arXiv subjects

Y. Fang

Publications and source records attributed to Y. Fang.

At least 235 records · Page 13Linked to original sources

arXiv2023

Precision measurement of the matrix elements for $η\toπ^+π^-π^0$ and $η\toπ^0π^0π^0$ decays

A precision measurement of the matrix elements for $η\toπ^+π^-π^0$ and $η\toπ^0π^0π^0$ decays is performed using a sample of $(10087\pm44)\times10^6$ $J/ψ$ decays collected with the BESIII detector. The decay $J/ψ\to γη$ is used to select clean samples of 631,686 $η\toπ^+π^-π^0$ decays and 272,322 $η\toπ^0π^0π^0$ decays. The matrix elements for both channels are in reasonable agreement with previous measurements. The non-zero $gX^2Y$ term for the decay mode $η\toπ^+π^-π^0$ is confirmed, as reported by the KLOE Collaboration, while the other higher-order terms are found to be insignificant. Dalitz plot asymmetries in the $η\toπ^+π^-π^0$ decay are also explored and are found to be consistent with charge conjugation invariance. In addition, a cusp effect is investigated in the $η\toπ^0π^0π^0$ decay, and no obvious structure around the $π^+π^-$ mass threshold is observed.

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arXiv2023

Search for baryon and lepton number violating decays of $Ξ^{0}$ hyperons

Using $(1.0087\pm0.0044)\times10^{10}$ $J/ψ$ events collected by the BESIII detector at the BEPCII collider, we report the first search for the baryon and lepton number violating decays $Ξ^{0} \rightarrow K^{-} e^{+}$ with $Δ(B-L)=0$ and $Ξ^{0} \rightarrow K^{+} e^{-}$ with $|Δ(B-L)|=2$, where $B$ ($L$) is the baryon (lepton) number. While no signal is observed, the upper limits on the branching fractions of these two decays are set to $\mathcal B(Ξ^{0} \rightarrow K^{-} e^{+})<3.6\times10^{-6}$ and $\mathcal B(Ξ^{0} \rightarrow K^{+} e^{-})<1.9\times10^{-6}$ at the 90\% confidence level, respectively. These results offer a direct probe of baryon number violating interactions involving a strange quark.

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arXiv2023

Determination of the $C\!P$-even fraction of $D^0\rightarrow K_S^0π^+π^-π^0$

Quantum-correlated $D\bar{D}$ pairs collected by the BESIII experiment at the $ψ(3770)$ resonance, corresponding to an integrated luminosity of 2.93 fb$^{-1}$, are used to study the $D^0 \rightarrow K^{0}_Sπ^{+} π^{-} π^{0}$ decay mode. The $C\!P$-even fraction of $D^0 \rightarrow K^{0}_Sπ^{+} π^{-} π^{0}$ decays is determined to be $0.235\pm 0.010\pm 0.002$, where the first uncertainty is statistical and the second is systematic.

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arXiv2023

Test of $C\!P$ Symmetry in Hyperon to Neutron Decays

The quantum entangled $J/ψ\to Σ^{+}\barΣ^{-}$ pairs from $(1.0087\pm0.0044)\times10^{10}$ $J/ψ$ events taken by the BESIII detector are used to study the non-leptonic two-body weak decays $Σ^{+} \to n π^{+}$ and $\barΣ^{-} \to \bar{n} π^{-}$. The $C\!P$-odd weak decay parameters of the decays $Σ^{+} \to n π^{+}$ ($α_{+}$) and $\barΣ^{-} \to \bar{n} π^{-}$ ($\barα_{-}$) are determined to be $-0.0565\pm0.0047_{\rm stat}\pm0.0022_{\rm syst}$ and $0.0481\pm0.0031_{\rm stat}\pm0.0019_{\rm syst}$, respectively. The decay parameter $\barα_{-}$ is measured for the first time, and the accuracy of $α_{+}$ is improved by a factor of four compared to the previous results. The simultaneously determined decay parameters allow the first precision $C\!P$ symmetry test for any hyperon decay with a neutron in the final state with the measurement of $A_{C\!P}=(α_{+}+\barα_{-})/(α_{+}-\barα_{-})=-0.080\pm0.052_{\rm stat}\pm0.028_{\rm syst}$. Assuming $C\!P$ conservation, the average decay parameter is determined as $\left< α_{+}\right>=(α_{+}- \barα_{-})/2 = -0.0506\pm0.0026_{\rm stat}\pm0.0019_{\rm syst}$, while the ratios $α_{+}/α_{0}$ and $\barα_{-}/\barα_{0}$ are $-0.0490\pm0.0032_{\rm stat}\pm0.0021_{\rm syst}$ and $-0.0571\pm0.0053_{\rm stat}\pm0.0032_{\rm syst}$, where $α_{0}$ and $\barα_{0}$ are the decay parameters of the decays $Σ^{+} \to p π^{0}$ and $\barΣ^{-} \to \bar{p} π^{0}$, respectively.

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arXiv2023

Measurement of $e^+ e^- \rightarrow ϕη^{\prime}$ cross sections at center-of-mass energies between 3.508 and 4.600 GeV

We present a measurement of the dressed cross sections for $e^+ e^- \rightarrow ϕη^{\prime}$ at different center-of-mass energies between 3.508 and 4.600 GeV based on 15.1 fb$^{-1}$ of $e^+ e^-$ annihilation data collected with the BESIII detector operating at the BEPCII collider. In addition, a search for the decay $Y(4230) \to ϕη^{\prime}$ is performed. No clear signal is observed and the corresponding upper limit is provided.

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arXiv2023

First Experimental Study of the Purely Leptonic Decay $D_s^{*+}\to e^+ν_e$

Using $7.33~\mathrm{fb}^{-1}$ of $e^+e^-$ collision data taken with the BESIII detector at the BEPCII collider, we report the first experimental study of the purely leptonic decay $D_s^{*+}\to e^+ν_e$. A signal for the decay $D_s^{*+}\to e^+ν_e$ is observed with a statistical significance of $2.9σ$. The branching fraction of ${D_s^{*+}\to e^+ν_e}$ is measured to be $(2.1{^{+1.2}_{-0.9}}_{\rm stat.}\pm0.2_{\rm syst.})\times 10^{-5}$, corresponding to an upper limit of $4.0\times10^{-5}$ at the 90\% confidence level. Taking the total width of the $D_s^{*+}$~(($0.070\pm0.028$) keV) predicted by lattice quantum chromodynamics as input, the decay constant of the $D^{*+}_s$ is determined to be $f_{D_s^{*+}}=(213.6{^{+61.0}_{-45.8}}_{\rm stat.}\pm43.9_{\rm syst.})$ MeV, corresponding to an upper limit of 353.8 MeV at the 90\% confidence level.

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arXiv2023

Measurement of Branching Fractions of Singly Cabibbo-suppressed Decays $Λ_c^+ \rightarrow Σ^{0} K^+$ and $Σ^{+} K_{S}^0$

Based on a sample of 4.4 $\mathrm{fb}^{-1}$ of $e^{+}e^{-}$ annihilation data collected in the energy region between 4.6 GeV and 4.7 GeV with the BESIII detector at BEPCII, two singly Cabibbo-suppressed decays $Λ_c^+ \rightarrow Σ^0 K^+$ and $Λ_{c}^{+} \rightarrow Σ^+ K_{S}^0$ are studied. The ratio of the branching fraction $\mathcal{B}(Λ_c^+ \rightarrow Σ^0 K^+)$ relative to $\mathcal{B}(Λ_c^+ \rightarrow Σ^0 π^+)$ is measured to be $0.0361 \pm 0.0073(\mathrm{stat.}) \pm 0.0005(\mathrm{syst.})$, and the ratio of $\mathcal{B}(Λ_c^+ \rightarrow Σ^+ K_{S}^0)$ relative to $\mathcal{B}(Λ_{c}^{+} \rightarrow Σ^+ π^+ π^-)$ is measured to be $0.0106 \pm 0.0031(\mathrm{stat.}) \pm 0.0004(\mathrm{syst.})$. After taking the world-average branching fractions of the reference decay channels, the branching fractions $\mathcal{B}(Λ_c^+ \rightarrow Σ^0 K^+)$ and $\mathcal{B}(Λ_{c}^{+} \rightarrow Σ^+ K_{S}^0)$ are determined to be $(4.7\pm 0.9(\mathrm{stat.})\pm 0.1(\mathrm{syst.}) \pm 0.3(\mathrm{ref.}))\times10^{-4}$ and $(4.8\pm 1.4(\mathrm{stat.})\pm 0.2(\mathrm{syst.}) \pm 0.3(\mathrm{ref.}))\times10^{-4}$, respectively. The branching fraction of the $Λ_{c}^{+} \rightarrow Σ^+ K_{S}^0$ decay is measured for the first time.

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arXiv2023

Observation of the decay $χ_{cJ} \to Ω^- \barΩ^+$

Using an $e^+e^-$ collision data sample of $(27.08 \pm 0.14) \times 10^{8}$ $ψ(3686)$ events collected by the BESIII detector, we report the first observation of $χ_{cJ} \to Ω^- \barΩ^+$ ($J=0,\,1,\,2$) decays with significances of $5.6σ$, $6.4σ$, and $18σ$, respectively, where the $χ_{cJ}$ mesons are produced in the radiative $ψ(3686)$ decays. The branching fractions are determined to be $\mathcal{B}(χ_{c0} \to Ω^- \barΩ^+) = (3.51 \pm 0.54 \pm 0.29) \times 10^{-5}$, $\mathcal{B}(χ_{c1} \to Ω^- \barΩ^+) = (1.49 \pm 0.23 \pm 0.10) \times 10^{-5}$, and $\mathcal{B}(χ_{c2} \to Ω^- \barΩ^+) = (4.52 \pm 0.24 \pm 0.18) \times 10^{-5}$, where the first and second uncertainties are statistical and systematic, respectively.

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arXiv2023

Evidence for $η_c$(2S)$\to\pipieta$ decay

The decay $η_c(2S)\to\pipieta$ is searched for through the radiative transition $ψ(3686) \toγη_c(2S)$ using 448 million $ψ$(3686) events accumulated at the BESIII detector. The first evidence of $η_c(2S)\toπ^+π^-η$ is found with a statistical significance of 3.5$σ$. The product of the branching fractions of $ψ(3686)\toγη_c(2S)$ and $η_c(2S)\to\pipieta$ is measured to be $Br(ψ(3686)\toγη_c(2S))\times Br(η_c(2S)\to\pipieta)=(2.97\pm0.81\pm0.26)\times10^{-6}$, where the first uncertainty is statistical and the second one is systematic. The branching fraction of the decay $η_c(2S)\to\pipieta$ is determined to be $Br(η_c(2S)\to\pipieta)=(42.4\pm11.6\pm3.8\pm30.3)\times10^{-4}$, where the third uncertainty is transferred from the uncertainty of the branching fraction of $ψ(3686)\toγη_c(2S)$.

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arXiv2023

Cross section measurements of $e^+e^- \to ΦK^+ K^-$ and $e^+ e^- \to ΦK_S^0 K_S^0$ at center-of-mass energies between 3.7730 GeV and 4.7008 GeV

Based on 22.7 fb$^{-1}$ of $e^+e^-$ annihilation data collected at 33 different center-of-mass energies between 3.7730 GeV and 4.7008 GeV with the BESIII detector at the BEPCII collider, Born cross sections of the two processes $e^+e^-\to ϕK^+ K^-$ and $e^+ e^- \to ϕK_{S}^{0} K_{S}^{0}$ are measured for the first time. No indication of resonant production through an intermediate vector state $V$ is observed, and the upper limits on the product of the electronic width $Γ_{e^+e^-}$ and the branching fraction $Br(V\rightarrow ϕK \bar{K})$ of the processes $e^+e^- \to V \to ϕK^+ K^-$ and $e^+e^- \to V \to ϕK_S^0K_S^0$ at the $90\%$ confidence level are obtained for a large parameter space in resonance masses and widths. For the current world average mass and width of the $ψ(4230)$ of $m=4.2187$ GeV$/c^2$ and $Γ=44$ MeV, we set upper limits on the $ϕK^+ K^-$ and $ϕK_S^0K_S^0$ final states of 1.75 eV and 0.47 eV at the $90\%$ confidence level, respectively.

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arXiv2023

Observation of a New $X(3872)$ Production Process $e^+e^-\toωX(3872)$

Using $4.7~\rm fb^{-1}$ of $e^+e^-$ collision data at center-of-mass energies from 4.661 to 4.951 GeV collected by the BESIII detector at the BEPCII collider, we observe the $X(3872)$ production process $e^{+}e^{-}\toωX(3872)$ for the first time. The significance is $7.8σ$, including both the statistical and systematic uncertainties. The $e^+e^-\toωX(3872)$ Born cross section and the corresponding upper limit at 90\% confidence level at each energy point are reported. The line shape of the cross section indicates that the $ωX(3872)$ signals may be from the decays of some non-trivial structures.

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arXiv2023

Search for an axion-like particle in radiative $J/ψ$ decays

We search for an axion-like particle (ALP) $a$ through the process $ψ(3686)\rightarrowπ^+π^-J/ψ$, $J/ψ\rightarrowγa$, $a\rightarrowγγ$ in a data sample of $(2.71\pm0.01)\times10^9$ $ψ(3686)$ events collected by the BESIII detector. No significant ALP signal is observed over the expected background, and the upper limits on the branching fraction of the decay $J/ψ\rightarrowγa$ and the ALP-photon coupling constant $g_{aγγ}$ are set at 95% confidence level in the mass range of $0.165\leq m_a\leq2.84\,\mbox{GeV}/c^2$. The limits on $B(J/ψ\rightarrowγa)$ range from $8.3\times10^{-8}$ to $1.8\times10^{-6}$ over the search region, and the constraints on the ALP-photon coupling are the most stringent to date for $0.165\leq m_a\leq1.468\,\mbox{GeV}/c^2$.

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arXiv2023

Measurements of the electric and magnetic form factors of the neutron for time-like momentum transfer

We present the first measurements of the electric and magnetic form factors of the neutron in the time-like (positive $q^2$) region as function of four-momentum transfer. We explored the differential cross sections of the reaction $e^+e^- \rightarrow \bar{n}n$ with data collected with the BESIII detector at the BEPCII accelerator, corresponding to an integrated luminosity of 354.6 pb$^{-1}$ in total at twelve center-of-mass energies between $\sqrt{s} = 2.0 - 2.95$ GeV. A relative uncertainty of 18% and 12% for the electric and magnetic form factors, respectively, is achieved at $\sqrt{s} = 2.3935$ GeV. Our results are comparable in accuracy to those from electron scattering in the comparable space-like (negative $q^2$) region of four-momentum transfer. The electromagnetic form factor ratio $R_{\rm em}\equiv |G_E|/|G_M|$ is within the uncertainties close to unity. We compare our result on $|G_E|$ and $|G_M|$ to recent model predictions, and the measurements in the space-like region to test the analyticity of electromagnetic form factors.

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arXiv2023

Observation of the $Y(4230)$ and evidence for a new vector charmonium-like state $Y(4710)$ in $e^{+}e^{-}\to K_{S}^{0} K_{S}^{0} J/ψ$

Cross sections for the process $e^{+} e^{-} \to K_{S}^{0} K_{S}^{0} J/ψ$ at center-of-mass energies from $4.128$ to $4.950$ GeV are measured using data samples with a total integrated luminosity of 21.2 fb$^{-1}$ collected by the BESIII detector operating at the BEPCII storage ring. The $Y(4230)$ state is observed in the energy dependence of the $e^{+} e^{-} \to K_{S}^{0} K_{S}^{0} J/ψ$ cross section for the first time with a statistical significance of 26.0$σ$. In addition, an enhancement around $4.710$ GeV, called the $Y(4710)$, is seen with a statistical significance of 4.2$σ$. There is no clear structure around $4.484$ GeV. Using a fit with a coherent sum of three Breit-Wigner functions, we determine the mass and width of the $Y(4230)$ state to be $4226.9 \pm 6.6 \pm 21.9$ MeV/$c^{2}$ and $71.7 \pm 16.2 \pm 31.4$ MeV, respectively, and the mass and width of the $Y(4710)$ state to be $4704.0 \pm 52.3 \pm 69.5$ MeV/$c^{2}$ and $183.2 \pm 114.0 \pm 90.8$ MeV, respectively, where the first uncertainties are statistical and the second are systematic. In addition, the average Born cross section ratio of $e^{+} e^{-} \to K_{S}^{0} K_{S}^{0} J/ψ$ to $e^{+} e^{-} \to K^{+} K^{-} J/ψ$ is measured to be $0.388_{-0.028}^{+0.035}\pm0.016$, or $0.426_{-0.031}^{+0.038}\pm0.018$ if three-body phase space is considered.

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arXiv2023

Study of the $h_c$($1^1P_1$) meson via $ψ(2S) \rightarrow π^0 h_c$ decays at BESIII

Using 448 million $ψ(2S)$ events, the spin-singlet $P$-wave charmonium state $h_c$(1$^1P_1$) is studied via the $ψ(2S) \rightarrow π^0 h_c$ decay followed by the $h_c \to γη_c$ transition. The branching fractions are measured to be $\mathcal{B}_{\rm Inc}(ψ(2S) \rightarrow π^0h_c) \times \mathcal{B}_{\rm Tag}(h_c \rightarrow γη_c) = (4.22 ^{+0.27}_{-0.26} \pm 0.19) \times 10^{-4}$ , $\mathcal{B}_{\rm Inc}(ψ(2S) \rightarrow π^0h_c) = (7.32 \pm 0.34 \pm 0.41) \times 10^{-4}$, and $\mathcal{B}_{\rm Tag}(h_c \rightarrow γη_c) = (57.66 ^{+3.62}_{-3.50} \pm 0.58)\%$, where the uncertainties are statistical and systematic, respectively. The $h_c$(1$^1P_1$) mass and width are determined to be $M = (3525.32 \pm 0.06 \pm 0.15)~\rm{MeV}/c^{\rm{2}}$ and ${\mathit Γ} = (0.78 ^{+0.27}_{-0.24} \pm 0.12)~\rm{MeV}$. Using the center of gravity mass of the three $χ_{cJ}$(1$^3 P_J$) mesons ($M(\rm c.o.g.)$), the $1P$ hyperfine mass splitting is estimated to be $Δ_{\rm hyp} = M(h_c) - M(\rm c.o.g.) = (0.03 \pm 0.06 \pm 0.15) ~ \rm{MeV}/c^{\rm{2}}$, which is consistent with the expectation that the $1P$ hyperfine splitting is zero at the lowest-order.

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arXiv2023

Observation of Three Charmoniumlike States with $J^{PC}=1^{--}$ in $e^{+}e^{-}\to D^{0}D^{-}π^{+}$

The Born cross sections of the process $e^{+}e^{-}\to D^{*0}D^{*-}π^{+}$ at center-of-mass energies from 4.189 to 4.951 GeV are measured for the first time. The data samples used correspond to an integrated luminosity of $17.9\,{\rm fb}^{-1}$ and were collected by the BESIII detector operating at the BEPCII storage ring. Three enhancements around 4.20, 4.47 and 4.67 GeV are visible. The resonances have masses of $4209.6\pm4.7\pm5.9\,{\rm MeV}/c^{2}$, $4469.1\pm26.2\pm3.6\,{\rm MeV}/c^{2}$ and $4675.3\pm29.5\pm3.5\,{\rm MeV}/c^{2}$ and widths of $81.6\pm17.8\pm9.0\,{\rm MeV}$, $246.3\pm36.7\pm9.4\,{\rm MeV}$, and $218.3\pm72.9\pm9.3\,{\rm MeV}$, respectively, where the first uncertainties are statistical and the second systematic. The first and third resonances are consistent with the $ψ(4230)$ and $ψ(4660)$ states, respectively, while the second one is compatible with the $ψ(4500)$ observed in the $e^{+}e^{-}\to K^{+}K^{-}J/ψ$ process. These three charmoniumlike $ψ$ states are observed in $e^{+}e^{-}\to D^{*0}D^{*-}π^{+}$ process for the first time.

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arXiv2023

Improved measurement of the absolute branching fraction of inclusive semileptonic $Λ_c^+$ decay

Using $4.5 \mathrm{fb}^{-1}$ of $e^+e^-$ annihilation data samples collected at center-of-mass energies ranging from 4.600 to 4.698 GeV with the BESIII detector at the BEPCII collider, we measured the absolute branching fraction for the inclusive semileptonic decay $Λ_c^+\rightarrow Xe^+ν_e$, where $X$ refers to any possible particle system. The branching fraction of the decay is determined to be $\mathcal{B}({\it Λ}^+_c\rightarrow Xe^+ν_e)=(4.06\pm0.10_{\rm stat.}\pm0.09_{\rm syst.})\%$. Our result improves the precision of previous measurement of $\mathcal{B}({\it Λ}^+_c\rightarrow Xe^+ν_e)$ by more than threefold. Using the known $Λ_c^+$ lifetime and the charge-averaged semileptonic decay width of nonstrange charmed mesons, we measure the ratio of inclusive semileptonic decay widths $Γ(Λ_c^+\rightarrow X e^+ν_e)/\barΓ(D\rightarrow Xe^+ν_e)=1.28\pm0.05$, where statistical and systematic uncertainties are combined.

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arXiv2023

Study of the $e^+e^- \to π^{+}π^{-}ω$ process at center-of-mass energies between 4.0 and 4.6 GeV

Using $15.6$ $\rm fb^{-1}$ of $e^+e^-$ collision data collected at twenty-four center-of-mass energies from $4.0$ to $4.6$ GeV with the BESIII detector, the helicity amplitudes of the process $e^+e^-\to π^{+}π^{-}ω$ are analyzed for the first time. Born cross section measurements of two-body intermediate resonance states with statistical significance greater than 5$σ$ are presented, such as $f_{0}(500)$, $f_{0}(980)$, $f_{2}(1270)$, $f_{0}(1370)$, $b_{1}(1235)^{\pm}$, and $ρ(1450)^{\pm}$. In addition, evidence of a resonance state in $e^+e^-\to π^+π^-ω$ production is found. The mass of this state obtained by line shape fitting is about 4.2 GeV/$c^2$, which is consistent with the production of $ψ(4160)$ or $Y(4220)$.

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