arXiv subjects

C. Geng

Publications and source records attributed to C. Geng.

At least 163 records · Page 9Linked to original sources

arXiv2021

First Measurement of the Absolute Branching Fraction of $Λ\to p μ^- \barν_μ$

The absolute branching fraction of $Λ\to p μ^- \barν_μ$ is reported for the first time based on an $e^+e^-$ annihilation sample of ten billion $J/ψ$ events collected with the BESIII detector at $\sqrt{s}=3.097$ GeV. The branching fraction is determined to be ${\mathcal B}(Λ\to pμ^- \barν_μ) = [1.48\pm0.21(\rm stat) \pm 0.08(\rm syst)]\times 10^{-4}$, which is a significant improvement in precision over the previous indirect measurements. Combining this result with the world average of ${\mathcal B}(Λ\to p e^- \barν_{e})$, we obtain the ratio, $\frac{Γ(Λ\to p μ^- \barν_μ)}{Γ(Λ\to p e^- \barν_{e})}$, to be $0.178 \pm 0.028$, which agrees with the standard model prediction assuming lepton flavor universality. The asymmetry of the branching fractions of $Λ\to p μ^- \barν_μ$ and $\barΛ \to \bar{p} μ^+ ν_μ$ is also determined, and no evidence for $CP$ violation is found.

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arXiv2021

Study of the process $e^{+}e^{-}\rightarrowϕη$ at center-of-mass energies between 2.00 and 3.08 GeV

The process $e^{+}e^{-} \rightarrow ϕη$ is studied at 22 center-of-mass energy points ($\sqrt{s}$) between 2.00 and 3.08 GeV using 715 pb$^{-1}$ of data collected with the BESIII detector. The measured Born cross section of $e^{+}e^{-} \rightarrow ϕη$ is found to be consistent with {\textsl{BABAR}} measurements, but with improved precision. A resonant structure around 2.175 GeV is observed with a significance of 6.9$σ$ with mass ($2163.5\pm6.2\pm3.0$) MeV/$c^{2}$ and width ($31.1_{-11.6}^{+21.1}\pm1.1$) MeV, where the first uncertainties are statistical and the second are systematic.

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arXiv2021

Search for the rare semi-leptonic decay $J/ψ\to D^{-}e^{+}ν_{e}+c.c.$

Using $10.1\times10^{9}$ $J/ψ$ events produced by the Beijing Electron Positron Collider (BEPCII) at a center-of-mass energy $\sqrt{s}=3.097~\rm{GeV}$ and collected with the BESIII detector, we present a search for the rare semi-leptonic decay $J/ψ\to D^{-}e^{+}ν_{e}+c.c.$. No excess of signal above background is observed, and an upper limit on the branching fraction $\mathcal{B}(J/ψ\to D^{-}e^{+}ν_{e}+c.c.)<7.1\times10^{-8}$ is obtained at $90\%$ confidence level. This is an improvement of more than two orders of magnitude over the previous best limit.

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arXiv2021

Search for the lepton number violating decay $Σ^{-} \to p e^{-} e^{-}$ and the rare inclusive decay $Σ^{-} \to Σ^{+} X$

Using a data sample of $(1310.6 \pm 7.0) \times 10^{6}$ $J/ψ$ events taken with the BESIII detector at the center-of-mass energy of 3.097 GeV, we search for the first time for the lepton number violating decay $Σ^{-} \to p e^{-} e^{-}$ and the rare inclusive decay $Σ^{-} \to Σ^{+} X$, where $X$ denotes any possible particle combination. The $Σ^-$ candidates are tagged in $J/ψ\to \barΣ(1385)^+Σ^-$ decays. No signal candidates are found, and the upper limits on the branching fractions at the 90\% confidence level are determined to be $\mathcal{B}(Σ^{-} \to p e^{-} e^{-}) < 6.7 \times 10^{-5}$ and $\mathcal{B}(Σ^{-} \to Σ^{+} X) < 1.2 \times 10^{-4}$.

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arXiv2021

Observation of the decays $χ_{cJ}\to n K^{0}_{S}\barΛ+ c.c.$

By analyzing $4.48\times10^8$ $ψ(3686)$ events collected with the BESIII detector, we observe the decays $χ_{cJ} \to n K^0_S\barΛ+ c.c.$ ($J=0$, 1, 2) for the first time, via the radiative transition $ψ(3686) \to γχ_{cJ}$. The branching fractions are determined to be $(6.67 \pm 0.26_{\rm stat} \pm 0.41_{\rm syst})\times10^{-4}$, $(1.71 \pm 0.12_{\rm stat} \pm 0.12_{\rm syst})\times10^{-4}$, and $(3.66 \pm 0.17_{\rm stat} \pm 0.23_{\rm syst})\times10^{-4}$ for $J=0$, 1, and 2, respectively.

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arXiv2021

Search for the charged lepton flavor violating decay $J/ψ\to eτ$

A search for the charged lepton flavor violating decay $J/ψ\to e^{\pm}τ^{\mp}$ with $τ^{\mp} \to π^{\mp}π^0ν_τ$ is performed with about $10$ billion $J/ ψ$ events collected with the BESIII detector at the BEPCII. No significant signal is observed, and an upper limit is set on the branching fraction $\mathcal{B}(J/ψ\to e^{\pm}τ^{\mp})<7.5\times10^{-8}$ at the 90$\%$ confidence level. This improves the previously published limit by two orders of magnitude.

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arXiv2021

Study of $e^+e^- \rightarrow π^{0}X(3872)γ$ and search for $Z_c(4020)^{0}\rightarrow X(3872)γ$

Using data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies from 4.178 to 4.600 GeV, we study the process $e^+e^-\rightarrowπ^{0}X(3872)γ$ and search for $Z_c(4020)^{0}\rightarrow X(3872)γ$. We find no significant signal and set upper limits on $σ(e^+e^-\rightarrowπ^{0}X(3872)γ)\cdot\mathcal{B}(X(3872)\rightarrowπ^{+}π^{-}J/ψ)$ and $σ(e^+e^-\rightarrowπ^{0}Z_c(4020)^{0})\cdot\mathcal{B}(Z_c(4020)^{0}\rightarrow X(3872)γ)\cdot\mathcal{B}(X(3872)\rightarrowπ^{+}π^{-}J/ψ)$ for each energy point at $90\%$ confidence level, which is of the order of several tenths pb.

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arXiv2021

Measurement of the doubly Cabibbo-suppressed decay $D^+\to K^+π^+π^-π^0$ with semileptonic tags

Using an $e^+e^-$ annihilation data sample corresponding to an integrated luminosity of $2.93\,\rm fb^{-1}$ collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, the doubly Cabibbo-suppressed decay $D^+\to K^+π^+π^-π^0$ is studied with a semileptonic tag method. After removing the decays containing narrow intermediate resonances, $D^+\to K^+η$, $D^+\to K^+ω$, and $D^+\to K^+ϕ$, the branching fraction for the decay $D^+\to K^+π^+π^-π^0$ is determined to be $(1.03 \pm 0.12_{\rm stat} \pm 0.06_{\rm syst})\times 10^{-3}$. The ratio of the branching fraction for $D^+\to K^+π^+π^-π^0$ to its Cabibbo-favored counterpart $D^+\to K^-π^+π^+π^0$ is measured to be $ (1.65\pm0.21)\%$, corresponding to $(5.73\pm0.73)\tan^4θ_C$, where $θ_C$ is the Cabibbo mixing angle. These results are consistent with our previous measurement with hadronic tags but are significantly larger than other doubly Cabibbo-suppressed decays in the charm sector.

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arXiv2021

Weak phases and CP-symmetry tests in sequential decays of entangled double-strange baryons

Using a sample of $1.31\times10^9$ $J/ψ$ events collected with the BESIII detector at the electron-positron collider BEPCII, we analyse the full $J/ψ\to$ $Ξ^-\overlineΞ^+$, $Ξ^-\to Λπ^-$, $Λ\to pπ^-$, $\overlineΞ^+\to\overlineΛπ^+$, $\overlineΛ\to\overline{p}π^+$ decay chain. A new method, exploiting the fact that the $Ξ^-\overlineΞ^+$ pair is entangled and sequentially decaying, and where the complete decay chains are reconstructed, is applied for the first time. This enables precision measurements of the decay parameters for the $Ξ^-\toΛπ^-$ decay ($α_Ξ$, $ϕ_Ξ$) as well as the $\overlineΞ^+\to\overlineΛπ^+$ decay ($\overlineα_Ξ$, $\overlineϕ_Ξ$). From the decay parameters, two independent CP tests were performed, quantified by the observables $A_{\rm CP}^Ξ$ and $Δϕ_Ξ$. Our results, $A_{\rm CP}^Ξ$ = $(6.0\pm13.4\pm5.6)\times10^{-3}$ and $Δϕ_Ξ= (-4.8\pm13.7\pm2.9)\times10^{-3}~{\rm rad}$, are consistent with CP symmetry. Furthermore, our method enables a separation of strong and weak $Ξ\toΛπ$ decay amplitudes. This results in the first direct measurement of the weak phase difference for any baryon decay. The result is found to be $(ξ_{P} - ξ_{S}) = (1.2\pm3.4\pm0.8)\times10^{-2}$ rad and is one of the most precise tests of CP symmetry for strange baryons. The strong phase difference is measured to be $(δ_P - δ_S) = (-4.0\pm3.3\pm1.7)\times10^{-2}$ rad. In addition, we provide an independent measurement of the recently debated $Λ$ decay parameter, $α_Λ = 0.757 \pm 0.011 \pm 0.008 $. The $Λ\overlineΛ$ asymmetry is measured to be $A_{\rm CP}^Λ = (-3.7\pm11.7\pm9.0)\times10^{-3}$.

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arXiv2021

Search for new decay modes of the $ψ_2(3823)$ and the process $e^+e^-\rightarrowπ^0π^0ψ_2(3823)$

The decays $ψ_2(3823)\rightarrowγχ_{c0,1,2}, π^+π^-J/ψ, π^0π^0J/ψ, ηJ/ψ$, and $π^0J/ψ$ are searched for using the reaction $e^+e^-\rightarrowπ^+π^-ψ_2(3823)$ in a 19 fb$^{-1}$ data sample collected at center-of-mass energies between 4.1 and 4.7 GeV with the BESIII detector. The process $ψ_2(3823)\rightarrowγχ_{c1}$ is observed in a 9 fb$^{-1}$ data sample in the center-of-mass energy range 4.3 to 4.7 GeV, which confirms a previous observation but with a higher significance of $11.8σ$, and evidence for $ψ_2(3823)\rightarrowγχ_{c2}$ is found with a significance of $3.2σ$ for the first time. The branching-fraction ratio $\frac{\mathcal{B}(ψ_2(3823)\rightarrowγχ_{c2})}{\mathcal{B}(ψ_2(3823)\rightarrowγχ_{c1})}$ is determined. No significant $ψ_2(3823)$ signals are observed for any of the other decay channels. Upper limits of branching-fraction ratios for $ψ_2(3823)\rightarrowπ^+π^-J/ψ, π^0π^0J/ψ, ηJ/ψ, π^0J/ψ, γχ_{c0}$ relative to $ψ_2(3823)\rightarrowγχ_{c1}$ are reported. The process $e^+e^-\rightarrowπ^0π^0ψ_2(3823)$ is also searched for, and we find evidence for the process with a significance of $4.3σ$. The average cross-section ratio $\frac{σ(e^+e^-\rightarrowπ^0π^0ψ_2(3823))}{σ(e^+e^-\rightarrowπ^+π^-ψ_2(3823))}$ is also determined.

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arXiv2021

Measurements of the branching fractions of $ψ(3686)\rightarrow\barΣ^{0}Λ+c.c.$ and $χ_{cJ (J = 0,1,2)} \rightarrow Λ\barΛ$

Based on $4.481\times10^8$ $ψ(3686)$ events collected with the BESIII detector at BEPCII, the branching fraction of the isospin violating decay $ψ(3686)\rightarrow\barΣ^{0}Λ+c.c.$ is measured to be $(1.60 \pm 0.31 \pm 0.13~\pm~0.58) \times 10^{-6}$, where the first uncertainty is statistical, the second is systematic, and the third is the uncertainty arising from interference with the continuum. This result is significantly smaller than the measurement based on CLEO-c data sets. The decays $χ_{cJ} \rightarrowΛ\barΛ$ are measured via $ψ(3686)\rightarrowγχ_{cJ}$, and the branching fractions are determined to be $\mathcal{B}\left(χ_{c0}\rightarrowΛ\barΛ\right)=(3.64 \pm 0.10 \pm 0.10 \pm 0.07)\times 10^{-4}$, $\mathcal{B}\left(χ_{c1}\rightarrowΛ\barΛ\right)=(1.31\pm0.06 \pm 0.06 \pm0.03)\times 10^{-4}$, $\mathcal{B}\left(χ_{c2}\rightarrowΛ\barΛ\right)=(1.91\pm0.08 \pm 0.17 \pm0.04)\times 10^{-4}$, where the third uncertainties are systematic due to the $ψ(3686) \rightarrow γχ_{c J}$ branching fractions.

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arXiv2021

Measurement of the absolute branching fraction of inclusive semielectronic $D_s^+$ decays

We measure the inclusive semielectronic decay branching fraction of the $D_s^+$ meson. A double-tag technique is applied to $e^+e^-$ annihilation data collected by the BESIII experiment at the BEPCII collider, operating in the center-of-mass energy range $4.178 - 4.230$ GeV. We select positrons from $D_s^+\rightarrow Xe^{+}ν_e$ with momenta greater than 200 MeV/$c$, and determine the laboratory momentum spectrum, accounting for the effects of detector efficiency and resolution. The total positron yield and semielectronic branching fraction are determined by extrapolating this spectrum below the momentum cutoff. We measure the $D_s^+$ semielectronic branching fraction to be $\mathcal{B}\left(D_s^+\rightarrow Xe^{+}ν_e\right)=\left(6.30\pm0.13\;(\text{stat.})\pm 0.10\;(\text{syst.})\right)\%$, showing no evidence for unobserved exclusive semielectronic modes. We combine this result with external data taken from literature to determine the ratio of the $D_s^+$ and $D^0$ semielectronic widths, $\frac{Γ(D_{s}^{+}\rightarrow Xe^+ν_e)}{Γ(D^0\rightarrow Xe^+ν_e)}=0.790\pm 0.016\;(\text{stat.})\pm0.020\;(\text{syst.})$. Our results are consistent with and more precise than previous measurements.

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arXiv2021

New Features in the Electromagnetic Structure of the Neutron

Here we present new results for the Born cross section and the effective form factor of the neutron at the center-of-mass energies ${\bf \sqrt{s}}$ between 2.0 and 3.08 GeV, using 18 data sets corresponding to an integrated luminosity of 647.9 pb${\bf ^{-1}}$ from e${\bf ^+}$e${\bf ^-}$ annihilation reactions collected at the BESIII experiment. The process $e^{+}e^{-}\to n\bar{n}$ is analyzed with three individual categories to improve the efficiency of $n\bar{n}$ reconstruction. The cross section of $e^{+}e^{-}\to n\bar{n}$ is measured at 18 c.m. energies where the best precision is 8.1\% at $\sqrt{s}=2.396$ GeV. The corresponding effective form factors are extracted under the assumption $|G_{E}|=|G_{M}|$. Our results improve the statistical precision on the neutron form factor by more than a factor of 60 over previous measurements from the FENICE and DM2 experiments and usher in a new era where neutron form factor data from annihilation in the time-like regime is on par with that from electron scattering experiments. In addition, an oscillatory behavior of the effective form factor observed for the proton is discussed for the neutron.

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arXiv2021

Search for the decay $D_s^+\to a_0(980)^0e^+ν_e$

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 $D_s^+\to a_0(980)^0 e^+ν_e,\,a_0(980)^0\rightarrow π^0η$, 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 $D_{s}^{+}\to a_0(980)^0 e^+ν_e$ and $a_0(980)^0\rightarrow π^0η$ decays.

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arXiv2021

Measurements of Sigma+ and Sigma- Time-like Electromagnetic Form Factors for center-of-mass energies from 2.3864 to 3.0200 GeV

The Born cross sections of the $e^{+}e^{-}\toΣ^{+}\barΣ^{-}$ and $e^{+}e^{-}\toΣ^{-}\barΣ^{+}$ processes are determined with high precision for center-of-mass energy from 2.3864 to 3.0200 GeV with the BESIII detector. Nonzero cross sections near threshold are observed. The resulting ratio of effective form factors for the $Σ^{+}$ and $Σ^{-}$ is consistent with 3, agreeing with the ratio of the incoherent sum of the squared charges of the $Σ^{+}$ and $Σ^{-}$ valence quarks, but disagreeing with various theoretical predictions. In addition, ratios of the $Σ^{+}$ electric and magnetic form factors, $|G_{E}/G_{M}|$, are obtained at three center-of-mass energies through an analysis of the angular distributions. These measurements, which are studied for the first time in the off-resonance region, provide precision experimental input for understanding baryonic structure. The observed novel features of the $Σ^{\pm}$ form factors require a new theoretical description for the hyperons.

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arXiv2021

Observation of $e^{+}e^{-}\rightarrowηψ(2S)$ at center-of-mass energies from 4.236 to 4.600 GeV

Using a total of $5.25~{\rm fb}^{-1}$ of $e^{+}e^{-}$ collision data with center-of-mass energies from 4.236 to 4.600 GeV, we report the first observation of the process $e^{+}e^{-}\to ηψ(2S)$ with a statistical significance of $5σ$. The data sets were collected by the BESIII detector operating at the BEPCII storage ring. We measure the yield of events integrated over center-of-mass energies and also present the energy dependence of the measured cross section.

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arXiv2021

Measurement of proton electromagnetic form factors in the time-like region using initial state radiation at BESIII

The electromagnetic process $e^{+}e^{-}\to p\bar{p}$ is studied with the initial-state-radiation technique using 7.5 fb$^{-1}$ of data collected by the BESIII experiment at seven energy points from 3.773 to 4.600 GeV. The Born cross section and the effective form factor of the proton are measured from the production threshold to 3.0 GeV/$c^{2}$ using the $p\bar{p}$ invariant-mass spectrum. The ratio of electric and magnetic form factors of the proton is determined from the analysis of the proton-helicity angular distribution.

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arXiv2021

Measurement of cross-section for $e^+e^-\toΞ^-\barΞ^+$ near threshold at BESIII

The Born cross-sections and effective form factors for process $e^+e^-\toΞ^-\barΞ^+$ are measured at eight center-of-mass energies between 2.644 and 3.080 GeV, using a total integrated luminosity of 363.9 pb$^{-1}$ $e^+e^-$ collision data collected with the BESIII detector at BEPCII. After performing a fit to the Born cross-section of $e^+e^-\toΞ^-\barΞ^+$, no significant threshold effect is observed.

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