arXiv subjects

X. Dong

Publications and source records attributed to X. Dong.

At least 649 records · Page 36Linked to original sources

arXiv2021

Observation of $D_{s}^{\pm}/D^0$ enhancement in Au+Au collisions at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV

We report on the first measurement of charm-strange meson $D_s^{\pm}$ production at midrapidity in Au+Au collisions at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV from the STAR experiment. The yield ratio between strange ($D_{s}^{\pm}$) and non-strange ($D^{0}$) open-charm mesons is presented and compared to model calculations. A significant enhancement, relative to a PYTHIA simulation of $p$+$p$ collisions, is observed in the $D_{s}^{\pm}/D^0$ yield ratio in Au+Au collisions over a large range of collision centralities. Model calculations incorporating abundant strange-quark production in the quark-gluon plasma (QGP) and coalescence hadronization qualitatively reproduce the data. The transverse-momentum integrated yield ratio of $D_{s}^{\pm}/D^0$ at midrapidity is consistent with a prediction from a statistical hadronization model with the parameters constrained by the yields of light and strange hadrons measured at the same collision energy. These results suggest that the coalescence of charm quarks with strange quarks in the QGP plays an important role in $D_{s}^{\pm}$ meson production in heavy-ion collisions.

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arXiv2021

Study of the decay $D^+\to K^*(892)^+ K_S^0$ in $D^+\to K^+ K_S^0 π^0$

Based on an $e^{+}e^{-}$ collision data sample corresponding to an integrated luminosity of 2.93 $\mathrm{fb}^{-1}$ collected with the BESIII detector at $\sqrt{s}=3.773 \mathrm{GeV}$, the first amplitude analysis of the singly Cabibbo-suppressed decay $D^{+}\to K^+ K_S^0 π^0$ is performed. From the amplitude analysis, the $K^*(892)^+ K_S^0$ component is found to be dominant with a fraction of $(57.1\pm2.6\pm4.2)\%$, where the first uncertainty is statistical and the second systematic. In combination with the absolute branching fraction $\mathcal{B}(D^+\to K^+ K_S^0 π^0)$ measured by BESIII, we obtain $\mathcal{B}(D^+\to K^*(892)^+ K_S^0)=(8.69\pm0.40\pm0.64\pm0.51)\times10^{-3}$, where the third uncertainty is due to the branching fraction $\mathcal{B}(D^+\to K^+ K_S^0 π^0)$. The precision of this result is significantly improved compared to the previous measurement.

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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

Azimuthal anisotropy measurements of strange and multistrange hadrons in U+U collisions at $\sqrt{s_{NN}} = 193$ GeV at the BNL Relativistic Heavy Ion Collider

We present systematic measurements of azimuthal anisotropy for strange and multistrange hadrons ($K^{0}_{s}$, $Λ$, $Ξ$, and $Ω$) and $ϕ$ mesons at midrapidity ($|y| <$ 1.0) in collisions of U + U nuclei at $\sqrt{s_{NN}} = 193$ GeV, recorded by the STAR detector at the Relativistic Heavy Ion Collider. Transverse momentum ($p_{\text{T}}$) dependence of flow coefficients ($v_{2}$, $v_{3}$, and $v_{4}$) is presented for minimum bias collisions and three different centrality intervals. Number of constituent quark scaling of the measured flow coefficients in U + U collisions is discussed. We also present the ratio of $v_{n}$ scaled by the participant eccentricity ($\varepsilon_{n}\left\lbrace 2 \right\rbrace$) to explore system size dependence and collectivity in U + U collisions. The magnitude of $v_{2}/\varepsilon_{2}$ is found to be smaller in U + U collisions than that in central Au + Au collisions contradicting naive eccentricity scaling. Furthermore, the ratios between various flow harmonics ($v_{3}/v_{2}^{3/2}$, $v_{4}/v_{2}^{4/2}$) are studied and compared with hydrodynamic and transport model calculations.

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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

Longitudinal double-spin asymmetry for inclusive jet and dijet production in polarized proton collisions at $\sqrt{s}=200$ GeV

We report high-precision measurements of the longitudinal double-spin asymmetry, $A_{LL}$, for midrapidity inclusive jet and dijet production in polarized $pp$ collisions at a center-of-mass energy of $\sqrt{s}=200\,\mathrm{GeV}$. The new inclusive jet data are sensitive to the gluon helicity distribution, $Δg(x,Q^2)$, for gluon momentum fractions in the range from $x \simeq 0.05$ to $x \simeq 0.5$, while the new dijet data provide further constraints on the $x$ dependence of $Δg(x,Q^2)$. The results are in good agreement with previous measurements at $\sqrt{s}=200\,\mathrm{GeV}$ and with recent theoretical evaluations of prior world data. Our new results have better precision and thus strengthen the evidence that $Δg(x,Q^2)$ is positive for $x > 0.05$.

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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

Measurement of transverse single-spin asymmetries of $π^0$ and electromagnetic jets at forward rapidity in 200 and 500 GeV transversely polarized proton-proton collisions

The STAR Collaboration reports measurements of the transverse single-spin asymmetry (TSSA) of inclusive $π^0$ at center-of-mass energies ($\sqrt s$) of 200 GeV and 500 GeV in transversely polarized proton-proton collisions in the pseudo-rapidity region 2.7 to 4.0. The results at the two different energies show a continuous increase of the TSSA with Feynman-$x$, and, when compared to previous measurements, no dependence on $\sqrt s$ from 19.4 GeV to 500 GeV is found. To investigate the underlying physics leading to this large TSSA, different topologies have been studied. $π^0$ with no nearby particles tend to have a higher TSSA than inclusive $π^0$. The TSSA for inclusive electromagnetic jets, sensitive to the Sivers effect in the initial state, is substantially smaller, but shows the same behavior as the inclusive $π^0$ asymmetry as a function of Feynman-$x$. To investigate final-state effects, the Collins asymmetry of $π^0$ inside electromagnetic jets has been measured. The Collins asymmetry is analyzed for its dependence on the $π^0$ momentum transverse to the jet thrust axis and its dependence on the fraction of jet energy carried by the $π^0$. The asymmetry was found to be small in each case for both center-of-mass energies. All the measurements are compared to QCD-based theoretical calculations for transverse-momentum-dependent parton distribution functions and fragmentation functions. Some discrepancies are found, which indicates new mechanisms might be involved.

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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

Global polarization of $Ξ$ and $Ω$ hyperons in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV

Global polarization of $Ξ$ and $Ω$ hyperons has been measured for the first time in Au+Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV. The measurements of the $Ξ^-$ and $\barΞ^+$ hyperon polarization have been performed by two independent methods, via analysis of the angular distribution of the daughter particles in the parity violating weak decay $Ξ\rightarrowΛ+π$, as well as by measuring the polarization of the daughter $Λ$-hyperon, polarized via polarization transfer from its parent. The polarization, obtained by combining the results from the two methods and averaged over $Ξ^-$ and $\barΞ^+$, is measured to be $\langle P_Ξ\rangle = 0.47\pm0.10~({\rm stat.})\pm0.23~({\rm syst.})\,\%$ for the collision centrality 20\%-80\%. The $\langle P_Ξ\rangle$ is found to be slightly larger than the inclusive $Λ$ polarization and in reasonable agreement with a multi-phase transport model (AMPT). The $\langle P_Ξ\rangle$ is found to follow the centrality dependence of the vorticity predicted in the model, increasing toward more peripheral collisions. The global polarization of $Ω$, $\langle P_Ω\rangle = 1.11\pm0.87~({\rm stat.})\pm1.97~({\rm syst.})\,\%$ was obtained by measuring the polarization of daughter $Λ$ in the decay $Ω\rightarrow Λ+ K$, assuming the polarization transfer factor $C_{ΩΛ}=1$.

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