Event Information

The Info class collects various one-of-a-kind information, some relevant for all events and others for the current event. An object info is a public member of the Pythia class, so if you e.g. have declared Pythia pythia, the Info methods can be accessed by pythia.info.method(). Most of this is information that could also be obtained e.g. from the event record, but is here more directly available. It is intended for processes generated internally in Pythia8, not for ones read in e.g. via the Les Houches Accord. Here are the currently available methods:

method name="list()"
a listing of most of the information set for the current event.

method name="idA(), idB()"
the identities of the two beam particles.

method name="pzA(), pzB()"
the longitudinal momenta of the two beam particles.

method name="eA(), eB()"
the energies of the two beam particles.

method name="mA(), mB()"
the masses of the two beam particles.

method name="eCM(), s()"
the cm energy and its square for the two beams.

method name="name(), code()"
the name and code of the process that occured.

method name="nFinal()"
the number of final-state partons in the hard process.

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

method name="isDiffractiveA(), isDiffractiveB()"
is either beam diffractively excited?

method name="isMinBias()"
is the process a minimum-bias one?

method name="hasSub()"
does the process have a subprocess classification? Currently only true for minbias, where it allows the hardest collision to be identified.

method name="nameSub(), codeSub(), nFinalSub()"
the name, code and number of final-state partons in the subprocess that occured when hasSub() is true. For instance, for a minimum-bias event the code would always be 101, while codeSub() would vary depending on the actual hardest interaction, e.g. 111 for g g -> g g. The methods below would also provide information for this particular subcollision.

method name="id1(), id2()"
the identities of the two partons coming in to the hard process.

method name="x1(), x2()"
x fractions of the two partons coming in to the hard process.

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

method name="QFac(), Q2Fac()"
the Q^2 or Q^2 factorization scale at which the densities were evaluated.

method name="alphaS(), alphaEM()"
the alpha_strong and alpha_electromagnetic values used for the hard process.

method name="QRen(), Q2Ren()"
the Q or Q^2 renormalization scale at which alpha_strong and alpha_electromagnetic were evaluated.

method name="mHat(), sHat()"
the invariant mass and its square for the hard process.

method name="tHat(), uHat()"
the remaining two Mandelstam variables; only defined for 2 -> 2 processes.

method name="pTHat(), pT2Hat()"
transverse momentum and its square in the rest frame of a 2 -> 2 processes.

method name="m3Hat(), m4Hat()"
the masses of the two outgoing particles in a 2 -> 2 processes.

method name="thetaHat(), phiHat()"
the polar and azimuthal scattering angles in the rest frame of a 2 -> 2 process.

method name="nTried(), nAccepted()"
the total number of tried phase-space points and accepted events, summed over all allowed subprocesses.

method name="sigmaGen(), sigmaErr()"
the estimated cross section and its estimated error, summed over all allowed subprocesses, in units of mb.

method name="bMI()"
the impact parameter b 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 name="enhanceMI()"
The choice of impact parameter implies an enhancement or depletion of the rate of subsequent interactiosn, 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 name="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 name="nISR(), nFSRinProc(), 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. Not yet fully implemented.