J. C. McGeorge - A2 Collaboration at MAMI

J. C. McGeorge
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J. C. McGeorge
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A2 Collaboration at MAMI
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Nuclear Experiment (46)
 
High Energy Physics - Experiment (16)
 
Nuclear Theory (7)
 
High Energy Physics - Phenomenology (6)
 
Physics - Instrumentation and Detectors (1)

Publications Authored By J. C. McGeorge

The reactions $\gamma p\to \eta p$ and $\gamma p\to \eta' p$ have been measured from their thresholds up to the center-of-mass energy $W=1.96$GeV with the tagged-photon facilities at the Mainz Microtron, MAMI. Differential cross sections were obtained with unprecedented accuracy, providing fine energy binning and full production-angle coverage. Read More

The Dalitz decay pi^0 -> e^+e^-gamma has been measured in the gamma p -> pi^0 p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the pi^0 electromagnetic transition form factor, a_pi = 0.030+/-0. Read More

The Dalitz decays eta -> e^+e^-g and omega -> pi^0 e^+e^- have been measured in the g p -> eta p and g p -> omega p reactions, respectively, with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The value obtained for the slope parameter of the electromagnetic transition form factor of eta, Lambda^{-2}_eta=(1.97+/-0. Read More

High statistics measurements of the photon asymmetry $\mathrm{\Sigma}$ for the $\overrightarrow{\gamma}$p$\rightarrow\pi^{0}$p reaction have been made in the center of mass energy range W=1214-1450 MeV. The data were measured with the MAMI A2 real photon beam and Crystal Ball/TAPS detector systems in Mainz, Germany. The results significantly improve the existing world data and are shown to be in good agreement with previous measurements, and with the MAID, SAID, and Bonn-Gatchina predictions. Read More

Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of $\pi^0\pi^0$ pairs off free protons and off nucleons bound in the deuteron. The experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557~MeV, which produced bremsstrahlung in thin radiator foils. Read More

Photoproduction of $\pi\eta$-pairs from nucleons has been investigated from threshold up to incident photon energies of $\approx$~1.4~GeV. The quasi-free reactions $\gamma p\rightarrow p\pi^0\eta$, $\gamma n\rightarrow n\pi^0\eta$, $\gamma p\rightarrow n\pi^+\eta$, and $\gamma n\rightarrow p\pi^-\eta$ were for the first time measured from nucleons bound in the deuteron. Read More

Differential cross sections for the gamma p -> pi^0 p reaction have been measured with the A2 tagged-photon facilities at the Mainz Microtron, MAMI C, up to the center-of-mass energy W=1.9 GeV. The new results, obtained with a fine energy and angular binning, increase the existing quantity of pi^0 photoproduction data by ~47%. Read More

A multi-cell He gas-scintillator active target, designed for the measurement of photoreaction cross sections, is described. The target has four main chambers, giving an overall thickness of 0.103 $\mathrm{g/cm^{2}}$ at an operating pressure of 2 MPa. Read More

Differential and total cross sections for the quasifree reactions $\gamma p\rightarrow\eta p$ and $\gamma n\rightarrow\eta n$ have been determined at the MAMI-C electron accelerator using a liquid deuterium target. Photons were produced via bremsstrahlung from the 1.5 GeV incident electron beam and energy-tagged with the Glasgow photon tagger. Read More

An experimental study of $\omega$ photoproduction on the proton was conducted by using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. The $\gamma p\to\omega p$ differential cross sections are measured from threshold to the incident-photon energy $E_\gamma=1.40$ GeV ($W=1. Read More

Precise angular distributions have been measured for the first time for the photoproduction of $\pi^{0}$-mesons off neutrons bound in the deuteron. The effects from nuclear Fermi motion have been eliminated by a complete kinematic reconstruction of the final state. The influence of final-state-interaction effects has been estimated by a comparison of the reaction cross section for quasi-free protons bound in the deuteron to the results for free protons and then applied as a correction to the quasi-free neutron data. Read More

Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of mixed-charge pion pairs in the reactions $\boldsymbol{\gamma}p\rightarrow n\pi^0\pi^+$ off free protons and $\boldsymbol{\gamma}d\rightarrow (p)p\pi^0\pi^-$ and $\boldsymbol{\gamma}d\rightarrow (n)n\pi^0\pi^+$ off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4 GeV. Circularly polarized photons were produced from bremsstrahlung of longitudinally polarized electrons and tagged with the Glasgow-Mainz magnetic spectrometer. Read More

Information on the size and shape of the neutron skin on $^{208}$Pb has been extracted from coherent pion photoproduction cross sections measured using the Crystal Ball together with the Glasgow tagger at the MAMI electron beam facility. On exploitation of an interpolated fit of a theoretical model to the measured cross sections the half-height radius and diffuseness of the neutron distribution are found to be 6.70$\pm 0. Read More

We report the first large-acceptance measurement of polarization transfer from a polarized photon beam to a recoiling nucleon, pioneering a novel polarimetry technique with wide application to future nuclear and hadronic physics experiments. The commissioning measurement of polarization transfer in the $^{1}H$($\vec{\gamma}$,$\vec{p}$)$\pi^{0}$ reaction in the range $0.4Read More

2013Sep
Affiliations: 1A2 Collaboration at MAMI, 2A2 Collaboration at MAMI, 3A2 Collaboration at MAMI, 4A2 Collaboration at MAMI, 5A2 Collaboration at MAMI, 6A2 Collaboration at MAMI, 7A2 Collaboration at MAMI, 8A2 Collaboration at MAMI, 9A2 Collaboration at MAMI, 10A2 Collaboration at MAMI, 11A2 Collaboration at MAMI, 12A2 Collaboration at MAMI, 13A2 Collaboration at MAMI, 14A2 Collaboration at MAMI, 15A2 Collaboration at MAMI, 16A2 Collaboration at MAMI, 17A2 Collaboration at MAMI, 18A2 Collaboration at MAMI, 19A2 Collaboration at MAMI, 20A2 Collaboration at MAMI, 21A2 Collaboration at MAMI, 22A2 Collaboration at MAMI, 23A2 Collaboration at MAMI, 24A2 Collaboration at MAMI, 25A2 Collaboration at MAMI, 26A2 Collaboration at MAMI, 27A2 Collaboration at MAMI, 28A2 Collaboration at MAMI, 29A2 Collaboration at MAMI, 30A2 Collaboration at MAMI, 31A2 Collaboration at MAMI, 32A2 Collaboration at MAMI, 33A2 Collaboration at MAMI, 34A2 Collaboration at MAMI, 35A2 Collaboration at MAMI, 36A2 Collaboration at MAMI, 37A2 Collaboration at MAMI, 38A2 Collaboration at MAMI, 39A2 Collaboration at MAMI, 40A2 Collaboration at MAMI, 41A2 Collaboration at MAMI, 42A2 Collaboration at MAMI, 43A2 Collaboration at MAMI, 44A2 Collaboration at MAMI, 45A2 Collaboration at MAMI, 46A2 Collaboration at MAMI, 47A2 Collaboration at MAMI, 48A2 Collaboration at MAMI, 49A2 Collaboration at MAMI, 50A2 Collaboration at MAMI, 51A2 Collaboration at MAMI, 52A2 Collaboration at MAMI, 53A2 Collaboration at MAMI, 54A2 Collaboration at MAMI, 55A2 Collaboration at MAMI, 56A2 Collaboration at MAMI, 57A2 Collaboration at MAMI, 58A2 Collaboration at MAMI, 59A2 Collaboration at MAMI, 60A2 Collaboration at MAMI, 61A2 Collaboration at MAMI, 62A2 Collaboration at MAMI, 63A2 Collaboration at MAMI, 64A2 Collaboration at MAMI, 65A2 Collaboration at MAMI, 66A2 Collaboration at MAMI, 67A2 Collaboration at MAMI, 68A2 Collaboration at MAMI, 69A2 Collaboration at MAMI, 70A2 Collaboration at MAMI, 71A2 Collaboration at MAMI, 72A2 Collaboration at MAMI, 73A2 Collaboration at MAMI, 74A2 Collaboration at MAMI, 75A2 Collaboration at MAMI, 76A2 Collaboration at MAMI

The Dalitz decay eta -> e^+ e^- gamma has been measured in the gamma p -> eta p reaction with the Crystal Ball and TAPS multiphoton spectrometers, together with the photon tagging facility at the Mainz Microtron MAMI. The experimental statistic used in this work is one order of magnitude greater than in any previous measurement of eta -> e^+ e^- gamma. The value obtained for the slope parameter 1/Lambda^2 of the eta transition form factor, 1/Lambda^2 = (1. Read More

Measurements of $\gamma p \rightarrow K^{+} \Lambda$ and $\gamma p \rightarrow K^{+} \Sigma^0$ cross-sections have been obtained with the photon tagging facility and the Crystal Ball calorimeter at MAMI-C. The measurement uses a novel $K^+$ meson identification technique in which the weak decay products are characterized using the energy and timing characteristics of the energy deposit in the calorimeter, a method that has the potential to be applied at many other facilities. The fine center-of-mass energy ($W$) resolution and statistical accuracy of the new data results in a significant impact on partial wave analyses aiming to better establish the excitation spectrum of the nucleon. Read More

Photoproduction of $\pi^{0}\pi^{0}$ and $\pi^{0}\pi^{\pm}$ pairs from nuclei has been measured over a wide mass range ($^2$H, $^{7}$Li, $^{12}$C, $^{40}$Ca, and $^{\rm nat}$Pb) for photon energies from threshold to 600 MeV. The experiments were performed at the MAMI accelerator in Mainz, using the Glasgow photon tagging spectrometer and a 4$\pi$ electromagnetic calorimeter consisting of the Crystal Ball and TAPS detectors. A shift of the pion-pion invariant mass spectra for heavy nuclei to small invariant masses has been observed for $\pi^0$ pairs but also for the mixed-charge pairs. Read More

Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of neutral pion pairs in the reactions $\vec{\gamma}p\rightarrow p\pi^0\pi^0$ and $\vec{\gamma}d\rightarrow (n)p\pi^0\pi^0$, $\vec{\gamma}d\rightarrow (p)n\pi^0\pi^0$ off free protons and off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4 GeV. Circularly polarized photons were produced from bremsstrahlung of longitudinally polarized electrons and tagged with the Glasgow magnetic spectrometer. Read More

Coherent photoproduction of $\pi^0$-mesons from threshold ($E_{th} \approx$ 136 MeV) throughout the $\Delta$-resonance region and of $\eta$-mesons close to the production threshold ($E_{th} \approx$ 570 MeV for $\eta$) has been measured for $^7$Li nuclei. The experiment was performed using the tagged-photon beam of the Mainz MAMI accelerator with the Crystal Ball and TAPS detectors combined to give an almost 4$\pi$ solid-angle electromagnetic calorimeter. The reactions were identified by a combined invariant-mass and missing-energy analysis. Read More

A new precise determination of the {\eta} meson mass is presented. It is based on a measurement of the threshold for the {\gamma}p -> p{\eta} reaction using the tagger focal-plane microscope detector at the MAMI-B facility in Mainz. The tagger microscope has a higher energy resolution than the standard tagging spectrometer and, hence, allowed an improvement in the accuracy compared to the previous {\eta} mass measurement at MAMI-B. Read More

Precise total cross-sections and invariant-mass distributions have been measured for photoproduction of pion pairs off the proton producing $p\pi^0\pi^0$ and $n\pi^+\pi^0$ final states from the threshold region up to 800 MeV incident photon energy. Additionally, beam helicity asymmetries have been measured in the second resonance region (550 MeV - 820 MeV). The experiment was performed at the tagged photon beam of the Mainz MAMI accelerator with the Crystal Ball and TAPS detectors combined to give an almost 4$\pi$ solid-angle electromagnetic calorimeter. Read More

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. Read More

2010Sep
Affiliations: 1The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 2The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 3The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 4The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 5The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 6The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 7The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 8The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 9The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 10The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 11The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 12The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 13The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 14The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 15The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 16The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 17The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 18The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 19The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 20The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 21The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 22The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 23The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 24The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 25The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 26The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 27The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 28The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 29The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 30The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 31The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 32The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 33The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 34The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 35The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 36The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 37The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 38The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 39The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 40The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 41The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 42The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 43The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 44The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 45The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 46The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 47The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 48The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 49The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 50The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 51The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 52The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 53The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 54The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 55The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 56The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 57The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 58The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 59The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 60The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 61The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 62The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 63The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 64The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 65The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 66The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 67The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 68The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 69The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 70The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 71The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 72The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 73The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 74The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 75The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 76The Crystal Ball at MAMI, TAPS, and A2 Collaborations, 77The Crystal Ball at MAMI, TAPS, and A2 Collaborations

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. Read More

2010Jul
Affiliations: 1Crystal Ball Collaboration at MAMI, 2Crystal Ball Collaboration at MAMI, 3Crystal Ball Collaboration at MAMI, 4Crystal Ball Collaboration at MAMI, 5Crystal Ball Collaboration at MAMI, 6Crystal Ball Collaboration at MAMI, 7Crystal Ball Collaboration at MAMI, 8Crystal Ball Collaboration at MAMI, 9Crystal Ball Collaboration at MAMI, 10Crystal Ball Collaboration at MAMI, 11Crystal Ball Collaboration at MAMI, 12Crystal Ball Collaboration at MAMI, 13Crystal Ball Collaboration at MAMI, 14Crystal Ball Collaboration at MAMI, 15Crystal Ball Collaboration at MAMI, 16Crystal Ball Collaboration at MAMI, 17Crystal Ball Collaboration at MAMI, 18Crystal Ball Collaboration at MAMI, 19Crystal Ball Collaboration at MAMI, 20Crystal Ball Collaboration at MAMI, 21Crystal Ball Collaboration at MAMI, 22Crystal Ball Collaboration at MAMI, 23Crystal Ball Collaboration at MAMI, 24Crystal Ball Collaboration at MAMI, 25Crystal Ball Collaboration at MAMI, 26Crystal Ball Collaboration at MAMI, 27Crystal Ball Collaboration at MAMI, 28Crystal Ball Collaboration at MAMI, 29Crystal Ball Collaboration at MAMI, 30Crystal Ball Collaboration at MAMI, 31Crystal Ball Collaboration at MAMI, 32Crystal Ball Collaboration at MAMI, 33Crystal Ball Collaboration at MAMI, 34Crystal Ball Collaboration at MAMI, 35Crystal Ball Collaboration at MAMI, 36Crystal Ball Collaboration at MAMI, 37Crystal Ball Collaboration at MAMI, 38Crystal Ball Collaboration at MAMI, 39Crystal Ball Collaboration at MAMI, 40Crystal Ball Collaboration at MAMI, 41Crystal Ball Collaboration at MAMI, 42Crystal Ball Collaboration at MAMI, 43Crystal Ball Collaboration at MAMI, 44Crystal Ball Collaboration at MAMI, 45Crystal Ball Collaboration at MAMI, 46Crystal Ball Collaboration at MAMI, 47Crystal Ball Collaboration at MAMI, 48Crystal Ball Collaboration at MAMI, 49Crystal Ball Collaboration at MAMI, 50Crystal Ball Collaboration at MAMI, 51Crystal Ball Collaboration at MAMI, 52Crystal Ball Collaboration at MAMI, 53Crystal Ball Collaboration at MAMI, 54Crystal Ball Collaboration at MAMI, 55Crystal Ball Collaboration at MAMI, 56Crystal Ball Collaboration at MAMI, 57Crystal Ball Collaboration at MAMI, 58Crystal Ball Collaboration at MAMI, 59Crystal Ball Collaboration at MAMI, 60Crystal Ball Collaboration at MAMI, 61Crystal Ball Collaboration at MAMI, 62Crystal Ball Collaboration at MAMI, 63Crystal Ball Collaboration at MAMI, 64Crystal Ball Collaboration at MAMI, 65Crystal Ball Collaboration at MAMI, 66Crystal Ball Collaboration at MAMI, 67Crystal Ball Collaboration at MAMI, 68Crystal Ball Collaboration at MAMI, 69Crystal Ball Collaboration at MAMI, 70Crystal Ball Collaboration at MAMI, 71Crystal Ball Collaboration at MAMI, 72Crystal Ball Collaboration at MAMI, 73Crystal Ball Collaboration at MAMI, 74Crystal Ball Collaboration at MAMI, 75Crystal Ball Collaboration at MAMI, 76Crystal Ball Collaboration at MAMI, 77Crystal Ball Collaboration at MAMI, 78Crystal Ball Collaboration at MAMI, 79Crystal Ball Collaboration at MAMI, 80Crystal Ball Collaboration at MAMI, 81Crystal Ball Collaboration at MAMI, 82Crystal Ball Collaboration at MAMI, 83Crystal Ball Collaboration at MAMI, 84Crystal Ball Collaboration at MAMI

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. Read More

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. Read More

After recent improvements to the Pavia model of two-nucleon knockout from $^{16}$O with electromagnetic probes the calculated cross sections are compared to experimental data from such reactions. Comparison with data from a measurement of the $^{16}$O(e,e$'$pn) reaction show much better agreement between experiment and theory than was previously observed. In a comparison with recent data from a measurement of the $^{16}$O($\gamma$,pn) reaction the model over-predicts the measured cross section at low missing momentum. Read More

Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz in the three isospin channels $\vec{\gamma}p\to \pi^{+}\pi^0n$, $\vec{\gamma}p\to \pi^{0}\pi^0p$ and $\vec{\gamma}p\to \pi^{+}\pi^{-}p$ . The circularly polarized photons, produced from bremsstrahlung of longitudinally polarized electrons, were tagged with the Glasgow magnetic spectrometer. Charged pions and the decay photons of $\pi^0$ mesons were detected in a $~4\pi$ electromagnetic calorimeter which combined the Crystal Ball detector with the TAPS detector. Read More

Cross sections for the ^{3}He(e,e'pn)p reaction were measured for the first time at energy transfers of 220 and 270 MeV for several momentum transfers ranging from 300 to 450 MeV/c. Cross sections are presented as a function of the momentum of the recoil proton and the momentum transfer. Continuum Faddeev calculations using the Argonne V18 and Bonn-B nucleon-nucleon potentials overestimate the measured cross sections by a factor 5 at low recoil proton momentum with the discrepancy becoming much smaller at higher recoil momentum. Read More

The Glasgow photon tagging spectrometer at Mainz has been upgraded so that it can be used with the 1500 MeV electron beam now available from the Mainz microtron MAMI-C. The changes made and the resulting properties of the spectrometer are discussed. Read More

We present the first detailed measurement of incoherent photoproduction of neutral pions to a discrete state of a residual nucleus. The $^{12}$C$(\gamma,\pi^{0})^{12}$C$^{*}_{4.4MeV}$ reaction has been studied with the Glasgow photon tagger at MAMI employing a new technique which uses the large solid angle Crystal Ball detector both as a $\pi^{0}$ spectrometer and to detect decay photons from the excited residual nucleus. Read More

The photoproduction of pi0pi0 and pi0pi+/- pairs off 40Ca has been investigated with the TAPS detector using the Glasgow photon tagging spectrometer at the Mainz MAMI accelerator. Data have been taken for incident photon energies in the energy range from 200 - 820 MeV. Total cross sections have been extracted from threshold up to the maximum photon energy and invariant mass distributions of the pion pairs have been obtained for incident photon energies between 400 - 500 MeV and 500 - 550 MeV. Read More

This paper reports on the first measurement of the ^16O(e,e'pn)^14N reaction. Data were measured in kinematics centred on a super-parallel geometry at energy and momentum transfers of 215 MeV and 316 MeV/c. The experimental resolution was sufficient to distinguish groups of states in the residual nucleus but not good enough to separate individual states. Read More

The sensitivity of the $^{12}$C$(\vec{\gamma},pd)$ reaction to photon linear polarisation has been determined at MAMI, giving the first measurement of the reaction for a nucleus heavier than $^{3}$He. Photon asymmetries and cross sections were measured for $E_{\gamma}$=170 to 350 MeV. For $E_{\gamma}$ below the $\Delta$ resonance, reactions leaving the residual $^{9}$Be near its ground state show a positive asymmetry of up to 0. Read More

Photoproduction of neutral pions from nuclei (carbon, calcium, niobium, lead) has been studied for incident photon energies from 200 MeV to 800 MeV with the TAPS detector using the Glasgow photon tagging spectrometer at the Mainz MAMI accelerator. Data were obtained for the inclusive photoproduction of neutral pions and the partial channels of quasifree single pi0, double pi0, and pi0pi+/- photoproduction. They have been analyzed in terms of the in-medium behavior of nucleon resonances and the pion - nucleus interaction. Read More

The photoproduction of eta-mesic 3He has been investigated using the TAPS calorimeter at the Mainz Microtron accelerator facility MAMI. The total inclusive cross section for the reaction gamma+3He->eta+X has been measured for photon energies from threshold to 820 MeV. The total and angular differential coherent eta cross sections have been extracted up to energies of 745 MeV. Read More

The reaction $\gamma p \to \pi^0 \pi^0 p$ has been measured using the TAPS BaF$_2$ calorimeter at the tagged photon facility of the Mainz Microtron accelerator. Chiral perturbation theory (ChPT) predicts that close to threshold this channel is significantly enhanced compared to double pion final states with charged pions. In contrast to other reaction channels, the lower order tree terms are strongly suppressed in 2$\pi^0$ photoproduction. Read More

Differential cross-sections for quasi-free $\pi^0$ photoproduction from the proton and neutron bound in the deuteron have been measured for $E_\gamma= 200 - 400$ MeV at $\theta^{\rm lab}_\gamma = 136.2^\circ$ usind the Glasgow photon tagger at MAMI, the Mainz 48 cm $\varnothing$ $\times$ 64 cm NaI(Tl) photon detector and the G\"ottingen SENECA recoil detector. For the proton measurements made with both liquid deuterium and liquid hydrogen targets allow direct comparison of "free" $\pi^0$ photoproduction cross-sections as extracted from the bound proton data with experimental free cross sections which are found to be in reasonable agreement below 320 MeV. Read More

The in-medium properties of the D13(1520) nucleon resonance were studied via photoproduction of pi0-mesons from nuclei (C, Ca, Nb, Pb) with the TAPS-detector at the Mainz MAMI accelerator. The inclusive (single and multiple pion production) data disagree with model predictions which explain the disappearance of the second resonance bump in total photoabsorption via a medium modification of the D13 --> N rho decay. The exclusive single pi0 production data show no broadening of the resonance structure beyond Fermi smearing. Read More

The $^{12}$C$(\gamma,ppn)$ reaction has been measured for E$_{\gamma}$=150-800 MeV in the first study of this reaction in a target heavier than $^3$He. The experimental data are compared to a microscopic many body calculation. The model, which predicts that the largest contribution to the reaction arises from final state interactions following an initial pion production process, overestimates the measured cross sections and there are strong indications that the overestimate arises in this two-step process. Read More

The reaction $\gamma p \to \pi^\circ \gamma^\prime p$ has been measured with the TAPS calorimeter at the Mainz Microtron accelerator facility MAMI for energies between $\sqrt{s}$ = 1221--1331 MeV. Cross sections differential in angle and energy have been determined for all particles in the final state in three bins of the excitation energy. This reaction channel provides access to the magnetic dipole moment of the $\Delta^{+}(1232)$ resonance and, for the first time, a value of $\mu_{\Delta^+} = (2. Read More

Differential cross sections for quasi-free Compton scattering from the proton and neutron bound in the deuteron have been measured using the Glasgow/Mainz tagging spectrometer at the Mainz MAMI accelerator together with the Mainz 48 cm $\oslash$ $\times$ 64 cm NaI(Tl) photon detector and the G\"ottingen SENECA recoil detector. The data cover photon energies ranging from 200 MeV to 400 MeV at $\theta^{LAB}_\gamma=136.2^\circ$. Read More