arXiv subjects

Y. Q. Chen

Publications and source records attributed to Y. Q. Chen.

At least 415 records · Page 23Linked to original sources

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

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

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 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

Measurement of the Branching Fraction for the Decay $ψ(3686) \rightarrow ϕK_{S}^{0} K_{S}^{0}$

Based on $(448.1 \pm 2.9 )\times 10^6$ $ψ(3686)$ events collected with the BESIII detector operating at the BEPCII collider, the decay $ψ(3686)\rightarrow ϕK_{S}^{0} K_{S}^{0}$ is observed for the first time. Taking the interference between $ψ(3686)$ decay and continuum production into account, the branching fraction of this decay is measured to be $\mathcal{B}(ψ(3686)\rightarrowϕK_S^0 K_S^0 )$ = $(3.53 $ $\pm$ $0.20$ $\pm$ $0.21$)$\times 10^{-5}$, where the first uncertainty is statistical and the second is systematic. Combining with the world average value for ${\mathcal B}(J/ψ\to ϕK^0_SK^0_S)$, the ratio $\mathcal{B}(ψ(3686)\rightarrow ϕK_{S}^{0} K_{S}^{0})/\mathcal{B}(J/ψ\rightarrow ϕK_{S}^{0} K_{S}^{0}) $ is determined to be $(6.0\pm 1.6)$%, which is suppressed relative to the 12% rule.

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arXiv2023

Measurement of the $e^{+}e^{-}\rightarrowΛ\barΛ$ cross section from threshold to 3.00 GeV using events with initial-state radiation

Using initial-state radiation events from a total integrated luminosity of 11.957 fb$^{-1}$ of $e^+e^-$ collision data collected at center-of-mass energies between 3.773 and 4.258 GeV with the BESIII detector at BEPCII, the cross section for the process $e^{+}e^{-}\rightarrowΛ\barΛ$ is measured in 16 $Λ\barΛ$ invariant mass intervals from the production threshold up to 3.00 GeV$/c^{2}$. The results are consistent with previous results from BaBar and BESIII, but with better precision and with narrower $Λ\barΛ$ invariant mass intervals than BaBar.

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arXiv2023

Determination of Spin-parity Quantum Numbers for the Narrow Structure Near the $p\barΛ$ Threshold in $e^+e^-\to pK^-\barΛ+c.c.$

A narrow structure in the $p\barΛ$ system near the mass threshold, named as $X(2085)$, is observed in the process $e^+e^- \to p K^-\barΛ$ with a statistical significance greater than $20σ$. Its spin and parity are determined for the first time to be $J^P=1^+$ in an amplitude analysis, with statistical significance greater than $5σ$ over other quantum numbers. The pole positions of $X(2085)$ are measured to be $M_{\rm pole}=(2086\pm4\pm6)$~MeV and $Γ_{\rm pole}=(56\pm5\pm16)$ MeV, where the first uncertainties are statistical and the second ones are systematic. The analysis is based on the study of the process $e^+e^-\to pK^-\barΛ$ and uses the data samples collected with the BESIII detector at the center-of-mass energies $\sqrt{s}=4.008$, $4.178$, $4.226$, $4.258$, $4.416$, and $4.682$ GeV with a total integrated luminosity of $8.35~\text{fb}^{-1}$.

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arXiv2023

Measurement of the $Ω_c^0$ lifetime at Belle II

We report on a measurement of the $Ω_c^0$ lifetime using $Ω_c^0 \to Ω^-π^+$ decays reconstructed in $e^+e^-\to c\bar{c}$ data collected by the Belle II experiment and corresponding to $207~{\rm fb^{-1}}$ of integrated luminosity. The result, $\rmτ(Ω_c^0)=243\pm48( stat)\pm11(syst)~fs$, agrees with recent measurements indicating that the $Ω_c^0$ is not the shortest-lived weakly decaying charmed baryon.

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arXiv2023

Observation of $e^+e^-\toωχ_{bJ}(1P)$ and search for $X_b \to ωΥ(1S)$ at $\sqrt{s}$ near 10.75 GeV

We study the processes $e^+e^-\toωχ_{bJ}(1P)$ ($J$ = 0, 1, or 2) using samples at center-of-mass energies $\sqrt{s}$ = 10.701, 10.745, and 10.805 GeV, corresponding to 1.6, 9.8, and 4.7 fb$^{-1}$ of integrated luminosity, respectively. These data were collected with the Belle II detector during special operations of the SuperKEKB collider above the $Υ(4S)$ resonance. We report the first observation of $ωχ_{bJ}(1P)$ signals at $\sqrt{s}$ = 10.745 GeV. By combining Belle II data with Belle results at $\sqrt{s}$ = 10.867 GeV, we find energy dependencies of the Born cross sections for $e^+e^-\to ωχ_{b1,b2}(1P)$ to be consistent with the shape of the $Υ(10753)$ state. These data indicate that the internal structures of the $Υ(10753)$ and $Υ(10860)$ states may differ. Including data at $\sqrt{s}$ = 10.653 GeV, we also search for the bottomonium equivalent of the $X(3872)$ state decaying into $ωΥ(1S)$. No significant signal is observed for masses between 10.45 and 10.65 GeV/$c^2$.

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arXiv2023

Measurement of the $B^{0} \rightarrow D^{*-} \ell^{+} ν_{\ell}$ branching ratio and $|V_{cb}|$ with a fully reconstructed accompanying $B$ meson in 2019-2021 Belle II data

We present a measurement of the $B^{0} \rightarrow D^{*-} \ell^{+} ν_{\ell}$ ($\ell=e,μ$) branching ratio and of the CKM parameter $|V_{cb}|$ using signal decays accompanied by a fully reconstructed $B$ meson. The Belle II data set of electron-positron collisions at the $Υ(4S)$ resonance, corresponding to 189.3$\,$fb$^{-1}$ of integrated luminosity, is analyzed. With the Caprini-Lellouch-Neubert form factor parameterization, the parameters $η_{\rm EW} F(1) |V_{cb}|$ and $ρ^{2}$ are extracted, where $η_{\rm EW}$ is an electroweak correction, $F(1)$ is a normalization factor and $ρ^{2}$ is a form factor shape parameter. We reconstruct 516 signal decays and thereby obtain $\mathcal{B} (B^{0} \rightarrow D^{*-} \ell^{+} ν_{\ell} ) = \left(5.27 \pm 0.22~\rm{\left(stat\right)} \pm 0.38~\rm{\left(syst\right)}\right) \%$, $η_{EW} F(1) |V_{cb}| \times 10^{3} = 34.6 \pm 1.8~\rm{\left(stat\right)} \pm 1.7~\rm{\left(syst\right)}$, and $ρ^{2} = 0.94 \pm 0.18~\rm{\left(stat\right)} \pm 0.11~\rm{\left(syst\right)}$.

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arXiv2022

Determination of U-spin breaking parameters with an amplitude analysis of the decay $D^0 \to K_{\rm L}^0π^+π^-$

We present a study of the resonant structure of the decay $D^0 \to K_{\rm L}^0π^+π^-$, using quantum-correlated $D^0\bar{D}^0$ data produced at $\sqrt{s}=3.773$ GeV. The data sample was collected by the BESIII experiment and corresponds to an integrated luminosity of $2.93$ fb$^{-1}$. This study is the first amplitude analysis of a decay mode involving a $K_{\rm L}^0$, which also results in the first measurement of the complex $\textit{U-spin breaking parameters}$ ($\hatρ$) related to various $\mathit{CP}$-eigenstate resonant modes through which the three-body decay proceeds. The moduli of the $\hatρ$ parameters have central values in a wide range from $0.4$ to $12.1$, which indicates substantial U-spin symmetry breaking. We present the fractional resonant contributions and average strong-phase parameters over regions of phase space for both $K_{\rm S}^0π^+π^-$ and $K_{\rm L}^0π^+π^-$ modes. We also report the ratio of the branching fractions between $K_{\rm L}^0π^+π^-$ and $K_{\rm S}^0π^+π^-$ decay modes and the $\mathit{CP}$-even fraction of the $K_{\rm L}^0π^+π^-$ state calculated using the U-spin breaking parameters.

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arXiv2022

First Direct Measurement of the Absolute Branching Fraction of $Σ^+ \to Λe^+ ν_{e}$

The first direct measurement of the absolute branching fraction of $Σ^+ \to Λe^+ ν_{e}$ is reported based on an $e^+e^-$ annihilation sample of $(10087\pm44) \times 10^6$ $J/ψ$ events collected with the BESIII detector at $\sqrt{s}=3.097$ GeV. The branching fraction is determined to be ${\mathcal B}(Σ^+ \to Λe^+ ν_{e}) = [2.93\pm0.74(\rm stat) \pm 0.13(\rm syst)]\times 10^{-5}$, which is the most precise measurement obtained in a single experiment to date and also the first result obtained at a collider experiment. Combining this result with the world average of ${\mathcal B}(Σ^- \to Λe^- \barν_{e})$ and the lifetimes of $Σ^{\pm}$, the ratio, $\frac{Γ(Σ^- \to Λe^- \barν_{e})}{Γ(Σ^+ \to Λe^+ ν_{e})}$, is determined to be $1.06 \pm 0.28$, which is within 1.8 standard deviations of the value expected in the absence of second-class currents that are forbidden in the Standard Model.

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arXiv2022

Reconstruction of $B \to ρ\ell ν_\ell$ decays identified using hadronic decays of the recoil $B$ meson in 2019 -- 2021 Belle II data

We present results on the semileptonic decays $B^0 \to ρ^- \ell^+ ν_\ell$ and $B^+ \to ρ^0 \ell^+ ν_\ell$ in a sample corresponding to 189.9/fb of Belle II data at the SuperKEKB $e^- e^+$ collider. Signal decays are identified using full reconstruction of the recoil $B$ meson in hadronic final states. We determine the total branching fractions via fits to the distributions of the square of the "missing" mass in the event and the dipion mass in the signal candidate and find ${\mathcal{B}(B^0\toρ^-\ell^+ ν_\ell) = (4.12 \pm 0.64(\mathrm{stat}) \pm 1.16(\mathrm{syst})) \times 10^{-4}}$ and ${\mathcal{B}({B^+\toρ^0\ell^+ν_\ell}) = (1.77 \pm 0.23 (\mathrm{stat}) \pm 0.36 (\mathrm{syst})) \times 10^{-4}}$ where the dominant systematic uncertainty comes from modeling the nonresonant $B\to (ππ)\ell^+ν_\ell$ contribution.

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arXiv2022

Measurement of $e^+e^-\rightarrowΛ\barΛη$ from 3.5106 to 4.6988 GeV and study of $Λ\barΛ$ mass threshold enhancement

Using data samples with a total integrated luminosity of approximately 18 fb$^{-1}$ collected by the BESIII detector operating at the BEPCII, the process $e^+e^-\rightarrowΛ\barΛ η$ is studied at center-of-mass energies between 3.5106 and 4.6988 GeV. The Born cross section for the process $e^+e^-\rightarrowΛ\barΛη$ is measured. No significant structure is observed in the Born cross section line shape. An enhancement near the $Λ\barΛ$ mass threshold is observed for the first time in the process. The structure can be described by an $S$-wave Breit-Wigner function. Neglecting contribution of excited $Λ$ states and potential interferences, the mass and width are determined to be ($2356\pm 7\pm17$) MeV/$c^2$ and ($304\pm28\pm54$) MeV, respectively, where the first uncertainties are statistical and the second are systematic.

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arXiv2022

Determination of $|V_{ub}|$ from untagged $B^0\toπ^- \ell^+ ν_{\ell}$ decays using 2019-2021 Belle II data

We present an analysis of the charmless semileptonic decay $B^0\toπ^- \ell^+ ν_{\ell}$, where $\ell = e, μ$, from 198.0 million pairs of $B\bar{B}$ mesons recorded by the Belle II detector at the SuperKEKB electron-positron collider. The decay is reconstructed without identifying the partner $B$ meson. The partial branching fractions are measured independently for $B^0\toπ^- e^+ ν_{e}$ and $B^0\toπ^- μ^+ ν_μ$ as functions of $q^{2}$ (momentum transfer squared), using 3896 $B^0\toπ^- e^+ ν_{e}$ and 5466 $B^0\toπ^- μ^+ ν_μ$ decays. The total branching fraction is found to be $(1.426 \pm 0.056 \pm 0.125) \times 10^{-4}$ for $B^0\toπ^- \ell^+ ν_{\ell}$ decays, where the uncertainties are statistical and systematic, respectively. By fitting the measured partial branching fractions as functions of $q^{2}$, together with constraints on the nonperturbative hadronic contribution from lattice QCD calculations, the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element $V_{ub}$, $(3.55 \pm 0.12 \pm 0.13 \pm 0.17) \times 10^{-3}$, is extracted. Here, the first uncertainty is statistical, the second is systematic and the third is theoretical.

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arXiv2022

Determination of $|V_{cb}|$ from $B\to D\ellν$ decays using 2019-2021 Belle II data

We present a determination of the magnitude of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element $V_{cb}$ using $B\to D\ellν$ decays. The result is based on $e^+e^-\toΥ(4S)$ data recorded by the Belle II detector corresponding to 189.2/fb of integrated luminosity. The semileptonic decays $B^0\to D^-(\to K^+π^-π^-)\ell^+ν_\ell$ and $B^+\to\bar D^0(\to K^+π^-)\ell^+ν_\ell$ are reconstructed, where $\ell$ is either electron or a muon. The second $B$ meson in the $Υ(4S)$ event is not explicitly reconstructed. Using the diamond-frame method, we determine the $B$ meson four-momentum and thus the hadronic recoil. We extract the partial decay rates as functions of $w$ and perform a fit to the decay form-factor and the CKM parameter $|V_{cb}|$ using the BGL parameterization of the form factor and lattice QCD input from the FNAL/MILC and HPQCD collaborations. We obtain $η_{EW}|V_{cb}|=(38.53\pm 1.15)\times 10^{-3}$, where $η_{EW}$ is an electroweak correction, and the error accounts for theoretical and experimental sources of uncertainty.

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arXiv2022

Measurement of the photon-energy spectrum in inclusive $B\rightarrow X_{s}γ$ decays identified using hadronic decays of the recoil $B$ meson in 2019-2021 Belle II data

We measure the photon-energy spectrum in radiative bottom-meson ($B$) decays into inclusive final states involving a strange hadron and a photon. We use SuperKEKB electron-positron collisions corresponding to $189~\mathrm{fb}^{-1}$ of integrated luminosity collected at the $Υ(4S)$ resonance by the Belle II experiment. The partner $B$ candidates are fully reconstructed using a large number of hadronic channels. The $B \rightarrow X_s γ$ partial branching fractions are measured as a function of photon energy in the signal $B$ meson rest frame in eight bins above $1.8~\mathrm{GeV}$. The background-subtracted signal yield for this photon energy region is $343 \pm 122$ events. Integrated branching fractions for three photon energy thresholds of $1.8~\mathrm{GeV}$, $2.0~\mathrm{GeV}$, and $2.1~\mathrm{GeV}$ are also reported, and found to be in agreement with world averages.

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