New pythia8 version

[u/mrichter/AliRoot.git] / PYTHIA8 / pythia8145 / xmldoc / EventInformation.xml

<chapter name="Event Information">

<h2>Event Information</h2>

The <code>Info</code> class collects various one-of-a-kind information, 
some relevant for all events and others for the current event. 
An object <code>info</code> is a public member of the <code>Pythia</code>
class, so if you e.g. have declared <code>Pythia pythia</code>, the
<code>Info</code> methods can be accessed by 
<code>pythia.info.method()</code>. Most of this is information that 
could also be obtained e.g. from the event record, but is here more
directly available. It is primarily intended for processes generated 
internally in PYTHIA, but many of the methods would work also for
events fed in via the Les Houches Accord.

<h3>List information</h3>

<method name="void Info::list()">
a listing of most of the information set for the current event. 
</method>

<h3>The beams</h3>

<method name="int Info::idA()">
</method>
<methodmore name="int Info::idB()">
the identities of the two beam particles. 
</methodmore>

<method name="double Info::pzA()"> 
</method>
<methodmore name="double Info::pzB()">
the longitudinal momenta of the two beam particles.
</methodmore>

<method name="double Info::eA()"> 
</method>
<methodmore name="double Info::eB()">
the energies of the two beam particles.
</methodmore>

<method name="double Info::mA()"> 
</method>
<methodmore name="double Info::mB()">
the masses of the two beam particles.
</methodmore>

<method name="double Info::eCM()"> 
</method>
<methodmore name="double Info::s()">
the CM energy and its square for the two beams. 
</methodmore>

<h3>Initialization</h3>

<method name="bool Info::tooLowPTmin()">
normally false, but true if the proposed <ei>pTmin</ei> scale was too low 
in timelike or spacelike showers, or in multiple interactions. In the former
case the <ei>pTmin</ei> is raised to some minimal value, in the latter the 
initialization fails (it is impossible to obtain a minijet cross section
bigger than the nondiffractive one by reducing <ei>pTmin</ei>).
</method>

<h3>The event type</h3>

<method name="string Info::name()"> 
</method>
<methodmore name="int Info::code()">
the name and code of the process that occured.
</methodmore>

<method name="int Info::nFinal()"> 
the number of final-state partons in the hard process.
</method>

<method name="bool Info::isResolved()"> 
are beam particles resolved, i.e. were PDF's used for the process?
</method>

<method name="bool Info::isDiffractiveA()"> 
</method>
<methodmore name="bool Info::isDiffractiveB()">
is either beam diffractively excited?
</methodmore>

<method name="bool Info::isMinBias()"> 
is the process a minimum-bias one?
</method>

<method name="bool Info::isLHA()"> 
has the process been generated from external Les Houches Accord 
information?
</method>

<method name="bool Info::atEndOfFile()"> 
true if a linked Les Houches class refuses to return any further 
events, presumably because it has reached the end of the file from 
which events have been read in.
</method>

<method name="bool Info::hasSub()"> 
does the process have a subprocess classification?
Currently only true for minbias and Les Houches events, where it allows 
the hardest collision to be identified. 
</method>

<method name="string Info::nameSub()"> 
</method>
<methodmore name="int Info::codeSub()">
</methodmore>
<methodmore name="int Info::nFinalSub()">
the name, code and number of final-state partons in the subprocess
that occured when <code>hasSub()</code> is true. For a minimum-bias event 
the <code>code</code> would always be 101, while <code>codeSub()</code> 
would vary depending on the actual hardest interaction, e.g. 111 for 
<ei>g g -> g g</ei>. For a Les Houches event the <code>code</code> would 
always be 9999, while <code>codeSub()</code> would be the external 
user-defined classification code. The methods below would also provide 
information for such particular subcollisions.  
</methodmore>

<h3>Hard process parton densities and scales</h3>

<method name="int Info::id1()"> 
</method>
<methodmore name="int Info::id2()">
the identities of the two partons coming in to the hard process.
</methodmore>

<method name="double Info::x1()"> 
</method>
<methodmore name="double Info::x2()">
<ei>x</ei> fractions of the two partons coming in to the hard process.
</methodmore>

<method name="double Info::y()"> 
</method>
<methodmore name="double Info::tau()">
rapidity and scaled mass-squared of the hard-process subsystem, as 
defined by the above <ei>x</ei> values. 
</methodmore>

<method name="double Info::pdf1()"> 
</method>
<methodmore name="double Info::pdf2()">
parton densities <ei>x*f(x,Q^2</ei> )evaluated for the two incoming 
partons; could be used e.g. for reweighting purposes. 
</methodmore>

<method name="double Info::QFac()"> 
</method>
<methodmore name="double Info::Q2Fac()">
the <ei>Q</ei> or <ei>Q^2</ei> factorization scale at which the 
densities were evaluated.
</methodmore>

<method name="bool Info::isValence1()"> 
</method>
<methodmore name="bool Info::isValence2()">
<code>true</code> if the two hard incoming partons have been picked 
to belong to the valence piece of the parton-density distribution, 
else <code>false</code>. Should be interpreted with caution.
Information is not set if you switch off parton-level processing. 
</methodmore>

<method name="double Info::alphaS()"> 
</method>
<methodmore name="double Info::alphaEM()">
the <ei>alpha_strong</ei> and <ei>alpha_electromagnetic</ei> values used 
for the hard process.
</methodmore>

<method name="double Info::QRen()"> 
</method>
<methodmore name="double Info::Q2Ren()">
the <ei>Q</ei> or <ei>Q^2</ei> renormalization scale at which 
<ei>alpha_strong</ei> and <ei>alpha_electromagnetic</ei> were evaluated.
</methodmore>

<h3>Hard process kinematics</h3>

<method name="double Info::mHat()">
</method>
<methodmore name="double Info::sHat()">
the invariant mass and its square for the hard process.
</methodmore>

<method name="double Info::tHat()"> 
</method>
<methodmore name="double Info::uHat()">
the remaining two Mandelstam variables; only defined for <ei>2 -> 2</ei>
processes. 
</methodmore>

<method name="double Info::pTHat()"> 
</method>
<methodmore name="double Info::pT2Hat()">
transverse momentum and its square in the rest frame of a <ei>2 -> 2</ei>
processes. 
</methodmore>

<method name="double Info::m3Hat()"> 
</method>
<methodmore name="double Info::m4Hat()">
the masses of the two outgoing particles in a <ei>2 -> 2</ei> processes. 
</methodmore>

<method name="double Info::thetaHat()"> 
</method>
<methodmore name="double Info::phiHat()">
the polar and azimuthal scattering angles in the rest frame of 
a <ei>2 -> 2</ei> process.
</methodmore>

<h3>Event weight and activity</h3>

<method name="double Info::weight()"> 
weight assigned to the current event. Is normally 1 and thus uninteresting.
However, in case of the <code><aloc href="PhaseSpaceCuts">
PhaseSpace:increaseMaximum = off</aloc></code> default strategy,
an event with a differential cross-section above the assumed one 
(in a given phase-space point) is assigned a weight correspondingly
above unity. This should happen only very rarely, if at all, and so
could normally be disregarded. For Les Houches events some strategies 
allow negative weights, which then after unweighting lead to events 
with weight -1. There are also Les Houches strategies where no unweighting 
is done, and therefore a nontrivial event weight must be used e.g. 
when filling histograms. 
</method>

<method name="int Info::nISR()"> 
</method>
<methodmore name="int Info::nFSRinProc()">
</methodmore>
<methodmore name="int Info::nFSRinRes()">
the number of emissions in the initial-state showering, in the final-state
showering excluding resonance decys, and in the final-state showering
inside resonance decays, respectively.
</methodmore>

<method name="double Info::pTmaxMI()"> 
</method>
<methodmore name="double Info::pTmaxISR()">
</methodmore>
<methodmore name="double Info::pTmaxFSR()">
Maximum <ei>pT</ei> scales set for MI, ISR and FSR, given the 
process type and scale choice for the hard interactions. The actual
evolution will run down from these scales.
</methodmore>

<method name="double Info::pTnow()">
The current <ei>pT</ei> scale in the combined MI, ISR and FSR evolution.
Useful for classification in <aloc href="UserHooks">user hooks</aloc>,
but not once the event has been evolved.  
</method>

<h3>Multiple interactions</h3>

<method name="double Info::bMI()"> 
the impact parameter <ei>b</ei> assumed for the current collision when
multiple interactions are simulated. Is not expressed in any physical
size (like fm), but only rescaled so that the average should be unity 
for minimum-bias events (meaning less than that for events with hard
processes). 
</method>

<method name="double Info::enhanceMI()"> 
The choice of impact parameter implies an enhancement or depletion of
the rate of subsequent interactions, as given by this number. Again
the average is normalized be unity for minimum-bias events (meaning 
more than that for events with hard processes).  
</method>

<method name="int Info::nMI()"> 
the number of hard interactions in the current event. Is 0 for elastic
and diffractive events, and else at least 1, with more possible from
multiple interactions.
</method>

<method name="int Info::codeMI(int i)"> 
</method>
<methodmore name="double Info::pTMI(int i)">
the process code and transverse momentum of the <code>i</code>'th 
subprocess, with <code>i</code> in the range from 0 to
<code>nMI() - 1</code>. The values for subprocess 0 is redundant with
information already provided above.  
</methodmore>

<method name="int Info::iAMI(i)"> 
</method>
<methodmore name="int Info::iBMI(i)">
are normally zero. However, if the <code>i</code>'th subprocess is
a rescattering, i.e. either or both incoming partons come from the 
outgoing state of previous scatterings, they give the position in the
event record of the outgoing-state parton that rescatters. 
<code>iAMI</code> and <code>iBMI</code> then denote partons coming from 
the first or second beam, respectively.
</methodmore>

<h3>Cross sections</h3>

Here are the currently available methods related to the event sample 
as a whole. While continuously updated during the run, it is recommended
only to study these properties at the end of the event generation, 
when the full statistics is available.

<method name="long Info::nTried()">
</method>
<methodmore name="long Info::nSelected()">
</methodmore>
<methodmore name="long Info::nAccepted()">
the total number of tried phase-space points, selected hard processes
and finally accepted events, summed over all allowed subprocesses.
The first number is only intended for a study of the phase-space selection
efficiency. The last two numbers usually only disagree if the user introduces 
some veto during the event-generation process; then the former is the number 
of acceptable events found by PYTHIA and the latter the number that also
were approved by the user. If you set <aloc href="ASecondHardProcess">a 
second hard process</aloc> there may also be a mismatch. 
</methodmore>

<method name="double Info::sigmaGen()">
</method>
<methodmore name="double Info::sigmaErr()">
the estimated cross section and its estimated error,
summed over all allowed subprocesses, in units of mb. The numbers refer to
the accepted event sample above, i.e. after any user veto. 
</methodmore>

<h3>Loop counters</h3>

Mainly for internal/debug purposes, a number of loop counters from
various parts of the program are stored in the <code>Info</code> class,
so that one can keep track of how the event generation is progressing.
This may be especially useful in the context of the  
<code><aloc href="UserHooks">User Hooks</aloc></code> facility.

<method name="int Info::getCounter(int i)">
the method that gives you access to the value of the various loop 
counters.
<argument name="i"> the counter number you want to access:
<argoption value="0 - 9"> counters that refer to the run as a whole, 
i.e. are set 0 at the beginning of the run and then only can increase.
</argoption>
<argoption value="0"> the number of successful constructor calls for the
<code>Pythia</code> class (can only be 0 or 1).
</argoption>
<argoption value="1"> the number of times a <code>Pythia::init(...)</code>
call has been begun.  
</argoption>
<argoption value="2"> the number of times a <code>Pythia::init(...)</code>
call has been completed successfully.  
</argoption>
<argoption value="3"> the number of times a <code>Pythia::next()</code>
call has been begun.  
</argoption>
<argoption value="4"> the number of times a <code>Pythia::next()</code>
call has been completed successfully.  
</argoption>
<argoption value="10 - 19"> counters that refer to each individual event, 
and are reset and updated in the top-level <code>Pythia::next()</code> 
method.  
</argoption>
<argoption value="10"> the number of times the selection of a new hard 
process has been begun. Normally this should only happen once, unless a 
user veto is set to abort the current process and try a new one.
</argoption>
<argoption value="11"> the number of times the selection of a new hard 
process has been completed successfully.  
</argoption>
<argoption value="12"> as 11, but additionally the process should
survive any user veto and go on to the parton- and hadron-level stages. 
</argoption>
<argoption value="13"> as 11, but additionally the process should 
survive the parton- and hadron-level stage and any user cuts. 
</argoption>
<argoption value="14"> the number of times the loop over parton- and
hadron-level processing has begun for a hard process. Is reset each
time counter 12 above is reached. 
</argoption>
<argoption value="15"> the number of times the above loop has successfully
completed the parton-level step.
</argoption>
<argoption value="16"> the number of times the above loop has successfully
completed the checks and user vetoes after the parton-level step.
</argoption>
<argoption value="17"> the number of times the above loop has successfully
completed the hadron-level step.
</argoption>
<argoption value="18"> the number of times the above loop has successfully
completed the checks and user vetoes after the hadron-level step.
</argoption>
<argoption value="20 - 39"> counters that refer to a local part of the 
individual event, and are reset at the beginning of this part.
</argoption>
<argoption value="20"> the current system being processed in 
<code>PartonLevel::next()</code>. Is almost always 1, but for double
diffraction the two diffractive systems are 1 and 2, respectively.
</argoption>
<argoption value="21"> the number of times the processing of the 
current system (see above) has begun.
</argoption>
<argoption value="22"> the number of times a step has begun in the 
combined MI/ISR/FSR evolution downwards in <ei>pT</ei> 
for the current system.
</argoption>
<argoption value="23"> the number of time MI has been selected for the 
downwards step above.
</argoption>
<argoption value="24"> the number of time ISR has been selected for the 
downwards step above.
</argoption>
<argoption value="25"> the number of time FSR has been selected for the 
downwards step above.
</argoption>
<argoption value="26">  the number of time MI has been accepted as the 
downwards step above, after the vetoes.
</argoption>
<argoption value="27">  the number of time ISR has been accepted as the 
downwards step above, after the vetoes.
</argoption>
<argoption value="28">  the number of time FSR has been accepted as the 
downwards step above, after the vetoes.
</argoption>
<argoption value="29"> the number of times a step has begun in the 
separate (optional) FSR evolution downwards in <ei>pT</ei> 
for the current system.
</argoption>
<argoption value="30"> the number of time FSR has been selected for the 
downwards step above.
</argoption>
<argoption value="31">  the number of time FSR has been accepted as the 
downwards step above, after the vetoes.
</argoption>
<argoption value="40 - 49"> counters that are unused (currently), and
that therefore are free to use, with the help of the two methods below.
</argoption>
</argument>
</method>

<method name="void Info::setCounter(int i, int value = 0)">
set the above counters to a given value. Only to be used by you 
for the unassigned counters 40 - 49.
<argument name="i"> the counter number, see above.
</argument>
<argument name="value" default="0"> set the counter to this number;
normally the default value is what you want.
</argument>

<method name="void Info::addCounter(int i, int value = 0)">
increase the above counters by a given amount. Only to be used by you 
for the unassigned counters 40 - 49.
<argument name="i"> the counter number, see above.
</argument>
<argument name="value" default="1"> increase the counter by this amount;
normally the default value is what you want.
</argument>

</method>



</chapter>

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