Discussion of the analysis results for Pythia6

On this web page the results of the involved particles are discussed for the generator Pythia6.

All the analyses are based on the HepMCAnalysis tool. Here is a documentation of the used release 3.2.
Back to overview of summerstudent project (2010).

Histograms for the W-boson:

	The charge of the generated W-bosons: It can be extracted from the plot that more W-bosons with a positive charge are produced. This behaviour is due to the fact, that the W+-boson can be produced from an up-type quark and an anti down-type quark, whereas the W--boson can be produced from a down-type quark and an anti up-type quark. The considered process is the collision of two protons, which contain each two up and one down valence quarks. Therefore the possibility that an up quark interacts is two times higher than the interaction of a down quark. Furthermore the parton distribution function of the anti-down quark is slightly higher than the one of the anti-u-quark
	The transverse momentum of the W-boson: The W-boson carries only a small transverse momentum because of its high mass. It is almost produced at rest and decays after a short time into the &tau -lepton and the neutrino.
	Pseudorapidity of the W-boson: The direction of the W-boson can also be determined of the pseudorapidity, which is defined as &eta=-ln[tan(^&theta/₂)]. If the W-boson is produced perpendicular to the beam axis, &theta=90°, the pseudorapidity becomes &eta=0. A large pseudorapidity implies a vanishing angle &theta. The pseudorapidity is symmetric with respect to the beam-axis.

Histograms for the decay particles &tau and &nu:

The transverse momenta of the decay productsy

Both particles have almost the same momentum distributions with a maximum around pT &asymp 40 GeV/c, which coincide with the half mass of the W-boson. Compared to the mother particle, the &tau -lepton (m = 1776.82 ± 0.16 MeV/c^2) as well as the neutrino are massless. This involves that both decaying particles get half of the energy of the W-boson which defines the momentum. In order to conservate transverse momenta, the particles must be emitted back-to-back.

Angle &Phi between the &tau and the neutrino:

The angle between the both particles is ± &pi. This signifies that the decay particles of the W-boson are emitted back-to-back.

Number of charged tracks in the decay of the &tau -lepton:

The &tau -lepton can either decay leptonically into electrons and muons and its corresponding neutrinos or either hadronically into &pi's or K-mesons. The plot indicates that the &tau decays more often into one charged particle, e.g. &tau &rarr &mu &nu + &nu or &tau &rarr &pi + &nu. The particle data group (PDG) quote that the &tau -lepton decays to 85.36 ± 0.08 % into one charged particle and with 15.56 ± 0.08 % into three charged particles. The ratio of the number of events with one track respectively three tracks compared to the total number of events in the histograms are in good agreement with the branching ratios of the PDG.

Histograms for the charged particles in the event:

The charged particle multiplicity:

The number of charged particles is varies between zero and approximately 140. The large number of charged particles can be explained by initial and final state radiation and the multiple parton interaction.Most of the particles are pions which are produced in the decay of the &tau -leptons as well as muons and electrons.