number of MAMBO iterations
		per weight
QIPARI(3)	300	Maximum number of phase space iterations
		per MAMBO weight
QIPARI(4)	3	Number of flavours, $n_f$
QIPARI(6)	10	Maximum allowed number of gluons
QIPARI(7)	20	Maximum number of iterations in
		matrix element weight generation step
QIPARI(9)	40	Maximum number of QIGMUL iterations
QIPARI(10)	3	Number of loops

Table 3: Control flags set in QIINIT.

Name	Default value	Description
QICONT(1)	.TRUE.	Use non-trivial kinematic weight
		for given phase space distribution
QICONT(2)	.TRUE.	Use standard routine (leading-order) to generate weight
		for given phase space distribution
QICONT(3)	.TRUE.	Use matrix element weight
QICONT(4)	.TRUE.	Disregard instanton minimum mass requirement
QICONT(5)	.TRUE.	Generate $Q^{\prime 2}$ before $x^\prime$
QICONT(6)	.TRUE.	Enforce mass of current quark in kinematics
QICONT(7)	.TRUE.	Dummy
QICONT(8)	.TRUE.	Dummy
QICONT(9)	.TRUE.	Enforce maximum allowed number of gluons
QICONT(10)	.TRUE.	Dummy
QICONT(11)	.TRUE.	Check that energy for gluon generation is sufficient
QICONT(12)	.TRUE.	Dummy
QICONT(13)	.TRUE.	Kill events with mass too high
QICONT(14)	.TRUE.	Use $z$ generation as $dz/z$
QICONT(15)	.TRUE.	Generate $x^\prime$ with efficiency parametrization
QICONT(16)	.TRUE.	Generate $Q^{\prime 2}$ with efficiency parametrization
QICONT(17)	.TRUE.	Dummy
QICONT(18)	.TRUE.	Use HERWIG [2] rather than JETSET [3] hadronization
QICONT(19)	.TRUE.	Dummy
QICONT(20)	.TRUE.	Random azimuthal angle
QICONT(21)	.TRUE.	Full hadronization (.FALSE.: parton level only)