+++ /dev/null
-<chapter name="Accessing Pythia6 Processes">
-
-<h2>Access PYTHIA 6 Processes</h2>
-
-Gradually all relevant processes from PYTHIA 6 are being
-re-implemented in PYTHIA 8, but this transition is not finished.
-For a while longer it may therefore at times be convenient to
-access the Fortran PYTHIA 6 process library. In order to give
-this access at runtime, and not only by writing/reading event files,
-an interface is provided to C++. This interface is residing in
-<code>Pythia6Interface.h</code>, and in addition the PYTHIA 6 library
-must be linked. The latter should normally be the most recent
-Fortran PYTHIA version, but must be at least 6.314, since this is
-the first version that allows processes to be output in the Les
-Houches format (and not only input).
-
-<p/>
-The routines interfaced are
-<ul>
-<li><code>pygive(command)</code> to give in a command to change a
-setting, e.g. to decide which processes should be generated,
-<li><code>pyinit( frame, beam, target, wIn)</code> to initialize
-the event generation chain,</li>
-<li><code>pyupin()</code> to fill this initialization information
-in the <code>HEPRUP</code> commonblock,</li>
-<li><code>pyupev()</code> to generate the next hard process and
-fill the event information in the <code>HEPEUP</code> commonblock,</li>
-<li><code>pylist( mode)</code> to list the event at the process
-level,</li>
-<li><code>pystat( mode)</code> to print statistics on the event
-generation process.</li>
-</ul>
-Details on allowed arguments are given in the PYTHIA 6.4 manual.
-
-<p/>
-These methods can be used in context of the
-<aloc href="LesHouchesAccord"><code>LHAupFortran</code></aloc> class.
-The existing code there takes care of converting <code>HEPRUP</code>
-and <code>HEPEUP</code> commonblock information from Fortran to C++,
-and of making it available to the PYTHIA 8 methods. What needs to be
-supplied are the two <code>LHAupFortran::fillHepRup()</code> and
-<code>LHAupFortran::fillHepEup()</code> methods. The first can
-contain an arbitrary number of <code>pygive(...)</code>, followed
-by <code>pyinit(...)</code> and <code>pyupin()</code> in that order.
-The second only needs to contain <code>pyupev()</code>. Finally,
-the use of <code>pylist(...)</code> and <code>pystat(...)</code>
-is entirely optional, and calls are best put directly in the
-main program.
-
-<p/>
-This means that all other Fortran routines have not been interfaced
-and cannot be accessed directly from the C++ code; there is no need
-for them in the current setup.
-
-<p/>
-PYTHIA 6.4 does its own rejection of events internally, according to
-the strategy option 3. However, the current runtime interface does not
-take cross-section information from PYTHIA 6.4. This means that both
-the initial maxima and the final cross sections printed by the PYTHIA 8
-routines are irrelevant in this case. Instead you have to study the
-standard PYTHIA 6.4 initialization printout and call on
-<code>pystat(...)</code> at the end of the run to obtain this information.
-It also means that you cannot mix with internally generated events,
-unlike what could have been allowed for strategy 3. Should a strong need
-arise, PYTHIA 6.4 could be modified to work with strategy option 1 and
-thus allow a mixing with internal processes, but we do not expect this
-to happen.
-
-<p/>
-An example of a <code>fillHepRup()</code> method to set up
-<ei>Z^0</ei> production at LHC, with masses above 50 GeV, would be
-<pre>
-bool LHAinitFortran::fillHepRup() {
- Pythia6Interface::pygive("msel = 11");
- Pythia6Interface::pygive("ckin(1) = 50.");
- Pythia6Interface::pyinit("cms","p","p",14000.);
- Pythia6Interface::pyupin();
- return true;
-}
-</pre>
-and the process-generic <code>fillHepEup()</code> method would be
-<pre>
-bool LHAupFortran::fillHepEup() {
- Pythia6Interface::pyupev();
- return true;
-}
-</pre>
-Note that, of all parameters that could be set with the
-<code>PYGIVE</code>, only those that influence the generation of the
-hard processes have any impact, since this is the only part of the
-Fortran code that is used. Also, if you want to set many parameters,
-you can easily collect them in one file (separate from PYTHIA 8
-input) and parse that file.
-
-<p/>
-All hard PYTHIA 6 processes should be available for full generation
-in PYTHIA 8, at least to the extent that they are defined for beams
-of protons and antiprotons, which is the key application for PYTHIA 8
-so far. Soft processes, i.e. elastic and diffractive scattering, as well
-as minimum-bias events, require a different kinematics machinery, and
-can only be generated with the internal PYTHIA 8 processes.
-
-<p/>
-A simple example is found in <code>main51.cc</code>, another with parsed
-input in <code>main52.cc</code> and a third with HepMC output in
-<code>main54.cc</code>.
-
-</chapter>
-
-<!-- Copyright (C) 2008 Torbjorn Sjostrand -->
git://git.uio.no / u / mrichter / AliRoot.git / blobdiff