arXiv subjects

W. Gradl

Publications and source records attributed to W. Gradl.

At least 271 records · Page 15Linked to original sources

arXiv2018

Measurement of $e^{+} e^{-} \rightarrow K^{+} K^{-}$ cross section at $\sqrt{s} = 2.00 - 3.08$ GeV

The cross section of the process $e^{+} e^{-} \rightarrow K^{+} K^{-}$ is measured at a number of center-of-mass energies $\sqrt{s}$ from 2.00 to 3.08 GeV with the BESIII detector at the Beijing Electron Positron Collider (BEPCII). The results provide the best precision achieved so far. A resonant structure around 2.2 GeV is observed in the cross section line shape. A Breit-Wigner fit yields a mass of $M=2239.2 \pm 7.1 \pm 11.3$~and a width of $Γ=139.8\pm12.3\pm20.6$ MeV, where the first uncertainties are statistical and the second ones are systematic. In addition, the time-like electromagnetic form factor of the kaon is determined at the individual center-of-mass energy points.

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arXiv2018

Dalitz Plot Analysis of the Decay $ω\rightarrow π^{+}π^{-}π^{0}$

Using a low-background sample of $2.6\times 10^5$ $J/ψ\rightarrowωη(ω\rightarrowπ^{+}π^{-}π^{0},η\rightarrowγγ)$ events, about 5 times larger statistics than previous experiments, we present a Dalitz plot analysis of the decay $ω\rightarrowπ^{+}π^{-}π^{0}$. It is found that the Dalitz plot distribution differs from the pure $P$-wave phase space with a statistical significance of $18.9σ$. The parameters from the fit to data are in reasonable agreement with those without the cross-channel effect within the dispersive framework, which indicates that the cross-channel effect in $ω\rightarrowπ^+π^-π^0$ is not significant.

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arXiv2018

Experimental study of the $γp\rightarrow K^0Σ^+$, $γn\rightarrow K^0Λ$, and $γn\rightarrow K^0 Σ^0$ reactions at the Mainz Microtron

This work measured $dσ/dΩ$ for neutral kaon photoproduction reactions from threshold up to a c.m.\ energy of 1855MeV, focussing specifically on the $γp\rightarrow K^0Σ^+$, $γn\rightarrow K^0Λ$, and $γn\rightarrow K^0 Σ^0$ reactions. Our results for $γn\rightarrow K^0 Σ^0$ are the first-ever measurements for that reaction. These data will provide insight into the properties of $N^*$ resonances and, in particular, will lead to an improved knowledge about those states that couple only weakly to the $πN$ channel. Integrated cross sections were extracted by fitting the differential cross sections for each reaction as a series of Legendre polynomials and our results are compared with prior experimental results and theoretical predictions.

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arXiv2018

Observation of the $W$-Annihilation Decay $D^{+}_{s} \rightarrow ωπ^{+}$ and Evidence for $D^{+}_{s} \rightarrow ωK^{+}$

We report on the observation of the $W$-annihilation decay $D^{+}_{s} \rightarrow ωπ^{+}$ and the evidence for $D_{s}^{+} \rightarrow ωK^{+}$ with a data sample corresponding to an integrated luminosity of 3.19 fb$^{-1}$ collected with the BESIII detector at the center-of-mass energy $\sqrt{s} = 4.178$ GeV. We obtain the branching fractions $\mathcal{B}(D^{+}_{s} \rightarrow ωπ^{+}) = (1.77\pm0.32_{\rm stat.}\pm0.11_{\rm sys.}) \times 10^{-3}$ and $\mathcal{B}(D^{+}_{s} \rightarrow ωK^{+}) = (0.87\pm0.24_{\rm stat.}\pm0.07_{\rm sys.}) \times 10^{-3}$, respectively.

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arXiv2018

Measurement of the Branching Fraction For the Semi-Leptonic Decays $D^{0(+)}\to π^{-(0)}μ^+ν_μ$ and Test of Lepton Flavor Universality

Using a data sample corresponding to an integrated luminosity of $2.93\,\rm fb^{-1}$ taken at a center-of-mass energy of 3.773\,GeV with the BESIII detector operated at the BEPCII collider, we perform an analysis of the semi-leptonic decays $D^{0(+)}\to π^{-(0)}μ^+ν_μ$. The branching fractions of $D^0\to π^-μ^+ν_μ$ and $D^+\to π^0μ^+ν_μ$ are measured to be $(0.272 \pm 0.008_{\rm stat.} \pm 0.006_{\rm syst.})\%$ and $(0.350 \pm 0.011_{\rm stat.} \pm 0.010_{\rm syst.})\%$, respectively, where the former is of much improved precision compared to previous results and the latter is determined for the first time. Using these results along with previous BESIII measurements of $D^{0(+)}\to π^{-(0)}e^+ν_e$, we calculate the branching fraction ratios to be ${\mathcal R}^0\equiv {\mathcal B}_{D^{0}\to π^{-}μ^+ν_μ}/{\mathcal B}_{D^{0}\to π^{-}e^+ν_e}=0.922\pm 0.030_{\rm stat.}\pm0.022_{\rm syst.}$ and ${\mathcal R}^+\equiv {\mathcal B}_{D^{+}\to π^{0}μ^+ν_μ}/{\mathcal B}_{D^{+}\to π^{0}e^+ν_e}=0.964\pm 0.037_{\rm stat.}\pm0.026_{\rm syst.}$, which are compatible with the theoretical expectation of lepton flavor universality within $1.7σ$ and $0.5σ$, respectively. We also examine the branching fraction ratios in different four-momentum transfer square regions, and find no significant deviations from the standard model predictions.

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arXiv2018

Observation of $h_1(1380)$ in the $J/ψ\to η^{\prime} K\bar K π$ Decay

Using $1.31 \times 10^9$ $J/ψ$ events collected by the BESIII detector at the BEPCII $e^+e^-$ collider, we report the first observation of the $h_1(1380)$ in $J/ψ\to η^{\prime} h_1(1380)$ with a significance of more than ten standard deviations. The mass and width of the possible axial-vector strangeonium candidate $h_1(1380)$ are measured to be $M = (1423.2 \pm 2.1 \pm 7.3)\mevcc$ and $Γ= (90.3 \pm 9.8 \pm 17.5)\mev$. The product branching fractions, assuming no interference, are determined to be $\mathcal{B}(J/ψ\to η^{\prime}h_1(1380)) \times \mathcal{B}(h_1(1380) \to K^{*}(892)^{+} K^{-} +c.c.) = (1.51 \pm 0.09 \pm 0.21) \times 10^{-4}$ in $η^{\prime}K^+K^-π^0$ mode and $\mathcal{B}(J/ψ\to η^{\prime}h_1(1380)) \times \mathcal{B}(h_1(1380) \to K^{*}(892)\bar K +c.c.) = (2.16 \pm 0.12 \pm 0.29) \times 10^{-4}$ in $η^{\prime}K_S^0K^{\pm}π^{\mp}$ mode. The first uncertainties are statistical and the second are systematic. Isospin symmetry violation is observed in the decays $h_1(1380) \to K^{*}(892)^{+} K^{-} +c.c.$ and $h_1(1380) \to K^{*}(892)^{0}\bar K^{0} +c.c.$. Based on the measured $h_1(1380)$ mass, the mixing angle between the states $h_1(1170)$ and $h_1(1380)$ is determined to be $(35.9\pm2.6)^{\circ}$, consistent with theoretical expectations.

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arXiv2018

Measurements of $e^+e^- \to K_{S}^{0}K^{\pm}π^{\mp}π^0$ and $K_{S}^{0}K^{\pm}π^{\mp}η$ at center-of-mass energies from $3.90$ to $4.60~\mathrm{GeV}$

Using $5.2 \ \mathrm{fb}^{-1}$ $e^+ e^-$ annihilation data samples collected with the BESIII detector, we measure the cross sections of $e^+e^- \to K_S^0 K^\pm π^\mp π^0$ and $K_{S}^{0}K^{\pm}π^{\mp}η$ at center-of-mass energies from $3.90$ to $4.60$ GeV. In addition, we search for the charmonium-like resonance $Y(4260)$ decays into $K_{S}^{0}K^{\pm}π^{\mp}π^0$ and $K_{S}^{0}K^{\pm}π^{\mp}η$, and $Z_c^{0,\pm}(3900)$ decays into $K_{S}^{0}K^{\pm}π^{\mp,0}$ and $K_{S}^{0}K^{\pm}η$. Corresponding upper limits are provided since no clear signal is observed.

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arXiv2018

First measurement of helicity-dependent cross sections in pi0-eta photoproduction from quasi-free nucleons

The helicity-dependent cross sections for the photoproduction of $π^0η$ pairs have been measured for the first time. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball - TAPS calorimeter. The experiment used a polarized deuterated butanol target and a circularly polarized photon beam. This arrangement allowed the $σ_{1/2}$ (photon and target spin antiparallel) and $σ_{3/2}$ (parallel spins) components to be measured for quasi-free production of $π^0η$ pairs off protons and neutrons. The main finding is that the two helicity components contribute identically, within uncertainties, for both participant protons and neutrons. The absolute couplings for protons and neutrons are also identical. This means that nucleon resonances contributing to this reaction in the investigated energy range have almost equal electromagnetic helicity couplings, $A_{1/2}^{n,p}$ and $A_{3/2}^{n,p}$. Identical couplings for protons and neutrons are typical for $Δ$ resonances and identical $A_{1/2}$ and $A_{3/2}$ components are only possible for $J\geq 3/2$ states, which constrains possible contributions of nucleon resonances.

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arXiv2018

First measurement of $e^+ e^- \to pK^{0}_{S}\bar{n}K^{-} + c.c.$ above open charm threshold

The process $e^+e^-\rightarrow pK^{0}_{S}\bar{n}K^{-} + c.c.$ and its intermediate processes are studied for the first time, using data samples collected with the BESIII detector at BEPCII at center-of-mass energies of 3.773, 4.008, 4.226, 4.258, 4.358, 4.416, and 4.600 GeV, with a total integrated luminosity of 7.4 fb$^{-1}$. The Born cross section of $e^+e^- \to p K^{0}_S\bar{n}K^- + c.c.$ is measured at each center-of-mass energy, but no significant resonant structure in the measured cross-section line shape between 3.773 and 4.600 GeV is observed. No evident structure is detected in the $pK^-$, $nK^{0}_S$, $pK^0_{S}$, $nK^+$, $p\bar{n}$, or $K^{0}_S K^-$ invariant mass distributions except for $Λ(1520)$. The Born cross sections of $e^+e^-\rightarrowΛ(1520)\bar{n}K^{0}_{S} + c.c.$ and $e^+e^-\rightarrow Λ(1520)\bar{p}K^{+} + c.c.$ are measured, and the 90\% confidence level upper limits on the Born cross sections of $e^+e^-\rightarrowΛ(1520)\barΛ(1520)$ are determined at the seven center-of-mass energies.

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arXiv2018

Polarization and Entanglement in Baryon-Antibaryon Pair Production in Electron-Positron Annihilation

Using a sample of $1.31\times 10^9$ $J/ψ$ events collected with the BESIII detector, we report the first observation of spin polarization of $Λ$ and $\barΛ$ hyperons from the coherent production in the $J/ψ\toΛ\barΛ$ decay. We measure the phase between the hadronic form factors to be $ΔΦ=(42.4\pm0.6\pm0.5)^\circ$. The decay parameters for $Λ\to pπ^-$ ($α_-$), $\barΛ\to\bar pπ^+$ ($α_+$) and $\barΛ\to\bar nπ^0$ ($\barα_0$) are measured to be $α_-=0.750\pm0.009\pm0.004$, $α_+=-0.758\pm0.010\pm0.007$ and $\barα_0=-0.692\pm0.016\pm0.006$, respectively. The obtained value of $α_-$ is higher by $(17\pm 3)\%$ than the current world average. In addition, the $CP$ asymmetry of $-0.006\pm0.012\pm0.007$ is extracted with substantially improved precision. The ratio $\barα_0/α_{+} = 0.913\pm 0.028 \pm 0.012$ is also measured.

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arXiv2018

Amplitude analysis of the $K_{S}K_{S}$ system produced in radiative $J/ψ$ decays

An amplitude analysis of the $K_{S}K_{S}$ system produced in radiative $J/ψ$ decays is performed using the $(1310.6\pm7.0)\times10^{6}$ $J/ψ$ decays collected by the BESIII detector. Two approaches are presented. A mass-dependent analysis is performed by parameterizing the $K_{S}K_{S}$ invariant mass spectrum as a sum of Breit-Wigner line shapes. Additionally, a mass-independent analysis is performed to extract a piecewise function that describes the dynamics of the $K_{S}K_{S}$ system while making minimal assumptions about the properties and number of poles in the amplitude. The dominant amplitudes in the mass-dependent analysis include the $f_{0}(1710)$, $f_{0}(2200)$, and $f_{2}^\prime(1525)$. The mass-independent results, which are made available as input for further studies, are consistent with those of the mass-dependent analysis and are useful for a systematic study of hadronic interactions. The branching fraction of radiative $J/ψ$ decays to $K_{S}K_{S}$ is measured to be $(8.1 \pm 0.4) \times 10^{-4}$, where the uncertainty is systematic and the statistical uncertainty is negligible.

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arXiv2018

Observation of $ψ(3686) \to η' e^+ e^- $

Using a data sample of $448.1 \times 10^6$ $ψ(3686)$ events collected with the BESIII detector at the BEPCII collider, we report the first observation of the electromagnetic Dalitz decay $ψ(3686) \to η' e^+ e^-$, with significances of 7.0$σ$ and 6.3$σ$ when reconstructing the $η'$ meson via its decay modes $η'\toγπ^+ π^-$ and $η'\toπ^+π^-η$ ($η\to γγ$), respectively. The weighted average branching fraction is determined to be $\mathcal{B}(ψ(3686) \to η' e^+ e^-)= (1.90 \pm 0.25 \pm 0.11) \times 10^{-6}$, where the first uncertainty is statistical and the second systematic.

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arXiv2018

Observation of $ψ(3686) \to n\bar{n}$ and improved measurement of $ψ(3686) \to p \bar{p}$

We observe the decay $ψ(3686) \to n \bar{n}$ for the first time and measure $ψ(3686) \to p \bar{p}$ with improved accuracy by using $1.07\times 10^8$ $ψ(3686)$ events collected with the BESIII detector. The measured branching fractions are $\mathcal{B}(ψ(3686) \to n \bar{n}) = (3.06 \pm 0.06 \pm 0.14)\times 10^{-4}$ and $\mathcal{B}(ψ(3686) \to p \bar{p}) = (3.05 \pm 0.02 \pm 0.12) \times 10^{-4}$. Here, the first uncertainties are statistical and the second ones systematic. With the hypothesis that the polar angular distributions of the neutron and proton in the center-of-mass system obey $1+α\cos^2θ$, we determine the $α$ parameters to be $α_{n\bar{n}} = 0.68 \pm 0.12 \pm 0.11$ and $α_{p\bar{p}} = 1.03 \pm 0.06 \pm 0.03$ for $ψ(3686)\to n\bar{n}$ and $ψ(3686)\to p\bar{p}$, respectively.

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arXiv2018

Search for invisible decays of $ω$ and $ϕ$ with $J/ψ$ data at BESIII

Using a data sample of $(1310.6 \pm 7.0)\times 10^6$ $J/ψ$ events collected with the BESIII detector operating at the BEPCII collider, we perform the first experimental search for invisible decays of a light vector meson ($V=ω,ϕ$) via $J/ψ\to V η$ decays. The decay of $η\to π^+π^-π^0$ is utilized to tag the $V$ meson decaying into the invisible final state. No evidence for a significant invisible signal is observed, and the upper limits on the ratio of branching fractions at the 90\% confidence level are determined to be $\frac{\mathcal{B}(ω\rightarrow \rm{invisible})}{\mathcal{B}(ω\to π^+π^-π^0)} < 8.1 \times 10^{-5}$ and $\frac{\mathcal{B}(ϕ\to \rm{invisible})}{\mathcal{B}(ϕ\to K^+K^-)} < 3.4\times 10^{-4}$. By using the world average values of $\mathcal{B}(ω\to π^+π^-π^0)$ and $\mathcal{B}(ϕ\to K^+K^-)$, the upper limits on the decay branching fractions at the $90\%$ confidence level are set as $\mathcal{B}(ω\to \rm{invisible})< 7.3 \times 10^{-5}$ and $\mathcal{B}(ϕ\to \rm{invisible})< 1.7\times 10^{-4}$, respectively.

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arXiv2018

Measurement of e+e- --> D Dbar Cross Sections at the psi(3770) Resonance

We report new measurements of the cross sections for the production of D Dbar final states at the psi(3770) resonance. Our data sample consists of an integrated luminosity of 2.93/fb of e+e- annihilation data produced by the BEPCII collider and collected and analyzed with the BESIII detector. We exclusively reconstruct three D0 and six D+ hadronic decay modes and use the ratio of the yield of fully reconstructed D Dbar events ("double tags") to the yield of all reconstructed D or Dbar mesons ("single tags") to determine the number of D0 D0bar and D+D- events, benefiting from the cancellation of many systematic uncertainties. Combining these yields with an independent determination of the integrated luminosity of the data sample, we find the cross sections to be σ(e+e- --> D0 D0bar)=(3.615 +- 0.010 +- 0.038) nb and σ(e+e- --> D+D-)=(2.830 +- 0.011 +- 0.026) nb, where the uncertainties are statistical and systematic, respectively.

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arXiv2018

Observation of $a^{0}_{0}(980)$-$f_{0}(980)$ Mixing

We report the first observation of $a^{0}_{0}(980)$-$f_{0}(980)$ mixing in the decays of $J/ψ\toϕf_{0}(980)\toϕa^{0}_{0}(980)\toϕηπ^{0}$ and $χ_{c1}\to a^{0}_{0}(980)π^{0}\to f_{0}(980)π^{0}\toπ^{+}π^{-}π^{0}$, using data samples of $1.31\times10^{9}$ $J/ψ$ events and $4.48\times10^{8}$ $ψ(3686)$ events accumulated with the BESIII detector. The signals of $f_{0}(980)\to a^{0}_{0}(980)$ and $a^{0}_{0}(980)\to f_{0}(980)$ mixing are observed at levels of statistical significance of $7.4σ$ and $5.5σ$, respectively. The corresponding branching fractions and mixing intensities are measured and the constraint regions on the coupling constants, $g_{a_{0}K^{+}K^{-}}$ and $g_{f_{0}K^{+}K^{-}}$, are estimated. The results improve the understanding of the nature of $a^{0}_{0}(980)$ and $f_{0}(980)$.

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arXiv2018

Precision Study of $η^\prime\rightarrowγπ^+π^-$ Decay Dynamics

Using a low background data sample of $9.7\times10^{5}$ $Jψ\rightarrowγη^\prime$, $η^\prime\rightarrowγπ^+π^-$ events, which are 2 orders of magnitude larger than those from the previous experiments, recorded with the BESIII detector at BEPCII, the decay dynamics of $η^\prime\rightarrowγπ^+π^-$ are studied with both model-dependent and model-independent approaches. The contributions of $ω$ and the $ρ(770)-ω$ interference are observed for the first time in the decays $η^\prime\rightarrowγπ^+π^-$ in both approaches. Additionally, a contribution from the box anomaly or the $ρ(1450)$ resonance is required in the model-dependent approach, while the process specific part of the decay amplitude is determined in the model-independent approach.

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arXiv2018

Measurement of the decay $η^{\prime}\toπ^{0}π^{0}η$ at MAMI

An experimental study of the $η'\to π^0π^0η\to 6γ$ decay has been conducted with the best up-to-date statistical accuracy, by measuring $η'$ mesons produced in the $γp \to η' p$ reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the $η'\to π^0π^0η$ matrix element are consistent with the most recent results for $η'\toππη$ decays, but have smaller uncertainties. The available statistics and experimental resolution allowed, for the first time, an observation of a structure below the $π^+π^-$ mass threshold, the magnitude and sign of which, checked within the framework of the nonrelativistic effective-field theory, demonstrated good agreement with the cusp that was predicted based on the $ππ$ scattering length combination, $a_0-a_2$, extracted from $K \to 3π$ decays.

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