Effect of underlying event activity on the measured kaon fraction
In order to study whether the underlying event can affect the properties of the sample of tracks that we use in the charm fragmentation study, we generate cc-bar events using the following tunes available for CDF data using PYTHIA version 8.145:
1) Tune 2C: Intended to give good agreement with much of the published CDF data.
2) Tune 2M: Uses a different PDF than Tune 2C, also intended to give good agreement with much of the published CDF data.
We pick the maximum-pT track in a cone of radius Δ R = 0.7 around a Ds±/D± meson found in an event, which is more likely to be correlated with the quark fragmentation process.
Then we measure the kaon fraction in the sample of tracks around prompt Ds±/D± in the opposite and same sign charge scenarios.
The plots below show the distribution of the kaon fraction as a function of pT of the maximum-pT track. The distribution is made for three scenarios:
1) Without any Tune for minimum-bias and underlying-event activity: Black points
2) Using Tune 2C for CDF data: Red points
3) Using Tune 2M for CDF data: Green points
Conclusions from the study:
1) Tuning the PYTHIA event generator to describe the minimum-bias and underlying-event activity does not affect the properties of kaons used in the charm fragmentation study.
2) The results of this study support the hypothesis that the maximum-pT kaon/track is more likely to be correlated with the fragmentation process, which is less likely to be affected by the underlying-event activity.