arXiv subjects

X. R. Chen

Publications and source records attributed to X. R. Chen.

At least 613 records · Page 34Linked to original sources

arXiv2019

Observation of $η_c\toωω$ in $J/ψ\toγωω$

Using a sample of $(1310.6\pm7.0)\times10^6$ $J/ψ$ events recorded with the BESIII detector at the symmetric electron positron collider BEPCII, we report the observation of the decay of the $(1^1 S_0)$ charmonium state $η_c$ into a pair of $ω$ mesons in the process $J/ψ\toγωω$. The branching fraction is measured for the first time to be $\mathcal{B}(η_c\toωω)= (2.88\pm0.10\pm0.46\pm0.68)\times10^{-3}$, where the first uncertainty is statistical, the second systematic and the third is from the uncertainty of $\mathcal{B}(J/ψ\toγη_c)$. The mass and width of the $η_c$ are determined as $M=(2985.9\pm0.7\pm2.1)\,$MeV/$c^2$ and $Γ=(33.8\pm1.6\pm4.1)\,$MeV.

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arXiv2019

First observations of $h_c \to$ hadrons

Based on $(4.48 \pm 0.03) \times 10^{8}$ $ψ(3686)$ events collected with the BESIII detector, five $h_c$ hadronic decays are searched for via process $ψ(3686) \to π^0 h_c$. Three of them, $h_c \to p \bar{p} π^+ π^-$, $π^+ π^- π^0$, and $2(π^+ π^-) π^0$ are observed for the first time, with statistical significances of 7.4$σ$, $4.9σ$, and 9.1$σ$, and branching fractions of $(2.89\pm0.32\pm0.55)\times10^{-3}$, $(1.60\pm0.40\pm0.32)\times10^{-3}$, and $(7.44\pm0.94\pm1.56)\times10^{-3}$, respectively, where the first uncertainties are statistical and the second systematic. No significant signal is observed for the other two decay modes, and the corresponding upper limits of the branching fractions are determined to be $B(h_c \to 3(π^+ π^-) π^0)<8.7\times10^{-3}$ and $B(h_c \to K^+ K^- π^+ π^-)<5.8\times10^{-4}$ at 90% confidence level.

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arXiv2019

Precision measurements of $σ_{B}(e^+e^- \to K_{S}^{0}K^{\pm}π^{\mp})$ at center-of-mass energies between 3.8 and 4.6 GeV

Using data samples collected by the BESIII detector operating at the BEPCII storage ring, we measure the $e^+e^- \to K_{S}^{0}K^{\pm}π^{\mp}$ Born cross sections at center-of-mass energies between 3.8 and 4.6\,GeV, corresponding to a luminosity of about 5.0~fb$^{-1}$. The results are compatible with the BABAR measurements, but with the precision significantly improved. A simple $1/s^n$ dependence for the continuum process can describe the measured cross sections, but a better fit is obtained by an additional resonance near 4.2\,GeV, which could be an excited charmonium or a charmonium-like state.

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arXiv2019

Measurement of the phase between strong and electromagnetic amplitudes of $J/ψ$ decays

Using 16 energy points of $e^{+}e^{-}$ annihilation data collected in the vicinity of the $J/ψ$ resonance with the BESIII detector and with a total integrated luminosity of around 100 pb$^{-1}$, we study the relative phase between the strong and electromagnetic amplitudes of $J/ψ$ decays. The relative phase between $Jψ$ electromagnetic decay and the continuum process ($e^{+}e^{-}$ annihilation without the $J/ψ$ resonance) is confirmed to be zero by studying the cross section lineshape of $μ^{+}μ^{-}$ production. The relative phase between $J/ψ$ strong and electromagnetic decays is then measured to be $(84.9\pm3.6)^\circ$ or $(-84.7\pm3.1)^\circ$ for the $2(π^{+}π^{-})π^{0}$ final state by investigating the interference pattern between the $J/ψ$ decay and the continuum process. This is the first measurement of the relative phase between $J/ψ$ strong and electromagnetic decays into a multihadron final state using the lineshape of the production cross section. We also study the production lineshape of the multihadron final state $ηπ^{+}π^{-}$ with $η\toπ^{+}π^{-}π^{0}$, which provides additional information about the phase between the $J/ψ$ electromagnetic decay amplitude and the continuum process. Additionally, the branching fraction of $J/ψ\to 2(π^{+}π^{-})π^{0}$ is measured to be $(4.73\pm0.44)\%$ or $(4.85\pm0.45)\%$, and the branching fraction of $J/ψ\toηπ^{+}π^{-}$ is measured to be $(3.78\pm0.68)\times10^{-4}$. Both of them are consistent with the world average values. The quoted uncertainties include both statistical and systematic uncertainties, which are mainly caused by the low statistics.

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arXiv2019

Measurement of the Dynamics of the Decays ${ D_s^+ \rightarrow η^{(\prime)} e^{+} ν_e}$

Using $e^+e^-$ annihilation data corresponding to an integrated luminosity of 3.19\,fb$^{-1}$ collected at a center-of-mass energy of 4.178~GeV with the BESIII detector, we measure the absolute branching fractions $\mathcal{B}_{D_s^+ \rightarrow ηe^{+} ν_e }$ = $(2.323\pm0.063_{\rm stat}\pm0.063_{\rm syst})\%$ and $\mathcal{B}_{D_s^+ \rightarrow η^{\prime} e^{+} ν_e}$ = $(0.824\pm0.073_{\rm stat}\pm0.027_{\rm syst})\%$ via a tagged analysis technique, where one $D_s$ is fully reconstructed in a hadronic mode. Combining these measurements with previous BESIII measurements of $\mathcal{B}_{D^+\toη^{(\prime)} e^{+} ν_e}$, the $η-η^\prime$ mixing angle in the quark flavour basis is determined to be $ϕ_{\rm P} = (40.1\pm2.1_{\rm stat}\pm0.7_{\rm syst})^\circ$. From the first measurements of the dynamics of $D^+_s\to η^{(\prime)}e^+ν_e$ decays, the products of the hadronic form factors $f_+^{η^{(\prime)}}(0)$ and the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cs}|$ are determined with different form factor parameterizations. For the two-parameter series expansion, the results are $f^η_+(0)|V_{cs}| = 0.4455\pm0.0053_{\rm stat}\pm0.0044_{\rm syst}$ and $f^{η^{\prime}}_+(0)|V_{cs}| = 0.477\pm0.049_{\rm stat}\pm0.011_{\rm syst}$.

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arXiv2019

Precision measurement of the branching fractions of $η^\prime$ decays

Based on a sample of $(1310.6 \pm 7.0) \times 10^6~J/ψ$ events collected with the BESIII detector, we present measurements of $J/ψ$ and $η^\prime$ absolute branching fractions using the process $J/ψ\rightarrowγη^\prime$. By analyzing events where the radiative photon converts into an $e^+e^-$ pair, the branching fraction for $J/ψ\rightarrow γη^\prime$ is measured to be $(5.27\pm0.03\pm0.05)\times 10^{-3}$. The absolute branching fractions of the five dominant decay channels of the $η^\prime$ are then measured independently for the first time and are determined to be $\mathcal{B}(η^\prime \rightarrow γπ^{+} π^{-})$ = (29.90$\pm$0.03$\pm$0.55)%, $\mathcal{B}(η^\prime \rightarrow ηπ^{+} π^{-})$ = (41.24$\pm$0.08$\pm$1.24)%, $\mathcal{B}(η^\prime \rightarrow ηπ^{0} π^{0})$ = (21.36$\pm$0.10$\pm$0.92)%, $\mathcal{B}(η^\prime \rightarrow γω)$ = (2.489$\pm$0.018$\pm$0.074)%, and $\mathcal{B}(η^\prime \rightarrow γγ)$ = (2.331$\pm$0.012$\pm$0.035)%, where the first uncertainties are statistical and the second systematic.

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arXiv2019

Observation of $D^+ \to f_0(500) e^+ν_e$ and Improved Measurements of $D \toρe^+ν_e$

Using a data sample corresponding to an integrated luminosity of 2.93~fb$^{-1}$ recorded by the BESIII detector at a center-of-mass energy of $3.773$ GeV, we present an analysis of the decays $\bar{D}^0\toπ^+π^0 e^-\barν_e$ and $D^+\toπ^-π^+ e^+ν_e$. By performing a partial wave analysis, the $π^+π^-$ $S$-wave contribution to $D^+\toπ^-π^+ e^+ν_e$ is observed to be $(25.7\pm1.6\pm1.1)$% with a statistical significance greater than 10$σ$, besides the dominant $P$-wave contribution. This is the first observation of the $S$-wave contribution. We measure the branching fractions $\mathcal{B}(D^{0} \to ρ^- e^+ ν_e) = (1.445\pm 0.058 \pm 0.039) \times10^{-3}$, $\mathcal{B}(D^{+} \to ρ^0 e^+ ν_e) = (1.860\pm 0.070 \pm 0.061) \times10^{-3}$, and $\mathcal{B}(D^{+} \to f_0(500) e^+ ν_e, f_0(500)\toπ^+π^-) = (6.30\pm 0.43 \pm 0.32) \times10^{-4}$. An upper limit of $\mathcal{B}(D^{+} \to f_0(980) e^+ ν_e, f_0(980)\toπ^+π^-) < 2.8 \times10^{-5}$ is set at the 90% confidence level. We also obtain the hadronic form factor ratios of $D\to ρe^+ν_e$ at $q^{2}=0$ assuming the single-pole dominance parameterization: $r_{V}=\frac{V(0)}{A_{1}(0)}=1.695\pm0.083\pm0.051$, $r_{2}=\frac{A_{2}(0)}{A_{1}(0)}=0.845\pm0.056\pm0.039$.

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arXiv2019

Observation of OZI suppressed decays $χ_{cJ}\toωϕ$

Decays $χ_{cJ}~(J=0,1,2)\toωϕ$ are studied using $(448.1\pm2.9)\times 10^{6} ~ψ(3686)$ events collected with the BESIII detector in 2009 and 2012. In addition to the previously established $χ_{c0}\toωϕ$, first observation of $χ_{c1} \to ωϕ$ is reported in this paper. The measured product branching fractions are ${\cal{B}}(ψ(3686)\toγχ_{c0})\times{\cal{B}}(χ_{c0}\toωϕ)=(13.83\pm 0.70\pm 1.01)\times10^{-6}$ and ${\cal{B}}(ψ(3686)\toγχ_{c1})\times{\cal{B}}(χ_{c1}\toωϕ)=(2.67\pm 0.31\pm 0.27)\times10^{-6}$, and the absolute branching fractions are ${\cal{B}}(χ_{c0}\toωϕ)=(13.84\pm 0.70\pm 1.08)\times10^{-5}$ and ${\cal{B}}(χ_{c1}\toωϕ)=(2.80\pm 0.32\pm 0.30)\times10^{-5}$. We also find a strong evidence for $χ_{c2}\toωϕ$ with a statistical significance of 4.8$σ$, and the corresponding product and absolute branching fractions are measured to be ${\cal{B}}(ψ(3686)\toγχ_{c2})\times{\cal{B}}(χ_{c2}\toωϕ)=(0.91\pm0.23\pm0.12)\times10^{-6} $ and ${\cal{B}}(χ_{c2}\toωϕ)=(1.00\pm0.25\pm0.14)\times10^{-5}$. Here, the first errors are statistical and the second ones systematic.

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arXiv2019

Measurement of $e^{+}e^{-}\rightarrow π^{+}π^{-}ψ(3686)$ from 4.008 to 4.600$\sim$GeV and observation of a charged structure in the $π^{\pm}ψ(3686)$ mass spectrum

We study the process $e^{+}e^{-} \rightarrow π^{+}π^{-}ψ(3686)$ using 5.1 $fb^{-1}$ of data collected at 16 center-of-mass energy ($\sqrt{s}$) points from 4.008 to 4.600$\sim$GeV by the BESIII detector operating at the BEPCII collider. The measured Born cross sections for $e^{+}e^{-}\rightarrow π^{+}π^{-}ψ(3686)$ are consistent with previous results, but with much improved precision. A fit to the cross section shows contributions from two structures: the first has $M=4209.5\pm7.4\pm1.4$$\sim$MeV/$c^{2}$ and $Γ=80.1\pm24.6\pm2.9$$\sim$MeV, and the second has $M=4383.8\pm4.2\pm0.8$$\sim$MeV/c$^{2}$ and $Γ=84.2\pm12.5\pm2.1$$\sim$MeV, where the first errors are statistical and the second systematic. The lower-mass resonance is observed in the process $e^{+}e^{-}\rightarrow π^{+}π^{-}ψ(3686)$ for the first time with a statistical significance of $5.8σ$. A charged charmonium-like structure is observed in the $π^{\pm}ψ(3686)$ invariant mass spectrum for data at $\sqrt{s} = 4.416~$GeV. A fit with an $S$-wave Breit-Wigner function yields a mass $M=4032.1\pm2.4$~$MeV$^{2}$, where the errors are statistical only. However, there are still unresolved discrepancies between the fit model and data. The width of the intermediate state varies in a wide range for different kinematic regions within the data set. Therefore no simple interpretation of the data has been found, and a future data sample with larger statistics and more theoretical input will be required to better understand this issue.

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arXiv2019

Study of the decay $D^0\rightarrow \bar{K}^0π^-e^+ν_e$

We report a study of the decay $D^0 \rightarrow \bar{K}^0π^-e^+ν_{e}$ based on a sample of $2.93~\mathrm{fb}^{-1}$ $e^+e^-$ annihilation data collected at the center-of-mass energy of 3.773~GeV with the BESIII detector at the BEPCII collider. The total branching fraction is determined to be $\mathcal{B}(D^0\rightarrow \bar{K}^0π^-e^+ν_{e})=(1.434\pm0.029({\rm stat.})\pm0.032({\rm syst.}))\%$, which is the most precise to date. According to a detailed analysis of the involved dynamics, we find this decay is dominated with the $K^{*}(892)^-$ contribution and present an improved measurement of its branching fraction to be $\mathcal{B}(D^0\rightarrow K^{*}(892)^-e^+ν_e)=(2.033\pm0.046({\rm stat.})\pm0.047({\rm syst.}))\%$. We further access their hadronic form-factor ratios for the first time as $r_{V}=V(0)/A_1(0)=1.46\pm0.07({\rm stat.})\pm0.02({\rm syst.})$ and $r_{2}=A_2(0)/A_1(0)=0.67\pm0.06({\rm stat.})\pm0.01({\rm syst.})$. In addition, we observe a significant $\bar{K}^0π^-$ $S$-wave component accounting for $(5.51\pm0.97({\rm stat.})\pm0.62({\rm syst.}))\%$ of the total decay rate.

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arXiv2019

First measurement of the form factors in $D^+_{s}\rightarrow K^0 e^+ν_e$ and $D^+_{s}\rightarrow K^{*0} e^+ν_e$ decays

We report on new measurements of Cabibbo-suppressed semileptonic $D_s^+$ decays using $3.19~\mathrm{fb}^{-1}$ of $e^+e^-$ annihilation data sample collected at a center-of-mass energy of 4.178~GeV with the BESIII detector at the BEPCII collider. Our results include branching fractions $\mathcal B({D^+_s\rightarrow K^0 e^+ν_{e}})=(3.25\pm0.38({\rm stat.})\pm0.16({\rm syst.}))\times10^{-3}$ and $\mathcal B({D^+_s\rightarrow K^{*0} e^+ν_{e}})=(2.37\pm0.26({\rm stat.})\pm0.20({\rm syst.}))\times10^{-3}$ which are much improved relative to previous measurements, and the first measurements of the hadronic form-factor parameters for these decays. For $D^+_s\rightarrow K^0 e^+ν_{e}$, we obtain $f_+(0)=0.720\pm0.084({\rm stat.})\pm0.013({\rm syst.})$, and for $D^+_s\rightarrow K^{*0} e^+ν_{e}$, we find form-factor ratios $r_V=V(0)/A_1(0)=1.67\pm0.34({\rm stat.})\pm0.16({\rm syst.})$ and $r_2=A_2(0)/A_1(0)=0.77\pm0.28({\rm stat.})\pm0.07({\rm syst.})$.

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arXiv2019

Search for rare decay $J/ ψ\to ϕe^+ e^-$

Using a data sample of $448.1\times10^6$ $ψ(3686)$ events collected at $\sqrt{s}=$ 3.686 GeV with the BESIII detector at the BEPCII, we search for the rare decay $J/ψ\to ϕe^+ e^-$ via $ψ(3686) \to π^+π^- J/ψ$. No signal events are observed and the upper limit on the branching fraction is set to be $\mathcal{B}(J/ψ\to ϕe^+ e^-) < 1.2 \times 10^{-7}$ at the 90\% confidence level, which is still about one order of magnitude higher than the Standard Model prediction.

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arXiv2019

Measurement of $\mathcal{B}(J/ψ\to η' e^+ e^- $) and search for a dark photon

Using a data sample of $(1310.6\pm7.0)\times10^{6}$ $J/ψ$ decay events collected with the BESIII detector at BEPCII, we study the electromagnetic Dalitz decay $J/ψ\to η' e^+e^-$ with two dominant $η'$ decay modes, $η' \to γπ^+ π^-$ and $η' \to π^+π^-η$. The branching fraction is determined to be $\mathcal{B}(J/ψ\to η' e^+e^-) = (6.59\pm0.07\pm0.17) \times 10^{-5}$, which improves in precision by a factor of 2 over the previous BESIII measurement. A search for the dark photon ($γ'$) is performed via $J/ψ\toη' γ', γ' \to e^{+}e^{-}$. Excluding the $ω$ and $ϕ$ mass regions, no significant signal is observed in the mass range from 0.1 to 2.1 GeV/$c^{2}$. We set upper limits at the 90\% confidence level on $\mathcal{B}(J/ψ\to η' γ')\times\mathcal{B}(γ' \to e^+e^-)$, $\mathcal{B}(J/ψ\toη' γ'$) and the mixing strength as a function of dark photon mass. This is among the first searches for dark photons in charmonium decays.

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arXiv2019

Observation of $χ_{cJ}\to4K_{S}^{0}$

By analyzing $(448.1\pm2.9)\times10^6$ $ψ(3686)$ events collected with the BESIII detector operating at the BEPCII collider, the decays of $χ_{cJ} \to 4K_S^0$ ($J=0,1,2$) are observed for the first time with statistical significances of 26.5$σ$, 5.9$σ$ and 11.4$σ$, respectively. The product branching fractions of $ψ(3686)\toγχ_{cJ}$, $χ_{cJ}\to4K_{S}^{0}$ are presented and the branching fractions of $χ_{cJ}\to4K_{S}^{0}$ decays are determined to be $\mathcal{B}_{χ_{c0}\to 4K_S^0}$=$(5.76\pm0.34\pm0.38)$$\times10^{-4}$, $\mathcal{B}_{χ_{c1}\to 4K_S^0}$=$(0.35\pm0.09\pm0.03)$$\times10^{-4}$ and $\mathcal{B}_{χ_{c2}\to 4K_S^0}$=$(1.14\pm0.15\pm0.08)$$\times10^{-4}$, where the first uncertainties are statistical and the second are systematic, respectively.

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arXiv2019

Search for a strangeonium-like structure $Z_s$ decaying into $ϕπ$ and a measurement of the cross section $e^+e^-\rightarrowϕππ$

Using a data sample of $e^+e^-$ collision data corresponding to an integrated luminosity of 108 pb$^{-1}$ collected with the BESIII detector at a center-of-mass energy of 2.125 GeV, we study the process $e^+e^-\rightarrow ϕππ$ and search for a strangeoniumlike structure $Z_s$ decaying into $ϕπ$. No signal is observed in the $ϕπ$ mass spectrum. Upper limits on the cross sections for $Z_s$ production at the 90\% confidence level are determined. In addition, the cross sections of $e^+e^-\rightarrowϕπ^{+}π^{-}$ and $e^+e^-\rightarrowϕπ^{0}π^{0}$ at 2.125 GeV are measured to be $(436.2\pm6.4\pm30.1)$ pb and $(237.0\pm8.6\pm15.4)$ pb, respectively, where the first uncertainties are statistical and the second systematic.

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arXiv2019

Amplitude analysis of $D^{+} \rightarrow K_{S}^{0} π^{+} π^{+} π^{-}$

The decay $D^{+} \rightarrow K_{S}^{0} π^{+} π^{+} π^{-}$ is studied with an amplitude analysis using a data set of 2.93${\mbox{\,fb}^{-1}}$ of $e^+e^+$ collisions at the $ψ(3770)$ peak accumulated by the BESIII detector. Intermediate states and non-resonant components, and their relative fractions and phases have been determined. The significant amplitudes, which contribute to the model that best fits the data, are composed of five quasi-two-body decays $ K_{S}^{0} a_{1}(1260)^{+}$, $ \bar{K}_{1}(1270)^{0} π^{+}$ $ \bar{K}_{1}(1400)^{0} π^{+}$, $ \bar{K}_{1}(1650)^{0} π^{+}$, and $ \bar{K}(1460)^{0} π^{+}$, a three-body decays $K_{S}^{0}π^{+}ρ^{0}$, as well as a non-resonant component $ K_{S}^{0}π^{+}π^{+}π^{-}$. The dominant amplitude is $ K_{S}^{0} a_{1}(1260)^{+}$, with a fit fraction of $(40.3\pm2.1\pm2.9)\%$, where the first and second uncertainties are statistical and systematic, respectively.

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arXiv2019

Observation of $D^+_s\rightarrow p\bar{n}$ and confirmation of its large branching fraction

The baryonic decay $D^+_s\rightarrow p\bar{n}$ is observed, and the corresponding branching fraction is measured to be $(1.21\pm0.10\pm0.05)\times10^{-3}$, where the first uncertainty is statistical and second systematic. The data sample used in this analysis was collected with the BESIII detector operating at the BEPCII $e^+e^-$ double-ring collider with a center-of-mass energy of 4.178~GeV and an integrated luminosity of 3.19~fb$^{-1}$. The result confirms the previous measurement by the CLEO Collaboration and is of greatly improved precision, which may deepen our understanding of the dynamical enhancement of the W-annihilation topology in the charmed meson decays.

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arXiv2019

Study of the $D^0\to K^-μ^+ν_μ$ dynamics and test of lepton flavor universality with $D^0\to K^-\ell^+ν_\ell$ decays

Using $e^+e^-$ annihilation data of $2.93~\mathrm{fb}^{-1}$ collected at center-of-mass energy $\sqrt{s}=3.773$ GeV with the BESIII detector, we measure the absolute branching fraction of $D^{0}\to K^{-}μ^{+}ν_μ$ with significantly improved precision: ${\mathcal B}_{D^{0}\to K^{-}μ^{+}ν_μ}=(3.413\pm0.019_{\rm stat.}\pm0.035_{\rm syst.})\%$. Combining with our previous measurement of ${\mathcal B}_{D^0\to K^-e^+ν_e}$, the ratio of the two branching fractions is determined to be ${\mathcal B}_{D^0\to K^-μ^+ν_μ}/{\mathcal B}_{D^0\to K^-e^+ν_e}=0.974\pm0.007_{\rm stat.}\pm0.012_{\rm syst.}$, which agrees with the theoretical expectation of lepton flavor universality within the uncertainty. A study of the ratio of the two branching fractions in different four-momentum transfer regions is also performed, and no evidence for lepton flavor universality violation is found with current statistics. Taking inputs from global fit in the standard model and lattice quantum chromodynamics separately, we determine $f_{+}^{K}(0)=0.7327\pm0.0039_{\rm stat.}\pm0.0030_{\rm syst.}$ and $|V_{cs}| = 0.955\pm0.005_{\rm stat.}\pm0.004_{\rm syst.}\pm0.024_{\rm LQCD}$.

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