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Register a new userEnergy dependence of hard bremsstrahlung production in proton-proton collisions in the Delta(1232) region
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Hard bremsstrahlung production in proton-proton collisions has been studied with the ANKE spectrometer at COSY-Juelich in the energy range of 353-800 MeV by detecting the final proton pair {pp}_s from the pp -> {pp}_s reaction with very low excitation energy. Differential cross sections were measured at small diproton c.m. angles from 0 to 20 degrees and the average over this angular interval reveals a broad peak at a beam energy around 650 MeV with a FWHM of about 220 MeV, suggesting the influence of Delta(1232)N intermediate states. Comparison with deuteron photodisintegration shows that the cross section for diproton production is up to two orders of magnitude smaller, due largely to differences in the selection rules.
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Differential and total cross sections for the pp -> ppK+K- reaction have been measured at a proton beam energy of 2.83 GeV using the COSY-ANKE magnetic spectrometer. Detailed model descriptions fitted to a variety of one-dimensional distributions permit the separation of the pp -> pp phi cross section from that of non-phi production. The differential spectra show that higher partial waves represent the majority of the pp -> pp phi total cross section at an excess energy of 76 MeV, whose energy dependence would then seem to require some s-wave phi-p enhancement near threshold. The non-phi data can be described in terms of the combined effects of two-body final state interactions using the same effective scattering parameters determined from lower energy data.
We report on the investigation of $Delta$(1232) production and decay in proton-proton collisions at a kinetic energy of 1.25 GeV measured with HADES. Exclusive dilepton decay channels $ppe^{+}e^{-}$ and $ppe^{+}e^{-}gamma$ have been studied and compared with the partial wave analysis of the hadronic $pppi^{0}$ channel. They allow to access both $Delta^+ to ppi^0(e^+e^-gamma)$ and $Delta^+ to pe^+e^-$ Dalitz decay channels. The perfect reconstruction of the well known $pi^0$ Dalitz decay serves as a proof of the consistency of the analysis. The $Delta$ Dalitz decay is identified for the first time and the sensitivity to N-$Delta$ transition form factors is tested. The $Delta$(1232) Dalitz decay branching ratio is also determined for the first time; our result is (4.19 $pm$ 0.62 syst. $pm$ 0.34 stat.) $times $ 10$^{-5}$, albeit with some model dependence.
The production of non-phi K+K- pairs by protons of 2.83 GeV kinetic energy on C, Cu, Ag, and Au targets has been investigated using the COSY-ANKE magnetic spectrometer. The K- momentum dependence of the differential cross section has been measured at small angles over the 0.2--0.9 GeV/c range. The comparison of the data with detailed model calculations indicates an attractive K- -nucleus potential of about -60 MeV at normal nuclear matter density at a mean momentum of 0.5 GeV/c. However, this approach has difficulty in reproducing the smallness of the observed cross sections at low K- momenta.
This paper reports results from a study of the reaction pp->pK0Sigma+ at beam momenta of p_{beam} = 2950, 3059, and 3200 MeV/c (excess energies of epsilon= 126, 161, and 206 MeV). Total cross sections were determined for all energies; a set of differential cross sections (Dalitz plots; invariant mass spectra of all two-body subsystems; angular distributions of all final state particles; distributions in helicity and Jackson frames) are presented for epsilon= 161 MeV. The total cross sections are proportional to the volume of available three-body phase-space indicating that the transition matrix element does not change significantly in this range of excess energies. It is concluded from the differential data that the reaction proceeds dominantly via the N(1710)P_{11} and/or N(1720)P_{13} resonance(s); N(1650)S_{11} and Delta(1600)P_{33} could also contribute.
Exclusive measurements of the $pp to pppi^0pi^0$ reaction have been performed at CELSIUS/WASA at energies from threshold up to $T_p$ = 1.3 GeV. Total and differential cross sections have been obtained. Here we concentrate on energies $T_p ge$ 1 GeV, where the $DeltaDelta$ excitation becomes the leading process. No evidence is found for a significant ABC effect beyond that given by the conventional $t$-channel $DeltaDelta$ excitation. This holds also for the double-pionic fusion to the quasibound $^2$He. The data are compared to model predictions, which are based on both pion and $rho$ exchange. Total and differential cross sections are at variance with these predictions and call for a profound modification of the $rho$-exchange. A phenomenological modification allowing only a small $rho$ exchange contribution leads to a quantitative description of the data.
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