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Search Results: 1 - 10 of 144361 matches for " B. Krusche "
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Photoproduction of eta-mesons from light nuclei
B. Krusche
Physics , 2003,
Abstract: In a series of experiments coherent and quasifree eta-photoproduction from light nuclei (4He, 3He, 2H) was investigated with the TAPS-detector at the Mainz MAMI-accelerator. The experiments were motivated by two different subjects: the determination of the isospin structure of the electromagnetic excitation of the S11(1535) resonance and the study of the eta-nucleon and eta-nucleus interaction at small momenta. The results for the deuteron and 4He are summarized and first preliminary results for 3He are presented.
Photoexcitation of Baryon Resonances - News from the D13(1520)
B. Krusche
Physics , 2003,
Abstract: The so-called second resonance region of the nucleon comprises the states P11(1440), D13(1520) and S11(1535). During the last few years photoproduction experiments have largely contributed to a better understanding of these states, but the strong suppression of the resonance structure in total photoabsorption experiments from nuclei is still not understood. The D13-resonance dominates the resonance structure due to its large photon coupling. In this contribution new results for the excitation and decay modes of the D13 on the free nucleon and first results for the in-medium behavior of the resonance are summarised.
Meson photoproduction in the first and second resonance region
B. Krusche
Physics , 2003,
Abstract: The study of baryon resonances via meson photoproduction reactions on the free proton and on nucleons in the nuclear medium is discussed. Special emphasis is laid on the production of neutral mesons which due to the suppression of non-resonant backgrounds are particularly well suited for the study of excited states of the nucleon. Experiments carried out during the last ten years with the TAPS-detector at the Mainz Microtron (MAMI) have very significantly contributed to a detailed investigation of the low lying nucleon resonances P33(1232), D13(1520) and S11(1535). The most recent results from single and double pion production and from eta-photoproduction are summarised.
Photoproduction of mesons from nuclei - In-medium properties of hadrons
B. Krusche
Physics , 2004, DOI: 10.1016/j.ppnp.2004.12.002
Abstract: Recent experimental results for the in-medium properties of hadrons obtained with photoproduction of mesons from nuclei are discussed. The experiments were done with the TAPS detector at the tagged photon beam of the MAMI accelerator in Mainz. Measured were the final states $\pi^o X$, $\eta X$, $2\pi^oX$, and $\pi^o\pi^{\pm}X$ for $^{12}$C, $^{40}$Ca, $^{93}$Nb, and $^{208}$Pb up to the second resonance region. The results were used for an investigation of the in-medium properties of the P$_{33}$(1232), the P$_{11}$(1440), the D$_{13}$(1520), and the S$_{11}$(1535) resonances. It was found that the cross sections can be spilt into a component which originates from the low density surface region of the nuclei and a component which scales like the nuclear volume. The energy dependence of the surface component is strikingly similar to the deuteron, it shows a clear signal for the second resonance peak. The volume component is lacking this peak and shows an enhancement at intermediate energies. Furthermore the measurement of coherent $\eta$-photoproduction and the final state $p\pi^o$ from $^3$He is discussed in the context of the search for $\eta$-mesic nuclei.
Photoproduction of mesons off nuclei
B. Krusche
Physics , 2011, DOI: 10.1140/epjst/e2011-01491-2
Abstract: Recent results for the photoproduction of mesons off nuclei are reviewed. These experiments have been performed for two major lines of research related to the properties of the strong interaction. The investigation of nucleon resonances requires light nuclei as targets for the extraction of the isospin composition of the electromagnetic excitations. This is done with quasi-free meson photoproduction off the bound neutron and supplemented with the measurement of coherent photoproduction reactions, serving as spin and/or isospin filters. Furthermore, photoproduction from light and heavy nuclei is a very efficient tool for the study of the interactions of mesons with nuclear matter and the in-medium properties of hadrons. Experiments are currently rapidly developing due to the combination of high quality tagged (and polarized) photon beams with state-of-the-art 4pi detectors and polarized targets.
In-medium properties of nucleon resonances
B. Krusche
Physics , 2004, DOI: 10.1556/APH.27.2006.1.14
Abstract: Recent experimental results for the in-medium properties of nucleon resonances are discussed. The experiments were done with the TAPS detector at the tagged photon beam of the MAMI accelerator in Mainz. Measured was the photoproduction of mesons (final states $\pi^o X$, $\eta X$, $2\pi^oX$ and $\pi^o\pi^{\pm}X$) from the nuclei $^{12}$C, $^{40}$Ca, $^{93}$Nb, and $^{208}$Pb up to the second resonance region. The results were analyzed in view of the in-medium properties of the P$_{33}$(1232), the D$_{13}$(1520), and the S$_{11}$(1535) resonances.
In-Medium Properties of Hadrons
B. Krusche
Physics , 2006, DOI: 10.1142/S0217751X07035598
Abstract: A diverse experimental program for the study of the photoproduction of mesons off nuclei has been carried out - and is still running - at the Mainz MAMI and Bonn ELSA electron accelerators with the TAPS, Crystal Barrel, and Crystal Ball calorimeters. It is motivated as a detailed study of the in-medium properties of hadrons and the meson - nucleus interactions. Typical examples for the in-medium behavior of vector mesons ($\omega$), scalar mesons ($\sigma$), and nucleon resonances (P$_{33}$(1232), S$_{11}$(1535), D$_{15}$(1520)) are discussed. Special attention is paid to meson - nucleus final state interactions.
Nuclear mass form factors from coherent photoproduction of $π^0$ mesons
B. Krusche
Physics , 2005, DOI: 10.1140/epja/i2005-10146-7
Abstract: Data for coherent photoproduction of $\pi^0$ mesons from nuclei ($^{12}$C, $^{40}$Ca, $^{93}$Nb, $^{nat}$Pb), recently measured with the TAPS detector at the Mainz MAMI accelerator, have been analyzed in view of the mass form factors of the nuclei. The form factors have been extracted in plane wave approximation of the $A(\gamma ,\pi^0)A$ reaction and corrected for final state interaction effects with the help of distorted wave impulse approximations. Nuclear mass rms-radii have been calculated from the slope of the form factors for $q^2\to 0$. Furthermore, the Helm model (hard sphere form factor folded with Gaussian) was used to extract diffraction radii from the zeroes of the form factor and skin thicknesses from the position and height of its first maximum. The diffraction radii from the Helm model agree with the corresponding charge radii obtained from electron scattering experiments within their uncertainties of a few per cent. The rms-radii from the slope of the form factors are systematically lower by up to 5% for PWIA and up to 10% for DWIA. Also the skin thicknesses extracted from the Helm model are systematically smaller than their charge counter parts.
Production of $η$ and $η'$ Mesons on Nucleons and Nuclei
B. Krusche,C. Wilkin
Physics , 2014, DOI: 10.1016/j.ppnp.2014.10.001
Abstract: The production of $\eta$ and $\eta^{\prime}$ mesons in photon- and hadron-induced reactions on free and quasi-free nucleons and on nuclei is reviewed. The extensive database on $\gamma N \to \eta N$, for both proton and neutron targets, is described in detail and its implications for the search for $N^{\star}$ resonances much heavier than the dominant $S_{11}(1535)$ discussed. Though less is currently known about the production of the $\eta^{\prime}$ or of $\eta\pi$ pairs, these also offer tantalizing prospects in the search for the missing isobars. The more limited data available on pion-induced production are still necessary ingredients in the partial wave analysis discussed. The production of the $\eta$-meson in $pp$ and $pn$ collisions shows once again the strong influence of the $S_{11}(1535)$ isobar, which is in contrast to the relatively weak behaviour seen near threshold for $\eta^{\prime}$ production. This difference is reflected in the important final state interaction effects of the $\eta$ in nuclei that may even lead to this meson being "bound" in some systems. The evidence for this is reviewed for both $\gamma A$ and $p A$ collisions. The inclusive photoproduction of $\eta$, $\eta^{\prime}$, and $\eta\pi$ pairs from nuclei provides further information regarding the production mechanism and the interaction of the $\eta$ and $\eta^{\prime}$ with nuclei and the $\eta\pi$ pairs may even allow access to low mass $\eta A$ systems that are forbidden in direct single-meson photoproduction.
Quasi-free photoproduction of pion-pairs off protons and neutrons
M. Oberle,B. Krusche
Physics , 2014, DOI: 10.1142/S2010194514601069
Abstract: Beam-helicity asymmetries and mass-differential cross sections have been measured at the MAMI accelerator in Mainz for the photoproduction of neutral and mixed-charge pion pairs in the reactions $\boldsymbol{\gamma}p\rightarrow n\pi^0\pi^+$ and $\boldsymbol{\gamma}p\rightarrow p\pi^0\pi^0$ off free protons and $\boldsymbol{\gamma}d \rightarrow (p)p\pi^0\pi^-$, $\boldsymbol{\gamma}d\rightarrow (n)p\pi^0\pi^0$ and $\boldsymbol{\gamma}d\rightarrow (n)n\pi^0\pi^+$, $\boldsymbol{\gamma}d\rightarrow (p)n \pi^0\pi^0$ off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4 GeV. Circularly polarized photons were produced in bremsstrahlung processes of longitudinally polarized electrons and tagged with the Glasgow-Mainz magnetic spectrometer. The decay products (photons, protons, neutrons, and charged pions) were detected in the $4\pi$ electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. Using a full kinematic reconstruction of the final state, excellent agreement was found between the results for free and quasi-free protons, indicating that the quasi-free neutron results are also a close approximation of the free-neutron results. Comparisons of the results to predictions from model calculations suggest that especially the reaction mechanisms in the production of the mixed-charge final states are still not well understood, in particular at low incident photon energies in the second nucleon resonance region.
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