Production cross sections of hyperons and charmed baryons from $e^{+}{e}^{-}$ annihilation near $\sqrt{s}=10.52\mathrm{GeV}$

We measure the inclusive production cross sections of hyperons and charmed baryons from $e^{+}{e}^{-}$ annihilation using a $800{\mathrm{fb}}^{-1}$ data sample taken near the $\mathrm{\Upsilon }(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. The feed-down contributions from heavy particles are subtracted using our data, and the direct production cross sections are presented for the first time. The production cross sections divided by the number of spin states for $S=-1$ hyperons follow an exponential function with a single slope parameter except for the $\mathrm{\Sigma }(1385{)}^{+}$ resonance. Suppression for $\mathrm{\Sigma }(1385{)}^{+}$ and $\mathrm{\Xi }(1530{)}^0$ hyperons is observed. Among the production cross sections of charmed baryons, a factor of 3 difference for ${\mathrm{\Lambda }}_c^{+}$ states over ${\mathrm{\Sigma }}_c$ states is observed. This observation suggests a diquark structure for these baryons.

Figure 1

(a) The invariant-mass spectrum of ($p$, ${\pi }^{-}$). The vertical lines demarcate the signal region for $\mathrm{\Lambda }$. (b), (c), (d) Invariant-mass spectra of ($\mathrm{\Lambda }$, $\gamma$), ($\mathrm{\Lambda }$, ${\pi }^{+}$), and ($p{K}^{-}$), respectively. Fit results, signal shapes, and background shapes are shown by solid, dashed, and dotted curves, respectively.

Figure 2

(a)–(c) Reconstructed mass spectra for $S=-2$ and $-3$ hyperon candidates. Fit results, signal shapes, and background shapes are shown by solid, dashed, and dotted curves, respectively.

Figure 3

Reconstructed mass spectra of charmed baryon candidates. (a) The invariant-mass spectrum of ${\mathrm{\Lambda }}_c^{+}$. The signal and sideband regions are indicated by the double-hatched and hatched histograms, respectively. (b) The mass-difference distribution of ${\mathrm{\Lambda }}_c^{+}{\pi }^{+}{\pi }^{-}-{\mathrm{\Lambda }}_c^{+}$. (c) The mass-difference distribution for ${\mathrm{\Lambda }}_c^{+}{\pi }^{-}-{\mathrm{\Lambda }}_c^{+}$. (d) The invariant-mass spectrum of ${\mathrm{\Omega }}^{-}{\pi }^{+}$. (e), (f) The invariant-mass spectra of ${\mathrm{\Xi }}^{-}{\pi }^{+}$ and ${\mathrm{\Omega }}^{-}{K}^{+}$, respectively.

Figure 4

Invariant mass (a) and rms width (b) of the fitted ${\mathrm{\Lambda }}_c^{+}$ and ${\overline{\mathrm{\Lambda }}}_c^{-}$ as a function of $x_p$.

Figure 5

Differential inclusive cross sections of hyperons with and without radiative corrections. The closed circles are shifted slightly to the left for clarity. The error bars and shaded boxes represent the statistical and systematic uncertainties, respectively. These distributions contain feed-down contributions from heavier particles. Triangle points show predictions by pythia with the default tune, where all radiative processes are turned off, and the feed-down contributions are obtained using pythia predictions and branching fractions given in Ref. [1].

Figure 6

Differential inclusive cross sections of charmed baryon production with and without radiative corrections. The closed circles are shifted slightly to the left for clarity. The error bars and shaded boxes represent the statistical and systematic uncertainties, respectively. These distributions contain feed-down contributions from heavier particles. Triangle points show predictions by pythia with the default tune, where all radiative processes are turned off, and the feed-down contributions are obtained using pythia predictions and branching fractions given in Ref. [1]. Note that the prediction for ${\mathrm{\Sigma }}_c(2520{)}^0$ is scaled by a factor of 0.5.

Figure 7

The differential cross sections of ${\mathrm{\Lambda }}_c^{+}$ production before the radiative correction, where the absolute branching fraction of $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to {\pi }^{+}{K}^{-}p)=0.0635$ is used to normalize the previous results [21, 22] for the comparison. To scale the multiplicity measurement by BABAR, the total hadronic cross section of 3.3 nb is utilized. The error bars represent the sum in quadrature of the statistical and systematic uncertainties; note that Belle’s previous measurement contains an additional uncertainty of 35% for the normalization.

Figure 8

Scaled direct production cross section as a function of mass of hyperons. $S=-1$, $-2$, $-3$ hyperons are shown with filled circles, open circles, and a triangle, respectively. The solid line shows the fit result using an exponential function [Eq. (1)] for $S=-1$ hyperons except for $\mathrm{\Sigma }(1385{)}^{+}$. The dashed line shows an exponential curve with the same slope parameter as $S=-1$ hyperons, which is normalized to the production cross section of ${\mathrm{\Xi }}^{-}$.

Figure 9

Scaled direct production cross section as a function of mass of charmed baryons. The solid and dashed lines show the fit results using exponential functions [Eq. (1)] for ${\mathrm{\Lambda }}_c$ baryons and ${\mathrm{\Sigma }}_c$ baryons, respectively.

Figure 10

Polar angular distribution for $\mathrm{\Lambda }$ (a) and ${\mathrm{\Lambda }}_c^{+}$ (b) in the laboratory system. Solid (dotted) histograms show the distributions of real (MC) data.

Figure 11

Reconstruction efficiencies for $S=-1$ hyperons.

Figure 12

Reconstruction efficiencies for $S=-2,-3$ hyperons.

Figure 13

Reconstruction efficiencies for charmed baryons.

Figure 14

Reconstruction efficiencies for charmed strange baryons.

Figure 15

Reconstruction efficiencies for ${\mathrm{\Xi }}^{-}$ hyperons in the $e^{+}{e}^{-}$ center-of-mass system.

Figure 16

Reconstruction efficiency over the Dalitz plot for ${\mathrm{\Lambda }}_c^{+}\to p{K}^{-}{\pi }^{+}$.