Finding hadrons inside jets

The figure shows the inclusive invariant pT differential cross section distributions for Ks, K and φ measured in this experiment. The predictions from PYTHIA are shown as dotted lines.

Physicists currently have a very good understanding of the Standard Model. Thus many of the results presented in this column can be understood in terms of the Standard Model theory of the strong interactions, called quantum chromodynamics. But the particle production from soft interactions — collisions usually referred to as minimum-bias (MB) events, in which outgoing particles scatter only minimally, and which dominated the cross section at the Tevatron — cannot be calculated from first principles. Neither can jets, which are the production of particles from high-energy quarks or gluons. Scientists have therefore developed phenomenological models, such as PYTHIA, by tuning to the data.

One goal of this analysis is to provide detailed particle production information at a center-of-mass energy of 1.96 TeV to refine current phenomenological models.

CDF physicists have looked at the rate of production of hadrons, strongly interacting particles, that contain a strange quark in MB events. The three particles we look for are Kshort (Ks), K(892) and φ(1020). The top plot shows that the φ cross section matches well with PYTHIA, that the Ks is a little lower than the data, and that K is a little higher than the data.

CDF scientists have also studied the transverse-momentum distributions of identified hadrons produced in jets. This is the first time scientists have measured this distribution. The hadrons we look for are the Ks and the Λ.

The lower figure shows a highlight of this analysis. Plotted is the ratio of the Λ hadron production cross section to Ks meson production as a function of the transverse momentum (pT) from MB events (top two plots) and jets (lower five plots). The top curve is taken from Fermilab E735, an early Tevatron collider experiment, and the second curve is taken from this experiment and from an earlier version of this experiment.

The ratios from MB events exhibit an excess production of Λ hyperons around 2 GeV/c pT. The results from jets are according to the transverse energy (ET) of jets. Unlike the ratios from MB events, the ratios from jets are fairly constant, hovering at approximately 0.25 for all transverse momenta. This implies that the process of producing Ks and Λ’s in jets is similar for all transverse momenta. Another interesting result is that the ratio from MB events merges with the ratios from jets as the transverse momentum increases. This could indicate that the particles above about 5 GeV/c in MB events are likely from soft jets.

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edited by Andy Beretvas

The cross-section ratios of Λ0 baryon to strange meson as a function of pT. The statistical and systematic uncertainties are added in quadrature.
These CDF physicists contributed to this data analysis.