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15} Special source: colliding beams


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Colliding beams as a source can be specified via command SPECSOUR and
SDUM
equal to PPSOURCE or ppsource, CROSSASY or CROSSSYM. One of the two colliding beams (from now on the "first beam") is a beam of hadrons (including protons or heavier nuclei), the other one (the "second beam") is a beam of protons or heavier nuclei but not of other hadrons. The different
SDUM
values allow to define the two beams in different ways. The first and the second continuation cards are identical for all
SDUM
options. For
SDUM
= PPSOURCE or ppsource: First card:
WHAT(1)
= lab momentum x-component for hadrons of the first beam (GeV/c)
WHAT(2)
= lab momentum y-component for hadrons of the first beam (GeV/c)
WHAT(3)
= lab momentum z-component for hadrons of the first beam (GeV/c)
WHAT(4)
= lab momentum x-component for nuclei of the 2nd beam (GeV/c)
WHAT(5)
= lab momentum y-component for nuclei of the 2nd beam (GeV/c)
WHAT(6)
= lab momentum z-component for nuclei of the 2nd beam (GeV/c)
SDUM
: PPSOURCE or ppsource First continuation card:
WHAT(1)
= sigma_x (cm) for the Gaussian sampling of the interaction position around XBEAM (the x position defined in the BEAMPOSit card)
WHAT(2)
= sigma_y (cm) for the Gaussian sampling of the interaction position around YBEAM (the y position defined in the BEAMPOSit card)
WHAT(3)
= sigma_z (cm) for the Gaussian sampling of the interaction position around ZBEAM (the z position defined in the BEAMPOSit card)
WHAT(4)
= sampling limit, in sigma, applying along x, y, and z =< 0: ignored (no limit)
WHAT(5)
= particle id number (or corresponding name) of hadrons of the first beam
Default
: as defined by the BEAM card (and by the HI-PROPErt card in case it is a heavy ion)
WHAT(6)
= mass number of the nuclei of the second beam = 0: it is a proton beam, and the second continuation card - if present - is ignored
SDUM
= "&" in any position in column 71 to 78 (or in the last field if free format is used) Second continuation card:
WHAT(1)
= atomic number of the nuclei of the second beam
WHAT(2)
-
WHAT(6)
: not used
SDUM
= "&&" in any position in column 71 to 78 (or in the last field if free format is used) For
SDUM
= CROSSASY (crossing asymmetric): First card:
WHAT(1)
= lab momentum of hadrons of the first beam (GeV/c)
WHAT(2)
= polar angle (rad) between the momentum of hadrons of the first beam and the z (positive) direction (must be between 0 and pi/2)
WHAT(3)
= azimuthal angle (deg) defining the crossing plane (see Note 2 below)
WHAT(4)
= lab momentum of nuclei of the second beam (GeV/c)
WHAT(5)
= polar angle (rad) between the momentum of nuclei of the second beam and the -z (negative) direction (must be between 0 and pi/2)
WHAT(6)
= not used
SDUM
: not used First and second continuation cards: as for
SDUM
= PPSOURCE (see above) For
SDUM
= CROSSSYM (crossing symmetric): First card:
WHAT(1)
= lab momentum for nuclei of both beams (GeV/c) (see Note 3)
WHAT(2)
= half crossing angle (rad) (must be between 0 and pi/2)
WHAT(3)
= azimuthal angle (deg) defining the crossing plane (see Note 2 below)
WHAT(4)
-
WHAT(6)
: not used First and second continuation cards: as for
SDUM
= PPSOURCE (see above)
Notes:
1) When SPECSOUR is used to define two colliding beams (
SDUM
= PPSOURCE, CROSSASY or CROSSSYM), DPMJET must be linked through the script $FLUPRO/flutil/ldpmqmd. A card PHYSICS with
SDUM
= LIMITS sets the maximum CMS momentum (GeV/c) in
WHAT(1)
for DPMJET initialization purposes. 2) With
SDUM
= CROSSASY and CROSSSYM, the half plane containing the two proton momenta at the sampled interaction point (XXX, YYY, ZZZ) is assumed to be limited by an axis z' passing through (XXX, YYY) and parallel to the z-axis. Polar and azimuthal angles are defined with respect to z', with
WHAT(3)
= 0 corresponding to the xz' half plane towards positive x,
WHAT(3)
= 90 corresponding to the yz' half plane towards positive y,
WHAT(3)
= 180 corresponding to the xz' half plane towards negative x,
WHAT(3)
= 270 corresponding to the yz' half plane towards negative y. 3) With
SDUM
= CROSSSYM, the particles of the two beams are identical and have the same momentum. They can only be protons or nuclei: other hadrons are excluded. 4) The particles produced in the interaction of two beams have generation number 1 (i.e., they are considered as primary particles) 5) All the scores in a run where the source consists of two colliding beams are normalised per beam interaction

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