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X. Dong

Publications and source records attributed to X. Dong.

At least 469 records · Page 26Linked to original sources
arXiv2023

First simultaneous measurement of $Ξ^0$ and $\barΞ^0$ asymmetry parameters in $ψ(3686)$ decay

The $Ξ^0$ asymmetry parameters are measured using entangled quantum $Ξ^0$-$\barΞ^0$ pairs from a sample of $(448.1 \pm 2.9) \times 10^6$ $ψ(3686)$ events collected with the BESIII detector at BEPCII. The relative phase between the transition amplitudes of the $Ξ^0 \barΞ^0$ helicity states is measured to be $ΔΦ= -0.050 \pm 0.150 \pm 0.020$~rad, which implies that there is no obvious polarization at the current level of statistics. The decay parameters of the $Ξ^0$ hyperon $(α_{Ξ^0}, α_{\barΞ^0}, ϕ_{Ξ^0}, ϕ_{\barΞ^0})$ and the angular distribution parameter $(α_{ψ(3686)})$ and $ΔΦ$ are measured simultaneously for the first time. In addition, the $CP$ asymmetry observables are determined to be $A^{Ξ^0}_{CP} = (α_{Ξ^0} + α_{\barΞ^0})/(α_{Ξ^0} - α_{\barΞ^0})$ $= -0.007$ $\pm$ 0.082 $\pm$ 0.025 and $Δϕ^{Ξ^0}_{CP} = (ϕ_{Ξ^0} + ϕ_{\barΞ^0})/2$ $= -0.079$ $\pm$ 0.082 $\pm$ 0.010 rad, which are consistent with $CP$ conservation.

hep-ex↗
arXiv2023

Measurement of $e^+e^-\to pK^-\barΛ+c.c.$ cross sections between 4.009 GeV and 4.951 GeV

Using $e^+e^-$ collision datasets corresponding to total integrated luminosity of 21.7 fb$^{-1}$ collected with the BESIII detector at the BEPCII collider at center-of-mass energies ranging from 4.009 GeV to 4.951 GeV, the energy-dependent cross sections of $e^+e^-\to pK^-\barΛ+c.c.$ are measured for the first time. By fitting these energy-dependent cross sections, we search for the excited $ψ$ states $ψ(4160)$ and $ψ(4415)$, and the vector charmonium-like states $ψ(4230)$, $ψ(4360)$, and $ψ(4660)$. No evidence for these is observed and the upper limits on the branching fractions of these states decaying into $pK^-\bar Λ+c.c.$ are set at the 90\% confidence level.

hep-ex↗
arXiv2023

Search for the semi-leptonic decays $Λ_c^+ \to Λπ^+ π^- e^+ ν_e$ and $Λ_c^+ \to p K_S^0 π^- e^+ ν_e$

We search for the semi-leptonic decays $Λ_c^+ \to Λπ^+ π^- e^+ ν_e$ and $Λ_c^+ \to p K_S^0 π^- e^+ ν_e$ in a sample of 4.5 $\mathrm{fb}^{-1}$ of $e^{+}e^{-}$ annihilation data collected in the center-of-mass energy region between 4.600 GeV and 4.699 GeV by the BESIII detector at the BEPCII. No significant signals are observed, and the upper limits on the decay branching fractions are set to be $\mathcal{B}(Λ_c^+ \to Λπ^+ π^- e^+ ν_e)<3.9\times10^{-4}$ and $\mathcal{B}(Λ_c^+ \to p K_S^0 π^- e^+ ν_e)<3.3\times10^{-4}$ at the 90% confidence level, respectively.

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arXiv2023

Measurement of electrons from open heavy-flavor hadron decays in Au+Au collisions at $\sqrt{s_{\rm NN}}=200$ GeV with the STAR detector

We report a new measurement of the production of electrons from open heavy-flavor hadron decays (HFEs) at mid-rapidity ($|y|<$ 0.7) in Au+Au collisions at $\sqrt{s_{\rm NN}}=200$ GeV. Invariant yields of HFEs are measured for the transverse momentum range of $3.5 < p_{\rm T} < 9$ GeV/$c$ in various configurations of the collision geometry. The HFE yields in head-on Au+Au collisions are suppressed by approximately a factor of 2 compared to that in $p$+$p$ collisions scaled by the average number of binary collisions, indicating strong interactions between heavy quarks and the hot and dense medium created in heavy-ion collisions. Comparison of these results with models provides additional tests of theoretical calculations of heavy quark energy loss in the quark-gluon plasma.

nucl-ex↗
arXiv2023

Observation of Directed Flow of Hypernuclei $^3_Λ$H and $^4_Λ$H in $\sqrt{s_{\rm NN}}$ = 3 GeV Au+Au Collisions at RHIC

We report here the first observation of directed flow ($v_1$) of the hypernuclei $^3_Λ$H and $^4_Λ$H in mid-central Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 3 GeV at RHIC. These data are taken as part of the beam energy scan program carried out by the STAR experiment. From 165 $\times$ 10$^{6}$ events in 5%-40% centrality, about 8400 $^3_Λ$H and 5200 $^4_Λ$H candidates are reconstructed through two- and three-body decay channels. We observe that these hypernuclei exhibit significant directed flow. Comparing to that of light nuclei, it is found that the midrapidity $v_1$ slopes of $^3_Λ$H and $^4_Λ$H follow baryon number scaling, implying that the coalescence is the dominant mechanism for these hypernuclei production in such collisions.

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arXiv2023

Measurements of Differential Cross Sections of Inclusive $π^0$ and $K^0_S$ Production in $e^{+}e^{-}$ Annihilation at Energies from 2.2324 to 3.6710 GeV

Based on electron positron collision data collected with the BESIII detector operating at the BEPCII storage rings, the differential cross sections of inclusive $π^0$ and $K^0_S$ production as a function of hadron momentum, normalized by the total cross section of the $e^{+}e^{-} \to$ hadrons process, are measured at six center-of-mass energies from 2.2324 to 3.6710 GeV. Our results with a relative hadron energy coverage from 0.1 to 0.9 significantly deviate from several theoretical calculations based on existing fragmentation functions, especially at lower energies.

hep-ex↗
arXiv2023

Measurements of the elliptic and triangular azimuthal anisotropies in central $^{3}$He+Au, $d$+Au and $p$+Au collisions at $\mbox{$\sqrt{s_{\mathrm{NN}}}$}$ = 200 GeV

The elliptic ($v_2$) and triangular ($v_3$) azimuthal anisotropy coefficients in central $^{3}$He+Au, $d$+Au, and $p$+Au collisions at $\mbox{$\sqrt{s_{\mathrm{NN}}}$}$ = 200 GeV are measured as a function of transverse momentum ($p_{\mathrm{T}}$) at mid-rapidity ($|η|<$0.9), via the azimuthal angular correlation between two particles both at $|η|<$0.9. While the $v_2(p_{\mathrm{T}})$ values depend on the colliding systems, the $v_3(p_{\mathrm{T}})$ values are system-independent within the uncertainties, suggesting an influence on eccentricity from sub-nucleonic fluctuations in these small-sized systems. These results also provide stringent constraints for the hydrodynamic modeling of these systems.

nucl-ex↗
arXiv2023

Study of $Λ_c^+\rightarrow Λμ^+ν_μ$ and Test of Lepton Flavor Universality with $Λ_c^+\rightarrow Λ\ell^+ν_{\ell}$ Decays

The measurement of the Cabibbo-favored semileptonic decay $Λ_c^+\rightarrow Λμ^+ν_μ$ is reported using $4.5~\mathrm{fb}^{-1}$ of $e^+e^-$ annihilation data collected at center-of-mass energies ranging from 4.600~GeV to 4.699~GeV. The branching fraction of the decay is measured to be $\mathcal{B}(Λ_c^+\rightarrow Λμ^+ν_μ)=(3.48\pm0.14_{\rm stat.}\pm0.10_{\rm syst.})\%$, three times more precise than the prior world average result. Tests of lepton flavor universality using $Λ_c^+\rightarrow Λ\ell^+ν_{\ell}$ ($\ell=e, μ$) decays are reported for the first time, based on measurements of the differential decay rates and the forward-backward asymmetries in separate four-momentum transfer regions. The results are compatible with Standard Model predictions. Furthermore, we improve the determination of the form-factor parameters in $Λ_c^+\rightarrow Λ\ell^+ν_{\ell}$ decays, which provide stringent tests and calibration for lattice quantum chromodynamics (LQCD) calculations.

hep-ex↗
arXiv2023

First study of reaction $Ξ^{0}n\rightarrowΞ^{-}p$ using $Ξ^0$-nucleus scattering at an electron-positron collider

Using $(1.0087\pm0.0044)\times10^{10}$ $J/ψ$ events collected with the BESIII detector at the BEPCII storage ring, the process $Ξ^{0}n\rightarrowΞ^{-}p$ is studied, where the $Ξ^0$ baryon is produced in the process $J/ψ\rightarrowΞ^0\barΞ^0$ and the neutron is a component of the $^9\rm{Be}$, $^{12}\rm{C}$ and $^{197}\rm{Au}$ nuclei in the beam pipe. A clear signal is observed with a statistical significance of $7.1σ$. The cross section of the reaction $Ξ^0+{^9\rm{Be}}\rightarrowΞ^-+p+{^8\rm{Be}}$ is determined to be $σ(Ξ^0+{^9\rm{Be}}\rightarrowΞ^-+p+{^8\rm{Be}})=(22.1\pm5.3_{\rm{stat}}\pm4.5_{\rm{sys}})$ mb at the $Ξ^0$ momentum of $0.818$ GeV/$c$, where the first uncertainty is statistical and the second is systematic. No significant $H$-dibaryon signal is observed in the $Ξ^-p$ final state. This is the first study of hyperon-nucleon interactions in electron-positron collisions and opens up a new direction for such research.

hep-ex↗
arXiv2023

Determination of spin and parity of $D^{*}_{(s)}$ mesons

The spin and parity of the charmed mesons $D_{s}^{*+}$, $D^{*0}$ and $D^{*+}$ are determined for the first time to be $J^P=1^{-}$ with significances greater than 10$σ$ over other hypotheses of $2^{+}$ and $3^{-}$, using an $e^+e^-$ collision data sample with an integrated luminosity of 3.19 fb$^{-1}$ collected by the BESIII detector at a center-of-mass energy of 4.178 GeV. Different spin-parity hypotheses for $D_{s}^{*+}$, $D^{*0}$, and $D^{*+}$ mesons are tested via a helicity amplitude analysis of the processes $e^+e^-\to D^{*+}_{s}D^{-}_{s}$, $D^{*0}D^{0}$ and $D^{*+}D^{-}$, with $D^{*+}_{s}\to D^{+}_{s} γ$, $D^{*0}\to D^{0}π^{0}$, and $D^{*+}\to D^{+}π^{0}$. The results confirm the quark model predictions.

hep-ex↗
arXiv2023

Precision Measurement of the Decay $Σ^{+} \rightarrow pγ$ in the Process $J/ψ\rightarrow Σ^{+}\barΣ^{-}$

Using $(10\:087\pm44)\times10^{6}$ $J/ψ$ events collected with the BESIII detector, the radiative hyperon decay $Σ\rightarrow pγ$ is studied at an electron-positron collider experiment for the first time. The absolute branching fraction is measured to be $\left(0.996 \pm 0.021_{\rm stat.}\pm 0.018_{\rm syst.}\right)\times 10^{-3}$, which is lower than its world average value by $4.2$ standard deviations. Its decay asymmetry parameter is determined to be $-0.652 \pm 0.056_{\rm stat.}\pm 0.020_{\rm syst.}$. The branching fraction and decay asymmetry parameter are the most precise to date, and the accuracies are improved by $78\%$ and $34\%$, respectively.

hep-ex↗
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.

hep-ex↗
arXiv2023

Beam Energy Dependence of Triton Production and Yield Ratio ($\mathrm{N}_t \times \mathrm{N}_p/\mathrm{N}_d^2$) in Au+Au Collisions at RHIC

We report the triton ($t$) production in mid-rapidity ($|y| <$ 0.5) Au+Au collisions at $\sqrt{s_\mathrm{NN}}$= 7.7--200 GeV measured by the STAR experiment from the first phase of the beam energy scan at the Relativistic Heavy Ion Collider (RHIC). The nuclear compound yield ratio ($\mathrm{N}_t \times \mathrm{N}_p/\mathrm{N}_d^2$), which is predicted to be sensitive to the fluctuation of local neutron density, is observed to decrease monotonically with increasing charged-particle multiplicity ($dN_{ch}/dη$) and follows a scaling behavior. The $dN_{ch}/dη$ dependence of the yield ratio is compared to calculations from coalescence and thermal models. Enhancements in the yield ratios relative to the coalescence baseline are observed in the 0\%-10\% most central collisions at 19.6 and 27 GeV, with a significance of 2.3$σ$ and 3.4$σ$, respectively, giving a combined significance of 4.1$σ$. The enhancements are not observed in peripheral collisions or model calculations without critical fluctuation, and decreases with a smaller $p_{T}$ acceptance. The physics implications of these results on the QCD phase structure and the production mechanism of light nuclei in heavy-ion collisions are discussed.

nucl-ex↗
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.

hep-ex↗
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.

hep-ex↗
arXiv2023

Evidence of Mass Ordering of Charm and Bottom Quark Energy Loss in Au+Au Collisions at RHIC

Partons traversing the strongly interacting medium produced in heavy-ion collisions are expected to lose energy depending on their color charge and mass. We measure the nuclear modification factors for charm- and bottom-decay electrons, defined as the ratio of yields, scaled by the number of binary nucleon-nucleon collisions, in $\sqrt{s_{\rm NN}}$ = 200 GeV Au+Au collisions to $p$+$p$ collisions ($R_{\rm AA}$), or in central to peripheral Au+Au collisions ($R_{\rm CP}$). We find the bottom-decay electron $R_{\rm AA}$ and $R_{\rm CP}$ to be significantly higher than that of charm-decay electrons. Model calculations including mass-dependent parton energy loss in a strongly coupled medium are consistent with the measured data. These observations provide clear evidence of mass ordering of charm and bottom quark energy loss when traversing through the strongly coupled medium created in heavy-ion collisions.

nucl-ex↗
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.

hep-ex↗
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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