Search for the charged lepton flavor violating decay J/ψ→eτ

A search for the charged lepton flavor violating decay J/ψ→e±τ∓ with τ∓→π∓π0ντ is performed with about 10×109 J/ψ events collected with the BESIII detector at the BEPCII. No significant signal is observed, and an upper limit is set on the branching fraction B(J/ψ→e±τ∓)<7.5×10−8 at the 90% confidence level. This improves the previously published limit by two orders of magnitude.

Observation of D0→K1(1270)−e+νe

Using 2.93 fb^{-1} of e^{+}e^{-} collision data taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, the observation of the D^{0}→K_{1}(1270)^{-}e^{+}ν_{e} semileptonic decay is presented. The statistical significance of the decay D^{0}→K_{1}(1270)^{-}e^{+}ν_{e} is greater than 10σ. The branching fraction of D^{0}→K_{1}(1270)^{-}e^{+}ν_{e} is measured to be (1.09±0.13_{-0.16}^{+0.09}±0.12)×10^{-3}. Here, the first uncertainty is statistical, the second is systematic, and the third originates from the assumed branching fraction of K_{1}(1270)^{-}→K^{-}π^{+}π^{-}. The fraction of longitudinal polarization in D^{0}→K_{1}(1270)^{-}e^{+}ν_{e} is determined for the first time t…

Observation of a Near-Threshold Structure in the K+ Recoil-Mass Spectra in e+e−→K+(Ds−D*0+Ds*−D0)

We report a study of the processes of e^{+}e^{-}→K^{+}D_{s}^{-}D^{*0} and K^{+}D_{s}^{*-}D^{0} based on e^{+}e^{-} annihilation samples collected with the BESIII detector operating at BEPCII at five center-of-mass energies ranging from 4.628 to 4.698 GeV with a total integrated luminosity of 3.7  fb^{-1}. An excess of events over the known contributions of the conventional charmed mesons is observed near the D_{s}^{-}D^{*0} and D_{s}^{*-}D^{0} mass thresholds in the K^{+} recoil-mass spectrum for events collected at sqrt[s]=4.681  GeV. The structure matches a mass-dependent-width Breit-Wigner line shape, whose pole mass and width are determined as (3982.5_{-2.6}^{+1.8}±2.1)  MeV/c^{2} and (…

Search for new decay modes of the ψ2(3823) and the process e+e−→π0π0ψ2(3823)

The decays ψ2(3823)→γχc0,1,2, π+π−J/ψ, π0π0J/ψ, ηJ/ψ, and π0J/ψ are searched for using the reaction e+e−→π+π−ψ2(3823) in a 19  fb−1 data sample collected at center-of-mass energies between 4.1 and ...

Measurements of Born cross sections of e+e−→Ds*+DsJ−+c.c.

The Born cross sections are measured for the first time for the processes $e^+e^-\to D_s^{*+}D_{s0}^*(2317)^- +c.c.$ and $e^+e^-\to D_s^{*+}D_{s1}(2460)^- +c.c.$ at the center-of-mass energy $\sqrt{s}=$ 4.600~GeV, 4.612~GeV, 4.626~GeV, 4.640~GeV, 4.660~GeV, 4.68~GeV, and 4.700~GeV, and for $e^+e^-\to D_s^{*+}D_{s1}(2536)^- +c.c.$ at $\sqrt{s}=$ 4.660~GeV, 4.680~GeV, and 4.700~GeV, using data samples collected with the BESIII detector at the BEPCII collider. No structures are observed in cross-section distributions for any of the processes.

Measurements of the branching fractions of ψ(3686)→Σ¯0Λ+c.c. and χcJ(J=0,1,2)→ΛΛ¯

Study of e+e−→γωJ/ψ and Observation of X(3872)→ωJ/ψ

We study the e^{+}e^{-}→γωJ/ψ process using 11.6  fb^{-1} e^{+}e^{-} annihilation data taken at center-of-mass energies from sqrt[s]=4.008  GeV to 4.600 GeV with the BESIII detector at the BEPCII storage ring. The X(3872) resonance is observed for the first time in the ωJ/ψ system with a significance of more than 5σ. The relative decay ratio of X(3872)→ωJ/ψ and π^{+}π^{-}J/ψ is measured to be R=1.6_{-0.3}^{+0.4}±0.2, where the first uncertainty is statistical and the second systematic (the same hereafter). The sqrt[s]-dependent cross section of e^{+}e^{-}→γX(3872) is also measured and investigated, and it can be described by a single Breit-Wigner resonance, referred to as the Y(4200), with …

Measurement of the Absolute Branching Fraction of Ds+→τ+ντ via τ+→e+νeν¯τ

Using a dataset of 6.32  fb^{-1} of e^{+}e^{-} annihilation data collected with the BESIII detector at center-of-mass energies between 4178 and 4226 MeV, we have measured the absolute branching fraction of the leptonic decay D_{s}^{+}→τ^{+}ν_{τ} via τ^{+}→e^{+}ν_{e}ν[over ¯]_{τ}, and find B_{D_{s}^{+}→τ^{+}ν_{τ}}=(5.27±0.10±0.12)×10^{-2}, where the first uncertainty is statistical and the second is systematic. The precision is improved by a factor of 2 compared to the previous best measurement. Combining with f_{D_{s}^{+}} from lattice quantum chromodynamics calculations or the |V_{cs}| from the CKMfitter group, we extract |V_{cs}|=0.978±0.009±0.012 and f_{D_{s}^{+}}=(251.1±2.4±3.0)  MeV, r…

Measurement of the absolute branching fractions of J/ψ→γη and η decay modes

Measurement of e+e−→γχc0,c1,c2 cross sections at center-of-mass energies between 3.77 and 4.60 GeV

Observation of e + e − → ηψ(2S) at center-of-mass energies from 4.236 to 4.600 GeV

Journal of high energy physics 2021(10), 177 (2021). doi:10.1007/JHEP10(2021)177

Study of the decay D+→K*(892)+KS0 in D+→K+KS0π0

Based on an $e^{+}e^{-}$ collision data sample corresponding to an integrated luminosity of 2.93 $\mathrm{fb}^{-1}$ collected with the BESIII detector at $\sqrt{s}=3.773 \mathrm{GeV}$, the first amplitude analysis of the singly Cabibbo-suppressed decay $D^{+}\to K^+ K_S^0 \pi^0$ is performed. From the amplitude analysis, the $K^*(892)^+ K_S^0$ component is found to be dominant with a fraction of $(57.1\pm2.6\pm4.2)\%$, where the first uncertainty is statistical and the second systematic. In combination with the absolute branching fraction $\mathcal{B}(D^+\to K^+ K_S^0 \pi^0)$ measured by BESIII, we obtain $\mathcal{B}(D^+\to K^*(892)^+ K_S^0)=(8.69\pm0.40\pm0.64\pm0.51)\times10^{-3}$, where…

Observation of a near-threshold enhancement in the ΛΛ¯ mass spectrum from e+e−→ϕΛΛ¯ at s from 3.51 to 4.60 GeV

The process e(+)e(-) -> phi Lambda(Lambda) over bar is studied using data samples collected with the BESIII detector at the BEPCII Collider at center of mass energies root S ranging from 3.51 Ge ...

Observation of the decay D0→ρ−μ+νμ

Measurement of the cross section for e+e−→ΛΛ¯ and evidence of the decay ψ(3770)→ΛΛ¯

Determination of the absolute branching fractions of D0→K−e+νe and D+→K¯0e+νe

Using 2.93 fb$^{-1}$ of $e^+e^-$ collision data collected with the BESIII detector at a center-of-mass energy of 3.773~GeV, we measure the absolute branching fractions of the decays $D^0\to K^-e^+\nu_e$ and $D^+\to \bar K^0 e^+\nu_e$ to be $(3.574\pm0.031_{\rm stat}\pm 0.025_{\rm syst})\%$ and $(8.70\pm0.14_{\rm stat}\pm 0.16_{\rm syst})\%$, respectively. Starting with the process $e^+e^-\to D\bar{D}$, a new reconstruction method is employed to select events that contain candidates for both $D\to \bar Ke^+\nu_e$ and $\bar D\to Ke^-\bar \nu_e$ decays. The branching fractions reported in this work are consistent within uncertainties with previous BESIII measurements that selected events conta…

Study of the process e+e−→ϕη at center-of-mass energies between 2.00 and 3.08 GeV

We study the process e^+e^− → π^+π^−ηγ, where the photon is radiated from the initial state. About 8000 fully reconstructed events of this process are selected from the BABAR data sample with an integrated luminosity of 469  fb^(-1). Using the π^+π^−η invariant mass spectrum, we measure the e^+e^− → π^+π^−η cross section in the e^+e^− center-of-mass energy range from 1.15 to 3.5 GeV. The cross section is well described by the Vector-Meson dominance model with four ρ-like states. We observe 49±9 events of the J/ψ decay to π^+π^−η and measure the product Γ_(J/Ψ → e^+e^−)B_(J/Ψ → π^+π^−η) = 2.34 ± 0.43_(stat) ± 0.16_(syst)  eV.

Observation of ψ(3686)→e+e−χcJ and χcJ→e+e−J/ψ

Using 4.479 x 10(8) psi(3686) events collected with the BESIII detector, we search for the decays psi(3686) -> e(+)e(-)chi(cJ) and chi(cJ) -> e(+)e(-)J/psi, where J = 0, 1, 2. The decays psi(3686) -> e(+)e(-)chi(cJ) and chi(cJ) -> e(+)e(-)J/psi are observed for the first time. The measured branching fractions are B(psi(3686) -> e(+)e(-)chi(cJ)) = (11.7 +/- 2.5 +/- 1.0) x 10(-4), (8.6 +/- 0.3 +/- 0.6) x 10(-4), (6.9 +/- 0.5 +/- 0.6) x 10(-4) for J = 0, 1, 2, and B(chi(cJ) -> e(+)e(-)J/psi) = (1.51 +/- 0.30 +/- 0.13)x10(-4), (3.73 +/- 0.09 +/- 0.25)x10(-3), (2.48 +/- 0.08 +/- 0.16)x10(-3) for J = 0, 1, 2, respectively. The ratios of the branching fractions B(psi(3686) -> e(+)e(-)chi(cJ))/B(ps…

Measurement of the Born cross sections for e+e−→η′π+π− at center-of-mass energies between 2.00 and 3.08 GeV

The Born cross sections for the process $e^+e^- \to \eta^\prime \pi^{+}\pi^{-}$ at different center-of-mass energies between $2.00$ and $3.08$~GeV are reported with improved precision from an analysis of data samples collected with the BESIII detector operating at the BEPCII storage ring. An obvious structure is observed in the Born cross section line shape. Fit as a Breit-Wigner resonance, it has a statistical significance of $6.3\sigma$ and a mass and width of $M=(2108\pm46\pm25)$~MeV/$c^2$ and $\Gamma=(138\pm36\pm30)$~MeV, where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in $e^+e^- \to \eta^\pri…

Amplitude analysis and branching-fraction measurement of D-s(+) -> K-S(0)pi(+)pi(0)

Journal of high energy physics 2021(6), 181 (2021). doi:10.1007/JHEP06(2021)181

Measurement of the doubly Cabibbo-suppressed decay D+→K+π+π−π0 with semileptonic tags

Search for the decay Ds+→a0(980)0e+νe

Using 6.32 fb$^{-1}$ of electron-positron collision data recorded by the BESIII detector at center-of-mass energies between 4.178 and 4.226~GeV, we present the first search for the decay $D_s^+\to a_0(980)^0 e^+\nu_e,\,a_0(980)^0\rightarrow \pi^0\eta$, which could proceed via $a_0(980)$-$f_0(980)$ mixing. No significant signal is observed. An upper limit of $1.2 \times 10^{-4}$ at the $90\%$ confidence level is set on the product of the branching fractions of $D_{s}^{+}\to a_0(980)^0 e^+\nu_e$ and $a_0(980)^0\rightarrow \pi^0\eta$ decays.

Cross section measurement of e+e−→pp¯η and e+e−→pp¯ω at center-of-mass energies between 3.773 GeV and 4.6 GeV

Using data samples with a total integrated luminosity of $20.1~\rm fb^{-1}$ collected by the BESIII detector operating at the BEPCII collider, the cross section of the process $e^+e^- \rightarrow \pi^+\pi^-\psi(3686)$ is measured at center-of-mass energies between 4.0076 and 4.6984 GeV. The measured cross section is consistent with previous results, but with much improved precision. A fit to the measured energy-dependent cross section, which includes three Breit-Wigner functions and a non-resonant contribution, confirms the existence of the charmonium-like states $Y(4220)$, $Y(4390)$, and $Y(4660)$. This is the first observation of the $Y(4660)$ at the BESIII experiment.