arXiv subjects

P. Drexler

Publications and source records attributed to P. Drexler.

61 records · Page 4Linked to original sources

arXiv2012

Study of the gamma p --> pi0 pi0 p reaction with the Crystal Ball/TAPS at the Mainz

The gamma p --> pi0 pi0 p reaction has been measured from threshold to 1.4 GeV using the Crystal Ball and TAPS photon spectrometers together with the photon tagging facility at the Mainz Microtron. The experimental results include total and differential cross sections as well as specific angular distributions, which were used to extract partial-wave amplitudes. In particular, the energy region below the D13(1520) resonance was studied.

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arXiv2012

Coherent photoproduction of eta-mesons off 3He - search for eta-mesic nuclei

Coherent photoproduction of $η$-mesons off $^3$He, i.e. the reaction $γ^3{He}\rightarrow η^3{He}$, has been investigated in the near-threshold region. The experiment was performed at the Glasgow tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball - TAPS detector. Angular distributions and the total cross section were measured using the $η\rightarrow γγ$ and $η\rightarrow 3π^0\rightarrow 6γ$ decay channels. The observed extremely sharp rise of the cross section at threshold and the behavior of the angular distributions are evidence for a strong $η{^3{He}}$ final state interaction, pointing to the existence of a resonant state. The search for further evidence of this state in the excitation function of $π^0$-proton back-to-back emission in the $γ^3{He}\rightarrow π^0 pX$ reaction revealed a very complicated structure of the background and could not support previous conclusions.

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arXiv2010

Study of the gp-->etap reaction with the Crystal Ball detector at the Mainz Microtron(MAMI-C)

The gp-->etap reaction has been measured with the Crystal Ball and TAPS multiphoton spectrometers in the energy range from the production threshold of 707 MeV to 1.4 GeV (1.49 =< W >= 1.87 GeV). Bremsstrahlung photons produced by the 1.5-GeV electron beam of the Mainz Microtron MAMI-C and momentum analyzed by the Glasgow Tagging Spectrometer were used for the eta-meson production. Our accumulation of 3.8 x 10^6 gp-->etap-->3pi0p-->6gp events allows a detailed study of the reaction dynamics. The gp-->etap differential cross sections were determined for 120 energy bins and the full range of the production angles. Our data show a dip near W = 1680 MeV in the total cross section caused by a substantial dip in eta production at forward angles. The data are compared to predictions of previous SAID and MAID partial-wave analyses and to thelatest SAID and MAID fits that have included our data.

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arXiv2010

First measurement of the circular beam asymmetry in the gamma p --> pi0 eta p reaction

The circular photon asymmetry for pi0 eta photoproduction on the proton was measured for the first time at the tagged photon facility of the MAMI C accelerator using the Crystal Ball/TAPS photon spectrometer. The experimental results are interpreted within a phenomenological isobar model that confirms the dominant role of the Delta(1700)D33 resonance. The measured asymmetry allows us to identify small contributions from positive-parity resonances via interference terms with the dominant D33 amplitude.

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arXiv2010

Radiative pi0 photoproduction on protons in the Delta+(1232) region

The reaction gamma p -> p pi0 gamma' has been measured with the Crystal Ball / TAPS detectors using the energy-tagged photon beam at the electron accelerator facility MAMI-B. Energy and angular differential cross sections for the emitted photon gamma' and angular differential cross sections for the pi0 have been determined with high statistics in the energy range of the Delta+(1232) resonance. Cross sections and the ratio of the cross section to the non-radiative process gamma p -> p pi0 are compared to theoretical reaction models, having the anomalous magnetic moment kappa_Delta+ as free parameter. As the shape of the experimental distributions is not reproduced in detail by the model calculations, currently no extraction of kappa_Delta+ is feasible.

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arXiv2009

Photoproduction of pi^0 eta on protons and the Delta(1700)D_{33} resonance

Total and differential cross sections for the reaction gamma p -> pi^o eta p have been measured with the Crystal Ball/TAPS detector using the tagged photon facility at the MAMI C accelerator in Mainz. In the energy range E_gamma=0.95-1.4 GeV the reaction is dominated by the excitation and sequential decay of the Delta(1700)D33 resonance. Angular distributions measured with high statistics allow us to determine the ratio of hadronic decay widths Γ_{ηΔ}/Γ_{πS11} and the ratio of the helicity amplitudes A_{3/2}/A_{1/2} for this resonance.

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arXiv2009

Measurement of the Slope Parameter $α$ for the $η\to 3π^0$ decay with the Crystal Ball detector at the Mainz Microtron (MAMI-C)

The dynamics of the $η\to 3π^0$ decay have been studied with the Crystal Ball multiphoton spectrometer and the TAPS calorimeter. Bremsstrahlung photons produced by the 1.5-GeV electron beam of the Mainz microtron MAMI-C and tagged by the Glasgow photon spectrometer were used for $η$-meson production. The analysis of $3 \times 10^6$ $γp \to ηp \to 3π^0 p \to 6γp$ events yields the value $α=-0.032\pm0.003$ for the $η\to 3π^0$ slope parameter, which agrees with the majority of recent experimental results and has the smallest uncertainty. The $π^0π^0$ invariant-mass spectrum was investigated for the occurrence of a cusplike structure in the vicinity of the $π^+π^-$ threshold. The observed effect is small and does not affect our measured value for the slope parameter.

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