Photon angular distribution of proton-proton bremsstrahlung at 190 MeV

Pion photoproduction in a dynamical coupled-channels model

“…This means it is very import to take into account properly the gauge-invariance-preserving interaction current for the pion photoproduction processes. The importance of this current corroborates similar findings reported for the N N bremsstrahlung reaction quite recently [65], where it was found to be crucial in reproducing the KVI data [67], something which had eluded theoretical attempts for a very long time. The important point here is that this was brought about simply by adding the gauge-invariancepreserving current M µ c , as it is determined here for pion photoproduction, as a novel four-point contact-current mechanism into the description of N N bremsstrahlung, without changing any of the other mechanisms for that reaction.…”

“…[65,66] that essential aspects of the bremsstrahlung process can be understood as time-reversed meson photoproduction processes N M → N γ (where M stands for a meson) whose dynamical details, therefore, can be described by the current building blocks from the corresponding meson-production formulation. The most important building block in this context turned out to be the fourpoint interaction current for the subprocess N M → N γ whose gauge-invariant construction in terms of its corresponding interaction-current WTI provided the contribution necessary to resolve the longstanding discrepancy of nearly a decade between the high-precision KVI data [67] and the then existing models of the N N bremsstrahlung reaction.…”

Measurement and analysis of thepp→ppγreaction at 310 MeV

“…In this approach the photon is coupled everywhere to a relativistic pp scattering amplitude in a way that ensures consistency with gauge invariance. Although this reproduces very well the detailed KVI pp → ppγ measurements at 190 MeV [9], it is possible that at 310 MeV the tail of the ∆ might have some influence. In this context it should be noted that the minimal inclusion of the ∆ isobar [18] (see also Ref.…”

“…Proton-proton bremsstrahlung has been studied in several experiments but, in general, these were undertaken by detecting the emerging protons in pairs of small counters, often placed on either side of the beam direction [7,8], which has led to the low E pp region being especially poorly sampled. The geometric acceptance was much increased in a series of refined KVI experiments at 190 MeV [9,10], but even here the low E pp region was not favored. Whereas the COSY time-of-flight spectrometer also has wider acceptance, the data obtained at 293 MeV have only limited statistics and no attempt was made to evaluate the cross section as a function of E pp [11].…”

“…The experimental data presented in this paper represent the most complete measurement of bremsstrahlung in proton-proton collisions at an energy so far above threshold. We therefore compare them with a refined model [16] that has recently been successfully applied [16,17] to describe both the TRIUMF data at 280 MeV [8] and the high-precision KVI data [9] at the lower proton energy of T p = 190 MeV. This solved a longstanding discrepancy between experiment and the, then, existing theory.…”