Sensitivity of pp-bremsstrahlung to meson-exchange currents

Eden, J. A.; Gari, M.

doi:10.1016/0370-2693(95)00086-z

Cited by 25 publications

(27 citation statements)

References 34 publications

(57 reference statements)

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“…This deviation takes the result away from the data. However, this is not too discomforting since other effects, like including the ∆-isobar, tend to push the analyzing power towards the data [1,2,3,4]. Including the negative-energy nucleonic current Fig.…”

Section: Resultsmentioning

confidence: 99%

The influence of negative-energy states on proton-proton bremsstrahlung

Jong

Nakayama

1996

Physics Letters B

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We investigate the effect of negative-energy states on proton-proton bremsstrahlung using a manifestly covariant amplitude based on a T-matrix constructed in a spectator model. We show that there is a large cancellation among the zeroth-order, single- and double-scattering diagrams involving negative-energy nucleonic currents. We thus conclude that it is essential to include all these diagrams when studying effects of negative-energy states.Comment: 12 pages revtex and 3 figure

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Section: Resultsmentioning

confidence: 99%

The influence of negative-energy states on proton-proton bremsstrahlung

Jong

Nakayama

1996

Physics Letters B

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“…With the presently achieved accuracies, one is sensitive to details of the nucleon-nucleon interaction. Stateof-the-art calculations [3][4][5][6] are now relativistic, showing the sensitivity to negative-energy states, and include nonnucleonic degrees of freedom such as the virtual excitation of the D and meson-exchange currents.…”

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confidence: 99%

Exclusive Measurements of Virtual Bremsstrahlung in Proton-Proton Scattering at 190 MeV

Messchendorp¹,

Bacelar²,

Goethem³

et al. 1999

Phys. Rev. Lett.

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Exclusive differential cross sections of virtual bremsstrahlung in proton-proton scattering below the pion-production threshold have been measured for the first time. The total cross section integrated over photon invariant masses of 15 to 80 MeV͞c 2 and integrated over the acceptance of the detector is 3.2 6 0.1 6 0.5 pb. The data are compared to a low-energy calculation and a fully relativistic microscopic model, which predict a virtual bremsstrahlung cross section of 3.4 and 5.9 pb, respectively. Over the entire experimentally covered phase space, the low-energy calculation gives a better description of the data than the microscopic model. [S0031-9007(99)08793-1] PACS numbers: 13.75.Cs, 25.10. + s, 25.20.LjThe study of real-photon bremsstrahlung emission during proton-proton collisions below pion-production threshold has recently received a large boost. Highquality, intense, polarized-proton beams together with high-precision detection equipment have provided accurate exclusive cross sections and polarization measurements [1,2]. With the presently achieved accuracies, one is sensitive to details of the nucleon-nucleon interaction. Stateof-the-art calculations [3-6] are now relativistic, showing the sensitivity to negative-energy states, and include nonnucleonic degrees of freedom such as the virtual excitation of the D and meson-exchange currents.The emission of virtual bremsstrahlung ͑p 1 p ! p 1 p 1 g ‫ء‬ ! p 1 p 1 e 1 1 e 2 ͒, on the other hand, has up to now not been investigated. The difficulty in the experimental study of this process arises from the fact that the cross section is lower by approximately a factor of a 1͞137, the fine-structure constant, than the already small cross section for bremsstrahlung associated with real-photon emission. The measurement of virtual photons allows the decomposition of the nucleon current into transverse and longitudinal components as well as interference terms, the so-called nucleonic response functions. Furthermore, the nucleon-nucleon-g ‫ء‬ vertex is measured in the timelike region. Calculations predict a large sensitivity of the nucleonic response functions to the details of the nucleon-nucleon interaction [7].In this paper we present the first measurements of the virtual bremsstrahlung cross section. These studies, performed at 190 MeV, obtained a total of 600 backgroundfree ppe 1 e 2 events. The angular distribution of virtual photons as well as the invariant-mass dependence was determined. The data are compared with predictions based on a relativistic low-energy theorem [8,9], as well as a relativistic microscopic calculation by Martinus et al. [7]. Within the experimental accuracy and phase-space coverage, the data are in rather good agreement with the calculation based on the low-energy theorem, which gives a cross section integrated over the experimentally covered phase space of 3.4 pb. The microscopic model seems to overestimate the experimental cross section, with a predicted cross section for virtual bremsstrahlung of 5.9 pb.The experiment was performed ...

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“…[10][11][12]. There are also a number of other microscopic model calculations throughout the 1990s [13][14][15][16][17][18][19][20][21], which are dynamically similar to Refs. [10][11][12], addressing a variety of issues in the N N bremsstrahlung process.…”

Section: Introductionmentioning

confidence: 61%

Gauge-invariant formulation ofNN→NNγ

Haberzettl

Nakayama

2012

Phys. Rev. C

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A complete, rigorous relativistic field-theory formulation of the nucleon-nucleon (N N ) bremsstrahlung reaction is presented. The resulting amplitude is unitary as a matter of course and it is gauge invariant, i.e., it satisfies a generalized Ward-Takahashi identity. The novel feature of this approach is the consistent microscopic implementation of local gauge invariance across all interaction mechanisms of the hadronic systems, thus serving as a constraint for all subprocesses. The formalism is quite readily adapted to approximations and thus can be applied even in cases where the microscopic dynamical structure of the underlying interacting hadronic systems is either not known in detail or too complex to be treated in detail. We point out how the interaction currents resulting from the photon being attached to nucleon-nucleon-meson vertices can be treated by phenomenological four-point contact currents that preserve gauge invariance. In an advance application of the present formalism [K. Nakayama and H. Haberzettl, Phys. Rev. C 80, 051001 (2009)], such interaction currents were found to contribute significantly in explaining experimental data. In addition, we provide a scheme that permits -through an introduction of phenomenological five-point contact currents -the approximate treatment of current contributions resulting from pieces of the N N interaction that cannot be incorporated exactly. In each case, the approximation procedure ensures gauge invariance of the entire bremsstrahlung amplitude. We also discuss the necessary modifications when taking into account baryonic states other than the nucleon N ; in detail, we consider the ∆(1232) resonance by incorporating the couplings of the N N to the N ∆ and ∆∆ systems, and the γN → ∆ transitions. We apply the formalism to the 280-MeV bremsstrahlung data from TRIUMF [Phys. Rev. D 41, 2689(1990] incorporating γN ∆ transition currents and find good agreement with the data.

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Sensitivity of pp-bremsstrahlung to meson-exchange currents

Cited by 25 publications

References 34 publications

The influence of negative-energy states on proton-proton bremsstrahlung

The influence of negative-energy states on proton-proton bremsstrahlung

Exclusive Measurements of Virtual Bremsstrahlung in Proton-Proton Scattering at 190 MeV

Gauge-invariant formulation ofNN→NNγ

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