Correlations between D and $\bar{D}$ mesons produced in 500 GeV/c $\pi^-$-nucleon interactions

TL;DR

This study investigates the correlations between D and anti-D mesons produced in high-energy pion-nucleon interactions, comparing experimental data with theoretical models to improve understanding of charm quark production.

Contribution

It provides detailed measurements of D and anti-D meson correlations and compares them with QCD calculations and Monte Carlo models, highlighting areas for model tuning.

Findings

Significant azimuthal angle correlations observed

Less transverse momentum correlation than models predict

Discrepancies in relative production rates of charm pairs

Abstract

We present a study of correlations between D and $\bar{D}$ mesons produced in 500 GeV/$c$ $\pi^-$-nucleon interactions, based on data from experiment E791 at Fermilab. We have fully reconstructed $791 \pm 44$ charm meson pairs to study correlations between the transverse and longitudinal momenta of the two D mesons and the relative production rates for different types of D meson pairs. We see slight correlations between the longitudinal momenta of the D and the $\bar D$, and significant correlations between the azimuthal angle of the D and the $\bar D$. The experimental distributions are compared to a next-to-leading-order QCD calculation and to predictions of the {\sc Pythia/Jetset} Monte Carlo event generator. We observe less correlation between transverse momenta and different correlations between longitudinal momenta than these models predict for the default values of the model parameters. Better agreement between data and theory might be achieved by tuning the model parameters or by adding higher order perturbative terms, thus contributing to a better understanding of charm production. The relative production rates for the four sets of charm pairs, $D^0\bar{D}^{0}$, $D^0D^-$, $D^+\bar{D}^{0}$, $D^+D^-$, as calculated in the {\sc Pythia/Jetset} event generator with the default parameters, agree with data as far as the relative ordering, but predict too many $D^+\bar{D}^{0}$ pairs and too few $D^+D^-$ pairs.