proton-proton bremsstrahlung at 280 mev

Abstract

A proton-proton bremsstrahlung experiment has been carried out at TRIUMF using a 280-MeV polarized proton beam impinging on a liquid-hydrogen target. All three outgoing particles were detected: the higher-energy proton in a magnetic spectrometer, the lower-energy proton with plastic scintillators, and the photon in lead-glass Cherenkov detectors. The experiment shows the first unambiguous evidence for off-shell effects in the free nucleon-nucleon interaction, in that the analyzing powers disagree strongly with the predictions of the soft-photon approximation (which incorporates only on-shell information) but are consistent with the results of calculations using the Bonn and Paris potentials.

Sensitivity of pp-bremsstrahlung to meson-exchange currents

“…To obtain new information from bremsstrahlung that is not already given by on-shell NN-scattering data, the kinematics of a recent experiment at TRIUMF [6] were optimized [7] to obtain large photon energies and highly off-shell nucleon-pole contributions. In earlier work [8] we compared this data from TRIUMF with relativistic meson-baryon model calculations that include only the processes of Fig.…”

Gauge-invariant formulation ofNN→NNγ

“…[1,2] for assigning the nucleon angles θ 1 and θ 2 which is just opposite to the one adopted in other studies [12,16,18]. Also, no arbitrary normalization factor of 2/3 to the data points [26] is applied here. The parameters h and a of the phenomenological four-point contact current determined in Ref.…”

“…In Sec. III, we report on our results for the TRIUMF data [26]. A summarizing assessment of the present work is given in Sec.…”

“…We felt justified, therefore, to restrict ourselves to the N N channel only and neglect the effects of coupling to other baryon-baryon channels. Here, we apply the formalism to some selected data sets from TRIUMF [26] at a higher incident energy of 280 MeV. This energy is just above the pion-production threshold energy and still well below the ∆(1232) resonance peak energy region of about 650 MeV.…”

“…Hence, we expect that simply subjecting the full bremsstrahlung current B µ of Eq. (14) to the reduction prescription (26) will not retain gauge invariance, and that, therefore, additional steps will be necessary to ensure gauge invariance. Since, from a formal point of view, any modification of a given current can, without lack of generality, always be expressed by adding an extra current, we may write the gauge-invariant current B µ r that results from a judicious adaptation of the threedimensional reduction procedure to B µ of Eq.…”