The process $e^{+}e^{-}\to \eta^{\prime} J/\psi$ is observed for the first time with a statistical significance of $8.6\sigma$ at center-of-mass energy $\sqrt{s} = 4.226$ GeV and $7.3\sigma$ at $\sqrt{s} = 4.258$ GeV using data samples collected with the BESIII detector. The Born cross sections are measured to be $(3.7 \pm 0.7 \pm 0.3)$ and $(3.9 \pm 0.8 \pm 0.3)$ pb at $\sqrt{s} = 4.226$ and $4.258$ GeV, respectively, where the first errors are statistical and the second systematic. Upper limits at the 90% confidence level of the Born cross sections are also reported at other 12 energy points.
Summary of the values used to calculate the Born cross section of $e^{+}e^{-}\to\eta^{\prime} J/\psi$. The upper limits are at the $90\%$ C.L.
Based on data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies $\sqrt{s} >$ 4.4 GeV, the processes $e^+e^- \rightarrow \omega \chi_{c1,2}$ are observed for the first time. With an integrated luminosity of $1074 pb^{-1}$ near $\sqrt{s} =$ 4.42 GeV, a significant $\omega \chi_{c2}$ signal is found, and the cross section is measured to be $(20.9 \pm 3.2 \pm 2.5)\pb$. With $567 pb^{-1}$ near $\sqrt{s} =$ 4.6 GeV, a clear $\omega \chi_{c1}$ signal is seen, and the cross section is measured to be $(9.5 \pm 2.1 \pm 1.3) \pb$, while evidence is found for an $\omega \chi_{c2}$ signal. The first errors are statistical and the second are systematic. Due to low luminosity or low cross section at other energies, no significant signals are observed. In the $\omega \chi_{c2}$ cross section, an enhancement is seen around $\sqrt{s} =$ 4.42 GeV. Fitting the cross section with a coherent sum of the $\psi(4415)$ Breit-Wigner function and a phase space term, the branching fraction $\mathcal{B}(\psi(4415)\to\omega\chi_{c2})$ is obtained to be of the order of $10^{-3}$.
Results on $e^+e^-\to \omega \chi_{c0}$. Shown in the table are the channels, the center-of-mass energy, the integrated luminosity $\mathcal{L}$, product of radiative correction factor, vacuum polarization factor, branching fraction and efficiency, $\mathcal{D}=(1+\delta)\frac{1}{|1-\Pi|^{2}}(\epsilon_{\pi}\mathcal{B}(\chi_{c0}\to\pi^+\pi^-)+\epsilon_{K}\mathcal{B}(\chi_{c0}\to K^+K^-))\mathcal{B}(\omega\to\pi^+\pi^{-}\pi^{0})\mathcal{B}(\pi^{0}\to\gamma\gamma)$ for $\omega\chi_{c0}$, number of observed events $N^{\rm {obs}}$, number of estimated background events $N^{\rm bkg}$, number of signal events $N^{\rm sig}$ determined as described in the text, Born cross section $\sigma^{\rm B}$(or upper limit at 90$\%$ C.L.) at each energy point.
Results on $e^+e^-\to \omega \chi_{c1}$. Shown in the table are the channels, the center-of-mass energy, the integrated luminosity $\mathcal{L}$, product of radiative correction factor, vacuum polarization factor, branching fraction and efficiency, $\mathcal{D}=(1 + \delta) \frac{1}{|1-\Pi|^{2}} (\epsilon_{e}\mathcal{B}_{e} + \epsilon_{\mu}\mathcal{B}_{\mu}) \mathcal{B}_{1}$ for $\omega\chi_{c1}$, number of observed events $N^{\rm {obs}}$, number of estimated background events $N^{\rm bkg}$, number of signal events $N^{\rm sig}$ determined as described in the text, Born cross section $\sigma^{\rm B}$(or upper limit at 90$\%$ C.L.) at each energy point. $N^{\rm sig}$ for $\omega\chi_{c1}$ at $\sqrt{s}$ = 4.416 and 4.599 GeV is taken from the fit. Dash means that the result is not applicable.
Results on $e^+e^-\to \omega \chi_{c2}$. Shown in the table are the channels, the center-of-mass energy, the integrated luminosity $\mathcal{L}$, product of radiative correction factor, vacuum polarization factor, branching fraction and efficiency, $\mathcal{D}=(1 + \delta) \frac{1}{|1-\Pi|^{2}} (\epsilon_{e}\mathcal{B}_{e} + \epsilon_{\mu}\mathcal{B}_{\mu}) \mathcal{B}_{1}$ for $\omega\chi_{c2}$, number of observed events $N^{\rm {obs}}$, number of estimated background events $N^{\rm bkg}$, number of signal events $N^{\rm sig}$ determined as described in the text, Born cross section $\sigma^{\rm B}$(or upper limit at 90$\%$ C.L.) at each energy point. $N^{\rm sig}$ for $\omega\chi_{c2}$ at $\sqrt{s}$ = 4.416 and 4.599 GeV is taken from the fit. Dash means that the result is not applicable.
The $e^+e^-\to K^+K^-$ cross section and charged-kaon electromagnetic form factor are measured in the $e^+e^-$ center-of-mass energy range ($E$) from 2.6 to 8.0 GeV using the initial-state radiation technique with an undetected photon. The study is performed using 469 fb$^{-1}$ of data collected with the BABAR detector at the PEP-II $e^+e^-$ collider at center-of-mass energies near 10.6 GeV. The form factor is found to decrease with energy faster than $1/E^2$, and approaches the asymptotic QCD prediction. Production of the $K^+K^-$ final state through the $J/\psi$ and $\psi(2S)$ intermediate states is observed. The results for the kaon form factor are used together with data from other experiments to perform a model-independent determination of the relative phases between single-photon and strong amplitudes in $J/\psi$ and $\psi(2S)\to K^+K^-$ decays. The values of the branching fractions measured in the reaction $e^+e^- \to K^+K^-$ are shifted relative to their true values due to interference between resonant and nonresonant amplitudes. The values of these shifts are determined to be about $\pm5\%$ for the $J/\psi$ meson and $\pm15\%$ for the $\psi(2S)$ meson.
The $K^+K^-$ invariant-mass interval ($M_{K^+K^-}$), number of selected events ($N_{\rm sig}$) after background subtraction, detection efficiency ($\varepsilon$), ISR luminosity ($L$), measured $e^+e^-\to K^+K^-$ cross section ($\sigma_{K^+K^-}$), and the charged-kaon form factor ($|F_K|$). For the number of events and cross section. For the form factor, we quote the combined uncertainty. For the mass interval 7.5 - 8.0 GeV/$c^2$, the 90$\%$ CL upper limits for the cross section and form factor are listed.
We present measurements of the total production rates and momentum distributions of the charmed baryon $\Lambda_c^+$ in $e^+e^- \to$ hadrons at a center-of-mass energy of 10.54 GeV and in $\Upsilon(4S)$ decays. In hadronic events at 10.54 GeV, charmed hadrons are almost exclusively leading particles in $e^+e^- \to c\bar{c}$ events, allowing direct studies of $c$-quark fragmentation. We measure a momentum distribution for $\Lambda_c^+$ baryons that differs significantly from those measured previously for charmed mesons. Comparing with a number of models, we find none that can describe the distribution completely. We measure an average scaled momentum of $\left< x_p \right> = 0.574\pm$0.009 and a total rate of $N_{\Lambda c}^{q\bar{q}} = 0.057\pm$0.002(exp.)$\pm$0.015(BF) $\Lambda_c^+$ per hadronic event, where the experimental error is much smaller than that due to the branching fraction into the reconstructed decay mode, $pK^-\pi^+$. In $\Upsilon (4S)$ decays we measure a total rate of $N_{\Lambda c}^{\Upsilon} = 0.091\pm$0.006(exp.)$\pm$0.024(BF) per $\Upsilon(4S)$ decay, and find a much softer momentum distribution than expected from B decays into a $\Lambda_c^+$ plus an antinucleon and one to three pions.
LAMBDA/C+ differential production rate per hadronic event for the continuum at cm energy 10.54 GeV.
The integrated number of LAMBDA/C+'s per hadronic event for the continuum at cm energy 10.54 GeV.
LAMBDA/C+ differential production rate per UPSILON(4S) decay at cm energy 10.58 GeV.
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