arXiv subjects

Q. An

Publications and source records attributed to Q. An.

At least 181 records · Page 10Linked to original sources

arXiv2025

Improved Measurements of $D^+ \to ηe^+ν_e$ and $D^+ \to ημ^+ν_μ$

Using 20.3 fb$^{-1}$ of $e^+e^-$ collision data collected at the center-of-mass energy of 3.773 GeV with the BESIII detector, we measure the branching fractions of $D^+\to ηe^+ν_e$ and $D^+\to ημ^+ν_μ$ to be $(9.75\pm0.29\pm0.28)\times10^{-4}$ and $(9.08\pm0.35\pm0.23)\times10^{-4}$, where the first and second uncertainties are statistical and systematic, respectively. From a simultaneous fit to their partial decay rates, we determine the product of the hadronic form factor $f^η_+(0)$ and the modulus of the $c\to d$ Cabibbo-Kobayashi-Maskawa matrix element $|V_{cd}|$ to be $f^η_+(0)|V_{cd}|=0.078\pm0.002\pm0.001$. Taking the $|V_{cd}|$ value from the Standard Model global fit as input, we obtain $f^η_+(0)=0.345\pm0.008\pm0.003$. The ratio between the measured branching fractions of $D^+\toη^+μ^+ν_μ$ and $D^+\toηe^+ν_e$, is determined to be $0.93\pm0.05_{\rm stat.}\pm0.02_{\rm syst.}$, indicating no violation of lepton flavor universality.

hep-ex↗

arXiv2025

Precision Measurement of the Branching Fraction of $D^{+}\to μ^{+}ν_μ$

Using $20.3~\mathrm{fb}^{-1}$ of $e^+e^-$ collision data collected at a center-of-mass energy of $E_{\rm c.m.}=3.773$ GeV with the BESIII detector operating at the BEPCII collider, we determine the branching fraction of the leptonic decay $D^+\toμ^+ν_μ$ to be $(4.034\pm0.080_{\rm stat}\pm0.040_{\rm syst})\times10^{-4}$. Interpreting our measurement with knowledge of the Fermi coupling constant $G_F$, the masses of the $D^+$ and $μ^+$ as well as the lifetime of the $D^+$, we determine $f_{D^+}|V_{cd}|=(48.02\pm0.48_{\rm stat}\pm0.24_{\rm syst}\pm0.12_{\rm input}\pm0.15_{\rm EM})~\mathrm{MeV}$ after taking into account necessary radiative corrections. This result is a factor of 2.3 more precise than the previous best measurement. Using the value of the magnitude of the $c\to d$ Cabibbo-Kobayashi-Maskawa matrix element $|V_{cd}|$ given by the global standard model fit, we obtain the $D^+$ decay constant $f_{D^+}=(213.5\pm2.1_{\rm stat}\pm1.1_{\rm syst}\pm0.8_{\rm input}\pm0.7_{\rm EM})$\,MeV. Alternatively, using the value of $f_{D^+}$ from a precise lattice quantum chromodynamics calculation, we extract $|V_{cd}|=0.2265\pm0.0023_{\rm stat}\pm0.0011_{\rm syst}\pm0.0009_{\rm input}\pm0.0007_{\rm EM}$.

hep-ex↗

arXiv2025

First Measurement of the $D_s^+\rightarrow K^0μ^+ν_μ$ Decay

We report the first measurement of the semileptonic decay $D^+_s \rightarrow K^0μ^+ν_μ$, using a sample of $e^+e^-$ annihilation data corresponding to an integrated luminosity of $7.33~\mathrm{fb}^{-1}$ collected at center-of-mass energies between 4.128 to 4.226~GeV with the BESIII detector at the BEPCII collider. The branching fraction of the decay is measured to be $\mathcal{B}(D^+_s\rightarrow K^0μ^+ν_μ) = (2.89 \pm 0.27_{\rm stat} \pm 0.12_{\rm syst})\times 10^{-3}$, where the first uncertainty is statistical and the second is systematic. Based on a simultaneous fit to the partial decay rates in $q^2$ intervals measured in $D^+_s \rightarrow K^0μ^+ν_μ$ and $D^+_s \rightarrow K^0e^+ν_{e}$ decays, the product value of the form factor $f^{K^0}_{+}(0)$ and the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cd}|$ is measured to be $f^{K^0}_{+}(0)|V_{cd}|=0.140\pm0.008_{\rm stat}\pm0.002_{\rm syst}$. Using $|V_{cd}|=0.22486\pm0.00068$ as an input, the hadronic form factor is determined to be $f^{K^0}_{+}(0)=0.623\pm0.036_{\rm stat} \pm 0.009_{\rm syst}$ at $q^2=0$. This is the most precise determination of $f^{K^0}_{+}(0)$ in the $D^+_s \rightarrow K^0$ transition to date. The measured branching fraction and form factor presented in this work provide the most stringent test on various non-perturbative theoretical calculations. Taking $f^{K^0}_{+}(0)=0.6307\pm0.0020$ from lattice calculations as an input, we obtain $|V_{cd}|=0.220\pm0.013_{\rm stat}\pm0.003_{\rm syst}\pm0.001_{\rm LQCD}$, which is the most precise determination of $|V_{cd}|$ using the $D_s^+\rightarrow K^0\ell^+ν_{\ell}$ decays. In addition, lepton flavor universality is tested for the first time with $D^+_s \rightarrow K^0\ell^+ν_{\ell}$ decays in full and separate $q^2$ intervals. No obvious violation is found.

hep-ex↗

arXiv2025

Search for $J/ψ\rightarrow K^{0}_{S}K^{0}_{S}$ and $ψ(3686)\rightarrow K^{0}_{S}K^{0}_{S}$

Using data samples of $(10087\pm 44)\times10^{6}$ $J/ψ$ events and $(2712.4\pm 14.3)\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, we search for the CP violating decays $J/ψ\rightarrow K^{0}_{S}K^{0}_{S}$ and $ψ(3686)\rightarrow K^{0}_{S}K^{0}_{S}$. No significant signals are observed over the expected background yields. The upper limits on their branching fractions are set as $\mathcal{B}(J/ψ\rightarrow K^{0}_{S}K^{0}_{S}) <4.7\times 10^{-9}$ and $\mathcal{B}(ψ(3686)\rightarrow K^{0}_{S}K^{0}_{S}) <1.1\times 10^{-8}$ at the 90% confidence level. These results improve the previous limits by a factor of three for $J/ψ\rightarrow K^{0}_{S} K^{0}_{S}$ and two orders of magnitude for $ψ(3686)\rightarrow K^{0}_{S} K^{0}_{S}$.

hep-ex↗

arXiv2025

Search for the lepton number violating decay $η\to π^+π^+e^-e^- + c.c.$ via $J/ψ\toϕη$

Based on a sample of $ (10.087\pm 0.044)\times 10^{9} J/ψ$ events collected by the BESIII detector at the BEPCII collider, we perform the first search for the lepton number violating decay $η\to π^+π^+ e^-e^- + \text{c.c.}$ No signal is found, and an upper limit on the branching fraction of $η\to π^+π^+ e^-e^- + c.c.$ is set to be $4.6 \times 10^{-6}$ at the 90\% confidence level.

hep-ex↗

arXiv2025

Observation of Transverse Polarization and Determination of Psionic Form Factors of the $Λ$ Hyperon at $\sqrt{s}= 3.773$ GeV

Using a data sample of $e^{+}e^{-}$ collision data corresponding to an integrated luminosity of 20.3 fb$^{-1}$ collected by the BESIII detector at the BEPCII collider, we present an observation of transverse polarization and a complete determination of the psionic form factors of the $Λ$ hyperon in $e^{+}e^{-}\toΛ\barΛ$ decay with the entangled $Λ-\barΛ$ pair at $\sqrt{s}=3.773$ GeV. The relative phase between the psionic form factors is determined to be $ΔΦ=(1.53\pm0.36\pm0.03)$~rad with a significance of 5.5 $σ$ taking into account systematic uncertainty. This result indicates a non-zero phase between the transition amplitudes of the $Λ\barΛ$ helicity states. Additionally, we measure the angular distribution parameter and the modulus of the ratio between the psionic form factors to be $η=0.86\pm0.05\pm0.03$ and $R(s)=|G_{E}(s)/G_{M}(s)|=0.47\pm0.08\pm0.05$, where the first uncertainty is statistical and the second systematic.

hep-ex↗

arXiv2025

Search for the radiative leptonic decay $D^+\toγe^+ν_e$ using Deep Learning

Using 20.3$~\rm fb^{-1}$ of $e^+e^-$ annihilation data collected at a center-of-mass energy of 3.773$~\rm GeV$ with the BESIII detector, we report an improved search for the radiative leptonic decay $D^+\toγe^+ν_e$. An upper limit on its partial branching fraction for photon energies $E_γ>10~\rm MeV$ was determined to be $1.2\times10^{-5}$ at 90\% confidence level; this excludes most current theoretical predictions. A sophisticated deep learning approach, which includes thorough validation and is based on the Transformer architecture, was implemented to efficiently distinguish the signal from massive backgrounds.

hep-ex↗

arXiv2025

Investigation of hadronic cross sections of cosmic ray carbon and oxygen on BGO from 200 GeV to 10 TeV energy at the DAMPE experiment

The Dark Matter Particle Explorer (DAMPE) has made significant progress in measuring the fluxes of cosmic rays. These new measurements are pivotal in advancing our understanding of the origins and propagation mechanisms of cosmic rays. The bismuth germanium oxide (BGO) calorimeter plays a crucial role in these measurements, particularly in the precise determination of cosmic ray fluxes. However, for a calorimetric experiment like DAMPE, uncertainties in hadronic models persist as a major barrier in achieving more accurate measurements of fluxes of cosmic ray nuclei. This study centers on the measurement of the inelastic hadronic cross sections of carbon and oxygen nuclei interacting with BGO crystals target over an extensive energy range, spanning from 200 GeV to 10 TeV. For carbon nuclei interacting with the BGO target, the measurements of the cross sections have achieved a total relative uncertainty of less than 10% below 8 TeV for carbon, and below 3 TeV for oxygen. For oxygen nuclei, the same level of precision was attained below 3 TeV. Additionally, we compare the experimental results with Geant4 and FLUKA simulations to validate the accuracy and consistency of these simulation tools. Through comprehensive analysis of the inelastic hadronic interaction cross sections, this research provides validation for the hadronic interaction models used in DAMPE's cosmic-ray flux measurements.

hep-ex↗

arXiv2025

Search for sub-GeV invisible particles in inclusive decays of $J/ψ$ to $ϕ$

A search for an invisible particle, $X$, with a mass between 0 and 0.96 $\textrm{GeV}/\textit{c}^{2}$, is performed in the process $J/ψ\rightarrowϕ+ X$ using $(8774.0\pm39.4)\times10^{6}$ $J/ψ$ events collected with the BESIII detector from 2017 to 2019. The $ϕ$ meson is fully reconstructed and an efficient veto of photons, neutral and charged hadrons up to twice the $K_L^0$ mass is applied to the rest of the event and the recoil mass against the $ϕ$ is obtained precisely from the kinematic constraint in the event. No significant signal over the expected background is observed in the investigated region and the upper limit on the inclusive branching fraction of $J/ψ\rightarrowϕ+ X$ is determined to be $7.0\times10^{-8}$ at 90\% confidence level. Upper limits at a 90\% confidence level are also given for this branching fraction as a function of the invisible particle mass, varying from $4\times10^{-9}$ to $4\times10^{-8}$ over the investigated mass range. Additionally, a 90\% confidence level upper limit on the branching fraction of $η\rightarrow \rm{invisible}$ is determined to $2.4\times10^{-5}$, which improves the previous best results by more than four times. The analysis technique in this work offers a clean window to search for sub-GeV invisible particles, which can be adapted for other $J/ψ$ decays and direct $e^+e^-$ annihilation experiments in future studies, and improve the sensitivity by orders of magnitude.

hep-ex↗

arXiv2025

First Observation of $Λ$ Hyperon Transverse Polarization in $ψ(3686)\toΛ\barΛ$

Based on $(448.1\pm2.9)\times10^{6}$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, we present the first observation of spin transverse polarization of $Λ$ and $\barΛ$ hyperons produced coherently in the decay $ψ(3686)\toΛ(\to pπ^-)\barΛ(\to\bar pπ^+)$. The relative phase between the electric and magnetic hadronic form factors is measured to be $ΔΦ=(21.0\pm3.7_{\rm stat.}\pm0.8_{\rm syst.})^{\circ}$. The angular distribution parameter $α_ψ=0.83\pm0.02_{\rm stat.}\pm0.01_{\rm syst.}$ is determined with a precision improved by a factor of 3.7 compared to the previous measurement. The relative phase between the $S$- and $D$-wave amplitudes for $Λ\barΛ$ is observed, and the effective interaction radius is determined to be $0.0450\pm0.0026_{\rm stat.}\pm0.0012_{\rm syst.}$ fm. These results provide new insights into the strong interaction mechanisms and the internal structure of baryons.

hep-ex↗

arXiv2025

Measurement of the space-like $π^0$ transition form factor

Based on $2.93\,\text{fb}^{-1}$ of $e^+e^-$ collision data taken with the BESIII detector at a center-of-mass energy of $3.773\,\text{GeV}$, the two-photon fusion process $e^+e^-\to e^+e^-π^0$ is investigated using a single-tag approach. The differential Born cross section $\text{d}σ/\text{d}Q^2$ and the space-like transition form factor $|F(Q^2)|$ of the $π^0$ are measured as functions of the squared momentum transfer $Q^2$ of the tagged, scattered lepton. The measurement covers the range $0.2 < Q^2 < 3.5\,\text{GeV}^2$. The results are consistent with previous measurements, and provide a significant improvement for $Q^2<2\,\text{GeV}^2$.

hep-ex↗

arXiv2025

Search for a bound state of $Λ_{c}\barΣ_{c}$ near threshold

We search for a possible $Λ_{c} \bar{Σ}_{c}$ bound state, denoted as $H_{c}^{\pm}$, via the $ e^{+}e^{-} \to π^{+} π^{-} Λ_{c}^{+}\barΛ_{c}^{-}$ process for the first time. This analysis utilizes 207.8 and 159.3 pb$^{-1}$ of $e^{+}e^{-}$ annihilation data at the center-of-mass energies of 4918.02 and 4950.93 MeV, respectively, collected with the BESIII detector at the BEPCII collider. No statistically significant signal is observed. The upper limits of the product of Born cross section and branching fraction $σ(e^{+}e^{-} \to π^{+} H_c^{-} + c.c.) \times \mathcal{B}(H_c^{-} \rightarrow π^{-}Λ_{c}^{+}\barΛ_{c}^{-})$ at a 90\% confidence level are reported at each energy point and for various $H_{c}$ mass hypotheses (4715, 4720, 4725, 4730, and 4735 MeV/$c^{2}$) and widths (5, 10, or 20 MeV), with the upper limits ranging from 1.1 pb to 6.4 pb.

hep-ex↗

arXiv2025

Search for $χ_{c1}\to π^{+}π^{-}η_c$ via $ψ(3686)\toγχ_{c1}$

Utilizing $(2712.4 \pm 14.3) \times 10^6$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, we search for the hadronic transition process $χ_{c1} \to π^+π^-η_c$ following the decay $ψ(3686)\to γχ_{c1}$. No significant signal is observed, and an upper limit of $\mathcal{B}(χ_{c1}\toπ^+π^-η_c)$ is determined to be $3.1 times 10^{-4}$~at 90\% confidence level, which is one order of magnitude more stringent than the previous measurement.

hep-ex↗

arXiv2025

Study of the $χ_{cJ}\rightarrowΛ\barΛη^\prime$ decays

Using a data sample of $(2.712\pm0.014)\times10^{9}$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, we investigate the decays $χ_{cJ} \rightarrow Λ\barΛ η^\prime$ for $J=0,~1,~2$ via the radiative transition $ψ(3686) \rightarrow γχ_{cJ}$. The decays $χ_{c0,2}\rightarrowΛ\barΛη^\prime$ are observed for the first time, with statistical significances of 6.7$\,σ$ and 6.4$\,σ$, respectively. Evidence for the decay $χ_{c1}\rightarrowΛ\barΛη^\prime$ is found with a statistical significance of 3.3$\,σ$. The corresponding branching fractions are measured to be $\mathscr{B}(χ_{c0}\rightarrowΛ\barΛη^\prime)=(7.56\pm1.42\pm0.90)\times10^{-5}$, $\mathscr{B}(χ_{c1}\rightarrowΛ\barΛη^\prime)=(1.54\pm0.51\pm0.16)\times10^{-5}$, and $\mathscr{B}(χ_{c2}\rightarrowΛ\barΛη^\prime)=(3.03\pm0.61\pm0.29)\times10^{-5}$, where the first uncertainties are statistical and the second systematic. No significant excited $Λ$ baryon states or $Λ\barΛ$ near-threshold enhancements are observed.

hep-ex↗

arXiv2025

Measurement of the branching fraction of $\psip \to ωηη$

Using a sample of (2.712 $\pm$ 0.014)$\times 10^{9}$ $\psip$ events collected with the BESIII detector at the BEPCII collider in 2009, 2012, and 2021, the decay $\psip \to ωηη$ is observed for the first time. The branching fraction of the $ψ(3686)\toωηη$ decay is measured to be (1.65 $\pm$ 0.02 $\pm$ 0.21)$\times 10^{-5}$, where the first uncertainty is statistical and the second systematic. Clear structures associated with the well-established $ω(1420)$ and $f_{0}(1710)$ resonances are observed in the $ωη$ and $ηη$ invariant-mass spectra, respectively.

hep-ex↗

arXiv2025

Measurement of separate electron and positron spectra from 10 GeV to 20GeV with the geomagnetic field on DAMPE

The cosmic-ray (CR) electrons and positrons in space are of great significance for studying the origin and propagation of cosmic-rays. The satellite-borne experiment DArk Matter Particle Explorer (DAMPE) has been used to measure the separate electron and positron spectra, as well as the positron fraction. In this work, the Earth's magnetic field is used to distinguish CR electrons and positrons, as the DAMPE detector does not carry an onboard magnet. The energy range for the measurements is from 10 to 20 GeV, being currently limited at high energy by the zenith pointing orientation of DAMPE. The results are consistent with previous measurements based on the magnetic spectrometer by AMS-02 and PAMELA, while the results of Fermi-LAT seem then to be systematically shifted to larger values.

astro-ph.HE↗

arXiv2025

Observation of Three Resonant Structures in the Cross Section of $e^+e^-\toπ^+π^- h_c$

Using $e^+e^-$ collision data collected with the BESIII detector operating at the Beijing Electron Positron Collider, the cross section of $e^+e^-\to π^+π^- h_c$ is measured at 59 points with center-of-mass energy $\sqrt{s}$ ranging from $4.009$ to $4.950~\mathrm{GeV}$ with a total integrated luminosity of $22.2~\mathrm{fb}^{-1}$. The cross section between $4.3$ and $4.45~\mathrm{GeV}$ exhibits a plateau-like shape and drops sharply around $4.5~\mathrm{GeV}$, which cannot be described by two resonances only. Three coherent Breit-Wigner functions are used to parameterize the $\sqrt{s}$-dependent cross section line shape. The masses and widths are determined to be $M_1=(4223.6_{-3.7-2.9}^{+3.6+2.6})~\mathrm{MeV}/c^2$, $Γ_1=(58.5_{-11.4-6.5}^{+10.8+6.7})~\mathrm{MeV}$, $M_2=(4327.4_{-18.8-9.3}^{+20.1+10.7})~\mathrm{MeV}/c^2$, $Γ_2=(244.1_{-27.1-18.3}^{+34.0+24.2})~\mathrm{MeV}$, and $M_3=(4467.4_{-5.4-2.7}^{+7.2+3.2})~\mathrm{MeV}/c^2$, $Γ_3=(62.8_{-14.4-7.0}^{+19.2+9.9})~\mathrm{MeV}$. The first uncertainties are statistical and the second are systematic. The inclusion of the relatively narrower third component proves crucial for reproducing the drop at around 4.5~GeV. The statistical significance of the three-resonance assumption over the two-resonance assumption is greater than $5σ$.

hep-ex↗

arXiv2025

Study of $f_1(1420)$ and $η(1405)$ in the decay $J/ψ\to γπ^{0}π^{0}π^{0}$

A partial-wave analysis is performed on the decay $J/ψ\toγπ^{0}π^{0}π^{0}$ within the $π^{0}π^{0}π^{0}$ invariant-mass region below 1.6 GeV$/c^{2}$, using $(10.09~\pm~0.04)\times10^{9} ~J/ψ$ events collected with the BESIII detector. Significant isospin-violating decays of $η(1405)$ and $f_1(1420)$ into $f_0(980)π^{0}$ are observed. For the first time, three axial-vectors, $f_1(1285)$, $f_1(1420)$ and $f_1(1510)$, are observed to decay into $π^{0}π^{0}π^{0}$. The product branching fractions of these resonances are reported.

hep-ex↗