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E. Bianco

Publications and source records attributed to E. Bianco.

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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.

hep-ex↗
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.

hep-ex↗
arXiv2023

Study of the $e^+e^- \to π^{+}π^{-}ω$ process at center-of-mass energies between 4.0 and 4.6 GeV

Using $15.6$ $\rm fb^{-1}$ of $e^+e^-$ collision data collected at twenty-four center-of-mass energies from $4.0$ to $4.6$ GeV with the BESIII detector, the helicity amplitudes of the process $e^+e^-\to π^{+}π^{-}ω$ are analyzed for the first time. Born cross section measurements of two-body intermediate resonance states with statistical significance greater than 5$σ$ are presented, such as $f_{0}(500)$, $f_{0}(980)$, $f_{2}(1270)$, $f_{0}(1370)$, $b_{1}(1235)^{\pm}$, and $ρ(1450)^{\pm}$. In addition, evidence of a resonance state in $e^+e^-\to π^+π^-ω$ production is found. The mass of this state obtained by line shape fitting is about 4.2 GeV/$c^2$, which is consistent with the production of $ψ(4160)$ or $Y(4220)$.

hep-ex↗
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.

hep-ex↗
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.

hep-ex↗
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 $8.35~\text{fb}^{-1}$.

hep-ex↗
arXiv2023

Improved measurement of the branching fractions of the inclusive decays $D^+ \to K_S^0X $ and $D^0 \to K_S^0X $

By analyzing 2.93 fb$^{-1}$ of $e^+e^-$ collision data taken at the center-of-mass energy of 3.773 GeV with the BESIII detector, the branching fractions of the inclusive decays $D^+\to K^0_S X$ and $D^0\to K^0_S X$ are measured to be $(32.78\pm 0.13\pm 0.27)\%$ and $(20.54\pm 0.12\pm 0.18)\%$, respectively, where the first uncertainties are statistical and the second are systematic. These results are consistent with the world averages of previous measurements, but with improved precision.

hep-ex↗
arXiv2023

Observation of $e^+e^-\toπ^0π^0ψ_2(3823)$

Using a data sample corresponding to an integrated luminosity of 11.3 $\rm fb^{-1}$ collected at center-of-mass energies from $4.23$ to $4.70$~GeV with the BESIII detector, we observe the process $e^+e^-\toπ^0π^0ψ_2(3823)$ for the first time with a statistical significance of $6.0σ$. The ratio of average cross sections for $e^+e^-\toπ^0π^0ψ_2(3823)$ over $π^+π^-ψ_2(3823)$ is determined to be $\mathcal{R}=\frac{σ[e^+e^-\toπ^0π^0ψ_2(3823)]}{σ[e^+e^-\toπ^+π^-ψ_2(3823)]}=0.57\pm 0.14\pm0.05$, which is consistent with expectations from isospin symmetry. Here and below, the first uncertainties are statistical and the second are systematic. The mass of the $ψ_2(3823)$ is measured to be $M[ψ_2(3823)]=3824.5\pm 2.4\pm 1.0$~MeV/$c^2$. Due to the limited statistics, the intrinsic width of the $ψ_2(3823)$ is measured as an upper limit of $18.8$~MeV at $90\%$ confidence level.

hep-ex↗
arXiv2023

Observation of the decay $D^+_s\to ωπ^+η$

Using 7.33 fb$^{-1}$ of $e^+e^-$ collision data collected by the BESIII detector at center-of-mass energies between 4.128 and 4.226~GeV, we observe for the first time the decay $D^{\pm}_s\to ωπ^{\pm}η$ with a statistical significance of 7.6$σ$. The measured branching fraction of this decay is $(0.54\pm0.12\pm0.04)\%$, where the first uncertainty is statistical and the second is systematic.

hep-ex↗
arXiv2023

Study of $e^+e^-\toγϕJ/ψ$ from $\sqrt{s}=4.600$ to $4.951$ GeV

Using data samples with an integrated luminosity of $6.4$~fb$^{-1}$ collected by the BESIII detector operating at the BEPCII storage ring, the process of $e^+e^-\toγϕJ/ψ$ is studied. The processes of $e^+e^-\toϕχ_{c1,c2}$, $χ_{c1,c2}\toγJ/ψ$ are observed with a significance of more than $10σ$. The $\sqrt{s}$-dependent cross section of $e^+e^- \to ϕχ_{c1,c2}$ is measured between 4.600 and 4.951~GeV, and evidence of a resonance structure is found for the first time in the $ϕχ_{c2}$ process. We also search for the processes of $e^+e^-\toγX(4140)$, $γX(4274)$ and $γX(4500)$ via the $γϕJ/ψ$ final state, but no obvious structures are found. The upper limits on the production cross section times the branching fraction for these processes at the 90% confidence level are reported.

hep-ex↗
arXiv2023

Search for hidden-charm tetraquark with strangeness in $e^{+}e^{-}\rightarrow K^+ D_{s}^{*-} D^{*0}+c.c.$

We report a search for a heavier partner of the recently observed $Z_{cs}(3985)^{-}$ state, denoted as $Z_{cs}^{\prime -}$, in the process $e^{+} e^{-}\rightarrow K^{+}D_{s}^{*-}D^{* 0}+c.c.$, based on $e^+e^-$ collision data collected at the center-of-mass energies of $\sqrt{s}=4.661$, 4.682 and 4.699 GeV with the BESIII detector. The $Z_{cs}^{\prime -}$ is of interest as it is expected to be a candidate for a hidden-charm and open-strange tetraquark. A partial-reconstruction technique is used to isolate $K^+$ recoil-mass spectra, which are probed for a potential contribution from $Z_{cs}^{\prime -}\to D_{s}^{*-}D^{* 0}$ ($c.c.$). We find an excess of $Z_{cs}^{\prime -}\rightarrow D_{s}^{*-}D^{*0}$ ($c.c.$) candidates with a significance of $2.1σ$, after considering systematic uncertainties, at a mass of $(4123.5\pm0.7_\mathrm{stat.}\pm4.7_\mathrm{syst.})\ \mathrm{MeV}/c^{2}$. As the data set is limited in size, the upper limits are evaluated at the 90\% confidence level on the product of the Born cross sections ($σ^{\mathrm{Born}}$) and the branching fraction ($\mathcal{B}$) of $Z_{cs}^{\prime-}\rightarrow D_{s}^{*-}D^{* 0}$, under different assumptions of the $Z_{cs}^{\prime -}$ mass from 4.120 to 4.140 MeV and of the width from 10 to 50 MeV at the three center-of-mass energies. The upper limits of $σ^{\rm Born}\cdot\mathcal{B}$ are found to be at the level of $\mathcal{O}(1)$ pb at each energy. Larger data samples are needed to confirm the $Z_{cs}^{\prime -}$ state and clarify its nature in the coming years.

hep-ex↗
arXiv2022

Observation of the $J/ψ$ and $ψ(3686)$ decays into $ηΣ^{+}\barΣ^{-}$

The decays $J/ψ\toηΣ^{+}\barΣ{}^-$ and $ψ(3686)\toηΣ^{+}\barΣ{}^-$ are observed for the first time, using $(10087 \pm 44)\times 10^{6}$ $J/ψ$ and $(448.1 \pm 2.9)\times 10^{6}$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider. We determine the branching fractions of these two decays to be ${\cal B}(J/ψ\toηΣ^{+}\barΣ{}^-)=(6.34 \pm 0.21 \pm 0.37)\times 10^{-5}$ and ${\cal B}(ψ(3686)\toηΣ^{+}\barΣ{}^-)=(9.59 \pm 2.37 \pm 0.61)\times 10^{-6}$, where the first uncertainties are statistical and the second are systematic. The ratio of these two branching fractions is determined to be $\frac{{\cal B}(ψ(3686)\toηΣ^{+}\barΣ{}^-)}{{\cal B}(J/ψ\toηΣ^{+}\barΣ{}^-)}=(15.1 \pm 3.8)\%$, which is in agreement with the "12\% rule."

hep-ex↗
arXiv2022

Observations of the Cabibbo-Suppressed decays $Λ_{c}^{+}\to nπ^{+}π^{0}$, $nπ^{+}π^{-}π^{+}$ and the Cabibbo-Favored decay $Λ_{c}^{+}\to nK^{-}π^{+}π^{+}$

Using electron-positron annihilation data samples corresponding to an integrated luminosity of 4.5 $\rm{{fb}^{-1}}$, collected by the BESIII detector in the energy region between $4600$ MeV and $4699$ MeV, we report the first observations of the Cabibbo-suppressed decays $Λ_c^+\to nπ^+π^0$, $Λ_c^+\to nπ^+π^-π^+$, and the Cabibbo-favored decay $Λ_c^+\to nK^-π^+π^+$ with statistical significances of $7.9σ$, $7.8σ$, and $>10σ$, respectively. The branching fractions of these decays are measured to be $\mathcal{B}(Λ_{c}^{+}\rightarrow nπ^{+}π^{0})=(0.64\pm0.09\pm0.02)\%$, $\mathcal{B}(Λ_{c}^{+}\rightarrow nπ^{+}π^{-}π^{+})=(0.45\pm0.07\pm0.03)\%$, and $\mathcal{B}(Λ_{c}^{+}\rightarrow nK^{-}π^{+}π^{+})=(1.90\pm0.08\pm0.09)\%$, where the first uncertainties are statistical and the second are systematic. We find that the branching fraction of the decay $Λ_{c}^{+}\rightarrow nπ^{+}π^{0}$ is about one order of magnitude higher than that of $Λ_{c}^{+}\rightarrow nπ^{+}$.

hep-ex↗
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.

hep-ex↗
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.

hep-ex↗
arXiv2022

Observation of $Ξ^{-}$ Hyperon Transverse Polarization in $ψ(3686)\rightarrowΞ^{-}\barΞ^{+}$

Using a sample of $(448.1~\pm~2.9)$ $\times 10^{6}$ $ψ(3686)$ decays collected with the BESIII detector at BEPCII, we report an observation of $Ξ^{-}$ transverse polarization with a significance of $7.3 σ$ in the decay $ψ(3686)\rightarrowΞ^{-}\barΞ^{+}$ ($Ξ^{-}\rightarrowπ^{-}Λ$, $\barΞ^{+}\rightarrowπ^{+}\barΛ$, $Λ\to pπ^{-}$, $\barΛ\to\bar{p}π^{+}$). The relative phase of the electric and magnetic form factors is determined to be $ΔΦ= (0.667 \pm 0.111 \pm 0.058)$ rad. This is the first measurement of the relative phase for a $ψ(3686)$ decay into a pair of $Ξ^{-}\barΞ^{+}$ hyperons. The $Ξ^{-}$ decay parameters ($α_{Ξ^{-}}$, $ϕ_{Ξ^-}$) and their conjugates ($α_{\barΞ^{+}}$, $ϕ_{\barΞ^{+}}$), the angular-distribution parameter $α_ψ$, and the strong-phase difference $δ_{p}-δ_{s}$ for $Λ$-$π^-$ scattering are measured to be consistent with previous BESIII results.

hep-ex↗
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.

hep-ex↗
arXiv2022

A kiloelectron-volt ultrafast electron micro-diffraction apparatus using low emittance semiconductor photocathodes

We report the design and performance of a time-resolved electron diffraction apparatus capable of producing intense bunches with simultaneously single digit micron probe size, long coherence length, and $200$ fs rms time resolution. We measure the 5d (peak) beam brightness at the sample location in micro-diffraction mode to be $7 \times 10^{13} \ \mathrm{A}/\text{m}^2\text{-rad}^2$. To generate high brightness electron bunches, the system employs high efficiency, low emittance semiconductor photocathodes driven with a wavelength near the photoemission threshold at a repetition rate up to 250 kHz. We characterize spatial, temporal, and reciprocal space resolution of the apparatus. We perform proof-of-principle measurements of ultrafast heating in single crystal Au samples and compare experimental results with simulations that account for the effects of multiple-scattering.

physics.acc-ph↗