Measurement of the $D^+$-meson production cross section at low transverse momentum in $p\overline{p}$ collisions at $\sqrt{s}$ = 1.96 TeV

We report on a measurement of the $D^+$-meson production cross section as a function of transverse momentum ($p_T$) in proton-antiproton ($p\overline{p}$) collisions at 1.96 TeV center-of-mass energy, using the full data set collected by the Collider Detector at Fermilab in Tevatron Run II and corresponding to 10 fb$^{−1}$ of integrated luminosity. We use $D^+ \to K^- \pi^+\pi^+$ decays fully reconstructed in the central rapidity region $|y| < 1$ with transverse momentum down to $1.5 GeV/c$, a range previously unexplored in $p\overline{p}$ collisions. Inelastic $p\overline{p}$ -scattering events are selected online using minimally biasing requirements followed by an optimized offline selection. The $K^-\pi^+\pi^+$ mass distribution is used to identify the $D^+$ signal, and the $D^+$ transverse impact-parameter distribution is used to separate prompt production, occurring directly in the hard-scattering process, from secondary production from b-hadron decays. We obtain a prompt $D^+$ signal of 2950 candidates corresponding to a total cross section $\sigma(D^+, 1.5 < p_T < 14.5 GeV/c, |y| < 1) = 71.9 \pm 6.8(stat) \pm 9.3(syst) \mu b$. While the measured cross sections are consistent with theoretical estimates in each $p_T$ bin, the shape of the observed $p_T$ spectrum is softer than the expectation from quantum chromodynamics. The results are unique in $p\overline{p}$ collisions and can improve the shape and uncertainties of future predictions