0000000000370179

AUTHOR

O. Jahn

showing 62 related works from this author

Compton scattering from the free and bound proton at backward angles above π-threshold

1999

Differential cross sections for Compton scattering from the free proton at Theta(gamma)(lab) = 130.7 degrees in the energy region from 200 MeV to 410 MeV and far quasi-free Compton scattering from the proton bound in the deuteron at Theta(gamma)(lab) = 148.8 degrees in the energy region from 200 MeV to 290 MeV have been measured. The free proton data are in agreement with dispersion-theory predictions based on standard parameters. The difference of the proton polarizabilities has been extracted from the quasi-free data. Our result, - = [9.1 +/- 1.7(stat + syst) +/- 1.2(mod)] x 10(-4) fm(3), is in reasonable agreement with the world average of the free proton data if the backward spin polari…

PhysicsNuclear and High Energy PhysicsBackscatterProton010308 nuclear & particles physicsAstrophysics::High Energy Astrophysical PhenomenaNuclear TheoryCompton scattering01 natural sciencesNuclear physicsDeuteriumPolarizabilityDispersion relation0103 physical sciencesNeutronAtomic physicsNuclear Experiment010306 general physicsSpin-½
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New determination of theηtransition form factor in the Dalitz decayη→e+e−γwith the Crystal Ball/TAPS detectors at the Mainz Microtron

2014

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 Lambda(-2) of the eta transition form factor, Lambda(-2) = (1.95 +/- 0.15(stat) +/- 0.10(syst)) GeV-2, is in good agreement with recent measurements conducted in eta -> e(+) e(-) gamma and eta -> mu(+) mu(-) gamma decays, as well as with recent form-factor calculations. The uncertainty obtained i…

PhysicsNuclear and High Energy PhysicsParticle physics010308 nuclear & particles physicsDetectorForm factor (quantum field theory)Gamma rayLambda01 natural sciencesNuclear physics0103 physical sciencesHigh Energy Physics::ExperimentNuclear Experiment010306 general physicsMicrotronCrystal BallPhysical Review C
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Double pion photoproduction off nuclei - Are there effects beyond final-state interaction?

2013

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. The precise results allow for the first time a model-independent analysis of the influence of pion final-sta…

PhysicsNuclear and High Energy PhysicsParticle physicsdouble pion photoproduction; crystal ball; sigma-in-medium modificationPhotonMeson010308 nuclear & particles physicsHadronNuclear TheoryCarbon-12FOS: Physical sciencesElementary particle01 natural sciences7. Clean energyNuclear physicsMassless particlePion0103 physical sciencesHigh Energy Physics::ExperimentNuclear Experiment (nucl-ex)010306 general physicsNuclear ExperimentNuclear ExperimentCrystal Ball
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Coherent photoproduction of η-mesons off 3He – search for η-mesic nuclei

2012

Coherent photoproduction of $\eta$-mesons off $^3$He, i.e. the reaction $\gamma ^3{He}\rightarrow \eta ^3{He}$, 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 $\eta\rightarrow \gamma\gamma$ and $\eta\rightarrow 3\pi^0\rightarrow 6\gamma$ 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 $\eta {^3{He}}$ final state interaction, pointing to the existence of a resonant …

PhysicsExcitation functionNuclear and High Energy PhysicsParticle physicsMesonHigh Energy Physics::PhenomenologyHadronGamma rayFOS: Physical sciencesBaryonNuclear physicsHigh Energy Physics::ExperimentNuclear Experiment (nucl-ex)total cross section ; photoproduction ; eta meson ; final-state interaction ; Crystal Ball ; MAMINucleonNuclear ExperimentNuclear ExperimentIsotopes of heliumCrystal Ball
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Measurement of theγp→K0Σ+reaction with the Crystal Ball/TAPS detectors at the Mainz Microtron

2013

The gamma p -> K-0 Sigma(+) reaction has been measured from threshold to E-gamma = 1.45 GeV (W-CM = 1.9 GeV) using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. In the present experiment, this reaction was searched for in the 3 pi(0)p final state, by assuming K-S(0) -> pi(0)pi(0) and Sigma(+) -> pi(0)p. The experimental results include total and differential cross sections as well as the polarization of the recoil hyperon. The new data significantly improve empirical knowledge about the gamma p -> K-0 Sigma(+) reaction in the measured energy range. The results are compared to previous measurements and model predict…

PhysicsNuclear and High Energy PhysicsPhotonSpectrometerProton010308 nuclear & particles physicsHyperonSigma01 natural sciencesNuclear physicsRecoil0103 physical sciences010306 general physicsMicrotronCrystal BallPhysical Review C
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The isospin structure of photoproduction of πη pairs from the nucleon in the threshold region

2015

Abstract Photoproduction of πη-pairs from nucleons has been investigated from threshold up to incident photon energies of ≈ 1.4 GeV. The quasi-free reactions γ p → p π 0 η , γ n → n π 0 η , γ p → n π + η , and γ n → p π − η were for the first time measured from nucleons bound in the deuteron. The corresponding reactions from a free-proton target were also studied to investigate final-state interaction effects (for neutral pions the free-proton results could be compared to previous measurements; the γ p → n π + η reaction was measured for the first time). For the π 0 η final state coherent production via the γ d → d π 0 η reaction was also investigated. The experiments were performed at the …

PhysicsNuclear and High Energy PhysicsPhotonPhysicsNuclear Theory7. Clean energylcsh:QC1-999photoproduction; final-state interaction; total cross section; Delta(1232) structure; deuteron; isospin; MAMIPionElectromagnetic calorimeterDeuteriumIsospinIsobarAtomic physicsNuclear ExperimentNucleonlcsh:PhysicsCrystal BallPhysics Letters B
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Quasi-free Compton Scattering and the Polarizabilities of the Neutron

2002

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 $\theta^{LAB}_\gamma=136.2^\circ$. Liquid deuterium and hydrogen targets allowed direct comparison of free and quasi-free scattering from the proton. The neutron detection efficiency of the SENECA detector was measured via the reaction $p(\gamma,\pi^+ n)$. The "free" proton Compton scattering cross sect…

Nuclear and High Energy PhysicsProtonNuclear TheoryFOS: Physical sciences7. Clean energy01 natural sciencesHigh Energy Physics - ExperimentNuclear physicsHigh Energy Physics - Experiment (hep-ex)High Energy Physics - Phenomenology (hep-ph)Polarizability0103 physical sciencesNeutron detectionNeutronNuclear Experiment (nucl-ex)010306 general physicsNuclear ExperimentNuclear ExperimentPhysics010308 nuclear & particles physicsScatteringCompton scatteringHigh Energy Physics - PhenomenologyDeuteriumCover (topology)High Energy Physics::Experiment
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Neutron Skin ofPb208from Coherent Pion Photoproduction

2014

Information on the size and shape of the neutron skin on (208)Pb is extracted from coherent pion photoproduction cross sections measured using the Crystal Ball detector 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 c(n)=6.70±0.03(stat.)  fm and a(n)=0.55±0.01(stat.)(-0.03)(+0.02)(sys.)  fm, respectively, corresponding to a neutron skin thickness Δr(np)=0.15±0.03(stat.)(-0.03)(+0.01)(sys.)  fm. The results give the first successful extraction of a neutron skin thickness with an electromagnetic p…

PhysicsEquation of stateMeson010308 nuclear & particles physicsScatteringGeneral Physics and AstronomyRadius01 natural sciencesNuclear physicsPion0103 physical sciencesHigh Energy Physics::ExperimentNeutronNuclear Experiment010306 general physicsMicrotronCrystal BallPhysical Review Letters
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Search for the charge-conjugation-forbidden decayω→ηπ0

2009

A new upper limit of 2.3x10{sup -4} on the branching ratio of the decay {omega}{yields}{eta}{pi}{sup 0} has been obtained using the Crystal Ball multiphoton spectrometer at the Mainz Microtron MAMI. This decay is forbidden by charge-conjugation invariance of the strong and electromagnetic interactions. We have also obtained the upper limit of 2.3x10{sup -4} for the forbidden decay {omega}{yields}3{pi}{sup 0} and the upper limit of 2.4x10{sup -4} for {omega}{yields}2{pi}{sup 0}.

PhysicsNuclear and High Energy PhysicsParticle physicsParticle decayPionMesonBranching fractionHadronAtomic physicsNuclear ExperimentOmega baryonOmegaCrystal BallPhysical Review C
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Determination of the η-transition form factor in the γp→pη→pγe+e− reaction

2011

The Dalitz decay η→γe+e− has been measured using the combined Crystal Ball and TAPS photon detector setup at the electron accelerator MAMI-C. Compared to the most recent transition form-factor measurement in the e+e− channel, statistics have been improved by one order of magnitude. The e+e− invariant mass distribution shows a deviation from the QED prediction for a point-like particle, which can be described by a form-factor. Using the usual monopole transition form-factor parameterization, F(m2)=(1−m2/Λ2)−1, a value of Λ−2=(1.92±0.35(stat)±0.13(syst)) GeV−2 has been determined. This value is in good agreement with a recent measurement of the η Dalitz decay in the μ+μ− channel and with rece…

PhysicsNuclear and High Energy PhysicsMass distribution010308 nuclear & particles physicsPoint particleBranching fractionForm factor (quantum field theory)Particle accelerator01 natural scienceslaw.inventionNuclear physicslaw0103 physical sciencesHigh Energy Physics::ExperimentInvariant massNuclear Experiment010306 general physicsOrder of magnitudeCrystal BallPhysics Letters B
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Beam-Helicity Asymmetries in Double-Pion Photoproduction off the Proton

2009

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. The precisely measured asymmetries are very sensitive to details of the production processes and are thus key observables in the modeling of the reaction d…

PhysicsParticle physicsProtonMeson010308 nuclear & particles physicsNuclear TheoryHadronFOS: Physical sciencesGeneral Physics and Astronomy7. Clean energy01 natural sciencesHelicity3. Good healthNuclear physicsPair productionPion0103 physical sciencesHigh Energy Physics::ExperimentInvariant massNuclear Experiment (nucl-ex)Nuclear Experiment010306 general physicsNuclear Experimentbeam-helicity asymmetries ; charged pions and the decay photonLeptonPhysical Review Letters
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Intermediate resonance excitation in the γp→pπ0π0 reaction

2005

The helicity dependence of the total cross section for the (gamma) over right arrow(p) over right arrow -> p pi(0)pi(0) reaction has been measured for the first time at incident photon energies from 400 to 800 MeV. The measurement, performed at the tagged photon beam facility of the MAMI accelerator in Mainz, used the large acceptance detector DAPHNE and a longitudinally polarized frozen-spin target. This channel is found to be excited predominantly when the photon and proton have a parallel spin orientation, most likely due to the intermediate production of the D-13(1520) resonance. However, the contribution of the antiparallel spin configuration, arising from other reaction mechanisms, is…

PhysicsNuclear and High Energy PhysicsPhotonProton010308 nuclear & particles physicsResonance01 natural sciencesHelicityCross section (geometry)Nuclear physicsExcited state0103 physical sciencesPhysics::Accelerator PhysicsAtomic physicsNuclear Experiment010306 general physicsNucleonSpin (physics)Physics Letters B
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Accurate Test of Chiral Dynamics in theγ→p→π0pReaction

2013

A precision measurement of the differential cross sections dσ/dΩ and the linearly polarized photon asymmetry Σ≡(dσ⊥-dσ∥)/(dσ⊥+dσ∥) for the γp→π0p reaction in the near-threshold region has been performed with a tagged photon beam and almost 4π detector at the Mainz Microtron. The Glasgow-Mainz photon tagging facility along with the Crystal Ball/TAPS multiphoton detector system and a cryogenic liquid hydrogen target were used. These data allowed for a precise determination of the energy dependence of the real parts of the S- and all three P-wave amplitudes for the first time and provide the most stringent test to date of the predictions of chiral perturbation theory and its energy region of a…

PhysicsPhotonChiral perturbation theory010308 nuclear & particles physicsmedia_common.quotation_subjectDetectorGeneral Physics and Astronomy01 natural sciences7. Clean energyAsymmetryNuclear physics0103 physical sciencesHermetic detectorAtomic physicsPerturbation theoryNuclear Experiment010306 general physicsMicrotronCrystal Ballmedia_commonPhysical Review Letters
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Photoproduction of $ \pi^{0}$ -pairs off protons and off neutrons

2015

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. The tagged photon beam covered energies up to 1400~MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cros…

Nuclear reactionPhysicsNuclear and High Energy PhysicsProtonMesonNuclear TheoryBremsstrahlung7. Clean energyDelta baryonNuclear physicsPhysics::Accelerator PhysicsNeutronAtomic physicsNuclear ExperimentNucleonNuclear ExperimentCrystal BallThe European Physical Journal A
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Quasifree photoproduction of eta mesons off protons and neutrons

2014

Differential and total cross sections for the quasifree reactions $\ensuremath{\gamma}p\ensuremath{\rightarrow}\ensuremath{\eta}p$ and $\ensuremath{\gamma}n\ensuremath{\rightarrow}\ensuremath{\eta}n$ have been determined at the MAMI-C electron accelerator by 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. Decay photons of the neutral decay modes $\ensuremath{\eta}\ensuremath{\rightarrow}2\ensuremath{\gamma}$ and $\ensuremath{\eta}\ensuremath{\rightarrow}3{\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}6\ensuremath{\gamma}$ and coincident recoil nucleons were detected in a combin…

PhysicsNuclear and High Energy PhysicsParticle physicsNuclear TheoryProtonMesonNuclear TheoryBremsstrahlung7. Clean energyHigh Energy Physics - ExperimentNuclear physicsRecoilNeutronNuclear ExperimentNucleonNuclear ExperimentEnergy (signal processing)Crystal BallPHYSICAL REVIEW C
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Measurement of the beam-helicity asymmetry I⊙ in the photoproduction of π0-pairs off the proton and off the neutron

2013

Abstract Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of neutral pion pairs in the reactions γ → p → p π 0 π 0 and γ → d → ( n ) p π 0 π 0 , γ → d → ( p ) n π 0 π 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. Decay photons from the π 0 mesons, recoil protons, and recoil neutrons were detected in the 4π covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. After kinematic reconstruction of…

PhysicsNuclear and High Energy PhysicsProtonMeson010308 nuclear & particles physicsNuclear TheoryHadron01 natural sciences7. Clean energyHelicityCharged particleNuclear physicsPion0103 physical sciencesHigh Energy Physics::ExperimentNeutronAtomic physicsNuclear Experiment010306 general physicsCrystal BallPhysics Letters B
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Neutron polarizabilities investigated by quasi-free Compton scattering from the deuteron

2002

Measuring Compton scattered photons and recoil neutrons in coincidence, quasifree Compton scattering by the neutron has been investigated at MAMI (Mainz) at ${\ensuremath{\theta}}_{\ensuremath{\gamma}}^{\mathrm{lab}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}136\ifmmode^\circ\else\textdegree\fi{}$ in an energy range from 200 to 400 MeV. From the data a polarizability difference of ${\ensuremath{\alpha}}_{n}\ensuremath{-}{\ensuremath{\beta}}_{n}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}9.8\ifmmode\pm\else\textpm\fi{}3.6(\mathrm{stat}{)}_{\ensuremath{-}1.1}^{+2.1}(\mathrm{syst})\ifmmode\pm\else\textpm\fi{}2.2(\mathrm{model})$ in units of ${10}^{\ensuremath{-}4}{\mathrm{fm}}^{…

Physics010308 nuclear & particles physicsAstrophysics::High Energy Astrophysical PhenomenaCompton scatteringGeneral Physics and AstronomyFOS: Physical sciencesAstrophysics::Cosmology and Extragalactic Astrophysics7. Clean energy01 natural sciencesHigh Energy Physics - ExperimentHigh Energy Physics - PhenomenologyHigh Energy Physics - Experiment (hep-ex)High Energy Physics - Phenomenology (hep-ph)Deuterium0103 physical sciencesNeutronHigh Energy Physics::ExperimentAtomic physicsNuclear Experiment (nucl-ex)010306 general physicsNuclear ExperimentNuclear ExperimentEnergy (signal processing)Astrophysics::Galaxy Astrophysics
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First measurement of the helicity dependence of 3He photoreactions in the Δ(1232) resonance region

2013

The first measurement of the helicity dependence of the total inclusive 3He photo-absorption cross section and of the partial cross sections for several reaction channels was carried out at MAMI (Mainz) in the photon energy range between 150 and 500 MeV. The experiment used the large acceptance Crystal Ball spectrometer, complemented by charged particle and vertex detectors, a circularly polarised tagged photon beam and a longitudinally polarised high-pressure 3He gas target. The results obtained give information on the GDH integral on 3He and on the neutron and allow an investigation of the modifications of nucleon properties inside 3He.

PhysicsNuclear reactionNuclear and High Energy PhysicsPhoton010308 nuclear & particles physicsNuclear TheoryNucleon spin structurePhoton energy01 natural sciencesResonance (particle physics)HelicityNuclear physics0103 physical sciencesNeutronNuclear Experiment010306 general physicsCrystal BallPhysics Letters B
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K+Λ and K+Σ0 photoproduction with fine center-of-mass energy resolution

2014

Measurements of γp→K+Λγp→K+Λ and γp→K+Σ0γp→K+Σ0 cross-sections have been obtained with the photon tagging facility and the Crystal Ball calorimeter at MAMI-C. The measurement uses a novel K+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. The new analyses disfavor a strong role for quark–diqua…

PhysicsNuclear and High Energy PhysicsPhotonMesonResolution (electron density)7. Clean energyCalorimeterNuclear physicsHigh Energy Physics::ExperimentCenter of massAtomic physicsNucleonExcitationCrystal BallPhysics Letters B
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Incoherent neutral pion photoproduction on 12C.

2007

We present the first detailed measurement of incoherent photoproduction of neutral pions to a discrete state of a residual nucleus. The C-12(gamma,pi(0))C-12(4.4 MeV)* 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. The technique has potential applications to a broad range of future nuclear measurements with the Crystal Ball and similar detector systems elsewhere. Such data are sensitive to the propagation of the Delta in the nuclear medium and will give the first information on matter transition form fa…

PhysicsNuclear reactionPhotonMesonmeasurement of incoherent photoproduction010308 nuclear & particles physicsHadronNuclear TheoryGeneral Physics and AstronomyElementary particle01 natural sciences7. Clean energyNuclear physicsPionExcited state0103 physical sciencesAtomic physics010306 general physicsNuclear ExperimentCrystal BallPhysical review letters
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Experimental study of theγp→ηpreaction with the Crystal Ball detector at the Mainz Microtron (MAMI-C)

2010

The gamma p - = 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) gamma p -< eta p -< 3 pi(0) p -< 6 gamma p events allows a detailed study of the reaction dynamics. The gamma p -< eta p 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 a…

PhysicsNuclear and High Energy PhysicsMeson010308 nuclear & particles physicsAstrophysics::High Energy Astrophysical PhenomenaPartial wave analysisHadronBremsstrahlung01 natural sciencesNuclear physicsParticle decay0103 physical sciencesNuclear Experiment010306 general physicsNucleonMicrotronCrystal BallPhysical Review C
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First measurement of the helicity-dependent γ p↦pη differential cross-section

2003

The helicity dependence of the (γ) over right arrow(p) over right arrow -+ peta reaction has been measured for the first time at a center-of-mass angle theta(eta)*= 70degrees in the photon energy range from 780 MeV to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4pi-detector system, a circularly polarized, tagged photon beam. and a longitudinally polarized frozen-spin target. The helicity 3/2 cross-section is found to be small and the results for helicity 1/2 agree with predictions from the MAID analysis.

PhysicsScattering cross-sectionNuclear and High Energy PhysicsParticle physics010308 nuclear & particles physicsHadronPhoton energy01 natural sciencesHelicityNuclear physics0103 physical sciencesPhysics::Accelerator PhysicsNuclear fusionPhoton beamNuclear Experiment010306 general physicsMicrotronThe European Physical Journal A
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Measurement of the Gerasimov-Drell-Hearn Integrand forH2from 200 to 800 MeV

2006

A measurement of the helicity dependence of the total inclusive photoabsorption cross section on the deuteron was carried out at MAMI (Mainz) in the energy range $200l{E}_{\ensuremath{\gamma}}l800\text{ }\text{ }\mathrm{MeV}$. The experiment used a $4\ensuremath{\pi}$ detection system, a circularly polarized tagged photon beam and a frozen-spin target which provided longitudinally polarized deuterons. The contribution to the Gerasimov-Drell-Hearn sum rule for the deuteron determined from the data is $407\ifmmode\pm\else\textpm\fi{}20(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}24(\mathrm{syst})\text{ }\text{ }\ensuremath{\mu}\mathrm{b}$ for $200l{E}_{\ensuremath{\gamma}}l800\text{ }\text{ }\m…

PhysicsParticle physicsMeson production010308 nuclear & particles physicsNuclear TheoryGeneral Physics and AstronomyComputer Science::Computation and Language (Computational Linguistics and Natural Language and Speech Processing)01 natural sciencesHelicityNuclear physics0103 physical sciencesSum rule in quantum mechanicsPhoton beamNuclear Experiment010306 general physicsEnergy (signal processing)Physical Review Letters
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Photoproduction of theωmeson on the proton near threshold

2015

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 -> omega p differential cross sections are measured from threshold to the incident-photon energy E-gamma = 1.40 GeV (W = 1.87 GeV for the center-of-mass energy) with 15-MeV binning in E-gamma and full production-angle coverage. The quality of the present data near threshold gives access to a variety of interesting physics aspects. As an example, an estimation of the omega N scattering length alpha(omega p) is provided.

PhysicsNuclear and High Energy PhysicsParticle physicsPhotonProtonMesonVector meson dominanceScattering length7. Clean energyOmegaNuclear physicsNuclear ExperimentMicrotronCrystal BallPhysical Review C
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Helicity dependence of the total inclusive cross section on the deuteron

2009

Abstract A measurement of the helicity dependence of the total inclusive photoabsorption cross section on the deuteron was carried out at MAMI (Mainz) in the energy range 200 E γ 800 MeV . The experiment used a 4 π detection system, a circularly polarized tagged photon beam and a frozen spin target which provided longitudinally polarized deuterons. These new results are a significant improvement on the existing data and allow a detailed comparison with state-of-the-art calculations.

PhysicsAngular momentumRange (particle radiation)Nuclear and High Energy PhysicsNuclear TheoryPolarization (waves)HelicityDeuteron photoabsorptionCharged particleNuclear physicsCross section (physics)DeuteriumPhysics and AstronomyDouble polarization experimentSpin (physics)Nuclear ExperimentPhysics Letters B
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Backward spin polarizabilityγπof the proton

2002

Using the Mainz $48\mathrm{cm}\ensuremath{\emptyset}\ifmmode\times\else\texttimes\fi{}64\mathrm{cm}$ NaI(Tl) detector and the segmented G\"ottingen recoil detector SENECA in coincidence, Compton scattering by the proton at ${\ensuremath{\theta}}_{\ensuremath{\gamma}}^{\mathrm{lab}}=136\ifmmode^\circ\else\textdegree\fi{}$ has been measured at MAMI (Mainz) in the energy range from 200 to 470 MeV. The new data confirm the previous observation that there is a systematic discrepancy between MAMI and LEGS (Brookhaven) data leading to different spin polarizabilities ${\ensuremath{\gamma}}_{\ensuremath{\pi}}=\ensuremath{-}38.7\ifmmode\pm\else\textpm\fi{}1.8$ and $\ensuremath{-}27.2\ifmmode\pm\else\…

Elastic scatteringPhysicsNuclear and High Energy PhysicsParticle physicsProton010308 nuclear & particles physicsHadronElementary particle01 natural sciencesOrientation (vector space)Nuclear physicsBaryon0103 physical sciences010306 general physicsNucleonEnergy (signal processing)Physical Review C
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Helicity dependence of the γ→p→→nπ+π0 reaction in the second resonance region

2003

The helicity dependence of the total cross section for the (γ) over right arrow(p) over right arrownpi(+) pi(0) reaction has been measured for the first time at incident photon energies from 400 to 800 MeV The measurement was performed with the large acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. This channel is found to be excited predominantly when the photon and proton have a parallel spin orientation, due to the intermediate production of the D-13 resonance. (C) 2002 Elsevier Science B.V. All rights reserved.

PhysicsNuclear and High Energy PhysicsPhotonProton010308 nuclear & particles physicsNuclear TheoryResonance01 natural sciencesHelicityCross section (geometry)Nuclear physicsExcited state0103 physical sciencesPiPhysics::Accelerator PhysicsAtomic physicsNuclear Experiment010306 general physicsSpin (physics)Physics Letters B
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Measurement of theH1(γ⃗, p⃗)π0Reaction Using a Novel Nucleon Spin Polarimeter

2014

We report the first large-acceptance measurement of polarization transfer from a polarized photon beam to a recoiling nucleon. The measurement pioneers a novel polarimetry technique, which can be applied to many other nuclear and hadron physics experiments. The commissioning reaction of $^{1}H(\mathrm{\ensuremath{\gamma}P\vec},\text{ }\mathrm{pP\vec}){\ensuremath{\pi}}^{0}$ in the range $0.4l{E}_{\ensuremath{\gamma}}l1.4\text{ }\text{ }\mathrm{GeV}$ validates the technique and provides essential new data to constrain the excitation spectrum of the nucleon.

PhysicsParticle physicsMeson productionPartial wave analysisNuclear TheoryGeneral Physics and AstronomyPolarimeterPolarization (waves)7. Clean energyNuclear physicsHadron physicsPhoton beamNuclear ExperimentNucleonExcitationPhysical Review Letters
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Photoproduction ofπ0Mesons off Neutrons in the Nucleon Resonance Region

2014

Precise angular distributions have been measured for the first time for the photoproduction of π0 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 quasifree protons bound in the deuteron to the results for free protons and then applied as a correction to the quasifree neutron data. The experiment was performed at the tagged photon facility of the Mainz Microtron MAMI with the Crystal Ball and TAPS detector setup for incident photon energies between 0.45 and 1.4 GeV…

PhysicsParticle physicsMesonProtonNuclear TheoryGeneral Physics and AstronomyPhoton energy7. Clean energyNuclear physicsIsospinNeutronNuclear ExperimentNucleonMicrotronCrystal BallPhysical Review Letters
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First measurement of the circular beam asymmetry in the γ→p→π0ηp reaction

2010

Abstract The circular photon asymmetry for π 0 η 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 Δ ( 1700 ) D 33 resonance. The measured asymmetry allows us to identify small contributions from positive-parity resonances via interference terms with the dominant D 33 amplitude.

PhysicsNuclear reactionNuclear and High Energy PhysicsPhotonProton010308 nuclear & particles physicsmedia_common.quotation_subjectResonanceElementary particle01 natural sciencesAsymmetryDelta baryonNuclear physics0103 physical sciencesNuclear Experiment010306 general physicsCrystal Ballmedia_commonPhysics Letters B
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Compton scattering from the free and bound proton above π-threshold

2000

The differential cross sections for Compton scattering from the proton have been measured at MAMI with three different detector setups. There is a good agreement among all the results. The theoretical calculation based on dispersion relations shows that there is no drastic change necessary in the parameters of this approach.

PhysicsNuclear and High Energy PhysicsProton010308 nuclear & particles physicsDetectorCompton scatteringCompton wavelengthInelastic scattering01 natural sciencesNuclear physicsDispersion relation0103 physical sciencesNuclear Experiment010306 general physics
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Narrow Structure in the Excitation Function of eta Photoproduction off the Neutron

2013

The photoproduction of $\eta$-mesons off nucleons bound in $^2$H and $^3$He has been measured in coincidence with recoil protons and recoil neutrons for incident photon energies from threshold up to 1.4 GeV. The experiments were performed at the Mainz MAMI accelerator, using the Glasgow tagged photon facility. Decay photons from the $\eta\rightarrow 2\gamma$ and $\eta\rightarrow 3\pi^0$ decays and the recoil nucleons were detected with an almost $4\pi$ electromagnetic calorimeter combining the Crystal Ball and TAPS detectors. The data from both targets are of excellent statistical quality and show a narrow structure in the excitation function of $\gamma n\rightarrow n\eta$. The results from…

ProtonMesonNuclear TheoryFOS: Physical sciencesGeneral Physics and AstronomyPhysics::OpticsPhoton energyη; meson; photoproduction off the neutron; MAMI01 natural sciences7. Clean energyNuclear physicsRecoil0103 physical sciencesNeutronNuclear Experiment (nucl-ex)010306 general physicsNuclear ExperimentNuclear ExperimentPhysicsExcitation function010308 nuclear & particles physicsPhysics::Accelerator PhysicsHigh Energy Physics::ExperimentAtomic physicsNucleonCrystal BallPHYSICAL REVIEW LETTERS
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Accurate Test of Chiral Dynamics in the \boldmath$\vec{\gamma} p \rightarrow \pi^0p$ Reaction

2012

A precision measurement of the differential cross sections $d\sigma/d\Omega$ and the linearly polarized photon asymmetry $\Sigma \equiv (d\sigma_\perp - d\sigma_\parallel) \slash (d\sigma_\perp + d\sigma_\parallel)$ for the $\vec{\gamma} p \rightarrow \pi^0p$ reaction in the near-threshold region has been performed with a tagged photon beam and almost $4\pi$ detector at the Mainz Microtron. The Glasgow-Mainz photon tagging facility along with the Crystal Ball/TAPS multi-photon detector system and a cryogenic liquid hydrogen target were used. These data allowed for a precise determination of the energy dependence of the real parts of the $S$- and all three $P$-wave amplitudes for the first t…

Nuclear ExperimentNuclear Experiment
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Photoproduction of π0-pairs off protons and off neutrons

2015

Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of π0π0 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 1557MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cross sections…

Nuclear TheoryNuclear Experiment
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Measurement of the $^{1}H$($\vec{\gamma}$, $\vec{p}$)$\pi^{0}$ reaction using a novel nucleon spin polarimeter

2013

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 $0.4<E_{\gamma}<1.4$ GeV is highly selective regarding the basic parameterizations used in partial wave analyses to extract the nucleon excitation spectrum. The new data strongly favor the recently proposed Chew-Mandelstam formalism.

Nuclear TheoryNuclear ExperimentNuclear Experiment
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"dcs09" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.7891 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"dcs02" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.7319 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"dcs13" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.8192 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"dcs04" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.7490 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"Table 3" of "Quasi-free Compton Scattering and the Polarizabilities of the Neutron"

2003

Energy dependence of the triple differential cross section w.r.t. the scattered proton.

PhotoproductionTriple Differential Cross SectionExclusiveGAMMA DEUT --&gt; GAMMA P NNuclear ExperimentD3SIG/DE/DOMEGA/DOMEGA
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"dcs05" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.7568 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"dcs19" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.8657 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"Table 1" of "Compton scattering from the free and bound proton at backward angles above pi threshold."

2000

No description provided.

Single Differential Cross SectionPhotoproduction1.12-1.284GAMMA P --&gt; P GAMMAExclusiveDSIG/DOMEGA
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"dcs06" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.7645 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"Table 2" of "Quasi-free Compton Scattering and the Polarizabilities of the Neutron"

2003

Energy dependence of the quasi-free proton differential cross section.

Single Differential Cross SectionPhotoproduction1.146-1.266ElasticNuclear TheoryPhysics::Accelerator PhysicsGAMMA P --&gt; GAMMA PNuclear ExperimentDSIG/DOMEGA
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"dcs11" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.8045 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"dcs12" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.8119 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"tcs" of "Photoproduction of the omega meson off the proton near threshold"

2022

Total cross section as a function of c.m. energy W.

PhotoproductionExclusiveGAMMA P --&gt; OMEGA PSIG
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"dcs17" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.8504 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"dcs01" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.7245 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"dcs20" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.8720 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"Table 5" of "Quasi-free Compton Scattering and the Polarizabilities of the Neutron"

2003

Energy dependence of the free neutron differential cross section.

Single Differential Cross SectionPhotoproductionElasticAstrophysics::High Energy Astrophysical PhenomenaGAMMA N --&gt; GAMMA NNuclear Theory1.125-1.255Nuclear ExperimentDSIG/DOMEGA
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"Table 4" of "Quasi-free Compton Scattering and the Polarizabilities of the Neutron"

2003

Energy dependence of the triple differential cross section w.r.t. the scattered neutron.

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaNuclear TheoryTriple Differential Cross SectionExclusiveGAMMA DEUT --&gt; GAMMA P NNuclear ExperimentD3SIG/DE/DOMEGA/DOMEGA
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"dcs18" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.8581 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"dcs16" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.8424 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"dcs07" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.7729 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"dcs03" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.7401 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"dcs14" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.8269 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"dcs10" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.7968 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"dcs08" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.7811 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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"Table 1" of "Quasi-free Compton Scattering and the Polarizabilities of the Neutron"

2003

Energy dependence of the free-proton differential cross section.

Single Differential Cross SectionPhotoproductionElasticNuclear TheoryPhysics::Accelerator PhysicsGAMMA P --&gt; GAMMA P1.13-1.327Nuclear ExperimentDSIG/DOMEGA
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"dcs15" of "Photoproduction of the omega meson off the proton near threshold"

2022

Differential cross section at W= 1.8348 GeV

PhotoproductionAstrophysics::High Energy Astrophysical PhenomenaExclusiveHigh Energy Physics::ExperimentGAMMA P --&gt; OMEGA PNuclear Experiment
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