Space-like virtualities of partons

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SUMMARY

The discussion centers on the use of PYTHIA, specifically version PYEEVT, to analyze parton showers resulting from the process e+ e- → γ*/Z0→q \bar{q}. The user observed that certain partons produced in this process exhibit imaginary masses, indicating space-like virtualities, despite the absence of initial state radiation. The user expresses confidence in PYTHIA's reliability, given its extensive development over the past thirty years, and seeks clarification on the implications of these space-like virtualities and their occurrence in the event list provided.

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  • Understanding of PYTHIA event generator
  • Familiarity with parton showers and QCD (Quantum Chromodynamics)
  • Knowledge of virtual particles and their properties
  • Basic concepts of particle physics, including mass and energy-momentum relations
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  • Research the implications of imaginary mass in particle physics
  • Explore the role of initial state radiation in particle interactions
  • Study the detailed workings of PYTHIA and its event generation algorithms
  • Learn about space-like and time-like virtualities in quantum field theory
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Particle physicists, researchers in quantum field theory, and students studying high-energy physics who are interested in the behavior of partons and the intricacies of event generation in simulations.

Kyong
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I used PYTHIA (an event generator) to have parton showers from the process e+ e- → γ*/Z0→q \bar{q}→parton showers (PYEEVT).
I realized that some partons (gluons or quarks) produced in this process have imaginary masses (Q2=E2-px2-py2-pz2<0), i.e. space-like virtualities.
As I know, space-like partons usually come from initail state radiation. However, in case of the above process, there is no initial state radiation.
I don't believe that PYTHIA was wrong because PYTHIA has been corrected and polished much by many people for about thirty years(?).
Can anybody explain me why the space-like virtualities happened and what they mean?
I attached a text file for an event list.
 

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Physics news on Phys.org
All particles 4-43 are virtual. Why do you expect a positive (real) mass there?
All particles after 44 look real.
 

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