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Register a new userHigh statistics study of the reaction $gamma pto p;2pi^0$
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The photoproduction of 2$pi^0$ mesons off protons was studied with the Crystal Barrel/TAPS experiment at the electron accelerator ELSA in Bonn. The energy of photons produced in a radiator was tagged in the energy range from 600,MeV to 2.5,GeV. Differential and total cross sections and $ppi^0pi^0$ Dalitz plots are presented. Part of the data was taken with a diamond radiator producing linearly polarized photons, and beam asymmetries were derived. Properties of nucleon and $Delta$ resonances contributing to the $ppi^0pi^0$ final state were determined within the BnGa partial wave analysis. The data presented here allow us to determine branching ratios of nucleon and $Delta$ resonances for their decays into $ppi^0pi^0$ via several intermediate states. Most prominent are decays proceeding via $Delta(1232)pi$, $N(1440)1/2^+pi$, $N(1520)3/2^-pi$, $N(1680)5/2^+pi$, but also $pf_0(500)$, $pf_0(980)$, and $pf_2(1270)$ contribute to the reaction.
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A measurement of the double-polarization observable $E$ for the reaction $gamma pto pi^0 p$ is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C$_4$H$_9$OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from $E_gamma =600$~MeV to $E_gamma =2310$~MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.
The reaction $gamma pto ppi^0eta$ has been studied with the CBELSA detector at the tagged photon beam of the Bonn electron stretcher facility. The reaction shows contributions from $Delta^+(1232)eta$, $N(1535)^+pi^0$ and $pa_0(980)$ as intermediate states. A partial wave analysis suggests that the reaction proceeds via formation of six $Delta$ resonances, $Delta(1600)P_{33}$, $Delta(1920)P_{33}$, $Delta(1700)D_{33}$, $Delta(1940)D_{33}$, $Delta(1905)F_{35}$, $Delta(2360)D_{33}$, and two nucleon resonances $N(1880)P_{11}$ and $N(2200)P_{13}$, for which pole positions and decay branching ratios are given.
The data available from the A2 Collaboration at MAMI were analyzed to select the $gamma pto pi^0eta p$ reaction on an event-by-event basis, which allows for partial-wave analyses of three-body final states to obtain more reliable results, compared to fits to measured distributions. These data provide the worlds best statistical accuracy in the energy range from threshold to $E_{gamma}=1.45$ GeV, allowing a finer energy binning in the measurement of all observables needed for understanding the reaction dynamics. The results obtained for the measured observables are compared to existing models, and the impact from the new data is checked by the fit with the revised Mainz model.
In the present work, we report our in depth study of 12C(p,pgamma)12C reaction both experimentally and theoretically with proton beam energy ranging from 8 MeV to 22 MeV. The angular distributions were measured at six different angles. We discuss the gamma angular distributions, total cross sections values for 4.438, 9.64, 12.7 and 15.1 MeV states. We also describe the theoretical interpretation of our measurements using optical model analysis. We also report the branching ratios from our measurements. For the first time, we have measured the the cross section and branching ratio for the 9.64 MeV state.
We develop an event mixing technique with a missing mass consistency (MMC) cut and a pion energy (PE) cut for the measurement of two-pion Bose-Einstein correlations (BEC) in reactions with only two identical pions produced in the final state. A multi mixing mode that allows one event to be mixed with multiple other events is proposed for the purpose of improving the statistics of mixed samples, and compared with the single mixing mode which requires one original event can be mixed only once. Numerical tests using the {gamma}p -> {pi}^0 {pi}^0 p events are used to testify its ability to measure two-pion correlations. To improve the mixing speed, the optimal MMC cut window is also explored via simulations.
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