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Gradl, W.

Publications and source records attributed to Gradl, W..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Extracting the femtometer structure of strange baryons using the vacuum polarization effect

Abstract One of the fundamental goals of particle physics is to gain a microscopic understanding of the strong interaction. Electromagnetic form factors quantify the structure of hadrons in terms of charge and magnetization distributions. While the nucleon structure has been investigated extensively, data on hyperons are still scarce. It has recently been demonstrated that electron-positron annihilations into hyperon-antihyperon pairs provide a powerful tool to investigate their inner structure. We present a method useful for hyperon-antihyperon pairs of different types which exploits the cross section enhancement due to the effect of vacuum polarization at theJ/ψresonance. Using the 10 billionJ/ψevents collected with the BESIII detector, this allows a precise determination of the hyperon structure function. The result is essentially a precise snapshot of the$$\bar{\Lambda }{\Sigma }^{0}\,(\Lambda {\bar{\Sigma }}^{0})$$ Λ ¯ Σ 0 ( Λ Σ ¯ 0 ) transition process, encoded in the transition form factor ratio and phase. Their values are measured to beR = 0.860 ± 0.029(stat.) ± 0.015(syst.),$$\Delta {\Phi }_{\bar{\Lambda }{\Sigma }^{0}}=(1.011\pm 0.094({{\rm{stat.}}})\pm 0.010({{\rm{syst.}}}))\,{{\rm{r}}}ad$$ Δ Φ Λ ¯ Σ 0 = ( 1.011 ± 0.094 ( stat. ) ± 0.010 ( syst. ) ) r a d and$$\Delta {\Phi }_{\Lambda {\bar{\Sigma }}^{0}}=(2.128\pm 0.094({{\rm{stat.}}})\pm 0.010({{\rm{syst.}}}))\,{{\rm{r}}}ad$$ Δ Φ Λ Σ ¯ 0 = ( 2.128 ± 0.094 ( stat. ) ± 0.010 ( syst. ) ) r a d . Furthermore, charge-parity (CP) breaking is investigated in this reaction and found to be consistent with CP symmetry.

Science & Technology - Other Topics↗
DOE OSTI2024

First Measurement Using Elliptically Polarized Photons of the Double-Polarization Observable E for γ p → p π 0 and γ p → n π +

We report the measurement of the helicity asymmetry E for the p π 0 and n π + final states using, for the first time, an elliptically polarized photon beam in combination with a longitudinally polarized target at the Crystal Ball experiment at MAMI. The results agree very well with data that were taken with a circularly polarized photon beam, showing that it is possible to simultaneously measure polarization observables that require linearly (e.g., G ) and circularly polarized photons (e.g., E ) and a longitudinally polarized target. The new data cover a photon energy range 270–1400 MeV for the p π 0 final state (230–842 MeV for the n π + final state) and the full range of pion polar angles, θ , providing the most precise measurement of the observable E . A moment analysis gives a clear observation of the p η cusp in the p π 0 final state. Published by the American Physical Society 2024

Physics↗
DOE OSTI2024

Observation of J / ψ decays to e + e − e + e − and e + e − μ + μ −

Using a data sample of 4.481 × 10 8 ψ ( 3686 ) events collected with the BESIII detector, we report the first observation of the four-lepton-decays J / ψ → e + e − e + e − and J / ψ → e + e − μ + μ − utilizing the process ψ ( 3686 ) → π + π − J / ψ . The branching fractions are determined to be [ 5.48 ± 0.31 ( stat ) ± 0.45 ( syst ) ] × 10 − 5 and [ 3.53 ± 0.22 ( stat ) ± 0.13 ( syst ) ] × 10 − 5 , respectively. The results are consistent with theoretical predictions. No significant signal is observed for J / ψ → μ + μ − μ + μ − , and an upper limit on the branching fraction is set at 1.6 × 10 − 6 at the 90% confidence level. A C P asymmetry observable is constructed for the first two channels, which is measured to be ( − 0.012 ± 0.054 ± 0.010 ) and ( 0.062 ± 0.059 ± 0.006 ) , respectively. No evidence for C P violation is observed in this process. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2023

First measurement of polarisation transfer $C$$^{n}_{x'}$ in deuteron photodisintegration

A first measurement of the polarisation transfer from a circularly-polarised photon to the final state neutron ($C$$^{n}_{x'}$) in deuterium photodisintegration has been carried out. This quantity is determined over the photon energy range 370 – 700 MeV and for neutron centre-of-mass breakup angles ~ 45 – 120°. The polarisation of the final state neutrons was determined by an ancillary large-acceptance nucleon polarimeter, surrounding a cryogenic liquid deuterium target within the Crystal Ball detector at MAMI. The polarimeter characterised (n, p) charge exchange of the ejected neutrons to determine their polarisation. The new $C$$^{n}_{x'}$ data are also compared to a theoretical model based on nucleonic and nucleon resonance degrees of freedom constrained by the current world-database of deuterium photodisintegration measurements. Structures in $C$$^{n}_{x'}$ observed in the region of the d*(2380) could not be explained by conventional models of deuteron photodisintegration.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Helicity amplitude analysis of χcJ → ϕϕ

Using (447.9 ± 2.3) million ψ(3686) events collected with the BESIII detector, the decays of χcJ → ΦΦ (J = 0, 1, 2) have been studied via the decay ψ(3686) → γχcJ. The branching fractions of the decays χcJ → ΦΦ (J = 0, 1, 2) are determined to be (8.59 ± 0.27 ± 0.20) × 10-4, (4.26 ± 0.13 ± 0.15) × 10-4, and (12.67 ± 0.28 ± 0.33) × 10-4, respectively, which are the most precise measurements to date. From a helicity amplitude analysis of the process ψ(3686) → γχcJ , χcJ → ΦΦ, Φ → K+K-, the polarization parameters of the χcJ → ΦΦ decays are determined for the first time.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Observation of e⁺e⁻ → pp$\bar{p}\bar{n}\pi^-$ + c. c.

Using data taken at 29 center-of-mass energies between 4.16 and 4.70 GeV with the BESIII detector at the Beijing Electron Positron Collider corresponding to a total integrated luminosity of approximately 18.8 fb -1 , the process e⁺e⁻ → pp$\overline{p}\overline{n}\pi^-$ + c. c. is observed for the first time with a statistical significance of 11.5σ. The average Born cross sections in the energy ranges of (4.160, 4.380) GeV, (4.400, 4.600) GeV and (4.610, 4.700) GeV are measured to be (21.5 ± 5.7 ± 1.2) fb, (46.3 ± 10.6 ± 2.5) fb and (59.0 ± 9.4 ± 3.2) fb, respectively, where the first uncertainties are statistical and the second are systematic. The line shapes of the $\overline{p}\overline{n}$ and ppπ⁻ invariant mass spectra are consistent with phase space distributions, indicating that no hexaquark or di-baryon state is observed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Study of η(1405)/η(1475) in $J/\psi \to \gamma {K}_S^0{K}_S^0{\pi}^0$ decay

Using a sample of (10 . 09 ± 0 . 04) × 10 9 J/ψ decays collected with the BESIII detector, partial wave analyses of the decay $ J/\psi \to \gamma {K}_S^0{K}_S^0{\pi}^0$ are performed within the ${K}_S^0{K}_S^0{\pi}^0$ invariant mass region below 1.6 GeV/ c 2 . The covariant tensor amplitude method is used in both mass independent and mass dependent approaches. Both analysis approaches exhibit dominant pseudoscalar and axial vector components, and show good consistency for the other individual components. Furthermore, the mass dependent analysis reveals that the ${K}_S^0{K}_S^0{\pi}^0$ invariant mass spectrum for the pseudoscalar component can be well described with two isoscalar resonant states using relativistic Breit-Wigner model, i.e., the η (1405) with a mass of $1391.7\pm {0.7}_{-0.3}^{+11.3}$ MeV/ c 2 and a width of $60.8\pm {1.2}_{-12.0}^{+5.5}$ MeV, and the η (1475) with a mass of $1507.6\pm {1.6}_{-32.2}^{+15.5}$ MeV/ c 2 and a width of $115.8\pm {2.4}_{-10.9}^{+14.8}$ MeV. The first and second uncertainties are statistical and systematic, respectively. Alternate models for the pseudoscalar component are also tested, but the description of the ${K}_S^0{K}_S^0{\pi}^0$ invariant mass spectrum deteriorates significantly.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Study of e + e - → Ω - Ω ¯ + at center-of-mass energies from 3.49 to 3.67 GeV

Using data samples of e + e - collisions collected with the BESIII detector at eight center-of-mass energy points between 3.49 and 3.67 GeV, corresponding to an integrated luminosity of 670 pb -1 , we present the upper limits of Born cross sections and the effective form factor for the process e + e - → $Ω$ - ⁢$\overline{Ω}$ + . A fit to the cross sections using a perturbative QCD-derived energy-dependent function shows no significant threshold effect. The upper limit on the measured effective form factor is consistent with a theoretical prediction within the uncertainty of 1⁢σ. These results provide new experimental information on the production mechanism of $Ω$.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗