SUBROUTINE QIKPAR - Generate 4-momentum of incoming gluon $g$

In this routine the momentum vector $g$ of the incoming, on-shell gluon (with mass $\sqrt{g^2}=m_g$ set in QIINIT) is calculated according to

$$g \equiv (g_t,g_x,g_y,g_z)$$ (1)

$$= \frac{1}{2}\left( z\, (P_t+\mid P_z\mid ) +\frac{m_g^2}{z\, (P_t+... ...} ,0,0,z\, (P_t+\mid P_z\mid ) -\frac{m_g^2}{z\, (P_t+\mid P_z\mid )} \right) ,$$

where $z$ denotes the generated momentum fraction and $P=(P_t,0,0,P_z)$ is the 4-momentum of the incoming proton. If $P_z\leq 0$, the direction is reversed, $g_z\to -g_z$.

Table 1: Variables set in QIKPAR.

Name	Description
QIPPAR(1)	$g_x$
QIPPAR(2)	$g_y$
QIPPAR(3)	$g_z$
QIPPAR(4)	$g_t$
QIPPAR(5)	$m_g=\sqrt{g^2}$