Direct Observation of a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>ρ</mml:mi></mml:math>Decay of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="italic">D</mml:mi></mml:mrow><mml:mrow><mml:mn>13</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mo>(</mml:mo><mml:mn>1520</mml:mn><mml:mo>)</mml:mo></mml:math>Baryon Resonance

Langgartner, W; Ahrens, J.; Beck, R.; Hejny, V.; Kotulla, M.; Krusche, B.; Kuhr, WG; Leukel, R.; McGregor, JD; Messchendorp, J. G.; Metag, V.; Novotny, R.; Leon, VO de; Owens, R.O.; Rambo, F.; Schadmand, S.; Schmidt, A.; Siodlaczek, U.; Ströher, H.; Weiss, Jeffrey M.; Wissmann, F.; Wolf, M.

doi:10.1103/physrevlett.87.052001

Cited by 58 publications

(37 citation statements)

References 18 publications

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“…Particularly, the invariant-mass distributions measured by DAPHNE for γn → pπ − π 0 [8] in quasi-free kinematics off neutrons bound in the deuteron and by TAPS for γp → nπ 0 π + [28] supported this interpretation. The latter results were taken as evidence for a significant contribution from the D 13 (1520) → N ρ decay to the photoproduction of mixed charge pairs [28], which was subsequently also confirmed for the π + π − final state in electroproduction [26].…”

Section: Introductionmentioning

confidence: 71%

“…The first precise measurements of the total cross section and the invariant-mass distributions of pion-pion and pion-nucleon pairs for the π 0 π + final state for photoproduction off the proton in the second resonance region was done with the DAPHNE [27] and TAPS [28] experiments at the MAMI accelerator in Mainz. They revealed strong discrepancies with all available model predictions [1,28]. It was then suggested that the main effect was caused by the neglect of ρ contributions in the models (due to the relatively large mass of this meson, ρ contributions had been neglected in the second resonance region.)…”

Section: Introductionmentioning

confidence: 99%

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Measurement of the beam-helicity asymmetry I⊙ in the photoproduction of $ \pi^{0}$ $ \pi^{\pm}$ pairs off protons and off neutrons

Oberle¹,

Ahrens²,

Annand³

et al. 2014

Eur. Phys. J. A

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Abstract. Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of mixed-charge pion pairs in the reactions γp → nπ 0 π + off free protons and γd → (p)pπ 0 π − and γd → (n)nπ 0 π + 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. The charged pions, recoil protons, recoil neutrons, and decay photons from π 0 mesons were detected in the 4π electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. Using a complete kinematic reconstruction of the final state, excellent agreement was found between the results for free and quasi-free protons, suggesting that the quasi-free neutron results are also a close approximation of the free-neutron asymmetries. A comparison of the results to the predictions of the Two-Pion-MAID reaction model shows that the reaction mechanisms are still not well understood, in particular at low incident photon energies in the second nucleon-resonance region.a

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Section: Introductionmentioning

confidence: 71%

Section: Introductionmentioning

confidence: 99%

Measurement of the beam-helicity asymmetry I⊙ in the photoproduction of $ \pi^{0}$ $ \pi^{\pm}$ pairs off protons and off neutrons

Oberle¹,

Ahrens²,

Annand³

et al. 2014

Eur. Phys. J. A

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“…During the last two decades, an extensive study of doublepion photoproduction for E γ < 1 GeV has been undertaken [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. The theoretical interpretation of the data in various isospin channels was carried out using different phenomenological analyses [15][16][17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

Experimental study of theγp→π0π0preaction with the Crystal Ball/TAPS detector system at the Mainz Microtron

Kashevarov¹,

Fix²,

Prakhov³

et al. 2012

Phys. Rev. C

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The γp → π 0 π 0 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 D 13 (1520) resonance was studied.

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“…where the propagators S and ∆ are single-particle Green's functions for the nucleon and the pion, respectively, in complete analogy to Eq. (14). The structures of all equations here are similar: For a physical current, the four-divergence of the current, with propagators attached to its external legs, is expressed as a commutator ofQ with the corresponding (connected) Green's function.…”

Section: A Gauge Invariancementioning

confidence: 99%

Theory of two-meson photo- and electroproduction off the nucleon

Haberzettl

Nakayama

2019

Phys. Rev. D

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A field-theoretical description of the electromagnetic production of two pions off the nucleon is derived and applied to photo-and electroproduction processes, assuming only one-photon exchange for the latter. The developed Lorentz-covariant theory is complete in the sense that all explicit three-body mechanisms of the interacting ππN system are considered based on three-hadron vertices. The modifications necessary for incorporating n-meson vertices for n ≥ 4 are discussed. The resulting reaction scenario subsumes and surpasses all existing approaches to the problem based on hadronic degrees of freedom. The full three-body dynamics of the interacting ππN system is accounted for by the Faddeev-type ordering structure of the Alt-Grassberger-Sandhas equations. The formulation is valid for hadronic two-point and three-point functions dressed by arbitrary internal mechanisms -even those of the self-consistent nonlinear Dyson-Schwinger type (subject to the three-body truncation) -provided all associated electromagnetic currents are constructed to satisfy their respective (generalized) Ward-Takahashi identities. It is shown that coupling the photon to the Faddeev structure of the underlying hadronic two-pion production mechanisms results in a natural expansion of the full twopion photoproduction current M µ ππ in terms of multiple dressed loops involving two-body subsystem scattering amplitudes of the ππN system that preserves gauge invariance as a matter of course order by order in the number of (dressed) loops. A closed-form expression is presented for the entire gauge-invariant current M µ ππ with complete three-body dynamics. Individually gauge-invariant truncations of the full dynamics most relevant for practical applications at the no-loop, one-loop, and two-loop levels are discussed in detail. An approximation scheme to the full two-pion amplitude for calculational purposes is also presented. It approximates, systematically, the full amplitude to any desired order of expansion in the underlying hadronic two-body amplitude. Moreover, it allows for the approximate incorporation of all neglected higher-order mechanisms in terms of a phenomenological remainder current. The effect and phenomenological usefulness of this remainder current is assessed in a tree-level calculation of the γN → KKΞ reaction.

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Direct Observation of aρDecay of theD13(1520)Baryon Resonance

Cited by 58 publications

References 18 publications

Measurement of the beam-helicity asymmetry I⊙ in the photoproduction of $ \pi^{0}$ $ \pi^{\pm}$ pairs off protons and off neutrons

Measurement of the beam-helicity asymmetry I⊙ in the photoproduction of $ \pi^{0}$ $ \pi^{\pm}$ pairs off protons and off neutrons

Experimental study of theγp→π0π0preaction with the Crystal Ball/TAPS detector system at the Mainz Microtron

Theory of two-meson photo- and electroproduction off the nucleon

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