arXiv subjects

W. Gradl

Publications and source records attributed to W. Gradl.

At least 199 records · Page 11Linked to original sources

arXiv2020

Future Physics Programme of BESIII

There has recently been a dramatic renewal of interest in the subjects of hadron spectroscopy and charm physics. This renaissance has been driven in part by the discovery of a plethora of charmonium-like $XYZ$ states at BESIII and $B$ factories, and the observation of an intriguing proton-antiproton threshold enhancement and the possibly related $X(1835)$ meson state at BESIII, as well as the threshold measurements of charm mesons and charm baryons. We present a detailed survey of the important topics in tau-charm physics and hadron physics that can be further explored at BESIII over the remaining lifetime of BEPCII operation. This survey will help in the optimization of the data-taking plan over the coming years, and provides physics motivation for the possible upgrade of BEPCII to higher luminosity.

hep-ex↗

arXiv2020

Study of $e^{+}e^{-} \to D^{+} D^{-} π^{+} π^{-} $ at center-of-mass energies from 4.36 to 4.60 GeV

We report a study of the $e^{+}e^{-} \to D^{+} D^{-} π^{+} π^{-}$ process using $e^{+}e^{-}$ collision data samples with an integrated luminosity of $2.5\,\rm{fb}^{-1}$ at center-of-mass energies from 4.36 to $4.60 \rm{GeV}$, collected with the BESIII detector at the BEPCII storage ring. The $D_{1}(2420)^+$ is observed in the $D^{+} π^{+} π^{-}$ mass spectrum. The mass and width of the $D_{1}(2420)^+$ are measured to be $(2427.2\pm 1.0_{\rm stat.}\pm 1.2_{\rm syst.}) \rm{MeV}/c^2$ and $(23.2\pm 2.3_{\rm stat.} \pm2.3_{\rm syst.}) \rm{MeV}$, respectively. The first errors are statistical and the second ones are systematic. In addition, the Born cross sections of the $e^{+}e^{-} \to D_{1}(2420)^+D^- + c.c. \to D^{+} D^{-} π^{+} π^{-}$ and $e^{+}e^{-} \to ψ(3770) π^{+} π^{-} \to D^{+} D^{-} π^{+} π^{-}$ processes are measured as a function of the center-of-mass energy.

hep-ex↗

arXiv2020

Observation of a cross-section enhancement near mass threshold in $e^{+}e^{-}\rightarrowΛ\barΛ$

The process $e^{+}e^{-}\rightarrowΛ\barΛ$ is studied using data samples at $\sqrt{s}=2.2324$, 2.400, 2.800 and 3.080 GeV collected with the BESIII detector operating at the BEPCII collider. The Born cross section is measured at $\sqrt{s}$=2.2324 GeV, which is 1.0 MeV above the $Λ\barΛ$ mass threshold, to be $305\pm45^{+66}_{-36}$ pb, where the first uncertainty is statistical and the second systematic. The substantial cross section near threshold is significantly larger than that expected from theory, which predicts the cross section to vanish at threshold. The Born cross sections at $\sqrt{s}$=2.400, 2.800 and 3.080 GeV are measured and found to be consistent with previous experimental results, but with improved precision. Finally, the corresponding effective electromagnetic form factors of $Λ$ are deduced.

hep-ex↗

arXiv2020

Observation of the $Y(4220)$ and $Y(4360)$ in the process $e^{+}e^{-} \to ηJ/ψ$

The cross sections of the process $e^{+}e^{-} \to ηJ/ψ$ at center-of-mass energies ($\sqrt{s}$) between 3.81 and 4.60 GeV are measured with high precision by using data samples collected with the BESIII detector operating at the BEPCII storage ring. Three structures are observed by analyzing the lineshape of the measured cross sections, and a maximum-likelihood fit including three resonances is performed by assuming the lowest lying structure is the $ψ(4040)$. For the other resonances, we obtain masses of $(4218.7 \pm 4.0 \pm 2.5)$ and $(4380.4 \pm 14.2 \pm 1.8)$ MeV/c$^{2}$ with corresponding widths of $(82.5 \pm 5.9 \pm 0.5)$ and $(147.0 \pm 63.0 \pm 25.8)$ MeV, respectively, where the first uncertainties are statistical and the second ones systematic. The measured resonant parameters are consistent with those of the $Y(4220)$ and $Y(4360)$ from pr evious measurements of different final states. For the first time, we observe the decays of the $Y(4220)$ and $Y(4360)$ into $ηJ/ψ$ final states.

hep-ex↗

arXiv2020

Partial wave analysis of $ψ(3686)\rightarrow K^{+}K^{-}η$

Using a sample of $(448.1\pm2.9)\times10^6$ $ψ(3686)$ events collected with the BESIII detector, we perform the first partial wave analysis of $ψ(3686)\rightarrow K^+K^-η$. In addition to the well established states, $ϕ(1020)$, $ϕ(1680)$, and $K_3^*(1780)$, contributions from $X(1750)$, $ρ(2150)$, $ρ_3(2250)$, and $K^*_2(1980)$ are also observed. The $X(1750)$ state is determined to be a $1^{--}$ resonance. The simultaneous observation of the $ϕ(1680)$ and $X(1750)$ indicates that the $X(1750)$, with previous observations in photoproduction, is distinct from the $ϕ(1680)$. The masses, widths, branching fractions of $ψ(3686)\rightarrow K^+K^-η$ and the intermediate resonances are also measured.

hep-ex↗

arXiv2020

Search for rare or forbidden decays of the $D^{0}$ meson

We present a search for nine lepton-number-violating and three lepton-flavor-violating neutral charm decays of the type $D^0\rightarrow h^{\prime -} h^{-}\ell^{\prime +} \ell^{+}$ and $D^0\rightarrow h^{\prime -} h^{+}\ell^{\prime\pm} \ell^{\mp}$, where $h$ and $h^{\prime}$ represent a $K$ or $π$ meson and $\ell$ and $\ell^{\prime}$ an electron or muon. The analysis is based on $468$ fb$^{-1}$ of $e^+e^-$ annihilation data collected at or close to the $Y(4S)$ resonance with the BaBar detector at the SLAC National Accelerator Laboratory. No significant signal is observed for any of the twelve modes and we establish 90% confidence level upper limits on the branching fractions in the range $(1.0 - 30.6)\times 10^{-7}$. The limits are between one and three orders of magnitude times more stringent than previous measurements.

hep-ex↗

arXiv2020

Search for baryon and lepton number violating decays $D^+\to\barΛ(\barΣ^0)e^+$ and $D^+\toΛ(Σ^0)e^+$

Using a 2.93 fb$^{-1}$ data sample of electron-positron collisions taken with the BESIII detector at a center-of-mass energy of 3.773 GeV, which corresponds to $(8296\pm31\pm64)\times10^3 D^+D^-$ pairs, we search for the baryon and lepton number violating decays $D^+\to\barΛ(\barΣ^0)e^+$ and $D^+\toΛ(Σ^0)e^+$. No obvious signals are found with the current statistics and upper limits on the branching fractions of these four decays are set at the level of $10^{-6}$ at 90% confidence level.

hep-ex↗

arXiv2020

Measurement of proton electromagnetic form factors in $e^+e^- \to p\bar{p}$ in the energy region 2.00-3.08 GeV

The process of $e^+e^- \rightarrow p\bar{p}$ is studied at 22 center-of-mass energy points ($\sqrt{s}$) from 2.00 to 3.08 GeV, exploiting 688.5~pb$^{-1}$ of data collected with the BESIII detector operating at the BEPCII collider. The Born cross section~($σ_{p\bar{p}}$) of $e^+e^- \rightarrow p\bar{p}$ is measured with the energy-scan technique and it is found to be consistent with previously published data, but with much improved accuracy. In addition, the electromagnetic form-factor ratio ($|G_{E}/G_{M}|$) and the value of the effective ($|G_{\rm{eff}}|$), electric ($|G_E|$) and magnetic ($|G_M|$) form factors are measured by studying the helicity angle of the proton at 16 center-of-mass energy points. $|G_{E}/G_{M}|$ and $|G_M|$ are determined with high accuracy, providing uncertainties comparable to data in the space-like region, and $|G_E|$ is measured for the first time. We reach unprecedented accuracy, and precision results in the time-like region provide information to improve our understanding of the proton inner structure and to test theoretical models which depend on non-perturbative Quantum Chromodynamics.

hep-ex↗

arXiv2020

Measurement of the cross section for $e^{+}e^{-}\rightarrowΞ^{-}\barΞ^{+}$ and observation of an excited $Ξ$ baryon

Using a total of 11.0 fb$^{-1}$ of $e^{+}e^{-}$ collision data with center-of-mass energies between 4.009 GeV and 4.6 GeV and collected with the BESIII detector at BEPCII, we measure fifteen exclusive cross sections and effective form factors for the process $e^{+}e^{-}\rightarrowΞ^{-}\barΞ^{+}$ by means of a single baryon-tag method. After performing a fit to the dressed cross section of $e^{+}e^{-}\rightarrowΞ^{-}\barΞ^{+}$, no significant $ψ(4230)$ or $ψ(4260)$ resonance is observed in the $Ξ^{-}\barΞ^{+}$ final states, and upper limits at the 90\% confidence level on $Γ_{ee}\mathcal{B}$ for the processes $ψ(4230)$/$ψ(4260)\rightarrowΞ^{-}\barΞ^{+}$ are determined. In addition, an excited $Ξ$ baryon at 1820 MeV/$c^{2}$ is observed with a statistical significance of 6.2 $\sim$ 6.5$σ$ by including the systematic uncertainty, and the mass and width are measured to be $M = (1825.5 \pm 4.7 \pm 4.7)$~MeV/$c^{2}$ and $Γ= (17.0 \pm 15.0 \pm 7.9)$~MeV, which confirms the existence of the $J^{P}=\frac{3}{2}^{-}$ state $Ξ(1820)$.

hep-ex↗

arXiv2020

Measurement of the beam-helicity asymmetry in photoproduction of $π^{0}η$ pairs on carbon, aluminum, and lead

The beam-helicity asymmetry was measured, for the first time, in photoproduction of $π^{0}η$ pairs on carbon, aluminum, and lead, with the A2 experimental setup at MAMI. The results are compared to an earlier measurement on a free proton and to the corresponding theoretical calculations. The Mainz model is used to predict the beam-helicity asymmetry for the nuclear targets. The present results indicate that the photoproduction mechanism for $π^{0}η$ pairs on nuclei is similar to photoproduction on a free nucleon. This process is dominated by the $D_{33}$ partial wave with the $ηΔ(1232)$ intermediate state.

nucl-ex↗

arXiv2020

Cross section measurement of $e^+e^- \rightarrow η'J/ψ$ from $\sqrt{s} = 4.178$ to $4.600$ GeV

The cross section of the process $e^+e^- \rightarrow η'J/ψ$ is measured at center-of-mass energies from $\sqrt{s} =$ 4.178 to 4.600 GeV using data samples corresponding to a total integrated luminosity of 11 fb$^{-1}$ collected with the BESIII detector operating at the BEPCII storage ring. The dependence of the cross section on $\sqrt{s}$ shows an enhancement around $4.2$ GeV. While the shape of the cross section cannot be fully explained with a single $ψ(4160)$ or $ψ(4260)$ state, a coherent sum of the two states does provide a reasonable description of the data.

hep-ex↗

arXiv2020

Observation of a resonant structure in $e^{+}e^{-} \to K^{+}K^{-}π^{0}π^{0}$

Using $e^{+}e^{-}$ collision data samples with center-of-mass energies ranging from 2.000 to 2.644 GeV, collected by the BESIII detector at the BEPCII collider, and with a total integrated luminosity of 300 pb^{-1}, a partial-wave analysis is performed for the process $e^{+}e^{-} \to K^{+}K^{-}π^{0}π^{0}$. The total Born cross sections for the process $e^{+}e^{-} \to K^{+}K^{-}π^{0}π^{0}$, as well as the Born cross sections f or the subprocesses $e^{+}e^{-} \to ϕπ^{0}π^{0}$, $K^{+}(1460)K^{-}$, $K^{+}_{1}(1400)K^{-}$, $K^{+}_{1}(1270)K^{-}$ and $K^{*+}(892)K^{*-}(892)$, are measured versus the center-of-mass energy. The corresponding results for $e^{+}e^{-} \to K^{+}K^{-}π^{0}π^{0}$ and $ϕπ^{0}π^{0}$ are consistent with those of BaBar and have much improved precision.By analyzing the cross sections for the four subprocesses, $K^{+}(1460)K^{-}$, $K^{+}_{1}(1400)K^{-}$, $K^{+ }_{1}(1270)K^{-}$ and $K^{*+}K^{*-}$, a structure with mass $M$ = (2126.5 $\pm$ 16.8 $\pm$ 12.4)~MeV/c^{2} and width $Γ$ = (106.9 $\pm$ 32.1 $\pm$ 28.1)~MeV is observed with an overall statistical significance of 6.3 $σ$, although with very limited significance in the subprocesses $e^{+}e^{-} \to K^{+}_{1}(1270)K^{-}$ and $K^{*+}(892)K^{*-}(892)$. The resonant parameters of the observed structure suggest it can be identified with the $ϕ(2170)$, thus the results provide valuable input to the internal nature of the $ϕ(2170)$.

hep-ex↗

arXiv2020

Measurement of {\boldmath $J/ψ\toΞ(1530)^{-}\barΞ^{+}$} and evidence for the radiative decay {\boldmath $Ξ(1530)^{-}\toγΞ^-$}

The SU(3)-flavor violating decay $J/ψ\toΞ(1530)^{-}\barΞ^{+}+c.c.$ is studied using $(1310.6\pm7.0)\times 10^{6} ~J/ψ$ events collected with the BESIII detector at BEPCII and the branching fraction is measured to be ${\cal{B}}(J/ψ\toΞ(1530)^{-}\barΞ^{+}+c.c.)=(3.17\pm0.02_{\rm stat.}\pm0.08_{\rm syst.})\times10^{-4}$. This is consistent with previous measurements with an improved precision. The angular parameter for this decay is measured for the first time and is found to be $α=-0.21\pm0.04_{\rm stat.}\pm0.06_{\rm syst.}$. In addition, we report evidence for the radiative decay $Ξ(1530)^{-}\toγΞ^- $ with a significance of 3.9$σ$, including the systematic uncertainties. The 90\% confidence level upper limit on the branching fraction is determined to be $\mathcal{B}(Ξ(1530)^{-}\toγΞ^- )\leq3.7$\%.

hep-ex↗

arXiv2019

Measurement of the $e^+e^-\toπ^+π^-π^0$ cross section from 0.7 GeV to 3.0 GeV via initial-state radiation

The cross section of the process $e^+e^-\toπ^+π^-π^0$ is measured with a precision of 1.6% to 25% in the energy range between $0.7$ and 3.0 GeV using the Initial State Radiation method. A data set with an integrated luminosity of $2.93$fb$^{-1}$ taken at the center-of-mass energy of $\sqrt{s}=3.773$GeV with the BESIII detector at the BEPCII collider is used. The product branching fractions for $ω$, $ϕ$, $ω(1420)$, and $ω(1650)$ are measured to be $\mathcal{B}(ω\to e^+e^-) \times \mathcal{B}(ω\to π^+π^-π^0)=(6.94\pm0.08\pm0.16) \times 10^{-5}$, $\mathcal{B}(ϕ\to e^+e^-) \times \mathcal{B}(ϕ\toπ^+π^-π^0) = (4.20\pm0.08\pm0.19) \times 10^{-5}$, $\mathcal{B}(ω(1420)\to e^+e^-) \times \mathcal{B}(ω(1420) \to π^+π^-π^0) = (0.84\pm0.09\pm0.09) \times 10^{-6}$, and $\mathcal{B}(ω(1650) \to e^+e^) \times \mathcal{B}(ω(1650)\to π^+π^-π^0) = (1.14\pm0.15\pm0.15)\times10^{-6}$, respectively. The branching fraction $\mathcal{B}(J/ψ\to π^+π^-π^0)$ is measured to be $(2.188 \pm 0.024 \pm 0.024 \pm0.040 (Γ_{ee}^{J/ψ}))\%$, where $Γ_{ee}^{J/ψ}$ is the dileptonic width of $J/ψ$. The first errors are of statistical, the second and third ones of systematic nature.

hep-ex↗

arXiv2019

Observation of the $X(2370)$ and search for the $X(2120)$ in $J/ψ\toγK\bar{K} η'$

Using a sample of $1.31\times10^{9} ~J/ψ$ events collected with the BESIII detector, we perform a study of $J/ψ\toγK\bar{K}η'$. The $X(2370)$ is observed in the $K\bar{K}η'$ invariant-mass distribution with a statistical significance of 8.3$σ$. Its resonance parameters are measured to be $M = 2341.6 \pm 6.5\text{(stat.)} \pm 5.7\text{(syst.)}$~MeV/$c^{2}$ and $Γ= 117 \pm 10 \text{(stat.)} \pm 8 \text{(syst.)}$~MeV. The product branching fractions for $J/ψ\to γX(2370), X(2370) \to K^{+} K^{-}η'$ and $J/ψ\to γX(2370), X(2370) \to K_{S}^{0} K_{S}^{0}η'$ are determined to be $(1.79 \pm 0.23 \text{(stat.)} \pm 0.65 \text{(syst.)}) \times 10^{-5}$ and $(1.18 \pm 0.32\ text{(stat.)} \pm 0.39 \text{(syst.)}) \times 10^{-5}$, respectively. No evident signal for the $X(2120)$ is observed in the $K\bar{K}η'$ invariant-mass distribution. The upper limits for the product branching fractions of $\mathcal{B}(J/ψ\to γX(2120)\toγK^{+} K^{-} η')$ and $\mathcal{B}(J/ψ\toγX(2120)\toγK_{S}^{0} K_{S}^{0} η')$ are determined to be $1.49\times10^{-5}$ and $6.38\times10^{-6}$ at the 90% confidence level, respectively.

hep-ex↗

arXiv2019

Observation of the Semileptonic $D^+$ Transition into an Axial-Vector Meson $\bar K_1(1270)^0$

By analyzing a 2.93~$\rm fb^{-1}$ data sample of $e^+e^-$ collisions, recorded at a center-of-mass energy of 3.773 $\rm \,GeV$ with the BESIII detector operated at the BEPCII collider, we have searched for the semileptonic $D^+$ transition into the axial-vector meson ${\bar{K}}_{1}(1270)^{0}$. The $D^{+} \rightarrow {\bar{K}}_{1}(1270)^{0}e^{+}ν_{e}$ decay is observed for the first time with a statistical significance greater than $10σ$. Its decay branching fraction is determined to be ${\mathcal B}[D^+\to \bar K_1(1270)^0 e^+ν_e]=(2.30\pm0.26\pm 0.18 \pm 0.25)\times10^{-3}$, where the first and second uncertainties are statistical and systematic, respectively, and the third originates from the input branching fraction of ${\bar{K}}_{1}(1270)^{0} \rightarrow K^{-} π^{+} π^{0}$.

hep-ex↗

arXiv2019

Measurement of Branching Fractions of $ψ(3686)\rightarrowϕη^\prime, ϕf_1(1285)$ and $ϕη(1405)$

Using a sample of $448.1\times10^6$ $ψ(3686)$ events collected with the BESIII detector, we perform a study of the decay $ψ(3686) \rightarrow ϕπ^{+}π^{-}η$. The branching fraction of $ψ(3686)\rightarrowϕη^\prime$ is determined to be $(1.51\pm0.16\pm0.12)\times 10^{-5}$, which is consistent with the previous measurement but with significantly improved precision. The resonances $f_{1}(1285)$ and $η(1405)$ are clearly observed in the $π^{+}π^{-}η$ mass spectrum with statistical significances of $18σ$ and $9.7σ$, respectively. The corresponding product branching fractions are measured to be $\mathcal{B}(ψ(3686)\rightarrowϕf_{1}(1285),f_{1}(1285)\rightarrowπ^{+}π^{-}η) =(1.03\pm0.10\pm0.09)\times 10^{-5}$ and $\mathcal{B}(ψ(3686)\rightarrowϕη(1405),η(1405)\rightarrowπ^{+}π^{-}η) =(8.46\pm1.37\pm0.92)\times 10^{-6}$.

hep-ex↗

arXiv2019

Observation of the leptonic decay $D^+ \to τ^+ ν_τ$

We report the first observation of $D^+\toτ^+ν_τ$ with a significance of $5.1σ$. We measure ${\cal B}(D^+\toτ^+ν_τ) = (1.20\pm0.24_{\text{stat.}}\pm0.12_{\text{syst.}})\times10^{-3}$. Taking the world average ${\cal B}(D^+\toμ^+ν_μ) = (3.74\pm0.17)\times10^{-4}$, we obtain $R_{τ/μ} =Γ(D^+\toτ^+ν_τ)/Γ(D^+\toμ^+ν_μ) = 3.21\pm0.64_{\text{stat.}}\pm0.43_{\text{syst.}}$, which is consistent with the Standard Model expectation of lepton flavor universality. Using external inputs, our results give values for the $D^+$ decay constant $f_{D^+}$ and the CKM matrix element $|V_{cd}|$ that are consistent with, but less precise than, other determinations.

hep-ex↗