The absolute branching fraction of the decay Λc(2625)+→Λc+π+π− is measured for the first time to be (50.2±5.7stat±3.5syst)% with 368.48 pb−1 of e+e− collision data collected by the BESIII detector at the center-of-mass energies of s=4.918 and 4.950 GeV. Although the central value of the result is lower than the theoretical prediction of 67%, obtained from isospin symmetry, they are consistent taking the uncertainties into account. This is the first absolute branching fraction measurement for Λc(2625)+ since it was found. This measurement is necessary to obtain the coupling constants for the transitions between s-wave and p-wave charmed baryons in heavy hadron chiral perturbation theory. In addition, we search for the decay Λc(2595)+→Λc+π+π−. No significant signal is observed, and the upper limit on its branching fraction is determined to be 85.0% at the 90% confidence level. Published by the American Physical Society 2024

Using data samples with an integrated luminosity of 22.42 fb−1 collected by the BESIII detector operating at the BEPCII storage ring, we measure the cross sections of the e+e−→ηJ/ψ process at center-of-mass energies from 3.808 to 4.951 GeV. Three structures are observed in the line shape of the measured cross sections. A maximum-likelihood fit with ψ(4040), two additional resonances, and a nonresonant component are performed. The mass and width of the first additional state are (4219.7±2.5±4.5) MeV/c2 and (80.7±4.4±1.4) MeV, respectively, consistent with the ψ(4230). For the second state, the mass and width are (4386±13±17) MeV/c2 and (177±32±13) MeV, respectively, consistent with the ψ(4360). The first uncertainties are statistical, and the second ones are systematic. The statistical significance of ψ(4040) is 8.0σ and those for ψ(4230) and ψ(4360) are more than 10.0σ. Published by the American Physical Society 2024

Using a data sample of (1310.6 ± 7.0)× 10^6 J/ψ events collected with the BESIII detector operating at the BEPCII collider, we perform the first experimental search for invisible decays of a light vector meson (V=ω,ϕ) via J/ψ→ V η decays. The decay of η→π^+π^-π^0 is utilized to tag the V meson decaying into the invisible final state. No evidence for a significant invisible signal is observed, and the upper limits on the ratio of branching fractions at the 90% confidence level are determined to be ℬ(ω→invisible)/ℬ(ω→π^+π^-π^0) < 8.1 × 10^-5 and ℬ(ϕ→invisible)/ℬ(ϕ→ K^+K^-) < 3.4× 10^-4. By using the world average values of ℬ(ω→π^+π^-π^0) and ℬ(ϕ→ K^+K^-), the upper limits on the decay branching fractions at the 90% confidence level are set as ℬ(ω→invisible)< 7.3 × 10^-5 and ℬ(ϕ→invisible)< 1.7× 10^-4, respectively.

Using data samples collected by the BESIII detector operating at BEPCII with center-of-mass energies between 3.8 and 4.6,GeV and with a total luminosity of about 5.0~fb$^{-1}$, we measure the Born cross sections of $e^+e^- to K_{S}^{0}K^{pm}pi^{mp}$, $sigma_{B}(e^+e^- to K_{S}^{0}K^{pm}pi^{mp})$. The cross sections are generally smaller than those of BABAR but with significantly improved precision. The line shape of the Born cross sections from this work cannot be well described by a simple $1/s^n$ dependence, which may suggest contributions from excited charmonium or charmonium-like states.

Using a data sample of $(1310.6pm7.0)times10^{6}$ $J/psi$ decay events collected with the BESIII detector at BEPCII, we study the electromagnetic Dalitz decay $J/psi etau0027 e^+e^-$ with two dominant $etau0027$ decay modes, $etau0027 gamma pi^+ pi^-$ and $etau0027 pi^+pi^-eta$. The branching fraction is determined to be $mathcal{B}(J/psi etau0027 e^+e^-) = (6.59pm0.07pm0.17) times 10^{-5}$, which improves in precision by a factor of 2 over the previous BESIII measurement. A search for the dark photon ($gamma u0027$) is performed via $J/psi toetau0027 gamma u0027, gammau0027 e^{+}e^{-}$. Excluding the $omega$ and $phi$ mass regions, no significant signal is observed in the mass range from 0.1 to 2.1 GeV/$c^{2}$. We set upper limits at the 90% confidence level on $mathcal{B}(J/psi etau0027 gamma u0027)timesmathcal{B}(gamma u0027 e^+e^-)$, $mathcal{B}(J/psi toetau0027 gammau0027$) and the mixing strength as a function of dark photon mass. This is among the first searches for dark photons in charmonium decays.

Using a sample of 1.31 x 10(9) J/Psi events collected with the BESIII detector at the BEPCII collider, we study the decays of J/Psi -> KSKL and KSKS. The branching fraction of J/Psi -> KSKL is determined to be B(J/Psi -> KSKL) = (1.93 +/- 0.01 (stat) +/- 0.05 (syst)) x 10(-4), which significantly improves on previous measurements. No clear signal is observed for the J/Psi -> KSKS process, and the upper limit at the 95% confidence level for its branching fraction is determined to be B(J/Psi -> KSKS) < 1.4 x 10(-8), which improves on the previous searches by 2 orders in magnitude and reaches the order of the Einstein-Podolsky-Rosen expectation.

We present the first study of the process J/psi -> gamma eta pi(0) using (223.7 +/- 1.4) x 10(6) J/psi events accumulated with the BESIII detector at the BEPCII facility. The branching fraction for J/psi -> gamma eta pi(0) is measured to be B(J/psi -> gamma eta pi(0)) = (2.14 +/- 0.18(stat) +/- 0.25(syst)) x 10(-5). With a Bayesian approach, the upper limits of the branching fractions B(J/psi -> gamma a(0)(980), a(0)(980) -> eta pi(0)) and B(J/psi -> gamma a(2)(1320), a(2)(1320) -> eta pi(0)) are determined to be 2.5 x 10(-6) and 6.6 x 10(-6) at the 95% confidence level, respectively. All of these measurements are given for the first time.

The China Spallation Neutron Source (CSNS) accelerator is designed to accelerate proton beam pulses to 1.6 GeV at 25 Hz repetition rate, striking a solid metal target to produce spallation neutrons. The accelerator provides a beam power of 100 kW on the target in the first phase and then 500 kW in the second phase by increasing the average beam intensity 5 times while raising the linac output energy. The project construction has been formally launched in 2011 and it is planned to complete the project in March 2018. It is one of the high intensity proton accelerator projects in the world and it imposes a great challenge to Chinese accelerator community. This presentation will cover the status and challenges of the CSNS project.

We search for the M1 radiative transition psi(3686) -> gamma eta(c)(2S) by reconstructing the exclusive eta(c)(2S) -> (KSK +/-)-K-0 pi(-/+)pi(+)pi(-) decay using 1.06 X 10(8) psi(3686) events collected with the BESIII detector. The signal is observed with a statistical significance of greater than 4 standard deviations. The measured mass of the eta(c)(2S) is 3646.9 +/- 1.6(stat) +/- 3.6(syst) MeV/c(2), and the width is 9.9 +/- 4.8(stat) +/- 2.9(syst) MeV/c(2). The product branching fraction is measured to be B(psi(3686) -> gamma eta(c)(2S)) X B(eta(c)(2S) -> gamma(KSK +/-)-K-0 pi(-/+)pi(+)pi(-) = (7.03 +/- 2.10(stat) +/- 0.70(syst)) X 10(-6). This measurement complements a previous BESIII measurement of psi(3686) -> gamma eta(c)(2S) with eta(c)(2S) -> (KSK +/-)-K-0 pi(-/+) and K+K-pi(0).

Based on 106 million c d3686_ events collected with the BESIII detector at the BEPCII, the decay psi(3686) -> omega K (K) over bar pi is studied. Enhancements around 1.44 GeV/c(2) and the f1(1285) are observed in the mass spectrum of K (K) over bar pi, and the corresponding branching fraction ( upper limit) is measured, as well as the branching fractions of psi(3686) -> omega K*+K- + c.c. and psi(3686) -> omega(KK0)-K-*0 + c.c., all for the first time.

Using a sample of 1.06 x 10(8) psi(2) events collected with the BESIII detector at BEPCII, the decay psi(2S) -> p (p) over bar eta is studied. A partial wave analysis determines that the intermediate state N(1535) with a mass of 1524 +/- 5(-4)(+10) MeV/c(2) and a width of 130(-24-10)(+27+57) MeV/c(2) is dominant in the decay; the product branching fraction is determined to be B(psi(2S) -> N(1535)(p) over bar x B(N(1535) -> p eta + c.c. = 5.2 +/- 0.3(-1.2)(+3.2)) x 10(-5). Furthermore, the branching fraction of psi(2S) -> p (p) over bar eta is measured to be (6.4 +/- 0.2 +/- 0.6) x 10(-5). Here, the first error is statistical and the second is systematic.

Using a data sample of 2.25 x 10(8) J/psi events collected with the BESIII detector, we present the first observation of the decays of eta(c) mesons to Sigma(+)(Sigma) over bar (-) and (sic)(-)(+) .The branching fractions are measured to be (2.11 +/- 0.28(stat) +/- 0.18(syst) +/- 0.50(PDG)) x 10(-3) and (0.89 +/- 0.16(stat) +/- 0.08(syst) +/- 0.21(PDG)) x 10(-3) for eta(c) -> Sigma(+)(Sigma) over bar (-) and (sic)(-)(+) , respectively. These branching fractions provide important information on the helicity selection rule in charmonium- decay processes. DOI: 10.1103/PhysRevD.87.012003

Using a sample of 225.3 million $J/\ensuremath{\psi}$ events collected with the BESIII detector at the BEPCII ${e}^{+}{e}^{\ensuremath{-}}$ collider in 2009, searches for the decays of $\ensuremath{\eta}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{e}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{e}+\mathrm{c}.\mathrm{c}.$ in $J/\ensuremath{\psi}\ensuremath{\rightarrow}\ensuremath{\phi}\ensuremath{\eta}$ and $\ensuremath{\phi}{\ensuremath{\eta}}^{\ensuremath{'}}$ are performed. The $\ensuremath{\phi}$ signals, which are reconstructed in ${K}^{+}{K}^{\ensuremath{-}}$ final states, are used to tag $\ensuremath{\eta}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}$ semileptonic decays. No signals are observed for either $\ensuremath{\eta}$ or ${\ensuremath{\eta}}^{\ensuremath{'}}$, and upper limits at the 90% confidence level are determined to be $7.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and $5.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ for the ratios $\frac{\mathcal{B}(\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{e}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{e}+\mathrm{c}.\mathrm{c}.)}{\mathcal{B}(\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0})}$ and $\frac{\mathcal{B}({\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{e}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{e}+\mathrm{c}.\mathrm{c}.)}{\mathcal{B}({\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}\ensuremath{\eta})}$, respectively. These are the first upper-limit values determined for $\ensuremath{\eta}$ and ${\ensuremath{\eta}}^{\ensuremath{'}}$ semileptonic weak decays.

Using a sample of 1.06×108 ψ(2S) events collected with the BESIII detector at BEPCII, the decay ψ(2S)→pp¯η is studied. A partial wave analysis determines that the intermediate state N(1535) with a mass of 1524±5−4+10 MeV/c2 and a width of 130−24−10+27+57 MeV/c2 is dominant in the decay; the product branching fraction is determined to be B(ψ(2S)→N(1535)p¯)×B(N(1535)→pη)+c.c.=(5.2±0.3−1.2+3.2)×10−5. Furthermore, the branching fraction of ψ(2S)→pp¯η is measured to be (6.4±0.2±0.6)×10−5. Here, the first error is statistical and the second is systematic.Received 9 April 2013DOI:https://doi.org/10.1103/PhysRevD.88.032010© 2013 American Physical Society

We search for the lepton-flavor-violating decay of the J/psi into an electron and a muon using (225.3 +/- 2.8) x 10(6) J/psi events collected with the BESIII detector at the BEPCII. Four candidate events are found in the signal region, consistent with background expectations. An upper limit on the branching fraction of B(J/psi -> e mu) <1.6 x 10(-7) (90% C.L.) is obtained.