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Gradl, W.

Publications and source records attributed to Gradl, W..

At least 289 records · Page 16
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DOE OSTI2018

Measurement of e + e - → $D\bar{D}$ cross sections at the ψ(3770) resonance

Here, we report new measurements of the cross sections for the production of $D\bar{D}$ final states at the ψ(3770) resonance. Our data sample consists of an integrated luminosity of 2.93 fb -1 of e + e - annihilation data produced by the BEPCII collider and collected and analyzed with the BESIII detector. We exclusively reconstruct three D 0 and six D + hadronic decay modes and use the ratio of the yield of fully reconstructed $D\bar{D}$ events ("double tags") to the yield of all reconstructed D or $\bar{D}$ mesons ("single tags") to determine the number of D 0 $\bar{D}$ 0 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 - → D 0 $\bar{D}$ 0 ) nb and σ(e + e - → D + D - ) = (2.830 ± 0.011 ± 0.026) nb, where the uncertainties are statistical and systematic, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Photoproduction of π 0 mesons off protons and neutrons in the second and third nucleon resonance regions

Background: Photoproduction of mesons off quasi-free nucleons bound in the deuteron allows to study the elec- tromagnetic excitation spectrum of the neutron and the isospin structure of the excitation of nucleon resonances. The database for such reactions is much more sparse than for free proton targets. Purpose: Study experimentally single π 0 photoproduction off quasi-free nucleons from the deuteron. Investigate nuclear effects by a comparison of the results for free protons and quasi-free protons. Use the quasi-free neutron data (corrected for nuclear effects) to test the predictions of reaction models and partial wave analysis (PWA) for $\gamma$n → nπ 0 derived from the analysis of the other isospin channels. Methods: High statistics angular distributions and total cross sections for the photoproduction of π 0 mesons off the deuteron with coincident detection of recoil nucleons have been measured for the first time. The experiment was performed at the tagged photon beam of the Mainz Microtron (MAMI) accelerator for photon energies between 0.45 GeV and 1.4 GeV, using an almost 4π electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. A complete kinematic reconstruction of the final state removed the effects of Fermi motion. Results: Significant effects from final state interactions (FSI) were observed for participant protons in comparison to free proton targets (between 30% and almost 40%). The data in coincidence with recoil neutrons were corrected for such effects under the assumption that they are identical for participant protons and neutrons. Reaction model predictions and PWA for $\gamma$n → nπ 0 , based on fits to data for the other isospin channels, disagreed between themselves and no model provided a good description of the new data. Conclusions: The results demonstrate clearly the importance of a measurement of the fully neutral final state for the isospin decomposition of the cross section. Model refits, for example from the Bonn-Gatchina analysis, show that the new and the previous data for the other three isospin channels can be simultaneously described when the contributions of several partial waves are modified. Finally, the results are also relevant for the suppression of the higher resonance bumps in total photoabsorption on nuclei, which are not well understood.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Study of the decays D + → η ( ' ) e + ν e

The charm semileptonic decays D + → ηe + v e and D + → η'e+v e are studied with a sample of e + e - collision data corresponding to an integrated luminosity of 2.93 fb -1 collected at $ \sqrt{s}=3.773 $ GeV with the BESIII detector. We measure the branching fractions for D+ → ηe+v e to be (10.74 ± 0.81 ± 0.51) x 10 -4 , and for D+ → → η'e+v e to be (1.91 ± 0.51 ± 0.13) x 10 -4 , where the uncertainties are statistical and systematic, respectively. In addition, we perform a measurement of the form factor in the decay D+ → ηe+v e . All the results are consistent with those obtained by the CLEO-c experiment.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Measurement of the integrated Luminosities of cross-section scan data samples around the ${\rm{\psi }}$(3770) mass region

To investigate the nature of the (3770) resonance and to measure the cross section for e + e - →D$\bar{D}$, a cross-section scan data sample, distributed among 41 center-of-mass energy points from 3.73 to 3.89 GeV, was taken with the BESIII detector operated at the BEPCII collider in the year 2010. By analyzing the large angle Bhabha scattering events, we measure the integrated luminosity of the data sample at each center-of-mass energy point. The total integrated luminosity of the data sample is 76.16±0.04±0.61 pb -1 , where the first uncertainty is statistical and the second systematic.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Experimental study of the γ p → π 0 η p reaction with the A2 setup at the Mainz Microtron

Here, the data available from the A2 Collaboration at MAMI were analyzed to select the γp → π 0 ηp reaction on an event-by-event basis, which allows for partial-wave analyses of three-body final states to obtain more reliable results, compared to fits to measured distributions. These data provide the world’s best statistical accuracy in the energy range from threshold to E γ = 1.45 GeV, allowing a finer energy binning in the measurement of all observables needed for understanding the reaction dynamics. The results obtained for the measured observables are compared to existing models, and the impact from the new data is checked by the fit with the revised Mainz model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗