arXiv subjects

L. Fava

Publications and source records attributed to L. Fava.

At least 127 records · Page 7Linked to original sources

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.

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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.

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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.

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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.

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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 $Q^2<2\,\text{GeV}^2$.

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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.

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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.

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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.

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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.

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arXiv2025

Precise Measurement of the $χ_{c0}$ Resonance Parameters and Branching Fractions of $χ_{c0,c2}\toπ^+π^-/K^+K^-$

By analyzing a $ψ(3686)$ data sample containing $(107.7\pm0.6)\times10^{6}$ events taken with the BESIII detector at the BEPCII storage ring in 2009, the $χ_{c0}$ resonance parameters are precisely measured using $χ_{c0,c2} \to π^+π^-/K^+K^-$ events. The mass of $χ_{c0}$ is determined to be $M(χ_{c0})=(3415.63\pm0.07\pm0.07\pm0.07$)~MeV/$c^2$, and its full width is $Γ(χ_{c0})=(12.52\pm0.12\pm0.13)~{\rm MeV}$, where the first uncertainty is statistical, the second systematic, and the third for mass comes from $χ_{c2}$ mass uncertainty. These measurements improve the precision of $χ_{c0}$ mass by a factor of four and width by one order of magnitude over the previous individual measurements, and significantly boost our knowledge about the charmonium spectrum. Together with additional $(345.4\pm2.6)\times10^{6}$ $ψ(3686)$ data events taken in 2012, the decay branching fractions of $χ_{c0,c2}\toπ^+π^-/K^+K^-$ are measured as well, with precision improved by a factor of three compared to previous measurements. These $χ_{c0}$ decay branching fractions provide important inputs for the study of glueballs.

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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 $5σ$.

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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.

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arXiv2025

Observation of resonant contribution to the $e^+e^-\to Ω^{-}\barΩ^{+}$ around 4.2 GeV and evidence of $ψ(3770)\to Ω^{-}\barΩ^{+}$

Using $e^+e^-$ collision data corresponding to a total integrated luminosity of 22.7 fb$^{-1}$, collected at center-of-mass energies between 3.7 and 4.7 GeV with the BESIII detector, we present a measurement of energy-dependent cross sections and effective form factors for the process of $e^+e^-\to Ω^{-}\barΩ^+$. By conducting a fit to the cross sections of $e^+e^-\to Ω^{-}\barΩ^+$ considering the continuum and resonant contributions, a clear resonant structure in the spectrum around 4.2 GeV is observed for the first time with a statistical significance exceeding 10$σ$, and it can be well described with the line shape of the $Y(4230)$ and $Y(4320)$ observed in $e^+e^-\to π^{+}π^{-}J/ψ$. Evidence for the decay $ψ(3770) \to Ω^-\barΩ^{+}$ is observed with a statistical significance of 4.4$σ$ by analyzing the measured cross sections together with earlier BESIII results, and the branching fraction is firstly measured to be $(4.0\pm1.0\pm0.6)$ $\times$ $10^{-5}$, where the first uncertainty is statistical and the second is systematic.

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arXiv2025

Measurement of the phase between strong and electromagnetic amplitudes in the decay $J/ψ\toϕη$

The first direct measurement of the relative phase between the strong and electromagnetic amplitudes for a $J/ψ$ decaying into a vector-pseudoscalar final state is performed using 26 energy points of $e^+e^-$ annihilation data between $3.00\ \text{GeV}$ and \mbox{3.12 GeV}. The data sets were collected by the BESIII detector with a total integrated luminosity of 452 pb$^{-1}$. By investigating the interference pattern in the cross section lineshape of $e^+e^-\toϕη$, the relative phase between the strong and electromagnetic amplitudes of $J/ψ$ decay is determined to be within $[133^\circ,228^\circ]$ at 68\% confidence level.

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arXiv2025

Measurement of the branching fractions of the Cabibbo-favored decays $Λ_{c}^{+}\toΛK_{S}^{0}K^{+}$ and $Λ_{c}^{+}\toΞ^{0}K_{S}^{0}π^{+}$ and search for $Λ_{c}^{+}\toΣ^{0} K_{S}^{0}K^{+}$

Based on $e^{+}e^{-}$ collision data corresponding to an integrated luminosity of about 4.5 fb$^{-1}$ collected at center-of-mass energies between 4599.53 MeV and 4698.82 MeV with the BESIII detector, the absolute branching fraction of the Cabibbo-favored decay $Λ_{c}^{+}\toΛK_{S}^{0}K^{+}$ is measured to be $(3.12\pm0.46\pm0.15)\times10^{-3}$. Combined with a previous measurement from the BESIII Collaboration, the branching fraction of the decay $Λ_{c}^{+}\toΛK_{S}^{0}K^{+}$ is calculated to be $(3.07\pm0.26\pm0.13)\times10^{-3}$. The decay $Λ_{c}^{+}\toΞ^{0}K_{S}^{0}π^{+}$ is observed for the first time with a statistical significance of $6.6σ$, and its branching fraction is determined to be $(3.70\pm0.60\pm0.21)\times10^{-3}$. In addition, a search for the decay $Λ_{c}^{+}\toΣ^{0} K_{S}^{0}K^{+}$ is performed and its branching fraction is determined to be $(0.80^{+0.28}_{-0.24}\pm0.16)\times10^{-3}$, corresponding to an upper limit of $1.28\times10^{-3}$ at $90\%$ confidence level. These measurements provide new information that can be used to distinguish between theoretical models.

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arXiv2025

Amplitude analysis of $ψ(3686)\to γK_S^0 K_S^0 $

Using $(2712\pm14)\times10^6$ $ψ(3686)$ events collected with the BESIII detector, we perform the first amplitude analysis of the radiative decay $ψ(3686)\to γK_S^0 K_S^0$ within the mass region $M_{K_S^0 K_S^0 }<2.8$ GeV/$c^2$. Employing a one-channel K-matrix approach for the description of the dynamics of the $K^0_S K^0_S$ system, the data sample is well described with four poles for the $f_0$-wave and three poles for the $f_2$-wave. The determined pole positions are consistent with those of well-established resonance states. The observed $f_0$ and $f_{2}$ states are found to be in agreement with those produced in radiative $J/ψ$ decays. The production behaviors of $f_0$ and $f_2$ poles in $ψ(3686)\toγK_S^0 K_S^0$ are qualified with their residues and the converted branching fractions. By comparing with $J/ψ\toγK_S^0 K_S^0$ decay, the ratios $\frac{\mathcal{B}(ψ(3686)\toγf_{0,2})}{\mathcal{B}(J/ψ\toγf_{0,2})}$ are determined, which provides crucial experimental inputs on the internal structure of the $f_{0,2}$ states, especially their potential mixing with glueball components.

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arXiv2025

First Measurement of the Decay Dynamics in the Semileptonic Transition of the $D^{+(0)}$ into the Axial-vector Meson $\bar K_1(1270)$

Using $e^+e^-$ data taken at the center-of-mass energy of 3.773 GeV with the BESIII detector, corresponding to an integrated luminosity of 20.3 fb$^{-1}$, we report the first measurement of the decay dynamics of the semileptonic decays $D^{+(0)}\to K^-π^+π^{0(-)} e^+ν_e$. The amplitude analysis gives the hadronic form factors of the semileptonic $D$ transitions into the axial-vector meson $\bar{K}_1(1270)$ to be $r_A=(-11.2\pm1.0_{\rm stat}\pm0.9_{\rm syst})\times10^{-2}$ and $r_V = (-4.3\pm 1.0_{\rm stat}\pm2.5_{\rm syst})\times 10^{-2}$. This is the first in the semileptonic decays of heavy mesons into axial-vector mesons. The angular analysis yields an up-down asymmetry $\mathcal{A}^\prime_{ud} = 0.01\pm0.11$, which is consistent with the Standard Model prediction. In addition, the branching fractions of $D^+\to \bar K_1(1270)^0 e^+ν_e$ and $D^0\to K_1(1270)^- e^+ν_e$ are determined with improved precision to be $(2.27\pm0.11_{\rm stat}\pm0.07_{\rm syst}\pm0.07_{\rm input})\times10^{-3}$ and $(1.02\pm0.06_{\rm stat}\pm0.06_{\rm syst}\pm0.03_{\rm input})\times10^{-3}$, respectively. No significant signals of $D^+\to \bar K_1(1400)^0 e^+ν_e$ and $D^0\to K_1(1400)^- e^+ν_e$ are observed and their branching fraction upper limits are set as $1.4\times10^{-4}$ and $0.7\times10^{-4}$ at 90\% confidence level, respectively.

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arXiv2025

Observation of the electromagnetic radiative decays of the \boldmath{$Λ(1520)$} and \boldmath{$Λ(1670)$} to \boldmath{$γΣ^0$}

Using $(10087\pm 44)\times10^6$ $J/ψ$ events collected with the BESIII detector, we report the first observation of the electromagnetic radiative decays of the $Λ(1520)$ and $Λ(1670)$ to $γΣ^0$, with a statistical significance of $16.6σ$ and $23.5σ$, respectively. The ratio of the branching fractions $\frac{\mathcal{B}(Λ(1520)\toγΛ)}{\mathcal{B}(Λ(1520)\toγΣ^0)}$ is determined to be $2.88\pm0.27(\text{stat.})\pm0.21(\text{syst.})$, which is in good agreement with flavor SU(3) symmetry. The branching fraction of $Λ(1520)\toγΣ^0$ is measured to be $\mathcal{B}(Λ(1520)\toγΣ^0)=(2.95\pm0.28(\text{stat.})\pm0.56(\text{syst.}))\times 10^{-3}$, corresponding to a partial width of $Γ(Λ(1520)\toγΣ^0)=(47.2\pm4.5(\text{stat.})\pm9.0(\text{syst.}))$ keV, which is inconsistent with predictions from the relativized constituent quark model and the Algebraic model. Additionally, we observe a clear resonant structure in the $γΣ^0$ mass spectrum around 1.67 GeV/$c^2$, attributed to the $Λ(1670)$. The product branching fraction $\mathcal{B}(J/ψ\to\barΛΛ(1670)+c.c.)\times\mathcal{B}(Λ(1670)\toγΣ^0)$ is measured for the first time as $(5.39\pm0.29(\text{stat.})\pm 0.44(\text{syst.}))\times 10^{-6}$. However, no corresponding structure is seen in the $γΛ$ mass spectrum, so an upper limit on the product branching fraction $\mathcal{B}(J/ψ\to\barΛΛ(1670)+c.c.)\times\mathcal{B}(Λ(1670)\toγΛ)$ is determined to be $5.97\times10^{-7}$ at the 90\% confidence level.

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