Measurement of azimuthal asymmetries in inclusive charged dipion production in e+e−e^+e^- annihilations at s\sqrt{s} = 3.65 GeV

We present a measurement of the azimuthal asymmetries of two charged pions in the inclusive process $e^+e^-\rightarrow \pi\pi X$ based on a data set of 62 $\rm{pb}^{-1}$ at the center-of-mass energy $\sqrt{s}=3.65$ GeV collected with the BESIII detector. These asymmetries can be attributed to the Collins fragmentation function. We observe a nonzero asymmetry, which increases with increasing pion momentum. As our energy scale is close to that of the existing semi-inclusive deep inelastic scattering experimental data, the measured asymmetries are important inputs for the global analysis of extracting the quark transversity distribution inside the nucleon and are valuable to explore the energy evolution of the spin-dependent fragmentation function.Comment: 7 pages, 5 figure

Measurement of the e+e−→π+π−\mathrm e^+\mathrm e^-\rightarrow\mathrm\pi^+\mathrm\pi^- Cross Section between 600 and 900 MeV Using Initial State Radiation

We extract the $e^+e^-\rightarrow \pi^+\pi^-$ cross section in the energy range between 600 and 900 MeV, exploiting the method of initial state radiation. A data set with an integrated luminosity of 2.93 fb$^{-1}$ taken at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider is used. The cross section is measured with a systematic uncertainty of 0.9%. We extract the pion form factor $|F_\pi|^2$ as well as the contribution of the measured cross section to the leading order hadronic vacuum polarization contribution to $(g-2)_\mu$. We find this value to be $a_\mu^{\pi\pi,\rm LO}(600-900\;\rm MeV) = (368.2 \pm 2.5_{\rm stat} \pm 3.3_{\rm sys})\cdot 10^{-10}$.Comment: 14 pages, 7 figures, accepted by PL

Measurements of absolute hadronic branching fractions of Λc+\Lambda_{c}^{+} baryon

Using $567\rm{pb}^{-1}$ of $e^+e^-$ collisions recorded at $\sqrt{s}=4.599\rm{GeV}$ with the BESIII detector, we report first measurements of absolute hadronic branching fractions of Cabibbo-favored decays of the $\Lambda_{c}^{+}$ baryon with a double-tag technique. A global least-square fitter is utilized to improve the measured precision. Among the measurements for twelve $\Lambda_{c}^{+}$ decay modes, the branching fraction for $\Lambda_{c}^{+} \rightarrow pK^-\pi^+$ is determined to be $(5.84\pm0.27\pm0.23)\%$, where the first uncertainty is statistical and the second is systematic. In addition, the measurements of the branching fractions of the other eleven Cabbibo-favored hadronic decay modes are significantly improved

Observation of e+e−→ωχc1,2e^+e^- \rightarrow \omega \chi_{c1,2} near s\sqrt{s} = 4.42 and 4.6 GeV

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 $10^{-3}$.Comment: 7 pages, 3 figure

Measurement of the Matrix Elements for the Decays η→π+π−π0\eta \rightarrow \pi^{+}\pi^{-}\pi^0 and η/η′→π0π0π0\eta/\eta^{\prime}\rightarrow\pi^0\pi^0\pi^0

Based on a sample of $1.31 \times 10^9$ $J/\psi$ events collected with the BESIII detector at the BEPCII collider, Dalitz plot analyses of selected 79,625 $\eta\rightarrow\pi^{+}\pi^{-}\pi^0$ events, 33,908 $\eta\rightarrow\pi^0\pi^0\pi^0$ events and 1,888 $\eta^{\prime}\rightarrow\pi^0\pi^0\pi^0$ events are performed. The measured matrix elements of $\eta\rightarrow\pi^+\pi^-\pi^0$ are in reasonable agreement with previous measurements. The Dalitz plot slope parameters of $\eta\rightarrow\pi^0\pi^0\pi^0$ and $\eta^{\prime}\rightarrow\pi^0\pi^0\pi^0$ are determined to be $-0.055 \pm 0.014 \pm 0.004$ and $-0.640 \pm 0.046 \pm 0.047$, respectively, where the first uncertainties are statistical and the second systematic. Both values are consistent with previous measurements, while the precision of the latter one is improved by a factor of three. Final state interactions are found to have an important role in those decays.Comment: 12 pages, 7 figure

An amplitude analysis of the π0π0\pi^{0}\pi^{0} system produced in radiative J/ψJ/\psi decays

An amplitude analysis of the $\pi^{0}\pi^{0}$ system produced in radiative $J/\psi$ decays is presented. In particular, a piecewise function that describes the dynamics of the $\pi^{0}\pi^{0}$ system is determined as a function of $M_{\pi^{0}\pi^{0}}$ from an analysis of the $(1.311\pm0.011)\times10^{9}$ $J/\psi$ decays collected by the BESIII detector. The goal of this analysis is to provide a description of the scalar and tensor components of the $\pi^0\pi^0$ system while making minimal assumptions about the properties or number of poles in the amplitude. Such a model-independent description allows one to integrate these results with other related results from complementary reactions in the development of phenomenological models, which can then be used to directly fit experimental data to obtain parameters of interest. The branching fraction of $J/\psi \to \gamma \pi^{0}\pi^{0}$ is determined to be $(1.15\pm0.05)\times10^{-3}$, where the uncertainty is systematic only and the statistical uncertainty is negligible.Comment: Submitted to Phys. Rev. D 19 pages, 4 figure

Measurement of the branching fractions of Ds+→η′XD_{s}^{+}\rightarrow \eta'X and Ds+→η′ρ+D_{s}^{+}\rightarrow \eta'\rho^{+} in e+e−→Ds+Ds−e^+e^-\to D^+_{s}D^-_{s}

We study $D_{s}^{+}$ decays to final states involving the $\eta'$ with a 482$\,$pb$^{-1}$ data sample collected at $\sqrt{s}$ = 4.009$\,$GeV with the \mbox{BESIII} detector at the BEPCII collider. We measure the branching fractions $\mathcal{B}(D^+_{s}\rightarrow \eta'X)$ = (8.8$\pm$1.8$\pm$0.5)$\%$ and $\mathcal{B}(D_{s}^{+}\rightarrow \eta'\rho^{+})$ = ($5.8\pm1.4\pm0.4$)$\%$ where the first uncertainty is statistical and the second is systematic. In addition, we estimate an upper limit on the non-resonant branching ratio $\mathcal{B}(D_{s}^{+}\rightarrow \eta'\pi^+\pi^0)<5.1\%$ at the 90$\%$ confidence level. Our results are consistent with CLEO's recent measurements and help to resolve the disagreement between the theoretical prediction and CLEO's previous measurement of $\mathcal{B}(D_{s}^{+}\rightarrow \eta'\rho^{+})$

Measurement of the leptonic decay width of J/ψJ/\psi using initial state radiation

Using a data set of 2.93 fb$^{-1}$ taken at a center-of-mass energy of $\sqrt{s}$ = 3.773 GeV with the BESIII detector at the BEPCII collider, we measure the process $e^+e^-\rightarrow J/\psi\gamma\rightarrow \mu^+\mu^-\gamma$ and determine the product of the branching fraction and the electronic width $\mathcal B_{\mu\mu}\cdot \Gamma_{ee} = (333.4 \pm 2.5_{\rm stat} \pm 4.4_{\rm sys})$~eV. Using the earlier-published BESIII result for $\mathcal B_{\mu\mu}$ = (5.973 $\pm$ 0.007$_{\rm stat}$ $\pm$ 0.037$_{\rm sys}$)\%, we derive the $J/\psi$ electronic width $\Gamma_{ee}$~= (5.58 $\pm$ 0.05$_{\rm stat}$ $\pm$ 0.08$_{\rm sys}$) keV.Comment: 8 pages, 2 figure