Correlated leading baryon-antibaryon production in $e^{+}{e}^{-}\to c\overline{c}\to {\Lambda }_c^{+}{\overline{\Lambda }}_c^{-}X$

We present a study of $649\pm 35$ $e^{+}{e}^{-}\to c\overline{c}$ events produced at $\sqrt{s}\approx 10.6\mathrm{GeV}$ containing both a ${\Lambda }_c^{+}$ baryon and a ${\overline{\Lambda }}_c^{-}$ antibaryon. The number observed is roughly 4 times that expected if the leading charmed hadron types are uncorrelated, confirming an observation by the CLEO Collaboration. We find a 2-jet topology in these events but very few additional baryons, demonstrating that the primary $c$ and $\overline{c}$ are predominantly contained in a correlated baryon-antibaryon system. In addition to the charmed baryons we observe on average $2.6\pm 0.2$ charged intermediate mesons, predominantly pions, carrying 65% of the remaining energy.

Figure 1

(a) Invariant mass distributions for the ${\Lambda }_c^{+}/{\overline{\Lambda }}_c^{-}$ candidates in selected events, reconstructed in the $pK\pi$ (gray) and $p{K}_S^0$ (black) decay modes. (b) Invariant mass of the ${\overline{\Lambda }}_c^{-}$ candidate vs that of the ${\Lambda }_c^{+}$ candidate in the same event, in $5\mathrm{MeV}/c^2$ square bins.

Figure 2

Background-subtracted distributions for the 649 ${\Lambda }_c^{+}{\overline{\Lambda }}_c^{-}X$ events in the data: (a) the numbers of additional tracks, identified $K^{\pm }$ and identified $p/\overline{p}$; and (b) missing mass, with imaginary masses given negative real values. Most events have no identified $K^{\pm }$ or $p/\overline{p}$ and the corresponding zero-multiplicity points are off the vertical scale in (a).

Figure 3

Invariant mass distributions for (a) ${\Lambda }_c^{+}{\pi }^{\pm }$ and ${\overline{\Lambda }}_c^{-}{\pi }^{\pm }$ and (b) ${\Lambda }_c^{+}/{\overline{\Lambda }}_c^{-}{\pi }^{+}{\pi }^{-}$ combinations. The points with errors represent the background-subtracted ${\Lambda }_c^{+}{\overline{\Lambda }}_c^{-}X$ events, and the weighted histograms are from the single-${\Lambda }_c^{+}/{\overline{\Lambda }}_c^{-}$ sidebands.