arXiv subjects

C. Geng

Publications and source records attributed to C. Geng.

At least 19 recordsLinked to original sources

arXiv2024

Observation of the Electromagnetic Dalitz Transition $h_c \rightarrow e^+e^-η_c$

Using $(27.12\pm 0.14)\times10^8$ $ψ(3686)$ decays and data samples of $e^+e^-$ collisions with $\sqrt{s}$ from 4.130 to 4.780~GeV collected with the BESIII detector, we report the first observation of the electromagnetic Dalitz transition $h_c\to e^+e^-η_c$ with a statistical significance of $5.4σ$. We measure the ratio of the branching fractions $\frac{\mathcal{B}(h_c\rightarrow e^+e^-η_c)}{\mathcal{B}(h_c\rightarrow γη_c)}$ separately for the $h_c$ samples produced via $ψ(3686)\toπ^0h_c$ and $e^+e^-\toπ^+π^-h_c$. The average ratio is determined to be $(0.59\pm0.10(\text{stat.})\pm0.04(\text{syst.}))\%$, where the uncertainty includes both statistical and systematic components.

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arXiv2024

Search for the leptonic decays $D^{+}\to e^+ν_e$ and $D^{+}\to μ^+ν_μ$

We present the first search for the leptonic decays $D^{*+}\to e^+ν_e$ and $D^{*+}\to μ^+ν_μ$ by analyzing a data sample of electron-positron collisions recorded with the BESIII detector at center-of-mass energies between 4.178 and 4.226 GeV, corresponding to an integrated luminosity of 6.32~fb$^{-1}$. No significant signal is observed. The upper limits on the branching fractions for $D^{*+}\to e^+ν_e$ and $D^{*+}\to μ^+ν_μ$ are set to be $1.1 \times 10^{-5}$ and $4.3 \times 10^{-6}$ at 90\% confidence level, respectively.

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arXiv2024

Study of excited $Ξ$ states in $ψ(3686)\rightarrow{}K^{-}Λ\overlineΞ^{+}+c.c.$

Based on a sample of $(448.1\pm2.9)\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector at BEPCII, the decays of $ψ(3686)\to{}K^{-}Λ\overlineΞ^{+} + c.c.$ with $\overlineΞ^+ \to \overlineΛ π^+$, $\overlineΛ\to \overline{p} π^+$ are studied.Two excited hyperons, $Ξ(1690)^-$ and $Ξ(1820)^-$, are observed with large significance ($ \gg 10 σ$) in the $K^{-}Λ$ invariant mass distributions. A partial wave analysis is performed, and the spin-parities of $Ξ(1690)^-$ and $Ξ(1820)^-$ are determined to be $\frac{1}{2}^{-}$ and $\frac{3}{2}^{-}$, respectively. The masses, widths, and product branching fractions of $Ξ(1690)^-$ and $Ξ(1820)^-$ are also measured.

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arXiv2024

Measurement of $Λ$ transverse polarization in $e^{+}e^{-}$ collisions at $\sqrt{s}= 3.68-3.71$ GeV

With data samples collected with the BESIII detector at seven energy points at $\sqrt{s}= 3.68 - 3.71$ GeV, corresponding to an integrated luminosity of 333 pb$^{-1}$, we present a study of the $Λ$ transverse polarization in the $e^+e^-\toΛ\barΛ$ reaction. The significance of polarization by combining the seven energy points is found to be 2.6$σ$ including the systematic uncertainty, which implies a non-zero phase between the transition amplitudes of the $Λ\barΛ$ helicity states. The modulus ratio and the relative phase of EM-$psionic$ form factors combined with all energy points are measured to be $R^Ψ =$ 0.71$^{+0.10}_{-0.10}$ $\pm$ 0.03 and $ΔΦ^Ψ$ = (23$^{+8.8}_{-8.0}$ $\pm$ 1.6$)^\circ$, where the first uncertainties are statistical and the second systematic.

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arXiv2024

Observation of $D^+_s\to η^\prime μ^+ν_μ$, Precision Test of Lepton Flavor Universality with $D^+_s\to η^{(\prime)} \ell^+ν_\ell$, and First Measurements of $D^+_s\to η^{(\prime)}μ^+ν_μ$ Decay Dynamics

By analyzing 7.33 fb$^{-1}$ of $e^+e^-$ annihilation data collected at center-of-mass energies between 4.128 and 4.226 GeV with the BESIII detector, we report the observation of the semileptonic decay $D^+_s\to η^\prime μ^+ν_μ$, with a statistical significance larger than 10$σ$, and the measurements of the $D_s^+ \to ημ^+ν_μ$ and $D_s^+ \to η^\primeμ^+ν_μ$ decay dynamics for the first time. The branching fractions of $D_s^+ \to ημ^+ν_μ$ and $D_s^+ \to η^\primeμ^+ν_μ$ are determined to be $(2.235\pm0.051_{\rm stat}\pm0.052_{\rm syst})\%$ and $(0.801\pm0.055_{\rm stat}\pm0.028_{\rm syst})\%$, respectively, with precision improved by factors of 6.0 and 6.6 compared to the previous best measurements. Combined with the results for the decays $D_s^+ \to ηe^+ν_e$ and $D_s^+ \to η^\prime e^+ν_e$, the ratios of the decay widths are examined both inclusively and in several $\ell^+ν_\ell$ four-momentum transfer ranges. No evidence for lepton flavor universality violation is found within the current statistics. The products of the hadronic form factors $f_{+,0}^{η^{(\prime)}}(0)$ and the $c\to s$ Cabibbo-Kobayashi-Maskawa matrix element $|V_{cs}|$ are determined. The results based on the two-parameter series expansion are $f^η_{+,0}(0)|V_{cs}| = 0.452\pm0.010_{\rm stat}\pm0.007_{\rm syst}$ and $f^{η^{\prime}}_{+,0}(0)|V_{cs}| = 0.504\pm0.037_{\rm stat}\pm0.012_{\rm syst}$, which help to constrain present models on $f_{+,0}^{η^{(\prime)}}(0)$. The forward-backward asymmetries are determined to be $\langle A_{\rm FB}^η\rangle=-0.059\pm0.031_{\rm stat}\pm0.005_{\rm syst}$ and $\langle A_{\rm FB}^{η^\prime}\rangle=-0.064\pm0.079_{\rm stat}\pm0.006_{\rm syst}$ for the first time, which are consistent with the theoretical calculation.

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arXiv2024

Study of light scalar mesons through $D_s^+ \to π^0 π^0 e^+ ν_e$ and $K_S^0 K_S^0 e^+ ν_e$ decays

Using 6.32~fb$^{-1}$ of $e^+e^-$ collision data recorded by the BESIII detector at center-of-mass energies between $4.178$ to $4.226$ GeV, we present the first measurement of the decay $D_s^+\to f_0(980)e^+ν_e,\,f_0(980)\to π^0π^0$. The product branching fraction of $D_s^+\to f_0(980)e^+ν_e,\,f_0(980)\to π^0π^0$ is measured to be $(7.9\pm1.4_{\rm stat} \pm0.3_{\rm syst})\times 10^{-4}$, with a statistical significance of $7.8σ$. Furthermore, the upper limits on the product branching fractions of $D_s^+\to f_0(500)e^+ν_e$ with $f_0(500)\to π^0π^0$ and the branching fraction of $D_s^+\to K_{S}^{0}K_{S}^{0}e^+ν_e$ are set to be $7.3\times 10^{-4}$ and $3.8\times 10^{-4}$ at 90\% confidence level, respectively. Our results provide valuable inputs to the understanding of the structures of light scalar mesons.

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arXiv2024

Search for the production of deuterons and antideuterons in e^+e^- annihilation at center-of-mass energies between 4.13 and 4.70 GeV

Using a data sample of $e^+e^-$ collision data corresponding to an integrated luminosity of 19 fb$^{-1}$ collected with the BESIII detector at the BEPCII collider, we search for the production of deuterons and antideuterons via $e^+e^-\to ppπ^-\bar{d}+c.c.$ for the first time at center-of-mass energies between 4.13 and 4.70 GeV. No significant signal is observed and the upper limit of the $e^+e^-\to ppπ^-\bar{d}+c.c.$ cross section is determined to be from 9.0 to 145 fb depending on the center-of-mass energy at the $90\%$ confidence level.

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arXiv2023

Observation of the hindered electromagnetic Dalitz decay $ψ(3686) \to e^+ e^- η_c$

Using a data sample of $(448.1 \pm 2.9)\times10^6 ~ψ(3686)$ decays collected at an $e^+ e^-$ center-of-mass energy of $3.686~\rm{GeV}$ by the BESIII detector at BEPCII, we report an observation of the hindered electromagnetic Dalitz decay $ψ(3686) \to e^+ e^- η_c$ with a significance of $7.9σ$. The branching fraction is determined to be $\mathcal{B} (ψ(3686) \to e^+ e^- η_c) = (3.77 \pm 0.40_{\rm stat.} \pm 0.18_{\rm syst.})\times 10^{-5}$, agreeing well with the prediction of the vector meson dominance model. This is the first measurement of the electromagnetic Dalitz transition between the $ψ(3686)$ and the $η_c$, which provides new insight into the electromagnetic properties of this decay, and offers new opportunities to measure the absolute branching fractions of $η_c$ decays.

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arXiv2023

Observation of $J/ψ$ decays to $e^{+}e^{-}e^{+}e^{-}$ and $e^{+}e^{-}μ^{+}μ^{-}$

Using a data sample of $4.481\times 10^8 ψ^\prime$ events collected with the BESIII detector, we report the first observation of the four-lepton-decays $J/ψ\to e^+e^-e^+e^-$ and $J/ψ\to e^+e^-μ^+μ^-$ utilizing the process $ψ^\prime\to π^+π^- J/ψ$. The branching fractions are determined to be $[5.48\pm0.31~(\rm stat)\pm0.45~(\rm syst)]\times 10^{-5}$ and $[3.53~\pm0.22~(\rm stat)\pm0.13~(\rm syst)]\times 10^{-5}$, respectively. The results are consistent with theoretical predictions. No significant signal is observed for $J/ψ\to μ^+μ^-μ^+μ^-$, and an upper limit on the branching fraction is set at $1.6\times 10^{-6}$ at the 90$\%$ confidence level. A CP asymmetry observable is constructed for the first two channels, which is measured to be $(-0.012\pm0.054\pm0.010)$ and $(0.062\pm0.059\pm0.006)$, respectively. No evidence for CP violation is observed in this process.

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arXiv2023

Novel method to extract the femtometer structure of strange baryons using the vacuum polarization effect

One of the fundamental goals of particle physics is to gain microscopic understanding of the strong interaction. Electromagnetic form factors quantify the structure of hadrons in terms of charge and magnetization distributions. While the nucleon structure has been investigated extensively, data on hyperons is still scarce. It has recently been demonstrated that electron-positron annihilations into hyperon-antihyperon pairs provide a powerful tools to investigate their inner structure. We present a novel method useful for hyperon-antihyperon pairs of different types which exploits the cross section enhancement due to the vacuum polarization effect at the $J/ψ$ resonance. Using the 10 billion $J/ψ$ events collected with the BESIII detector, this allows a thorough determination of the hyperon structure . The result is essentially a precise snapshot of a $\barΛΣ^0$~($Λ\barΣ^0$) pair in the making, encoded in the form factor ratio and the phase. Their values are measured to be $R = 0.860\pm0.029({\rm stat.})\pm0.010({\rm syst.})$, $ΔΦ_1=(1.011\pm0.094({\rm stat.})\pm0.010({\rm syst.}))~\rm rad$ for $\barΛΣ^0$ and $ΔΦ_2=(2.128\pm0.094({\rm stat.})\pm0.010({\rm syst.}))~\rm rad$ for $Λ\barΣ^0$, respectively. Furthermore, charge-parity (CP) breaking is investigated for the first time in this reaction and found to be consistent with CP symmetry.

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arXiv2023

Observation of $χ_{cJ}\to Λ\bar Λη$

By analyzing $(448.1\pm2.9)\times10^6$ $ψ(3686)$ events collected with the BESIII detector operating at the BEPCII collider, the decays of $χ_{cJ} \to Λ\bar Λη$ ($J=0$, 1 and 2) are observed for the first time with statistical significances of $13.9σ$, $6.7σ$, and $8.2σ$, respectively. The product branching fractions of $ψ(3686)\toγχ_{cJ}$ and $χ_{cJ}\to Λ\bar Λη$ are measured. Dividing by the world averages of the branching fractions of $ψ(3686)\toγχ_{cJ}$, the branching fractions of $χ_{cJ}\to Λ\bar Λη$ decays are determined to be $(2.31\pm0.30\pm0.21)\times10^{-4}$, $(5.86\pm1.38\pm0.68)\times10^{-5}$, and $(1.05\pm0.21\pm0.15)\times10^{-4}$ for $J=0$, 1 and 2, respectively, where the first uncertainties are statistical and the second systematic.

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arXiv2023

Measurements of the branching fractions of the inclusive decays $D^{0}(D^{+})\to π^+π^+π^-X$

Using $e^+e^-$ annihilation data corresponding to an integrated luminosity of 2.93 fb$^{-1}$ taken at a center-of-mass energy of 3.773 GeV with the BESIII detector, we report the first measurements of the branching fractions of the inclusive decays $D^0\to π^+π^+π^-X$ and $D^+\to π^+π^+π^-X$, where pions from $K^0_S$ decays have been excluded from the $π^+π^+π^-$ system and $X$ denotes any possible particle combination. The branching fractions of $D^0(D^+)\to π^+π^+π^-X$ are determined to be ${\mathcal B}(D^0\to π^+π^+π^-X)=(17.60\pm0.11\pm0.22)\%$ and ${\mathcal B}(D^+\to π^+π^+π^-X)=(15.25\pm0.09\pm0.18)\%$, where the first uncertainties are statistical and the second systematic.

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arXiv2023

Measurement of the branching fraction of $D_s^+\to τ^+ ν_τ$ via $τ^+ \to μ^+ ν_μ\bar{ν_τ}$

Utilizing $7.33~\mathrm{fb}^{-1}$ of $e^+e^-$ collision data taken at the center-of-mass energies of 4.128, 4.157, 4.178, 4.189, 4.199, 4.209, 4.219, and 4.226 GeV with the BESIII detector, the branching fraction of the leptonic decay $D_s^+\toτ^+ν_τ$ via $τ^+\toμ^+ν_μ\bar ν_τ$ is measured to be $\mathcal{B}_{D_s^+\toτ^+ν_τ}=(5.34\pm0.16_{\rm stat}\pm0.10_{\rm syst})\%$. Combining this branching fraction with the world averages of the measurements of the masses of $τ^+$ and $D_s^+$ as well as the lifetime of $D_s^+$, we extract the product of the decay constant of $D_s^+$ and the $c\to s$ Cabibbo-Kobayashi-Maskawa matrix element to be $f_{D_s^+}|V_{cs}|=(246.2\pm3.7_{\rm stat}\pm2.5_{\rm syst})~\mathrm{MeV}$. Taking $|V_{cs}|$ from a global fit in the standard model we obtain $f_{D_s^+}=(252.7\pm3.8_{\rm stat}\pm2.6_{\rm syst})$ MeV. Conversely, taking $f_{D_s^+}$ from lattice quantum chromodynamics calculations, we obtain $|V_{cs}| = 0.984\pm0.015_{\rm stat}\pm0.010_{\rm syst}$.

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arXiv2023

Measurement of the $e^{+}e^{-}\rightarrowωπ^{0}π^{0}$ cross section at center-of-mass energies from 2.0 to 3.08 GeV

The cross section of the process $e^{+}e^{-}\toωπ^{0}π^{0}$ is measured at nineteen center-of-mass energies from 2.0 to 3.08 GeV using data collected with the BESIII detector at the BEPCII storage ring. A resonant structure around 2.20 GeV is observed with statistical significance larger than $5σ$. Using a coherent fit to the cross section line shape, the mass and width are determined to be $M=2222\pm7\pm2~{\rm MeV}/c^2$ and $\varGamma=59\pm30\pm6~{\rm MeV}$, respectively, where the first uncertainties are statistical and the second ones are systematic.

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arXiv2023

Search for the lepton number violation decay $ϕ\to π^+ π^+ e^- e^-$ via $J/ψ\to ϕη$

Using $(1.0087\pm0.0044)\times10^{10}$ $J/ψ$ events collected by the BESIII detector at the BEPCII collider, we search for the lepton number violation decay $ϕ\to π^+ π^+ e^- e^-$ via $J/ψ\to ϕη$. No signal is found and the upper limit on the branching fraction of $ϕ\to π^+ π^+ e^- e^-$ is set to be $9.7\times10^{-6}$ at the 90\% confidence level.

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arXiv2023

Measurement of the absolute branching fraction of the inclusive decay $\barΛ_{c}^{-} \to \bar{n} + X$

Based on $e^+e^-$ collision data corresponding to an integrated luminosity of 4.5 $fb^{-1}$ collected at the center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at BEPCII, the absolute branching fraction of the inclusive decay $Λ^{+}_{c}\to n + X$, where $X$ refers to any possible final state particles, is measured. The absolute branching fraction is determined to be $\mathcal{B}(Λ^{+}_{c}\to n + X) = (32.4 \pm 0.7 \pm 1.5)\% $, where the first uncertainty is statistical and the second systematic. Assuming $CP$ symmetry, the measurement indicates that about one-fourth of $Λ^{+}_{c}$ ($\barΛ_{c}^-$) decay modes with a neutron (an anti-neutron) in the final state have not been observed.

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arXiv2023

Measurement of the absolute branching fraction of the inclusive decay $D_s^+\to π^+π^+π^- X$

Using an $e^+ e^-$ collision data sample with a total integrated luminosity of $3.19$ fb$^{-1}$ collected with the BESIII detector at a center-of-mass energy of 4.178 GeV, the branching fraction of the inclusive decay of the $D_s^+$ meson to final states including at least three charged pions is measured for the first time to be ${\cal B}(D_s^+\toπ^+ π^+ π^- X) = (32.81 \pm 0.35_{\rm stat} \pm {0.63_{\rm syst}})\%$. In this measurement the charged pions from $K_S^0$ meson decays are excluded. The partial branching fractions of $D_s^+\toπ^+ π^+ π^- X$ are also measured as a function of the $π^+ π^+ π^-$ invariant mass.

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arXiv2023

Measurement of the $C\!P$-even fraction of $D^0\to K^+K^-π^+π^-$

A determination of the $C\!P$-even fraction $F_+$ in the decay $D^0 \to K^+K^-π^+π^-$ is presented. Using $2.93$ fb$^{-1}$ of $e^+e^-\toψ(3770)\to D\bar{D}$ data collected by the BESIII detector, one charm meson is reconstructed in the signal mode and the other in a $C\!P$ eigenstate or the decay $D\to K_{S, L}^0π^+π^-$. Analysis of the relative rates of these double-tagged events yields the result $F_+ = 0.730 \pm 0.037 \pm 0.021$, where the first uncertainty is statistical and the second is systematic. This is the first model-independent measurement of $F_+$ in $D^0 \to K^+K^-π^+π^-$ decays.

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