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Q. An

Publications and source records attributed to Q. An.

At least 325 records · Page 18Linked to original sources
arXiv2024

Observation of the Anomalous Shape of $X(1840)$ in $J/ψ\rightarrow γ3(π^+ π^-)$ Indicating a Second Resonance Near $p\bar{p}$ Threshold

Using a sample of $(10087\pm44)\times 10^6$ $J/ψ$ events, which is about 45 times larger than that was previously analyzed, a further investigation on the $J/ψ\rightarrow γ3(π^+π^-)$ decay is performed. A significant distortion at 1.84 GeV/$c^2$ in the line-shape of the $3(π^+π^-)$ invariant mass spectrum is observed for the first time, which could be resolved by two overlapping resonant structures, $X(1840)$ and $X(1880)$. The new state $X(1880)$ is observed with a statistical significance larger than $10σ$. The mass and width of $X(1880)$ are determined to be $1882.1\pm1.7\pm0.7$ MeV/$c^2$ and $30.7\pm5.5 \pm2.4$ MeV, respectively, which indicates the existence of a $p\bar{p}$ bound state.

hep-ex↗
arXiv2024

Observation of $ψ(3686) \to Ω^- K^+ \barΞ^0 $+c.c

Using $(27.12 \pm 0.14) \times 10^{8}$ $ψ(3686)$ events collected with the BESIII detector at BEPCII, the decay of $ψ(3686) \to Ω^- K^+ \barΞ^0 +c.c.$ is observed for the first time. The branching fraction of this decay is measured to be $\mathcal{B}_{ψ(3686) \to Ω^- K^+ \barΞ^0 +c.c.}=(2.78 \pm 0.40 \pm 0.18 ) \times 10^{-6}$, where the first uncertainty is statistical and the second is systematic. Possible baryon excited states are searched for in this decay, but no evident intermediate state is observed with the current sample size.

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arXiv2024

Search for $ΔS=2$ nonleptonic hyperon decays $Ω^-\toΣ^{0}π^{-}$ and $Ω^-\to nK^{-}$

Using $(27.12 \pm 0.14) \times 10^{8}$ $ψ(3686)$ events collected by the BESIII detector at the center-of-mass energy of $\sqrt{s} = 3.686$ GeV, we search for the first time for two nonleptonic hyperon decays that change strangeness by two units, $Ω^-\toΣ^{0}π^-$ and $Ω^-\to nK^{-}$. No significant signal is observed. The upper limits on their decay branching fractions are determined to be $\mathcal{B}(Ω^-\toΣ^{0}π^-) < 5.4\times 10^{-4}$ and $\mathcal{B}(Ω^-\to nK^{-}) < 2.4\times 10^{-4}$ at the $90\%$ confidence level.

hep-ex↗
arXiv2024

Observation of $D \to a_{0}(980)π$ in the decays $D^{0} \rightarrow π^{+}π^{-}η$ and $D^{+} \rightarrow π^{+}π^{0}η$

We report the first amplitude analysis of the decays $D^{0} \to π^{+} π^{-} η$ and $D^{+} \rightarrow π^{+}π^{0}η$ using a data sample taken with the BESIII detector at the center-of-mass energy of 3.773 GeV, corresponding to an integrated luminosity of 7.9 ${\rm fb}^{-1}$. The contribution from the process $D^{0(+)} \to a_{0}(980)^{+} π^{-(0)}$ is significantly larger than the $D^{0(+)} \to a_{0}(980)^{-(0)} π^{+}$ contribution. The ratios $\mathcal{B}(D^{0} \rightarrow a_{0}(980)^{+}π^{-})/\mathcal{B}(D^{0} \rightarrow a_{0}(980)^{-}π^{+})$ and $\mathcal{B}(D^{+} \rightarrow a_{0}(980)^{+}π^{0})/\mathcal{B}(D^{+} \rightarrow a_{0}(980)^{0}π^{+})$ are measured to be $7.5^{+2.5}_{-0.8\,\mathrm{stat.}}\pm1.7_{\mathrm{syst.}}$ and $2.6\pm0.6_{\mathrm{stat.}}\pm0.3_{\mathrm{syst.}}$, respectively. The measured $D^{0}$ ratio disagrees with the theoretical predictions by orders of magnitudes, thus implying a substantial contribution from final-state interactions.

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arXiv2024

Measurement of $e^{+}e^{-}\to ωη^{\prime}$ cross sections at $\sqrt{s}=$ 2.000 to 3.080 GeV

The Born cross sections for the process $e^{+}e^{-}\to ωη^{\prime}$ are measured at 22 center-of-mass energies from 2.000 to 3.080 GeV using data collected with the BESIII detector at the BEPCII collider. A resonant structure is observed with a statistical significance of 9.6$σ$. A Breit-Wigner fit determines its mass to be $M_R=(2153\pm30\pm31)~{\rm{MeV}}/c^{2}$ and its width to be $Γ_{R}=(167\pm77\pm7)~\rm{MeV}$, where the first uncertainties are statistical and the second are systematic.

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arXiv2024

Measurement of the Born cross section for $e^{+}e^{-}\to ηh_c $ at center-of-mass energies between 4.1 and 4.6\,GeV

We measure the Born cross section for the reaction $e^{+}e^{-} \rightarrow ηh_c$ from $\sqrt{s} = 4.129$ to $4.600$~GeV using data sets collected by the BESIII detector running at the BEPCII collider. A resonant structure in the cross section line shape near 4.200~GeV is observed with a statistical significance of 7$σ$. The parameters of this resonance are measured to be \MeasMass\ and \MeasWidth, where the first uncertainties are statistical and the second systematic.

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arXiv2024

Search for the Rare Decays $D_s^+\to h^+(h^{0})e^+e^-$

Using 7.33~fb$^{-1}$ of $e^{+}e^{-}$ collision data collected by the BESIII detector at center-of-mass energies in the range of $\sqrt{s}=4.128 - 4.226$~GeV, we search for the rare decays $D_{s}^+\to h^+(h^{0})e^{+}e^{-}$, where $h$ represents a kaon or pion. By requiring the $e^{+}e^{-}$ invariant mass to be consistent with a $ϕ(1020)$, $0.98<M(e^{+}e^{-})<1.04$ ~GeV/$c^2$, the decay $D_s^+\toπ^+ϕ,ϕ\to e^{+}e^{-}$ is observed with a statistical significance of 7.8$σ$, and evidence for the decay $D_s^+\toρ^+ϕ,ϕ\to e^{+}e^{-}$ is found for the first time with a statistical significance of 4.4$σ$. The decay branching fractions are measured to be $\mathcal{B}(D_s^+\toπ^+ϕ, ϕ\to e^{+}e^{-} )=(1.17^{+0.23}_{-0.21}\pm0.03)\times 10^{-5}$, and $\mathcal{B}(D_s^+\toρ^+ϕ, ϕ\to e^{+}e^{-} )=(2.44^{+0.67}_{-0.62}\pm 0.16)\times 10^{-5}$, where the first uncertainties are statistical and the second systematic. No significant signal for the three four-body decays of $D_{s}^{+}\to π^{+}π^{0}e^{+}e^{-},\ D_{s}^{+}\to K^{+}π^{0}e^{+}e^{-}$, and $D_{s}^{+}\to K_{S}^{0}π^{+}e^{+}e^{-}$ is observed. For $D_{s}^{+}\to π^{+}π^{0}e^{+}e^{-}$, the $ϕ$ mass region is vetoed to minimize the long-distance effects. The 90$\%$ confidence level upper limits set on the branching fractions of these decays are in the range of $(7.0-8.1)\times 10^{-5}$.

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arXiv2024

LHAASO-KM2A detector simulation using Geant4

KM2A is one of the main sub-arrays of LHAASO, working on gamma ray astronomy and cosmic ray physics at energies above 10 TeV. Detector simulation is the important foundation for estimating detector performance and data analysis. It is a big challenge to simulate the KM2A detector in the framework of Geant4 due to the need to track numerous photons from a large number of detector units (>6000) with large altitude difference (30 m) and huge coverage (1.3 km^2). In this paper, the design of the KM2A simulation code G4KM2A based on Geant4 is introduced. The process of G4KM2A is optimized mainly in memory consumption to avoid memory overffow. Some simpliffcations are used to signiffcantly speed up the execution of G4KM2A. The running time is reduced by at least 30 times compared to full detector simulation. The particle distributions and the core/angle resolution comparison between simulation and experimental data of the full KM2A array are also presented, which show good agreement.

astro-ph.IM↗
arXiv2024

Search for a massless particle beyond the Standard Model in the $Σ^+\rightarrow p+{\rm invisible}$ decay

A massless particle beyond the Standard Model is searched for in the two-body decay $Σ^+\rightarrow p+{\rm invisible}$ using $(1.0087\pm0.0044)\times10^{10}$ $J/ψ$ events collected at a center-of-mass energy of $\sqrt{s}=3.097$ GeV with the BESIII detector at the BEPCII collider. No significant signal is observed, and the upper limit on the branching fraction $B(Σ^+\rightarrow p+{\rm invisible})$ is determined to be $3.2\times10^{-5}$ at the 90% confidence level. This is the first search for a flavor-changing neutral current process with missing energy in hyperon decays which plays an important role in constraining new physics models.

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arXiv2024

Improved measurements of the Dalitz decays $η/η'\rightarrowγe^{+}e^{-}$

Based on a data sample of 10 billion $J/ψ$ events collected with the BESIII detector, improved measurements of the Dalitz decays $η/η'\rightarrowγe^+e^-$ are performed, where the $η$ and $η'$ are produced through the radiative decays $J/ψ\rightarrowγη/η'$. The branching fractions of $η\rightarrowγe^+e^-$ and $η'\rightarrowγe^+e^-$ are measured to be $(7.07 \pm 0.05 \pm 0.23)\times10^{-3}$ and $(4.83\pm0.07\pm0.14)\times10^{-4}$, respectively. Within the single pole model, the parameter of electromagnetic transition form factor for $η\rightarrowγe^+e^-$ is determined to be $Λ_η=(0.749 \pm 0.027 \pm 0.007)~ {\rm GeV}/c^{2}$. Within the multi-pole model, we extract the electromagnetic transition form factors for $η'\rightarrowγe^+e^-$ to be $Λ_{η'} = (0.802 \pm 0.007\pm 0.008)~ {\rm GeV}/c^{2}$ and $γ_{η'} = (0.113\pm0.010\pm0.002)~ {\rm GeV}/c^{2}$. The results are consistent with both theoretical predictions and previous measurements. The characteristic sizes of the interaction regions for the $η$ and $η'$ are calculated to be $(0.645 \pm 0.023 \pm 0.007 )~ {\rm fm}$ and $(0.596 \pm 0.005 \pm 0.006)~ {\rm fm}$, respectively. In addition, we search for the dark photon in $η/η^\prime\rightarrowγe^{+}e^{-}$, and the upper limits of the branching fractions as a function of the dark photon are given at 90\% confidence level.

hep-ex↗
arXiv2024

Evidence of the $h_c\to K_S^0 K^+π^-+c.c.$ decay

Based on $(2.712\pm0.014)\times10^9$ $ψ(3686)$ events collected by the BESIII collaboration, evidence of the hadronic decay $h_c\to K_S^0K^+π^-+c.c.$ is found with a significance of $4.3σ$ in the $ψ(3686)\toπ^0 h_c$ process. The branching fraction of $h_c\to K_S^0 K^+π^- +c.c.$ is measured to be $(7.3\pm0.8\pm1.8)\times10^{-4}$, where the first and second uncertainties are statistical and systematic, respectively. Combining with the exclusive decay width of $η_c\to K\bar{K}π$, our result indicates inconsistencies with both pQCD and NRQCD predictions.

hep-ex↗
arXiv2024

Amplitude Analysis of the Decays $D^0\toπ^+π^-π^+π^-$ and $π^+π^-π^0π^0$

Using $e^+e^-$ annihilation data corresponding to an integrated luminosity of 2.93 $\rm fb^{-1}$ taken at the center-of-mass energy $\sqrt{s}=3.773$~GeV with the BESIII detector, a joint amplitude analysis is performed on the decays $D^0\toπ^+π^-π^+π^-$ and $D^0\toπ^+π^-π^0π^0$(non-$η$). The fit fractions of individual components are obtained, and large interferences among the dominant components of $D^{0}\to a_{1}(1260)π$, $D^{0}\toπ(1300)π$, $D^{0}\toρ(770)ρ(770)$ and $D^{0}\to2(ππ)_{S}$ are found in both channels. With the obtained amplitude model, the $CP$-even fractions of $D^0\to π^+π^-π^+π^-$ and $D^0\toπ^+π^-π^0π^0$(non-$η$) are determined to be $(75.2\pm1.1_{\rm stat.}\pm1.5_{\rm syst.})\%$ and $(68.9\pm1.5_{\rm stat.}\pm 2.4_{\rm syst.})\%$, respectively. The branching fractions of $D^0\to π^+π^-π^+π^-$ and $D^0\toπ^+π^-π^0π^0$(non-$η$) are measured to be $(0.688\pm0.010_{\rm stat.}\pm 0.010_{\rm syst.})\%$ and $(0.951\pm0.025_{\rm stat.}\pm 0.021_{\rm syst.})\%$, respectively. The amplitude analysis provides an important model for binning strategy in the measurements of the strong phase parameters of $D^0 \to 4π$ when used to determine the CKM angle $γ(ϕ_{3})$ via the $B^{-}\to D K^{-}$ decay.

hep-ex↗
arXiv2024

First observation of the decay $Λ^+_c\to nK^{0}_{S}π^+π^0$

Based on 4.5 fb$^{-1}$ of $e^{+}e^{-}$ collision data accumulated at center-of-mass energies between $4599.53$ MeV and $4698.82$ MeV with the BESIII detector, the decay $Λ_{c}^{+}\to nK_{S}^{0}π^+π^0$ is observed for the first time with a significance of $9.2σ$. The branching fraction is measured to be $(0.85\pm0.13\pm0.03)\%$, where the first uncertainty is statistical and the second systematic, which differs from the theoretical prediction based on isospin by 4.4$σ$. This indicates that there may be resonant contributions or some unknown dynamics in this decay.

hep-ex↗
arXiv2024

Observation of $D^{+}\to K_{S}^{0}a_{0}(980)^{+}$ in the amplitude analysis of $D^{+} \to K_{S}^{0}π^+η$

We perform for the first time an amplitude analysis of the decay $D^{+}\to K_{S}^{0}π^+η$ and report the observation of the decay $D^{+}\to K_{S}^{0}a_{0}(980)^{+}$ using 2.93 fb$^{-1}$ of $e^+e^-$ collision data taken at a center-of-mass energy of 3.773 GeV with the BESIII detector. As the only W-annihilation free decay among $D$ to $a_{0}(980)$-pseudoscalar, $D^{+}\to K_{S}^{0}a_{0}(980)^{+}$ is the ideal decay to extract the contributions of the external and internal $W$-emission amplitudes involving $a_{0}(980)$ and study the final-state interactions. The absolute branching fraction of $D^{+}\to K_{S}^{0}π^+η$ is measured to be $(1.27\pm0.04_{\rm stat.}\pm0.03_{\rm syst.})\%$. The product branching fractions of $D^{+}\to K_{S}^{0}a_{0}(980)^{+}$ with $a_{0}(980)^{+}\to π^+η$ and $D^{+}\to π^+ K_0^*(1430)^0$ with $K_0^*(1430)^0\to K_{S}^{0}η$ are measured to be $(1.33\pm0.05_{\rm stat.}\pm0.04_{\rm syst.})\%$ and $(0.14\pm0.03_{\rm stat.}\pm0.01_{\rm syst.})\%$, respectively.

hep-ex↗
arXiv2024

Observation of the semileptonic decays $D^0\rightarrow K_S^0π^-π^0 e^+ ν_e$ and $D^+\rightarrow K_S^0π^+π^- e^+ ν_e$

By analyzing $e^+e^-$ annihilation data corresponding to an integrated luminosity of 2.93 $\rm fb^{-1}$ collected at a center-of-mass energy of 3.773 GeV with the \text{BESIII} detector, the first observation of the semileptonic decays $D^0\rightarrow K_S^0π^-π^0 e^+ ν_e$ and $D^+\rightarrow K_S^0π^+π^- e^+ ν_e$ is reported. With a dominant hadronic contribution from $K_1(1270)$, the branching fractions are measured to be $\mathcal{B}(D^0\rightarrow {K}_1(1270)^-(\to K^0_Sπ^-π^0)e^+ν_e)=(1.69^{+0.53}_{-0.46}\pm0.15)\times10^{-4}$ and $\mathcal{B}(D^+\to \bar{K}_1(1270)^0(\to K^0_Sπ^+π^-)e^+ν_e)=(1.47^{+0.45}_{-0.40}\pm0.20)\times10^{-4}$ with statistical significance of 5.4$σ$ and 5.6$σ$, respectively. When combined with measurements of the $K_1(1270)\to K^+π^-π$ decays, the absolute branching fractions are determined to be $\mathcal{B}(D^0\to K_1(1270)^-e^+ν_e)=(1.05^{+0.33}_{-0.28}\pm0.12\pm0.12)\times10^{-3}$ and $\mathcal{B}(D^+\to \bar{K}_1(1270)^0e^+ν_e)=(1.29^{+0.40}_{-0.35}\pm0.18\pm0.15)\times10^{-3}$. The first and second uncertainties are statistical and systematic, respectively, and the third uncertainties originate from the assumed branching fractions of the $K_1(1270)\to Kππ$ decays.

hep-ex↗
arXiv2024

Measurements of All-Particle Energy Spectrum and Mean Logarithmic Mass of Cosmic Rays from 0.3 to 30 PeV with LHAASO-KM2A

We present the measurements of all-particle energy spectrum and mean logarithmic mass of cosmic rays in the energy range of 0.3-30 PeV using data collected from LHAASO-KM2A between September 2021 and December 2022, which is based on a nearly composition-independent energy reconstruction method, achieving unprecedented accuracy. Our analysis reveals the position of the knee at $3.67 \pm 0.05 \pm 0.15$ PeV. Below the knee, the spectral index is found to be -$2.7413 \pm 0.0004 \pm 0.0050$, while above the knee, it is -$3.128 \pm 0.005 \pm 0.027$, with the sharpness of the transition measured with a statistical error of 2%. The mean logarithmic mass of cosmic rays is almost heavier than helium in the whole measured energy range. It decreases from 1.7 at 0.3 PeV to 1.3 at 3 PeV, representing a 24% decline following a power law with an index of -$0.1200 \pm 0.0003 \pm 0.0341$. This is equivalent to an increase in abundance of light components. Above the knee, the mean logarithmic mass exhibits a power law trend towards heavier components, which is reversal to the behavior observed in the all-particle energy spectrum. Additionally, the knee position and the change in power-law index are approximately the same. These findings suggest that the knee observed in the all-particle spectrum corresponds to the knee of the light component, rather than the medium-heavy components.

astro-ph.HE↗
arXiv2024

Observation of structures in the processes $e^+e^-\rightarrowωχ_{c1}$ and $ωχ_{c2}$

We present measurements of the Born cross sections for the processes $e^+e^-\rightarrowωχ_{c1}$ and $ωχ_{c2}$ at center-of-mass energies $\sqrt{s}$ from 4.308 to 4.951 GeV. The measurements are performed with data samples corresponding to an integrated luminosity of 11.0 $\rm{fb}^{-1}$ collected with the BESIII detector operating at the BEPCII storage ring. Assuming the $e^+e^-\rightarrowωχ_{c2}$ signals come from a single resonance, the mass and width are determined to be $M=(4413.6\pm9.0\pm0.8)$ MeV/$c^2$ and $Γ=(110.5\pm15.0\pm2.9)$ MeV, respectively, which is consistent with the parameters of the well-established resonance $ψ(4415)$. In addition, we also use one single resonance to describe the $e^+e^-\rightarrowωχ_{c1}$ lineshape, and determine the mass and width to be $M=(4544.2\pm18.7\pm1.7)$ MeV/$c^2$ and $Γ=(116.1\pm33.5\pm1.7)$ MeV, respectively. The structure of this lineshape, observed for the first time, requires further understanding.

hep-ex↗
arXiv2024

Measurement of $Λ$ transverse polarization in $e^{+}e^{-}$ collisions at $\sqrt{s}= 3.68-3.71$ GeV

With data samples collected with the BESIII detector at seven energy points at $\sqrt{s}= 3.68 - 3.71$ GeV, corresponding to an integrated luminosity of 333 pb$^{-1}$, we present a study of the $Λ$ transverse polarization in the $e^+e^-\toΛ\barΛ$ reaction. The significance of polarization by combining the seven energy points is found to be 2.6$σ$ including the systematic uncertainty, which implies a non-zero phase between the transition amplitudes of the $Λ\barΛ$ helicity states. The modulus ratio and the relative phase of EM-$psionic$ form factors combined with all energy points are measured to be $R^Ψ =$ 0.71$^{+0.10}_{-0.10}$ $\pm$ 0.03 and $ΔΦ^Ψ$ = (23$^{+8.8}_{-8.0}$ $\pm$ 1.6$)^\circ$, where the first uncertainties are statistical and the second systematic.

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