arXiv subjects

X. Fang

Publications and source records attributed to X. Fang.

At least 91 records · Page 5Linked to original sources

arXiv2018

Study of two-photon decays of pseudoscalar mesons via $J/ψ$ radiative decays

Using a sample of $4.48\times10^{8}$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, we study the two-photon decays of the pseudoscalar mesons $π^0$, $η$, $η^\prime$, $η(1405)$, $η(1475)$, $η(1760)$, and $X(1835)$ in $J/ψ$ radiative decays using $ψ(3686)\toπ^{+}π^{-}J/ψ$ events. The $π^0$, $η$ and $η^\prime$ mesons are clearly observed in the two-photon mass spectra, and the branching fractions are determined to be $B(J/ψ\toγπ^{0}\to3γ)=(3.57\pm0.12\pm0.16)\times10^{-5}$, $B(J/ψ\toγη\to3γ)=(4.42\pm0.04\pm0.18)\times10^{-4}$, and $B(J/ψ\toγη'\to3γ)=(1.26\pm0.02\pm0.05)\times10^{-4}$, where the first errors are statistical and the second systematic. No clear signal for $η(1405)$, $η(1475)$, $η(1760)$ or $X(1835)$ is observed in the two-photon mass spectra, and upper limits at the $90\%$ confidence level on the product branching fractions are obtained.

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arXiv2018

Observation of $e^{+}e^{-} \rightarrow K\bar{K}J/ψ$ at center-of-mass energies from 4.189 to 4.600 GeV

We investigate the process $e^{+}e^{-} \rightarrow K\bar{K}J/ψ$ at center-of-mass energies from 4.189 to 4.600 GeV using 4.7 fb$^{-1}$ of data collected by the BESIII detector at the BEPCII collider. The Born cross sections for the reactions $e^{+}e^{-} \rightarrow K^{+}K^{-}J/ψ$ and $K_{S}^{0} K_{S}^{0} J/ψ$ are measured as a function of center-of-mass energy. The energy dependence of the cross section for $e^{+}e^{-} \rightarrow K^{+}K^{-}J/ψ$ is shown to differ from that for $π^{+}π^{-}J/ψ$ in the region around the $Y(4260)$. In addition, there is evidence for a structure around 4.5 GeV in the $e^{+}e^{-} \rightarrow K^{+}K^{-}J/ψ$ cross section that is not present in $π^{+}π^{-}J/ψ$.

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arXiv2018

Measurement of the matrix elements for the decays $η^{\prime}\rightarrowηπ^+π^-$ and $η^{\prime}\rightarrowηπ^0π^0$

Based on a sample of $1.31\times10^9$ $J/ψ$ events collected with the BESIII detector, the matrix elements for the decays $η^{\prime}\toηπ^{+}π^{-}$ and $η^{\prime}\toηπ^{0}π^{0}$ are determined using 351,016 $η^{\prime}\to(η\toγγ)π^+π^-$ and 56,249 $η^{\prime}\to(η\toγγ)π^0π^0$ events with background levels less than 1\%. Two commonly used representations are used to describe the Dalitz plot density. We find that an assumption of a linear amplitude does not describe the data well. A small deviation of the obtained matrix elements between $η^{\prime}\toηπ^{+}π^{-}$ and $η^{\prime}\toηπ^{0}π^{0}$ is probably caused by the mass difference between charged and neutral pions or radiative corrections. No cusp structure in $η^{\prime}\toηπ^{0}π^{0}$ is observed.

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arXiv2018

Study of $η(1475)$ and $X(1835)$ in radiative $J/ψ$ decays to $γϕ$

The decay $J/ψ\rightarrow γγϕ$ is studied using a sample of $1.31 \times10^{9}$ $J/ψ$ events collected with the BESIII detector. Two structures around 1475 MeV/c$^2$ and 1835 MeV/c$^2$ are observed in the $γϕ$ invariant mass spectrum for the first time. With a fit on the $γϕ$ invariant mass, which takes into account the interference between the two structures, and a simple analysis of the angular distribution, the structure around 1475 MeV/c$^2$ is found to favor an assignment as the $η(1475)$ and the mass and width for the structure around 1835 MeV/c$^2$ are consistent with the $X(1835)$. The statistical significances of the two structures are $13.5 σ$ and $6.3 σ$, respectively. The results indicate that both $η(1475)$ and $X(1835)$ contain a sizeable $s\bar{s}$ component.

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arXiv2018

Search for $ψ(3686)\to γη_c(η(1405))\to γπ^{+}π^{-}π^{0}$

Using a sample of $448.1\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector, a search for the isospin violating decay $η_{c}\toπ^{+}π^{-}π^{0}$ via $ψ(3686)\toγη_{c}$ is presented. No signal is observed, and the upper limit on $\mathcal{B}(ψ(3686)\to γη_{c}\to γπ^{+}π^{-}π^{0} )$ is determined to be $1.6\times10^{-6}$ at the $90\%$ confidence level. In addition, a search for $η(1405)\to f_{0}(980)π^{0}$ in $ψ(3686)$ radiative decays is performed. No signal is observed, and the branching fraction $\mathcal{B}(ψ(3686)\toγη(1405)\to γf_{0}(980)π^{0}\toγπ^+π^-π^0 )$ is calculated to be less than $ 5.0\times10^{-7}$ at the $90\%$ confidence level.

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arXiv2017

Observation of $χ_{c2}\toη'η'$ and $χ_{c0,2}\toηη'$

Using a sample of $447.9\times 10^6$ $ψ(3686)$ events collected with the BESIII detector in 2009 and 2012, we study the decays $χ_{c0,2}\to$ $η'η'$ and $ηη'$. The decays $χ_{c2}\toη'η'$, $χ_{c0}\toηη'$ and $χ_{c2}\toηη'$ are observed for the first time with statistical significances of $9.6σ$, $13.4σ$ and $7.5σ$, respectively. The branching fractions are determined to be $\mathcal{B}(χ_{c0}\toη'η') =(2.19\pm0.03\pm0.14)\times10^{-3}$, $\mathcal{B}(χ_{c2}\toη'η') = (4.76\pm0.56\pm0.38)\times10^{-5}$, $\mathcal{B}(χ_{c0}\toηη') = (8.92\pm0.84\pm0.65)\times10^{-5}$ and $\mathcal{B}(χ_{c2}\toηη') = (2.27\pm0.43\pm0.25)\times10^{-5}$, where the first uncertainties are statistical and the second systematic. The precision for the measurement of $\mathcal{B}(χ_{c0}\toη'η')$ is significantly improved compared to previous measurements. Based on the measured branching fractions, the role played by the doubly and singly Okubo-Zweig-Iizuka disconnected transition amplitudes for $χ_{c0,2}$ decays into pseudoscalar meson pairs can be clarified.

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arXiv2017

Branching fraction measurement of $J/ψ\rightarrow K_S K_L$ and search for $J/ψ\rightarrow K_S K_S$

Using a sample of $1.31 \times 10^{9}$ $J/ψ$ events collected with the BESIII detector at the BEPCII collider, we study the decays of $J/ψ\rightarrow K_S K_L$ and $K_S K_S$. The branching fraction of$J/ψ\rightarrow K_S K_L$ is determined to be ${\cal B}(J/ψ\rightarrow K_S K_L)=(1.93\pm0.01~(\rm{stat.})\pm0.05~(\rm{syst.}))\times10^{-4}$, which significantly improves on previous measurements. No clear signal is observed for the $J/ψ\rightarrow K_S K_S$ process, and the upper limit at the 95% confidence level for its branching fraction is determined to be ${\cal B}(J/ψ\rightarrow K_S K_S)<1.4\times10^{-8}$, which improves on the previous searches by two orders in magnitude and reaches the order of the Einstein-Podolsky-Rosen expectation.

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arXiv2017

Measurement of the absolute branching fraction of $D_{s0}^{*\pm}(2317)\to π^0 D_{s}^{\pm}$

The process $e^+ e^- \to D_{s}^{*+} D_{s0}^{*-}(2317)+c.c.$ is observed for the first time with the data sample of 567~pb$^{-1}$ collected with the BESIII detector operating at the BEPCII collider at a center-of-mass energy $\sqrt{s} = 4.6$~GeV. The statistical significance of the $D_{s0}^{*-}(2317)$ signal is $5.8σ$ and the mass is measured to be ($2318.3\pm 1.2\pm 1.2$)~MeV/$c^{2}$. The absolute branching fraction $\mathcal{B}(D_{s0}^{*-}(2317)\to π^0 D_{s}^{-})$ is measured as $1.00^{+0.00}_{-0.14}\pm 0.14$ for the first time. The uncertainties are statistical and systematic, respectively.

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arXiv2017

Dark Photon Search in the Mass Range Between 1.5 and 3.4 GeV/$c^2$

Using a data set of 2.93 fb$^{-1}$ taken at a center-of-mass energy $\sqrt{s}$ = 3.773 GeV with the BESIII detector at the BEPCII collider, we perform a search for an extra U(1) gauge boson, also denoted as a dark photon. We examine the initial state radiation reactions $e^+e^-\rightarrow e^+e^-γ_{\rm ISR}$ and $e^+e^-\rightarrow μ^+μ^-γ_{\rm ISR}$ for this search, where the dark photon would appear as an enhancement in the invariant mass distribution of the leptonic pairs. We observe no obvious enhancement in the mass range between 1.5 and 3.4 GeV/$c^{2}$ and set a 90% confidence level upper limit on the mixing strength of the dark photon and the Standard Model photon. We obtain a competitive limit in the tested mass range.

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arXiv2017

Measurement of Singly Cabibbo Suppressed Decays $Λ_c^{+}\to pπ^{+}π^{-}$ and $Λ_c^{+}\to pK^{+}K^{-}$

Using 567 $pb^{-1}$ of data collected with the BESIII detector at a center-of-mass energy of $\sqrt{s}=$ 4.599 $GeV$, near the $Λ_{c}^{+}Λ_{c}^{-}$ threshold, we study the singly Cabibbo-suppressed decays $Λ_c^{+}\to pπ^{+}π^{-}$ and $Λ_c^{+}\to pK^{+}K^{-}$. By normalizing with respect to the Cabibbo-favored decay $Λ_c^{+}\to pK^{-}π^{+}$, we obtain ratios of branching fractions: $\frac{\mathcal{B}(Λ_c^{+}\to pπ^{+}π^{-})}{\mathcal{B}(Λ_c^{+}\to pK^{-}π^{+})}$ = $(6.70 \pm 0.48 \pm 0.25)\%$, $\frac{\mathcal{B}(Λ_c^{+}\to pϕ)}{\mathcal{B}(Λ_c^{+}\to pK^{-}π^{+})}$ = $(1.81 \pm 0.33 \pm 0.13)\%$, and $\frac{\mathcal{B}(Λ_c^{+}\to pK^{+}K^{-}_{\text{non-}ϕ})}{\mathcal{B}(Λ_c^{+}\to pK^{-}π^{+})}$ = $(9.36 \pm 2.22 \pm 0.71)\times10^{-3}$, where the uncertainties are statistical and systematic, respectively. The absolute branching fractions are also presented. Among these measurements, the decay $Λ_c^{+}\to pπ^{+}π^{-}$ is observed for the first time, and the precision of the branching fraction for $Λ_c^{+}\to pK^{+}K^{-}_{\text{non-}ϕ}$ and $Λ_c^{+}\to pϕ$ is significantly improved.

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arXiv2017

Measurement of $e^{+}e^{-} \to π^{0}π^{0}ψ(3686)$ at $\sqrt{s}$ from 4.009 to 4.600 GeV and observation of a neutral charmoniumlike structure

Using $e^{+}e^{-}$ collision data collected with the BESIII detector at the BEPCII collider corresponding to an integrated luminosity of 5.2 $fb^{-1}$ at center-of-mass energies ($\sqrt{s}$) from 4.009 to 4.600 GeV, the process $e^{+}e^{-} \to π^{0} π^{0}ψ(3686)$ is studied for the first time. The corresponding Born cross sections are measured and found to be half of those of the reaction $e^{+}e^{-} \to π^{+}π^{-}ψ(3686)$. This is consistent with the expectation from isospin symmetry. Furthermore, the Dalitz plots for $π^{0}π^{0}ψ(3686)$ are accordant with those of $π^{+}π^{-}ψ(3686)$ at all energy points, and a neutral analogue to the structure in $π^\pm ψ(3686)$ around 4040 MeV/$c^{2}$ first observed at $\sqrt{s}$=4.416 GeV is observed in the isospin neutral mode at the same energy.

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arXiv2017

Search for the rare decays $J/ψ\to D^{0} e^{+}e^{-} +c.c.$ and $ψ(3686) \to D^{0} e^{+}e^{-} +c.c.$

Using the data samples of $(1310.6\pm7.2 )\times 10^{6}$ $J/ψ$ events and $(448.1\pm2.9)\times 10^{6}$ $ψ(3686)$ events collected with the BESIII detector, we search for the rare decays $J/ψ\to D^{0} e^{+}e^{-} +c.c.$ and $ψ(3686) \to D^{0} e^{+}e^{-} +c.c.$. No significant signals are observed and the corresponding upper limits on the branching fractions at the $90\%$ confidence level are determined to be $Br(J/ψ\to D^{0} e^{+}e^{-} +c.c.)< 8.5\times 10^{-8}$ and $Br (ψ(3686) \to D^{0} e^{+}e^{-} +c.c.)<1.4\times 10^{-7}$, respectively. Our limit on $Br(J/ψ\to D^{0} e^{+}e^{-} +c.c.)$ is more stringent by two orders of magnitude than the previous results, and the $Br(ψ(3686) \to D^{0} e^{+}e^{-} +c.c.)$ is measured for the first time.

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arXiv2017

Measurement of the integrated luminosity and the center-of-mass energy of the data taken by BESIII at $\sqrt{s} = 2.125$ GeV

To study the nature of the state $Y(2175)$, a dedicated data set of $e^+e^-$ collision data was collected at the center-of-mass energy of 2.125 GeV with the BESIII detector at the BEPCII collider. By analyzing large-angle Bhabha scattering events, the integrated luminosity of this data set is determined to be $108.49\pm0.02\pm0.85$ pb$^{-1}$, where the first uncertainty is statistical and the second one is systematic. In addition, the center-of-mass energy of the data set is determined with radiative dimuon events to be $2126.55\pm0.03\pm0.85$ MeV, where the first uncertainty is statistical and the second one is systematic.

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arXiv2017

Improved measurements of two-photon widths of the $χ_{cJ}$ states and helicity analysis for $χ_{c2}\toγγ$

Based on $448.1 \times 10^6$ $ψ(3686)$ events collected with the BESIII detector, the decays $ψ(3686)\toγχ_{cJ}, χ_{cJ} \to γγ~(J=0, 1, 2)$ are studied. The decay branching fractions of $χ_{c0,c2} \to γγ$ are measured to be $\mathcal{B}(χ_{c0}\toγγ) = (1.93 \pm 0.08 \pm 0.05 \pm 0.05)\times 10^{-4}$ and $\mathcal{B}(χ_{c2}\toγγ) = (3.10 \pm 0.09 \pm 0.07 \pm 0.11)\times 10^{-4} $, which correspond to two-photon decay widths of $Γ_{γγ}(χ_{c0}) = 2.03 \pm 0.08 \pm 0.06 \pm 0.13 ~\rm{keV}$ and $Γ_{γγ}(χ_{c2}) = 0.60 \pm 0.02 \pm 0.01 \pm 0.04 ~\rm{keV}$ with a ratio of $\mathcal{R}=Γ_{γγ}(χ_{c2})/Γ_{γγ}(χ_{c0})= 0.295 \pm 0.014 \pm 0.007 \pm 0.027$, where the uncertainties are statistical, systematic and associated with the uncertainties of $\mathcal{B}(ψ(3686)\toγχ_{c0,c2})$ and the total widths $Γ(χ_{c0,c2})$, respectively. For the forbidden decay of $χ_{c1}\toγγ$, no signal is observed, and an upper limit on the two-photon width is obtained to be $Γ_{γγ}(χ_{c1})<5.3 ~\rm{eV}$ at the 90\% confidence level. The ratio of the two-photon widths between helicity-zero and helicity-two components in the decay $χ_{c2}\toγγ$ is also measured to be $f_{0/2} = Γ^{λ=0}_{γγ}(χ_{c2})/Γ^{λ=2}_{γγ}(χ_{c2}) = (0.0 \pm 0.6 \pm 1.2)\times 10^{-2}$, where the uncertainties are statistical and systematic, respectively.

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arXiv2017

Determination of the number of $ψ(3686)$ events at BESIII

The numbers of $ψ(3686)$ events accumulated by the BESIII detector for the two rounds of data taking during 2009 and 2012 are determined to be $(107.0\pm0.8)\times 10^6$ and $(341.1\pm 2.1)\times 10^6$, respectively, by counting inclusive hadronic events, where the uncertainty is dominated by systematics and the statistical uncertainty is negligible. The number of events for the sample taken in 2009 is consistent with that of the previous measurement. The total number of $ψ(3686)$ events for the two data-taking periods is $(448.1\pm2.9)\times10^6$.

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arXiv2017

Measurement of cross sections of the interactions $e^+e^-\rightarrow ϕϕω$ and $e^+e^-\rightarrow ϕϕϕ$ at center-of-mass energies from 4.008 to 4.600 GeV

Using data samples collected with the BESIII detector at the BEPCII collider at six center-of-mass energies between 4.008 and 4.600 GeV, we observe the processes $e^+e^-\rightarrow ϕϕω$ and $e^+e^-\rightarrow ϕϕϕ$. The Born cross sections are measured and the ratio of the cross sections $σ(e^+e^-\rightarrow ϕϕω)/σ(e^+e^-\rightarrow ϕϕϕ)$ is estimated to be $1.75\pm0.22\pm0.19$ averaged over six energy points, where the first uncertainty is statistical and the second is systematic. The results represent first measurements of these interactions.

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arXiv2017

Measurement of branching fractions for $ψ(3686)\rightarrowγη',γη$ and $γπ^{0}$

Using a data sample of $448\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector operating at the BEPCII storage ring, the decays $ψ(3686)\rightarrowγη$ and $ψ(3686)\rightarrowγπ^{0}$ are observed with a statistical significance of $7.3σ$ and $ 6.7σ$, respectively. The branching fractions are measured to be $\mathcal{B}(ψ(3686)\rightarrowγη)=(0.85\pm0.18\pm0.05)\times10^{-6}$ and $\mathcal{B}(ψ(3686)\rightarrowγπ^{0})=(0.95\pm0.16\pm0.05)\times10^{-6}$. In addition, we measure the branching fraction of $ψ(3686)\rightarrowγη'$ to be $\mathcal{B}(ψ(3686)\rightarrowγη')=(125.1\pm2.2\pm6.2)\times 10^{-6}$, with improved precision compared to previous results.

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arXiv2017

Observation of the doubly radiative decay $η^{\prime}\to γγπ^0$

Based on a sample of $1.31$ billion $J/ψ$ events collected with the BESIII detector, we report the study of the doubly radiative decay $η^\prime\to γγπ^0$ for the first time, where the $η^\prime$ meson is produced via the $J/ψ\to γη^\prime$ decay. The branching fraction of $η^\prime\to γγπ^0$ inclusive decay is measured to be ${\cal B}(η^\prime\to γγπ^0)_{\text{Incl.}}$ = $(3.20\pm0.07\mbox{(stat)}\pm0.23\mbox{(sys)})\times 10^{-3}$, while the branching fractions of the dominant process $η^\prime\rightarrowγω$ and the non-resonant component are determined to be ${\cal B}(η^\prime\to γω)\times {\cal B}(ω\to γπ^0) = (23.7 \pm1.4\mbox{(stat)}\pm1.8\mbox{(sys)})\times 10^{-4}$ and ${\cal B}(η^\prime\to γγπ^0)_{\text{NR}} = (6.16\pm0.64\mbox{(stat)} \pm0.67\mbox{(sys)})\times 10^{-4}$, respectively. In addition, the $M^2_{γγ}$-dependent partial widths of the inclusive decay are also presented.

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