We present a measurement of the azimuthal asymmetries of two charged pions in the inclusive process $e^+e^-rightarrow pipi X$ 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.
We report a study of the process $e^{+} e^{-} to (D^{*} bar{D}^{*})^{0} pi^0$ using $e^+e^-$ collision data samples with integrated luminosities of $1092 rm{pb}^{-1}$ at $sqrt{s}=4.23 rm{GeV}$ and $826 rm{pb}^{-1}$ at $sqrt{s}=4.26 rm{GeV}$ collected
with the BESIII detector at the BEPCII storage ring. We observe a new neutral structure near the $(D^{*} bar{D}^{*})^{0}$ mass threshold in the $pi^0$ recoil mass spectrum, which we denote as $Z_{c}(4025)^{0}$. Assuming a Breit-Wigner line shape, its pole mass and pole width are determined to be $(4025.5^{+2.0}_{-4.7}pm3.1) rm{MeV}/c^2$ and $(23.0pm 6.0pm 1.0) rm{MeV}$, respectively. The Born cross sections of $e^{+}e^{-}to Z_{c}(4025)^{0} pi^0to (D^{*} bar{D}^{*})^{0}pi^0$ are measured to be $(61.6pm8.2pm9.0) rm{pb}$ at $sqrt{s}=4.23 rm{GeV}$ and $(43.4pm8.0pm5.4) rm{pb}$ at $sqrt{s}=4.26 rm{GeV}$. The first uncertainties are statistical and the second are systematic.
The decay $Z_c(3900)^pmtoomegapi^pm$ is searched for using data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies $sqrt{s}=4.23$ and $4.26$~GeV. No significant signal for the $Z_c(3900)^pm$ is
found, and upper limits at the 90% confidence level on the Born cross section for the process $e^+e^-to Z_c(3900)^pmpi^mptoomegapi^+pi^-$ are determined to be $0.26$ and $0.18$ pb at $sqrt{s}=4.23$ and 4.26 GeV, respectively.
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 $mathcal{B}(D^+_{s}right
arrow etaX)$ = (8.8$pm$1.8$pm$0.5)$%$ and $mathcal{B}(D_{s}^{+}rightarrow etarho^{+})$ = ($5.8pm1.4pm0.4$)$%$ where the first uncertainty is statistical and the second is systematic. In addition, we estimate an upper limit on the non-resonant branching ratio $mathcal{B}(D_{s}^{+}rightarrow etapi^+pi^0)<5.1%$ at the 90$%$ confidence level. Our results are consistent with CLEOs recent measurements and help to resolve the disagreement between the theoretical prediction and CLEOs previous measurement of $mathcal{B}(D_{s}^{+}rightarrow etarho^{+})$.
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 $(1.311pm0.011)times10^{9}$ $J/psi$ decays collected by the BESIII detector. The goal of this analysis is to provide a description of the scalar and tensor components of the $pi^0pi^0$ 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 $(1.15pm0.05)times10^{-3}$, where the uncertainty is systematic only and the statistical uncertainty is negligible.
Using a sample of 1.31 billion $J/psi$ events collected with the BESIII detector at the BEPCII collider, the decays $J/psi to phi pi^{+}pi^{-}pi^{0}$ and $J/psi to phi pi^{0}pi^{0}pi^{0}$ are investigated. The isospin violating decay $J/psi to phi pi
^{0} f_{0}(980)$ with $f_{0}(980) to pipi$, is observed for the first time. The width of the $f_{0}(980)$ obtained from the dipion mass spectrum is found to be much smaller than the world average value. In the $pi^{0} f_{0}(980)$ mass spectrum, there is evidence of $f_1(1285)$ production. By studying the decay $J/psi to phieta$, the branching fractions of $eta to pi^{+}pi^{-}pi^{0}$ and $eta to pi^{0}pi^{0}pi^{0}$, as well as their ratio, are also measured.
Using $2.92$ fb$^{-1}$ of electron-positron annihilation data collected at $sqrt{s} = 3.773$~GeV with the BESIII detector, we report the results of a search for the flavor-changing neutral current process $D^0togammagamma$ using a double-tag techniqu
e. We find no signal and set an upper limit at $90%$ confidence level for the branching fraction of $B(D^0togammagamma) < 3.8times10^{-6}$. We also investigate $D^0$-meson decay into two neutral pions, obtaining a branching fraction of $B(D^0topi^0pi^0) = (8.24pm0.21(text{stat.})pm0.30(text{syst.}))times10^{-4}$, the most precise measurement to date and consistent with the current world average
Using the data sets taken at center-of-mass energies above 4 GeV by the BESIII detector at the BEPCII storage ring, we search for the reaction e+e- -> gamma_ISR X(3872) -> gamma_ISR pi+pi-J/psi via the Initial State Radiation technique. The productio
n of a resonance with quantum numbers J^PC = 1^++ such as the X(3872) via single photon e+e- annihilation is forbidden, but is allowed by a next-to-leading order box diagram. We do not observe a significant signal of X(3872), and therefore give an upper limit for the electronic width times the branching fraction Gamma_ee^X(3872)Br(X(3872) -> pi+pi-Jpsi) < 0.13 eV at the 90% confidence level. This measurement improves upon existing limits by a factor of 46. Using the same final state, we also measure the electronic width of the psi(3686) to be Gamma_ee^psi(3686) = 2231 +- 18 +- 99 eV.
We report a measurement of the branching fraction of $psi(3770)togammachi_{c1}$ and search for the transition $psi(3770)rightarrow gamma chi_{c2}$ based on 2.92~fb$^{-1}$ of $e^+e^-$ data accumulated at $sqrt{s}=3.773$~GeV with the BESIII detector at
the BEPCII collider. The measured branching fraction of $psi(3770) rightarrow gamma chi_{c1}$ is $mathcal B(psi(3770) rightarrow gamma chi_{c1})=(2.48 pm 0.15 pm 0.23) times 10^{-3}$, which is the most precise measurement to date. The upper limit on the branching fraction of $psi(3770)rightarrow gamma chi_{c2}$ at a $90%$ confidence level is $mathcal B(psi(3770) rightarrow gamma chi_{c2})<0.64 times 10^{-3}$. The corresponding partial widths are $Gamma(psi(3770) to gamma chi_{c1}) =(67.5pm 4.1pm 6.7)$~keV and $Gamma(psi(3770) to gamma chi_{c2}) < 17.4$~keV.
Using a sample of $1.31$ billion $J/psi$ events accumulated with the BESIII detector at the BEPCII collider, we report the observation of the decay $J/psi rightarrow phipi^{0}$, which is the first evidence for a doubly Okubo-Zweig-Iizuka suppressed e
lectromagnetic $J/psi$ decay. A clear structure is observed in the $K^{+} K^{-}$ mass spectrum around 1.02 GeV/$c^2$, which can be attributed to interference between $J/psi rightarrow phipi^{0}$ and $J/psi rightarrow K^{+}K^{-}pi^{0}$ decays. Due to this interference, two possible solutions are found. The corresponding measured values of the branching fraction of $J/psi to phipi^{0}$ are $[2.94 pm 0.16text{(stat.)} pm 0.16text{(syst.)}] times 10^{-6}$ and $[1.24 pm 0.33text{(stat.)} pm 0.30text{(syst.)}] times 10^{-7}$.
